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Engine Swap Everything about swapping an engine into your Third Gen.....be it V6, V8, LTX/LSX, crate engine, etc. Pictures, questions, answers, and work logs.

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Old 09-05-2012, 11:26 PM   #1
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383 stroker- massive hp on pump gas?

ok so heres my deal. ive got a fresh 350 block, already bored .030 over and ready. i plan on doing everything like i have before - forged and balanced internals, aluminum heads, etc. but the part im hung up on is what ill be looking at for compression. I would like to push this motor as far as possible while running high octane pump gas, which is about 91 octane at its best in my area. I would like to run as high as a .600 lift hydraulic roller cam with a fairly high duration,,, something close to .290 - .300. and yea yea i know about overlap and vaccuum and power brakes and im not too worried about all that noise so no advice needed there. just wondering what I should be looking at getting for a combined set up of pistons and heads with that big of a cam to try to maintain something close to 10.5:1 compression,,, or if its even possible? no real rush so opinions welcome.

thanks
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Old 09-06-2012, 01:40 AM   #2
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Re: 383 stroker- massive hp on pump gas?

Everything your saying is kind of vague. Well,kind of like your pulling numbers out of the air. Can you narrow this down to a specific detailed parts list??. It works off formulas.
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Old 09-06-2012, 04:18 AM   #3
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Re: 383 stroker- massive hp on pump gas?

I had 11:1 compression with my 383 SBC with Dart Pro 1 Heads and it ran great on pump gas. Cam was a solid roller 256/260@.05 .623/.627 lift. It ran 10.80's @ 123mph and was suprisingly streetable. The max most people go on compression is somewhere around 11-11.5:1 when using 93 octane pump gas. A few people go up to 12:1 but that is rare it all depends on cam selection and dynamic compression.
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Old 09-06-2012, 07:11 AM   #4
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Re: 383 stroker- massive hp on pump gas?

Yeah id say 11 to 1 is max with big cam and 91 oct. if you want max effort, throw a set of speier 215 small bore heads on it and solid roller cam.
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Old 09-06-2012, 07:41 AM   #5
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Re: 383 stroker- massive hp on pump gas?

DCR max is 9.0,well some have gotten away with 9.0.I like a margin of how gas varies to have a 8.5 DCR.

Interesting how he has a bored block already and plans of using forged pistons. With forged pistons you want the pistons in hand to set the bore size.
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Old 09-06-2012, 08:42 AM   #6
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Re: 383 stroker- massive hp on pump gas?

Quote:
Originally Posted by jbenge View Post
I had 11:1 compression with my 383 SBC with Dart Pro 1 Heads and it ran great on pump gas. Cam was a solid roller 256/260@.05 .623/.627 lift. It ran 10.80's @ 123mph and was suprisingly streetable. The max most people go on compression is somewhere around 11-11.5:1 when using 93 octane pump gas. A few people go up to 12:1 but that is rare it all depends on cam selection and dynamic compression.
Before we have herds of guys buying dome whatever's,it takes more than setting a goal that most wouldn't approach.

For the record:

Recommended to smooth out any sharp edges so you don't have hot spots.

You do really have to know and understand DCR's to apply it to the build.

If you buy "the deal" cheapie forged pistons,the skirts measure all over the map and are so bad we have gone through a number of sets before we could get it even close.(customer builds.Wouldn't buy any for our engines) Without question what suffers everytime is Q.C. on the "the deal" you think your getting,but are not.Same holds true of the rods,crank,bearings(high embedding factor),valve train.

You should run open breathers on a tightly sealed engine

You have to know how to apply vehicle's wt,t/c stall,rear end gear ratios,tire size.

You have to accept a cam of that size is really built for W.O.T. and what is does to the lower end of the power curve. Likely a real pig below 4,000 to 4,500 rpm.

Given the fact a cam of that size and it's design is for W.O.T.,accept fouled plugs often with street use.

Have a induction system(carb/injection system,fuel pump,filter,intake manifold,regulator) to feed this engine.

Have a aftermarket ignition system to fire in the higher rpm ranges.

Aftermarket rear end is almost critical. Yeah,tons of guys say well I use a 10 bolt..............knowing it is just a matter of time.........that's just dumb.

Edit:I assumed everyone knows the piston to valve clearances have to be checked and the cam has to be a small base circle type with those cam to rods clearances checked.
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Last edited by 1gary; 09-06-2012 at 08:54 AM.
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Old 09-06-2012, 06:33 PM   #7
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Re: 383 stroker- massive hp on pump gas?

ok ill clarify a bit here, tho i do appreciate your info so far. wasnt trying to sound uneducated and blank i just threw this up quick to get a couple opinions. but to be more in depth here is my situation: i know it isnt the best choice to bore a block before i even know what im doing with it,, but it's just something that fell into my lap. i bought this block off of somebody who had already bored and rebuilt it with nothing more than a performer cam and intake pkg (355). I would like to go ahead and put a 383 assembly together just because its a good block to work with being a 4 bolt with a 1 piece rms,, i know this isnt really a crucial part of building this motor but why not have a few more cubes. i havent really started with anything yet so im open to any suggestion someone may have, which is half of the reason i lacked any details in my original post.

as far as a cam, to specify exactly what was influencing me to begin with, i was looking at a skip white/howards hydraulic roller cam. i will need to run a retrofit cam, which makes little difference but the specs on the one i was looking into are as follows- .600 lift and .304int/.312exh duration. i know this is kind of an oddly sized cam with such a large duration but thats why im posting this, i was sticking to something close to a .600 lift but if i infact do have the ability i would like to go bigger. just wondering what some thoughts are on that.

heads: I was looking moreso into a set of procomp version 2 aluminum heads, 64combustion 210runner. im open to any suggestions here also. i liked these heads just because ive heard a lot of good about them (that being the version 2/revised procomps) and also because they are a spot where i could save a few bucks but im willing to spend more if needed.

for my trans ill be running a built th350 with a stall of about 3500rpm, which i know is nothing insanely huge or "drag strip only", it may be a little much for the street but im willing to deal with it beings i make a 4500 stall work on the street in my other car.

and as far as the rear end goes- i dont do any mind numbing drugs so i absolutely will not be running the 10 bolt rear, i have a moser ford 9 with 373s and a detroit.

and all this is also backed up by proper suspension mods and so on, nothing too advanced like a four-link, just 1 inch drop coils with bags and tubular control arms, also a 1 inch drop coil front.

but thanks for any advice to come and already given
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Old 09-06-2012, 09:16 PM   #8
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Re: 383 stroker- massive hp on pump gas?

I really like the Howards stuff. In fact I own a Howards track smart forged 3.75 crank. I am guessing the cam your talking about is a small base circle one.
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Old 09-06-2012, 10:00 PM   #9
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Re: 383 stroker- massive hp on pump gas?

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DCR max is 9.0,well some have gotten away with 9.0.I like a margin of how gas varies to have a 8.5 DCR.

Interesting how he has a bored block already and plans of using forged pistons. With forged pistons you want the pistons in hand to set the bore size.
Been there done that once before; Had to have it rebored again. Finally sold that block as it ticked me off..
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Old 09-06-2012, 11:02 PM   #10
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Re: 383 stroker- massive hp on pump gas?

well then maybe it wouldnt be a bad idea to just leave it a 355. and to 1gary- yes, its their max torque retrofit, so basically just focuses on a high duration
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Old 09-07-2012, 12:28 AM   #11
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Re: 383 stroker- massive hp on pump gas?

355 or 383 the same applies to the bore. Look why don't you sell off the block and find a donor vehicle for a BBC 454. Costs more for parts??. Yes it does. But it will produce much bigger results easier.
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Old 09-07-2012, 07:01 AM   #12
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Re: 383 stroker- massive hp on pump gas?

Just take some bore measurements and talk to a builder to see if they have pistons that will be tight. Depending on your power goals a shelf piston may not be that far out and still make good power. Details like piston to cyl wall clearance can extract all the power out of it but you may not need to worry. It may spec out within range and still make power.
Hell even some blower motors with wide ring gaps and low comp have made good power when run natural aspirated on dynos for break in.
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Old 09-07-2012, 06:31 PM   #13
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Re: 383 stroker- massive hp on pump gas?

Quote:
Originally Posted by Orr89RocZ View Post
Yeah id say 11 to 1 is max with big cam and 91 oct. if you want max effort, throw a set of speier 215 small bore heads on it and solid roller cam.
You're one of the few here I'd expect to know better than this. Gary's closer to correct with DCR, but even that hasn't accounted for atmospheric density effects of temp and elevation. These are helpful tools, but ultimately, the only number we really care about is cranking compression, with a goal of 200 psi for the upper limit of pump gas. It's a good goal, because you can carry a couple of bottles of pour-in octane booster, just in case. Predicting cranking compression is not practical, which is why we pay attention to DCR. But for a goal of big HP, a N/A 383 isn't even close. Better to put the money into good EFI then adding boost to a typical Vortec 350, it'll make all the HP a prepped stock block can survive.
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Old 09-07-2012, 09:09 PM   #14
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Re: 383 stroker- massive hp on pump gas?

if thought about a big block, but I just dont know about putting it under the hood of my 82 z28, pretty tight in there
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Old 09-07-2012, 10:46 PM   #15
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Re: 383 stroker- massive hp on pump gas?

Hood scoops resolve that.
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Old 09-08-2012, 10:18 AM   #16
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Re: 383 stroker- massive hp on pump gas?

Thats why i said big cam. If you keep chambers cool with cool plugs limit timing abit and run big enough cam it should be very possible.

My 11 to 1 383 with a so so cam would run on 91 with afr heads just fine but lucky for me i have 93 available
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Old 09-08-2012, 10:39 AM   #17
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Re: 383 stroker- massive hp on pump gas?

buddy of mine ran a 355 at 12:1 with an LT1 for years, but it is reverse cooled. solid roller in the upper 230's duration. street car, drove it to work everyday. went 10.60's with a 6 speed and nitrous, then he changed the car around and went autocrossing with it.
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Old 09-10-2012, 03:00 AM   #18
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Re: 383 stroker- massive hp on pump gas?

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Thats why i said big cam. If you keep chambers cool with cool plugs limit timing abit and run big enough cam it should be very possible.

My 11 to 1 383 with a so so cam would run on 91 with afr heads just fine but lucky for me i have 93 available
Hey Bud.Big enough cam???. You know that is just lowering that SCR along with aluminum heads dropping about a point.Sure,alot depends on what big enough cam,but maybe your still taking about only a 8.5 DCR.
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Old 09-10-2012, 06:57 AM   #19
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Re: 383 stroker- massive hp on pump gas?

My dcr was 8.3 on my car. It ran fine.
11 to one on aluminum with fairly decent cam size is safe imo. I know plenty of ppl on 93 oct and near 11 to 1
Dcr is not the end all be all criteria for determining pump gas compatibility. Head chamber shape plays a roll and so does spark plug type and location as well as your cooling system.

There are 9 to 1 comp race motors that have high cranking compressions because of the cam events. You can cam to increase and decrease cranking compression. Just another variable.
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Old 09-10-2012, 04:01 PM   #20
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Re: 383 stroker- massive hp on pump gas?

Well Orr,the 632 is pretty close to the SCR because of a cam design and etc,etc.
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