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Old 09-09-2007, 04:05 AM   #1
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The real reason the DZ302 SBC revved so high...

Many times, the younger members of TGO listen to their dads (and grandpas) talk about the famous DZ302 (the original Z/28) engine and how it would rev beyond 7,000 rpm. Most attribute it to the short stroke. But, in reality, it was the camshaft that was the real reason.

I say this because I have helped build and tune a number of engines for various friends over the years (and yes, I actually could drive when the DZ302 was out and actually test drove one). I can tell you that the stroke is not the "magic secret" but the camshaft.

The camshaft was a solid flat-tappet cam with 254/254 duration @ .050 with .485/.458 lift. For those guys who know cams, they know that duration is huge, even on a 383. That is also the reason that car had absolutely no bottom end torque (and why I did not buy the car either).

That cam was designed exactly what GM primarily intended the Z/28 - RACING! GM only sold the Z/28 because it was a requirement to meet the Trans/Am rules.

For those people that doubt me, I suggest that instead of trying to 'destroke' their 350. Instead, install that cam (Crane makes a blueprinted copy which Summit sells P/N CRN-967251) in your 350 instead. It would be best if you could also get a copy of the heads, but with so many great aftermarket heads today, you can easily find a better head that will flow more.

Trust me, that same cam with the better heads we have today will rev just the same as the original Z/28 and though you may not have the same compression ratio (again a good thing as we don't have gas with enough octane to support the original Z/28's 11:1 compression ratio), you will have not only an engine that will make darn near the same power and rev the same BUT you will have something the original DZ302 never had - TORQUE!

But when this cam is installed in a 350 (with decent flowing heads) you can have everything that was great about the DZ302 without it's one weakness (lack of torque). You can now have your cake and eat it.

The stroke was never the secret to the DZ302's ability to rev, it was the cam. But most of us old-timers knew this.
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Old 09-09-2007, 04:30 AM   #2
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Re: The real reason the DZ302 SBC revved so high...

Is there ANY advantage to having a short stroke?
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Old 09-09-2007, 04:42 AM   #3
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Re: The real reason the DZ302 SBC revved so high...

There was a "comparison" done by a magazine a number of years ago (CHP I think) where they took destroked a 400 (377) and stroked a 350 (383) which are fairly close in displacement. They then build the engines identical (camshaft, heads, etc). And then placed them on a dyno.

The 383 made more torque and had it's peak HP slightly lower. The 377 made less torque and higher HP and at a slightly higher rpm. But, the differences were minor. The peak TQ of the 383 was about 10 lb/ft higher and the 377 made about 10 more HP at approx 500 rpm higher.

In the article, they clearly stated that in both cases, a step higher camshaft in the 383 would make up for the HP & rpm differnce. And, in fact, felt the extra TQ of the 383 made it a better street engine than a 377.

In road racing, where you want maximum HP for a specific displacement limitation; there can be advantage to a larger bore/shorter stroke combo because you can run bigger valves with less shrouding from the bore. Plus, they don't need to "idle & cruise" with good driveabilty as a street car does. In racing, you want to stay in your powerband as much as possible, so the limitations of a large bore/short stroke engine is not a concern. I should also point out, that is where a large duration cam (such as used in the DZ302) is best utilized too - in racing.

But, for day-to-day driving, you want torque. And that is where a smaller bore/longer stroke can have a big advantage, especially with a shorter duration cam.

If the Fox-based Mustang weighed as much as a 3rd Gen, I think a drag race between the Ford's 302 and Chev 305 TPI would be a lot closer. Had the 305 had a shorter runner length, the Aluminum Vette heads and a better cam (from day one); the 305 would easily had beaten the 302 and would be a motor fondly remembered (instead of collecting rust in wrecking yards). One of the main reasons for the Ford Mustang being as quick as it was, was due to it's light weigh, so the lack of torque in the 302 was not a problem. Have you ever noticed that the "quick" Mustang 302s are usually 5-speed sticks?

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Old 09-09-2007, 03:46 PM   #4
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Re: The real reason the DZ302 SBC revved so high...

Quote:
Originally Posted by InfernalVortex View Post
Is there ANY advantage to having a short stroke?
Not really... the only reason GM built it as a 302ci was to meet the Trans Am 5.0L (305ci) displacement limit - the production versions also had to have the 5.0L limit.

That rule was dropped for 1970, which is why the '70 Z28 had the LT-1 instead of the DZ engine. The LT1 is pretty well identical to the DZ engine - same heads, camshaft, intake, carb, ignition system, 11:1 compression, etc etc... the difference is that the LT-1 was built on a 350ci bottom end instead of a 302ci bottom end. (don't bring up the dual carb setup for the 302, that was an over-the-counter add-on, not a factory-equipped option.)

The LT-1 was a much better behaved engine than the 302 was just because of the cubic inch increase, and it made more power doing it. Because of the cubic inch increase - and torque increase that came with it - the Z28 in 1970 could be had now with an automatic and A/C. The 302 cars were 4-spd only and no A/C.
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Old 09-09-2007, 03:57 PM   #5
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Re: The real reason the DZ302 SBC revved so high...

i have heard smaller stroke motors and shorter rod motors are less hard on rotating parts. Think about it...you have a piston weight that needs to travel more distance with a longer stroke for the same rpm. that throwing the weight up and down will create more forces acting on the rods and crank.

Kinda simple physics to me, but thats my take on shorter stroke. I think for higher revving motors, its beneficial to have short stroke and larger bores for a set cubic inch motor size. Not for hp gains but for strength and longer internal life of the parts

But not to get offtopic, the cam in those DZ motors must have been huge and its nice to know the real specs. thats a big cam for a small motor. Any motor can rev high but its the cam that will make it pull to that rpm. i accidently took my L98 to 6500 rpms once for a split second. wasnt making power there but the motor still can rev that high
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Old 09-09-2007, 04:10 PM   #6
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Re: The real reason the DZ302 SBC revved so high...

A 254 duration cam? Good grief. Did the cross ram Z/28's have any differences to the engine aside from the cross ram itself?

What kind of rocker arms did they have on those high revving DZ302 cars? Were they generic small block 350 rockers or were they shaft mounted? Anything exotic?
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Old 09-09-2007, 04:32 PM   #7
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Re: The real reason the DZ302 SBC revved so high...

The cam that was previously mentioned is not correct for the DZ 302, it is the service cam(3965754). Service cam was the old equivalent to what the LT4 Hot-cam is. It was an over the counter race cam from GM. The specifications for it were 292/302 @ lash point and .495/.512" lift. The 1969 DZ 302 had a cam (3927140) that spec'd 273/286 @ lash point, which is seat to seat. The lift was .463/.482. The 1970-1972 cam (3972178) was 280/308 @ lash point and had .438/.455 lift. The 178 was in the 1970 LT1s. The 140 was in the old DZ 302. The LT-1 Vette engine had a bigger camshaft, because the exhaust was more free-flowing and the engine was overall larger. The LT-1 in a Camaro vs. a Vette, lost 10 gross HP in the Camaro due to the exhaust setup. The Vette was 370 HP @ 5,600, the Camaro was 360 HP @ 5,600. Both were slightly under-rated and would turn to 7,000 rpm. The red-line on non-a/c LT1 cars was 7,200 rpm.
Attached Images
File Type: jpg DZ 302 Dyno.jpg (310.4 KB, 56 views)
File Type: jpg 1970 LT-1 350.jpg (310.3 KB, 42 views)

Last edited by Fast355; 09-09-2007 at 04:50 PM.
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Old 09-09-2007, 04:47 PM   #8
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Re: The real reason the DZ302 SBC revved so high...

Quote:
Originally Posted by Reid Fleming View Post
A 254 duration cam? Good grief. Did the cross ram Z/28's have any differences to the engine aside from the cross ram itself?

What kind of rocker arms did they have on those high revving DZ302 cars? Were they generic small block 350 rockers or were they shaft mounted? Anything exotic?
The only things exotic were forged crank, forged "pink" X rods, forged TRW pop-up style pistons with floating pins. The oil pump was a standard volume pump with a pink 60 psi spring. The oil pan had special baffeling and their was a windage tray. The cam was a solid tappet design, that used stiff Z/28 valve springs. The heads were large port, large valve, closed chamber design.
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Old 09-09-2007, 06:20 PM   #9
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Re: The real reason the DZ302 SBC revved so high...

Grim: Back in the day, many people that bought the 68-69 Z28 for the street swapped the 30-30 cam out for the 327-350hp "151" hyd cam with 221@.050 .447" valve lift.
With this more streetable setup the lil 302 had much more low end torque, much more drivable yet still pulled to 6000rpm+. (didn't loose any usable power) The stock 302 Z28 motor with the 327-350hp cam swap actually ended up faster.

The 30-30 cammed 302 needed at gear swap to at least a 4.88 and headers to work.
When it came to rpm the "Z28 offroad" 140 cam would buzz even higher.
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Old 09-10-2007, 08:09 AM   #10
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Re: The real reason the DZ302 SBC revved so high...

Quote:
Originally Posted by Fast355 View Post
The cam that was previously mentioned is not correct for the DZ 302, it is the service cam(3965754). Service cam was the old equivalent to what the LT4 Hot-cam is. It was an over the counter race cam from GM. The specifications for it were 292/302 @ lash point and .495/.512" lift. The 1969 DZ 302 had a cam (3927140) that spec'd 273/286 @ lash point, which is seat to seat. The lift was .463/.482. The 1970-1972 cam (3972178) was 280/308 @ lash point and had .438/.455 lift. The 178 was in the 1970 LT1s. The 140 was in the old DZ 302. The LT-1 Vette engine had a bigger camshaft, because the exhaust was more free-flowing and the engine was overall larger. The LT-1 in a Camaro vs. a Vette, lost 10 gross HP in the Camaro due to the exhaust setup. The Vette was 370 HP @ 5,600, the Camaro was 360 HP @ 5,600. Both were slightly under-rated and would turn to 7,000 rpm. The red-line on non-a/c LT1 cars was 7,200 rpm.
I suggest you contact Crane and tell them they are incorrect on their specs for their "Blueprint Cams" which are suppose to be EXACTLY as per spec (but with closer tolerance than production).

Amazing that they got this one so wrong when the specs on some f the other "Blueprint Cams" is so right.

Summit Racing sells it under P/N CRN-967251 and Crane is 967251.

Tell us what they say.
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Old 09-10-2007, 08:24 AM   #11
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Re: The real reason the DZ302 SBC revved so high...

Quote:
Originally Posted by F-BIRD'88 View Post
Grim: Back in the day, many people that bought the 68-69 Z28 for the street swapped the 30-30 cam out for the 327-350hp "151" hyd cam with 221@.050 .447" valve lift.
With this more streetable setup the lil 302 had much more low end torque, much more drivable yet still pulled to 6000rpm+. (didn't loose any usable power) The stock 302 Z28 motor with the 327-350hp cam swap actually ended up faster.

The 30-30 cammed 302 needed at gear swap to at least a 4.88 and headers to work.
When it came to rpm the "Z28 offroad" 140 cam would buzz even higher.
I have 222*/222* @.050 .447"/.447" for that cam, which is insignificant difference. But yes, I can see that as being a much better cam, as well as maintence free (being hydraulic) as another reason for swapping to that cam (though I may have a conern about the springs in the head if those weren't changed as well).

Noting the specs, that is why the Comp Cams 224/230 Hydraulic Roller is such a popular cam for the L98 (with an intake change).

Face it, GM's real intent for the Z/28 was never for the street but TransAM racing and in those days, to qualify for racing the manufacturers also needed to sell a certain number for the street.

But my real point in all this is to dispell the myth of bore/stroke ratio as the reason for the Z/28's ability to rev. It was the camshaft and a mechnical camshaft at that which required frequent adjustments in those days. It was not a "street friendly" engine nor terribly quick (until you changed the intake, exhaust & gears...and that made it even less suitable for the street with it's 4,000 rpm when travelling on the freeway).
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Old 09-10-2007, 10:22 AM   #12
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Re: The real reason the DZ302 SBC revved so high...

Quote:
Originally Posted by Grim Reaper View Post
I suggest you contact Crane and tell them they are incorrect on their specs for their "Blueprint Cams" which are suppose to be EXACTLY as per spec (but with closer tolerance than production).

Amazing that they got this one so wrong when the specs on some f the other "Blueprint Cams" is so right.

Summit Racing sells it under P/N CRN-967251 and Crane is 967251.

Tell us what they say.
My specs came from How to Hotrod Small Block Chevy's that Smokey Yunick had a hand in writing. I would trust this early 70s book over what crane has listed for their blue-print line. That blue-print cam is the off-road service cam.
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Old 09-10-2007, 02:52 PM   #13
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Re: The real reason the DZ302 SBC revved so high...

Quote:
Originally Posted by Grim Reaper
The stroke was never the secret to the DZ302's ability to rev, it was the cam. But most of us old-timers knew this.
Grim, there's still a pretty strong debate as to how much peak horsepower the DZ302's were "actually" making at the time. Any insight on this, including all out race form....?
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Old 09-10-2007, 04:34 PM   #14
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Re: The real reason the DZ302 SBC revved so high...

Quote:
Originally Posted by Fast355 View Post
My specs came from How to Hotrod Small Block Chevy's that Smokey Yunick had a hand in writing. I would trust this early 70s book over what crane has listed for their blue-print line. That blue-print cam is the off-road service cam.
And books are notorious for being incorrect. There has been a number of others also researching this.

Crane says 256/256 @ .050 with .485/.485 is the correct cam.

And here is another place that came across this very question.

http://www.automotiveforums.com/t384725.html

Here, someone says 255/255 which is 1 degree out.

The part number from GM is 3849346

There were some "off-road" versions:

3927140 Mechanical - 257/269 - .493/.512 - 112 - Off Road
3965724 Mechanical - 262/273 - .488/.509 - 112 - 2nd design road race, short track

But GM P/N 3849346 was the DZ302's cam

Last edited by Grim Reaper; 09-10-2007 at 04:52 PM.
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Old 09-10-2007, 08:58 PM   #15
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Re: The real reason the DZ302 SBC revved so high...

Grim & Fast are obviously both very experienced, knowledgable
and honorable contributors.

That being said...
These urinating olympiads are just one of the reasons I'm
addicted to this forum.

PS.
If signature info is to be believed, I give the nod to Grim
There's no substitute for torque, & for torque, there's
no substitue for ci's.

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Old 09-10-2007, 09:30 PM   #16
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Re: The real reason the DZ302 SBC revved so high...

Quote:
Originally Posted by Street Lethal View Post
Grim, there's still a pretty strong debate as to how much peak horsepower the DZ302's were "actually" making at the time. Any insight on this, including all out race form....?
I can tell you that Smokey Yunick was able to make over 465 Gross HP out of the 302 with a single 4bbl on it.

I also happened to pull out my old Peterson's manual that covers many cars from 1970-1979, 1980 edittion. The cam for the 1970 LT-1 is listed differently again. THe cam speced 317/346 advertised duration, lift of .459/.485. Weirdness

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Old 09-10-2007, 09:40 PM   #17
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Re: The real reason the DZ302 SBC revved so high...

The camshaft gave it the power at those high rpms but the reason it revved so high was because people knew it wouldnt blow up at those high rpms lol... but yeah anyone know the lobe separation on that camshaft?
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Old 09-10-2007, 10:48 PM   #18
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Re: The real reason the DZ302 SBC revved so high...

Quote:
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The camshaft gave it the power at those high rpms but the reason it revved so high was because people knew it wouldnt blow up at those high rpms lol... but yeah anyone know the lobe separation on that camshaft?
The 256/256 @ .050 .485"/.485" (1.5) had a 114* LSA

I guess the wider LSA was for a "smoother idle" (not...it was all for top end power).

While Fast & I may disagree on the specs and there is some disagreement on the Internet at other sites. The one I am stating is the one that most often is acknowledge as the correct cam.

But Fast & I do agree on one thing - it was a mechanical cam. The duration I am quoting would also make sense with the DZ's static compression ratio (11.25:1 as I recall). A shorter duration cam would have made that compression ratio highly prone to detonation, especially with iron heads. But a long duration cam would make that compression ratio work due to the "self-EGRing".

In fact, to install that cam in anything with a duration under 10:1 would have made it sluggish. People often forget that duration & compression ratio work "hand-in-hand". And a long duration cam is often a "fix" for too much static compression. I enjoy talking about these types of cams as it seems to be an area that people think as "black magic"...similar to ECM/eproms 10 years ago.

For more info, here is what a Moderator on Hot Rod Magazine states it to be cam for the DZ302 as well:

http://forums.hotrod.com/70/1335383/...tor/page3.html

They say 254/254 @ .050 though.
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Old 09-10-2007, 10:52 PM   #19
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Re: The real reason the DZ302 SBC revved so high...

Regardless of whoever's specs you choose, it's a sizeable cam.

One of the other popular features of the DZ302 were the "Z28 valvesprings", which for years were pretty much the only "performance" valvespring you could get your hands on until the aftermarket grew up. They were also an important part of the high-revving package.
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Old 09-10-2007, 10:58 PM   #20
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Re: The real reason the DZ302 SBC revved so high...

Quote:
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I can tell you that Smokey Yunick was able to make over 465 Gross HP out of the 302 with a single 4bbl on it.
I bet Smokey could make 400 Naturally Aspirate Gross HP out of the old VW horizontal four.

One of the problems with comparing the old DZ302 HP with today's engines, the DZ used the old "Gross" rating which is around 25% higher than the Net rating we use today...and even that is subject to debate (and manipulation).

And, even if the DZ did produce a high Gross HP; it lacked torque which made it not a very street friendly car. The LT-1 was a better street engine IMO. And I recall a magazine did a comparison of the (then) new LT1 to the older LT-1...and the LT1 was slightly quicker. But, I cannot recall if the older LT-1 used older period tires or modern tires...a big factor.
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Quote:
Originally Posted by Apeiron View Post
Regardless of whoever's specs you choose, it's a sizeable cam.

One of the other popular features of the DZ302 were the "Z28 valvesprings", which for years were pretty much the only "performance" valvespring you could get your hands on until the aftermarket grew up. They were also an important part of the high-revving package.
Agreed. I guess my REAL POINT is; drop that same cam in a stroker 383 (and all else the same) and I bet it kicks that 302s butt (and revs damn close to 7,000 rpm as well). It might even be a half decent street engine now that it has some bottom end torque.

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Old 09-10-2007, 11:26 PM   #21
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Re: The real reason the DZ302 SBC revved so high...

The 114 LSA of that monster cam was to increase top end HP? I thought a wider LSA "table-topped" (yep, it's a verb now), the power band, where a short LSA "peaked" it. At least that's the long and short of it to me.
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Old 09-10-2007, 11:58 PM   #22
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Re: The real reason the DZ302 SBC revved so high...

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Originally Posted by Sonix View Post
The 114 LSA of that monster cam was to increase top end HP? I thought a wider LSA "table-topped" (yep, it's a verb now), the power band, where a short LSA "peaked" it. At least that's the long and short of it to me.
Typically, with a long duration cam in a street engine, you tend to tighten the LSA to increase the mid-range torque as you already so much top-end because of the long duration that you can "sacrifice" some of the top-end to help out in the mid-range area. Remember, the DZ302's cam was basically intended for racing, not street use IMO. Today, with that kind of duration, you would probably want an LSA in the 106-108 range to help out in the mid-range area if you planned to use it on a street engine.

For example, if you were to take this cam and change it to a 110 LSA, you would have more TQ but the HP would peak sooner (and thus you would have less HP). Instead of making max HP at a "guestimate" 7,200+ rpm (like that cam would), it would peak out at a whimpy 6,800 rpm. I'm sure someone is going to run the DZ302 with this cam's specs in DesktopDyno and will tell us what HP & rpm DD said it produced...as well as try playing with the LSA.

FYI, a buddy of mine is using a solid roller of 248/256* @.050 (lift is around .600") with a 110 LSA on a 383 and that engine pulls hard well past 7,000 rpm. We put a rev-limit of 6,800 rpm, not because his engine exceed peak power, but because he was concerned that his bottom end may not be able to take it. I told him to go with a narrower LSA, but he whimped out on me as he was concerned with the tuning issues (though I was responsible for the tuning).

Basically I think we are saying the same thing..but using different terminology.

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Old 09-11-2007, 04:59 AM   #23
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Re: The real reason the DZ302 SBC revved so high...

Quote:
Originally Posted by F-BIRD'88 View Post
Grim: Back in the day, many people that bought the 68-69 Z28 for the street swapped the 30-30 cam out for the 327-350hp "151" hyd cam with 221@.050 .447" valve lift.
With this more streetable setup the lil 302 had much more low end torque, much more drivable yet still pulled to 6000rpm+. (didn't loose any usable power) The stock 302 Z28 motor with the 327-350hp cam swap actually ended up faster.
Even though Sofakingdom disses on that particular cam every chance he gets, I can say from personal experience that it's pretty damn impressive in a street engine. I ran the Crane Blueprint L79, 327/350HP cam (i.e. "151"), using "462" casting fuelies in my old-school 355 for quite a few years. Have a Weiand X-Celerator single plane intake and a Holley 650DP on top. That motor would start pulling around 1800 rpms, and just kept on pulling stronger all the way to 6K. I was always amazed at how broad the midrange power was with it. I've since switched to a Crower Ultra Compu-Pro grind (288/296 dur.,234/246@.050, 497/504 lift, 112 LSA). The new cam starts to pull around 2200, and the heads, or possibly intake, start shutting it down at about 63-6400.
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Old 09-11-2007, 07:02 AM   #24
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Re: The real reason the DZ302 SBC revved so high...

Short strokes' to improve longevity of the engine (especially at high RPMs).

- Piston reciprocation is shorter, therefore slower piston speed, less inertia to change direction
- Use of a longer rod, for better accel/decel of the piston and a less stressful rod angle
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Old 09-11-2007, 09:29 AM   #25
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Re: The real reason the DZ302 SBC revved so high...

Just to clarify The factory installed cam for the 68-69 302Z28
was the "30-30" 254-254@.050" .485-.485 114LSA cam
It was also used on the early '70 350 Z28-LT-1 and the old 327-365carbed vette motor and the 327-375hp FI vette motor (1964 1965)
All these motors use standard SBC valve springs. Thats why the clearance ramps were sooooooo long.

The 1st design offroad cam 257-269@.050" .493-.512 112LSA had to be bought and installed by the owner. There were headers and a crossram manifold also that you could buy from the GM dealer. Used special stock diameter hi pressure springs. At that point people would remove the cylinder heads and port them and shave 'em to get the cr up to 12:1

The 2nd design off road cam 262-273 .512 .536 112 was even wilder and required larger diameter valve springs and cylinder head machining. The rpm was so high that roller rockers were required as the stock rockers would scuff the rocker ***** under continious high rpm (7500rpm+) use.

late 1970 corvette LT-1 (with auto trans) and 1971-1972 350 Z-28/LT-1 motors got a revised cam for increased drivability especially with a auto trans.
The exhaust lobe was the same as the "30-30" lobes. The intake lobe was a small block version of the Big block 375-425-450hp street solid lifter cam used on 396 L-78 -427 L-72 and 454 LS-6 motors. the new combined specs were 242-254@.050" .459-.485" 116LSA
The 30-30 cam is a real mutt with a auto trans unless you have a 4000 stall converter. Needs 11:1 ++ compression and lots of rear gear.
There are much better cams available today.

I remember when these cars were new and you bought your race parts right from the GM dealer parts counter. We all used the Z/28 off road valve springs in any motor that you wanted to rev high.
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Old 09-11-2007, 02:54 PM   #26
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Re: The real reason the DZ302 SBC revved so high...

Regarding the comments on the "wide" 114 lobe separation on the DZ cam:
I'm sure some of you already understand this, but it hasn't been stated yet, so I'll do it for those who are still wondering.
The LSA (lobe separation angle) really isn't a parameter that one picks when designing a cam for a particular engine for a particular powerband. It's simply a result of the PROPER valve opening and closing events. And a true cam designer will pick those events based on the position and velocity of the piston in the bore, NOT in crank degrees. He then converts those positions to crank degrees for the cam to be ground. And that's the basis of my point: For a large rod/stroke ratio like the DZ had, the LSA is naturally going to be wider than it will be for a smaller R/S ratio 383 stroker, even when you're targeting the same rpm powerband.
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Old 09-11-2007, 03:23 PM   #27
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Re: The real reason the DZ302 SBC revved so high...

Quote:
Originally Posted by 86LG4Bird
The LSA (lobe separation angle) really isn't a parameter that one picks when designing a cam for a particular engine for a particular powerband. It's simply a result of the PROPER valve opening and closing events....
Exactly. When grinding a cam for a particular application, your basing such symmetry on very critical valve events. LSA is simply the byproduct....
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Old 09-11-2007, 03:32 PM   #28
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Re: The real reason the DZ302 SBC revved so high...

I was born back in those days ... so if grimreaper could drive he must be near 55-60
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Old 09-11-2007, 03:36 PM   #29
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Re: The real reason the DZ302 SBC revved so high...

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Originally Posted by 86LG4Bird View Post
For a large rod/stroke ratio like the DZ had, the LSA is naturally going to be wider than it will be for a smaller R/S ratio 383 stroker, even when you're targeting the same rpm powerband.
But, in reality, based on what you are describing, you really want the opposite. Assuming a cam with the same duration; the 302 with it's higher bore/stroke ratio, it is better off with a narrower LSA (110 or less) as it is naturally short on torque but high on HP. A narrow LSA will promote the much needed mid-range torque (while sacrificing a little top-end).

Conversely, a 305 with it's lower bore/stroke ratio that is more torque oriented, it benefits from a wider LSA (assuming all the remaining cam specs are the same) as it does not need to promote it's mid-range torque but could use a little help on the top-end HP.

Of course, we haven't even got into the cam lobe profile and retarding/advancing the cam. Which can greatly affect the torque/power characteristics of the cam.

But you are right, there is an interplay in all of this that most people don't bother looking at to see if they have a "good match". The "30-30" cam in the DZ302 was perfect for what it was really designed for: racing.

Frankly, even on a bigger engine like a 383, I feel the "30-30" cam would be completely wrong for a car whose primary use is for the street - even though it would be better on the street than the original DZ302 was. (But it sure would rev - and that is more what I am trying to convey to some of the younger members who believe that the secret to the DZ302 was it's bore/stroke ratio - when it was the cam).

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Old 09-11-2007, 03:43 PM   #30
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Re: The real reason the DZ302 SBC revved so high...

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Originally Posted by Jproz1167 View Post
I was born back in those days ... so if grimreaper could drive he must be near 55-60
Actually, you were born in 1967 and you are right I am in my 50s. Is there a point to your non-technical post?

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Old 09-11-2007, 03:49 PM   #31
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Re: The real reason the DZ302 SBC revved so high...

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Originally Posted by Street Lethal View Post
Exactly. When grinding a cam for a particular application, your basing such symmetry on very critical valve events. LSA is simply the byproduct....
Yes it is...but a very interesting by-product that must fall within a specific range. Go outside of that range and the cam becomes useless.

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Old 09-11-2007, 05:17 PM   #32
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Re: The real reason the DZ302 SBC revved so high...

I remember my dad talking about the 30-30 cam. In fact, he calls it the "Duntov" cam, referring to old Zora Arkus Duntov of Corvette fame. Way back in the mid-sixties, he had a 55 Chevy that he dropped a 327 in with the 30-30 cam. He didn't have any problem meeting the gearing requirements of that cam. He was running a 3 speed manual with 4.56 gears out back. He said it was great for the local dragstrip, but once he grew up and needed a car to drive longer distances in, sadly, that's when the 55 got sold. Another cool story he always tells me is how he used to see Ed Lunati run at the same dragstrip back then. He grew up in Memphis, TN, and there was a local track called Lakeland back then. One of my best friends also has a 69 Camaro like me, and he's actually got one of the rare crossram setups complete from the base to the air cleaner. It's just sitting on a shelf collecting dust though. He's too worried about it being a dog on the street with that setup since his 350 isn't built really wild. He's just running the single 4 bbl. Quadrajet on it at the moment. It does have a functional cowl hood setup with the flapper door and the big old air cleaner that seals to the hood. Pretty neat stuff. I think he's running the old GM 350/350HP cam IIRC. Of course he's only running a mild-stalled TH350 and 3.31 gears out back. He'd definitely have to upgrade the drivetrain to take full advantage of a crossram setup. I apologize in advance if I'm getting too far off the original topic. Just thought I'd share.
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Old 09-11-2007, 05:49 PM   #33
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Re: The real reason the DZ302 SBC revved so high...

Quote:
Originally Posted by Grim Reaper
Yes it is...but a very interesting by-product that must fall within a specific range. Go outside of that range and the cam becomes useless.
That is correct, which is the main reason why I mentioned symmetry. Too many variables; cubic inch displacement, RPM range, velocity / AFR, all in relation to IVC, IVO EVC, Overlap, etc....
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Old 09-11-2007, 06:40 PM   #34
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Re: The real reason the DZ302 SBC revved so high...

Go research the bore/stroke ratio of a Ferrari sometime... or other exotic high RPM motor. While looking you might find the variations lie elsewhere.

I have a "Brand F" 302 and the difference in RPM range from the anemic stock cam to a 'performance' cam to the F Motorsport cam I have now is... significant. I havent touched the stroke. I'd imagine, based on my current configuration and the changes I've made to the same engine, that an additional ~20 degrees duration would put the power curve somewhere north of 7k RPM if anything else could possibly support that RPM. There are also people that claim a 289 will rev a lot more than a 302 because of the shorter stroke, bunch of nonsense if you ask me. Its more like it HAS to because the cam is now oversized.
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Old 09-12-2007, 09:48 AM   #35
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Re: The real reason the DZ302 SBC revved so high...

Quote:
Originally Posted by Grim Reaper View Post
But, in reality, based on what you are describing, you really want the opposite. Assuming a cam with the same duration; the 302 with it's higher bore/stroke ratio, ......
Whoa there! I think you misread me. Sorry I may have thrown you off by bringing up ROD/stroke ratio to help folks understand that the 114 LSA for that cam was not on the high side at all. BORE/stroke ratio has nothing to do with my comments on LSA.
Your last comment in that post is absolutely correct; a correct cam choice for a street/mild 383, typically with a R/S ratio around 1.6, will end up with a LSA down in the 106-108 range, never up around 114 unless it's for a blower application.

Quote:
Originally Posted by Grim Reaper View Post
Of course, we haven't even got into the cam lobe profile and retarding/advancing the cam. Which can greatly affect the torque/power characteristics of the cam.
Why of course! When discussing one variable, we don't want to be messing with the others at the same time!

Bottom line: The 114 LSA had virtually nothing to do with the powerband of the DZ engine with the 30-30 cam. The huge duration numbers are what gave it its character.

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Old 09-12-2007, 05:31 PM   #36
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Re: The real reason the DZ302 SBC revved so high...

Quote:
Originally Posted by 86LG4Bird View Post
Bottom line: The 114 LSA had virtually nothing to do with the powerband of the DZ engine with the 30-30 cam. The huge duration numbers are what gave it its character.
Actually it does. If you take the same cam specs but narrow the LSA to 106-108* it will increase the mid-range torque but sacrifice a little off the top end; especially if you build in some advance at the same time.

That would make the DZ302 more "streetable", but GM chose the specs for the 30-30 cam for a particular reason (the Z/28 wasn't really intended for the street but for Trans/AM Racing).
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Old 09-12-2007, 05:49 PM   #37
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Re: The real reason the DZ302 SBC revved so high...

Now that's what throws me.
"They" say that a 114 LSA gives a smoother idle, and makes things more computer friendly, i'd take that to mean more "streetable".
vs. say... a similar cam on a 106 LSA would have a GNARLY idle, and I would assume be LESS streetable.
However "they" (good ol' "they" again), say that a tigher LSA like 106 increases midrange torque.

This might be part of why most people think camshafts are black magic voodoo stuff...
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Old 09-12-2007, 07:13 PM   #38
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Re: The real reason the DZ302 SBC revved so high...

Quote:
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Now that's what throws me.
"They" say that a 114 LSA gives a smoother idle, and makes things more computer friendly, i'd take that to mean more "streetable".
vs. say... a similar cam on a 106 LSA would have a GNARLY idle, and I would assume be LESS streetable.
However "they" (good ol' "they" again), say that a tigher LSA like 106 increases midrange torque.

This might be part of why most people think camshafts are black magic voodoo stuff...
IT IS VOODOO! And if you follow this enough, you'll become a zombie.

I NEVER look for LSA to compensate for idle. If you have a big duration cam, it's going to have a "lumpy idle" even if you have a wide LSA because of the amount of overlap.

If you want a smooth idle and great street characteristics or low-end pulling power, get a short duration cam. If you want top-end power, get a long duration cam and you suffer the idle; because with a long duration cam, no matter how wide you make the LSA it will still have a lumpy idle. But, you also need the "other parts" to match (a short duration cam will not work on a high compression motor and detonate like crazy, and a long duration cam will "bleed too much" to work on a low compression motor).

Similar with heads - large port heads are useless on a low compression, short duration cam motor. You would be better off with a smaller, high velocity port head.

Lastly, unless you are prepared to get a custom grind and pay the high cost with no returns (unless if you can prove it was ground wrong), you are pretty much stuck with the grinds the cam manufacturers offer. And generally, the you have a limited choice of couple LSAs with a particular duration.

Personally, unless you REALLY know what you want, you are best to discuss your "objective" with the tech rep and go with the cam they suggest. The last thing they want is for you to go with a cam (say the 30-30) on your basically stock TBI 305 just because the idle sounds GNARLY!

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Old 09-12-2007, 07:17 PM   #39
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Re: The real reason the DZ302 SBC revved so high...

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just because the idle sounds GNARLY!
No, they have entire lines of cams much better than the 30-30 for people silly enough to just want gnarly idle. Fortunately those cams also make the car slow enough that those people aren't going to hurt themselves.
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Old 09-12-2007, 07:27 PM   #40
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Re: The real reason the DZ302 SBC revved so high...

thought I heard somebody talkin' bout' the WABBIT
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Old 09-12-2007, 07:34 PM   #41
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Re: The real reason the DZ302 SBC revved so high...

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No, they have entire lines of cams much better than the 30-30 for people silly enough to just want gnarly idle. Fortunately those cams also make the car slow enough that those people aren't going to hurt themselves.
Heh, heh, I even know how to make the idle sound "gnarly" on a basically stock car too. Don't even have to waste the time swapping the cam. But it won't pass emissions (or a transit bus either) but it will sound "gnarly".
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Old 09-12-2007, 09:14 PM   #42
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Re: The real reason the DZ302 SBC revved so high...

Grim Reaper, if you were around in the days of the DZ302, then you are as old as dirt, which means you are about my age or even older !!!! and thats pretty scary. Hey, can you help my with my post? No cranking.

My take on the DZ302: it was the short stroke, the cam, and great breathing heads.
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Old 09-13-2007, 03:07 AM   #43
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Re: The real reason the DZ302 SBC revved so high...

Quote:
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My take on the DZ302: it was the short stroke, the cam, and great breathing heads.
Doc, it is my assertion that the single biggest contributor is still the cam.

Take the DZ302 engine but stroke it to 383 - but keep the same cam, heads & intake. That engine will still rev very high and make power nearly the same (but a few rpm lower).

But, put the 305 "peanut cam" in a DZ302, it won't be making power much past 5,000-5,500 rpm. (Though I am sure some moron will keep reving it to 6,500 rpm and swear on a stack of bibles it still works).
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Old 09-13-2007, 06:52 AM   #44
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Re: The real reason the DZ302 SBC revved so high...

So you put a huge cam in anyting it can safely rev to a really high rpm??

What about valve float ect? A short stroke is still key, I think--less rotating mass. I am no expert though.

A cam just determines the powerband, no?
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Old 09-13-2007, 08:13 AM   #45
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Re: The real reason the DZ302 SBC revved so high...

[quote=Grim Reaper;3463430]Actually it does. If you take the same cam specs but narrow the LSA to 106-108* it will increase the mid-range torque but sacrifice a little off the top end; especially if you build in some advance at the same time........quote]
Ok, since it is your thread after all, I'll shut up and let you have the last word. Hopefully some of the readers understand the point I was making.
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Old 09-13-2007, 04:38 PM   #46
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Re: The real reason the DZ302 SBC revved so high...

Speaking of "Gnarly" sounding engines, this (Click Here) DZ-302 sounds extremely healthy....
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Old 09-13-2007, 04:45 PM   #47
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Re: The real reason the DZ302 SBC revved so high...

Music to my ears, the LT-1s sounded very strong too. http://www.youtube.com/watch?v=9WuRoiLrW58
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Old 09-13-2007, 04:55 PM   #48
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Re: The real reason the DZ302 SBC revved so high...

so if its the cam, can i put it in my 305, notch the cylinders, swap the heads and make the same power as the dz302?
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Old 09-13-2007, 05:31 PM   #49
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Re: The real reason the DZ302 SBC revved so high...

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Originally Posted by jonmark1985 View Post
so if its the cam, can i put it in my 305, notch the cylinders, swap the heads and make the same power as the dz302?
I wouldn't use any of those old parts myself in a modern engine build. You can get so much more HP/TQ and fuel efficiency out of modern parts. Lets start with some 305 Vortecs, ZZ4 aluminum or Trickflow 175 heads. DO NOT NOTCH THE CYLINDERS!!! The discussion here is about how the camshaft was responsible for the rpm potential. A properly sized modern camshaft grind will make great hp/tq and have ALOT better driveability. It is easy to build a streetable 305 that makes tons of power below 6,500 rpm.
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Old 09-13-2007, 11:13 PM   #50
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Re: The real reason the DZ302 SBC revved so high...

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Originally Posted by Fast355 View Post
I wouldn't use any of those old parts myself in a modern engine build. You can get so much more HP/TQ and fuel efficiency out of modern parts. Lets start with some 305 Vortecs, ZZ4 aluminum or Trickflow 175 heads. DO NOT NOTCH THE CYLINDERS!!! The discussion here is about how the camshaft was responsible for the rpm potential. A properly sized modern camshaft grind will make great hp/tq and have ALOT better driveability. It is easy to build a streetable 305 that makes tons of power below 6,500 rpm.
jon, I agree with Fast emphatically. Now a 305 has some limitations just because of the very small bore which that limits head selection. And, building an engine to rev so high THAT WILL SURVIVE is another matter again (which you will see after you read this).

Your example would be simpler if it was an L98 (and pretend that you were dumping EFI and going with a carb)...yes the 350 would rev damn near the same as the DZ302 (though max TQ would be higher and peak HP would occur approx 500 rpm sooner). But, the L98s interals would probably not survive very long if you kept taking it to those rpms on a regular basis.

This is when you would want forged internals (crank, rods & pistons) that would be able to handle those high rpms on a regular basis. As well, you would probably be best to have a 4 bolt block instead of a 2 bolt block.

But, as Fast355 just said, with today's modern technology, I would go with a modern solid roller cam; something like a buddy of mine is using ... 248/256* @ .050 with .600" lift as well as modern heads say AFR 195s or maybe even AFR 210s. Lastly, a better intake say a Victor. And to compare all things equal use the 11:1 compression ratio, but on a real engine I would recommend dropping that at least a 1/2 point even with aluminum heads so it can survive on today's pump gas.

That engine will also rev like crazy and probably make around 485 TQ @ 5,000 and 550 HP @ 6,500 ...more than the DZ302 was ever claimed to make.

And if you stroked it to 383, that same combo would make roughly the same HP but 250-500 rpm sooner (which is a good thing in my books). However, TQ would increase over the entire TQ curve, especially the lower RPM range by around 30-35 lb/ft with peak TQ now around 515 lb/ft just before 5,000 rpm. You can see, even when just comparing a 350 to a 383, the HP still remains nearly the same but you get that extra TQ through out the lower rpms and end up with a better engine IMO for both the street & strip.

But you would definitely want good forged internals with a 4 bolt block to ensure it can handle the extreme forces when reving out and "keep it together". And this is where I would have problem trying to do this to a 305 as 305s are all two bolt. If you start getting into the machining costs to convert it to a splayed 4 bolt, the cost alone would make it simple economics to start with a good 350 4-bolt core instead (as well as the fact you cannot bolt on a set of AFR 210s).

Last edited by Grim Reaper; 09-13-2007 at 11:31 PM.
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Old 09-13-2007, 11:13 PM
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