loopy

iTrader: (1)

Hi All

I have been researching for days through old threads but haven't been able to answer my own questions (too many contradictions through out the threads) so maybe some helpful person here can advise me.

I have 83 Camaro Berlinetta
700r4 std stall
3.73 Gears.

I am swapping in a vortec 350 crate roller engine, the 255hp one.

I intend keeping the bottom end standard for now but have in mind the following upgrades to hopefully reach the mid 300HP area.

edelbrock RPM air-gap manifold
600CFM carby, probably a Holley Vac 2'ndary
Alex's valve springs
screw in studs
Hedman shorty headers
3" exhaust, no cats, single.

The shop selling me the parts has suggested an edelbrock 2204 cam, but this seems like way over the top to me considering I have stock compression and factory torque converter. As the list above is running me close to $6000 dollars (New Zealand) I cant really afford much in the way of machine work.

90% of this cars running is on the open road so wont see much stop/start driving so lumpy idle wont worry me ( I do like lumpy idles!) but I do want to max the power within the confines of the stock bottom end and head flows.

I do intend to join a car club and do some track days, maybe the odd run down the strip but 90% onroad use.

Can anyone advise me about a more realistic cam profile /size for what I am trying to achieve?

A couple more questions, Will the air gap manifold fit under the standard hood?
Do the hedman shorties Bolt up to the vortec heads ( I read in one thread that they didn't line up yet others have had no trouble at all).

So, yeah that's my plan once I have sorted my confusion

Any comments much appreciated

Cheers
Geoff

skinny z

Cam selection is intimately tied to compression ratio (amongst other things). You're right in your thinking about the cam suggested by the shop you're dealing with. That size of cam would work well with a static compression ratio (SCR) in or around 11:1. I doubt very much your crate engine has more than 9:1.
What you'll need to find out is the actual compression ratio of the engine you're getting. That may be easier said than done.
Here's a primer for you on cam duration vs compression ratio. You may find it interesting. It deals only with the facts.
http://cochise.uia.net/pkelley2/DynamicCR.html

loopy

iTrader: (1)

Hi Skinny

That's a very good link. I wasn't aware of most of that.

The engine I am getting is just the bog std replacement vortec engine for 96-2000 chevy trucks. CR is advertised as 9.4:1.

I am pretty sure its this engine though from a NZ supplier....

http://www.jegs.com/i/Chevrolet-Perf...30283/10002/-1


I wont know actual compression till I get the engine and disassemble and CC the chambers and top of the bores I guess. I do know it has dished pistons.

From reading that article I am guessing that I will need to deck the block and/or maybe shave the heads a bit to run the kind of cam I am after.


Thing is, I wont be toughening up the bottom end in the short term ( I may be able to get it balanced, not sure yet) due to financial constraints so the cam/engine combination needs to make its power within the rev limits of the std block/rod/pistons etc. I guess that means below 5800-6000 RPM in short bursts while making good use of the vortecs torque down low.

Any more advice you may have would be appreciated

Cheers
Geoff

skinny z

The combination of parts you've assembled so far closely resembles my own Vortec build. I had flat top pistons and with a piston below deck value of .030" plus and a .026" head gasket, the SCR came in at 10:1 even. That worked well with the Comp XR276HR. Enough to get my 3700 lb IROC to 12.7 @ 107. Nice sounding idle too since you have that in your considerations. It also netted 22+ miles per Imperial gallon on the open highway. 9.4:1 isn't too far removed from that and popular opinion says that you would hardly notice the slight mismatch. I think Comp even recommends 9 - 9.5:1 for that cam but I believe they tend to be conservative in that regard.
While my short block was stock (NOS 1979 350 4-bolt main) I had ARP rod bolts installed. Although power arguably peaked at 5700 rpm (+/-), it revved cleanly to 6500. (That gave me a better 1-2 shift because of the wide ratio spread in the 700R4).
Some may argue about the size of the carb you have but in all reality 600 cfm should suit your needs particularly if you went with a slightly smaller cam (than the 276). If you target 5500 rpm for peak power and allow a couple of hundred rpm for overspeed, given the volumetric effeciency of an engine like this may have, you should find that 600 cfm will do the trick. As a benefit, part throttle drivabilty and torque as well as fuel economy will be up.
1 HP per cubic inch is completely realistic with the parts you have provided you get the cam right and there are a lot of choices there.

loopy

iTrader: (1)

Funnily enough I was just looking at the XR262 HR cam when you replied.

If I could get an engine that could potentially pull a high 12sec 1/4 mile I would be an extremely happy camper.

I don't mind splashing out on some rod bolts, cheap insurance.

Did you use screw in studs on your build?

As for the carb, its due to the fact the car is 90% street driven.

I don't mind shelling out later for bigger if reqd. For now it will do.

EDIT..... what about a quickfuel 650HR ? I found one locally reasonably cheap. Looks nicer than a holley 600. Cheaper too.
I am assuming that the extra 70 CFM is still within the sensible limits of my build?

Cheers

skinny z

I couldn't find a 262 cam for a Gen 1 SBC but there is a XR264HR.
I did a quick reverse engineering dynamic compression ratio (DCR) calculation and to get 9.4:1 the engine would have to have a flat top piston given the 64 cc Vortec heads, a stock piston to deck height of .025" and a typical .040" gasket. If there's a dished piston in there as you said, then it's not likely to have a SCR of 9.4:1. Having that bit of information is crucial to your cam selection.
That said, with 9.4:1, the 264 will produce a DCR of 7.9:1. That's a fine number for a street driven pump gas car especially with the limitation of the iron heads. My combination required premium fuel. 94 octane is the best we have at the pumps here and I optimized my ignition timing to take advantage of it.
Timing is worth a LOT more than a higher compression ratio.
Cranking compression was north of 200 psi.
I tried to max out on compression and had to be cautious of engine temps and timing otherwise I had detonation issues. My current build which is using an aftermarket Vortec head has a SCR of about 9.8:1 with a custom cam slightly smaller in advertised duration than the 276. Cranking compression is about 185 psi. I feel that leaves me some detonation resistance as I'm big on optimum timing. Not just for the performance aspect but the resulting fuel economy as well.
Getting into the 12's is another matter. Vehicle weight and traction will be the limits here. People have gone 12's with less engine than you're building but with lighter cars than stock 3rd gens. Sticky tires are a must. I run a MT ET street and with a suspension that's orientated more towards cruising than drag racing, I find I'm at the limit of traction at the strip.
Having the heads modified for screw-in studs is the way to go. I went with the Comp 26918 Beehive spring and it all went together with plenty of room for valve lifts approaching .550". No machining required although I did have the guides cut for an aftermarket Viton seal.
If you intend to take the engine apart when you get it (and it sounds like you are) then rod bolts are indeed cheap insurance. Like I said, my stock bottom end (cast crank, stock rods w/ ARP bolts) spun to 6000 for tens of thousands of miles.
The QFT 670 is my carb of choice for a 350/355 that has the specs we're dealing with here. I'm presently running a BG 750 vac sec and find from a driveabilty standpoint it's difficult to tune although I have managed to get decent mileage out of it. Although still undetermined, it should perform well at the track in terms of trap speed if the street performance is any indication. The QFT is on my winter project list.

Fast355

iTrader: (2)

Stock Vortec 5.7 is right at 9.4:1 SCR. The engine I put togather was 9.39:, the stock 12cc dished piston was .015" down the hole, using a stock GM .028" compressed head gasket, and 64.5cc chamber.

skinny z

There you go. The machining tolerances look to be quite a bit better with a later model block than with my old 1979 casting. In fact my piston to deck height varied from .025" to .034". That's all GM stuff except for the Speed Pro hypereutectic pistons.
I wasn't sure which gasket GM would provide in this application. I used the equivalent Victor Reinz 5746 at .026" to boost the compression and optimize quench. I selected an .040" gasket for the OPs compression calculations.
So, if 9.4:1 is the actual compression ratio, then you can go from there.

loopy

iTrader: (1)

Wow awesome information. Thanks so much guys!

I've learnt so much here

vortech2

Hi loopy, I used the GM Hot cam on my vortec build. I bought it as a kit with valve springs and 1.6 roller rockers. Lift is 525 and has a wonderfully lumpy idle.Still running stock converter so its a bit soft down low, but not to bad.I had to have the heads machined for the higher lift cam (standard vortecs will only take 475 lift on a good day)
I am also running the Holley 600 vac sec carb and it is perfect for street use.
I am using hooker 1 5/8 shorty headers and they bolt up perfectly to the vortec heads.
I have had mine dyno'd at 310 hp at the back wheels.
CCH in Christchurch did the mods on my heads,2 inch inlet valves port work and screw in studs.
I haven't touched the bottom end.
You might want to beef up your 700 R4 as well, The extra power of these vortec engines is to much for the standard clutches (mine lasted 300 miles!
Hope this is of some use to you.

loopy

iTrader: (1)

Hi Vortech2

Thanks for replying.

I went with Alex's valve springs to avoid extra ,machine work. They come with shims, retainers and Viton seals.
I brought the QF 670HR today off trade me, was cheaper than the 600 Holleys and Edelbrocks I had been looking at.
I paid for the crate engine last night so hopefully will have it in the next week or so.
Theres a trader on TM with the Hedman 1 5/8" primary shorties so I'll score those too.
Now I just need to know whether a Edelbrock Performer Air-gap manifold will fit under my bonnet.

If you don't mind me asking, who did your auto and what did it cost?
we don't have any auto-trans shops in Blenheim. ( PM if you prefer)


Skinny

The 262 was an oldsmobile one ( Me dumbass _).

So based on theory and what fast said about actual CR, what do you think of the comp XE270HR. Comps site say largest cam with stock converter and its one size below yours. I do prefer to run nothing higher than 96 octane as higher octane are hard to find where I live. We have 91 or 96 (ron) octane locally.

Cheers

Geoff

vortech2

The XE270HR cam is a great choice also, Just don't forget you need a melonised gear with that cam.
I have a Edelbrock RPM manifold on mine with a drop base air cleaner and it only just touches the underside of the hood.
My motor has the mount but not drilling in the block for the fuel pump, Does the motor you purchased have that to? I just put a TBI pump in the tank and run a regulator to reduce the pressure from 15 psi to 6psi.
Hutt automatics did my auto, cost was around $2000. Ouch!
Just make sure your TV is adjusted properly as this really affects the life of the auto also. I fitted a Holley Part# 20-121 linkage geometry corrector also because the geometry is wrong for the TV cable if you just put it straight onto the carb linkage.

loopy

iTrader: (1)

I think mine has the blocked off port too. I was just going to run electric + reg.

I haven't looked too far into that yet, still early days lol.

I have just been into the local engine rebuilders. I'm going to get him to re-assemble the heads with the new springs and seals and fit the screw in studs for me. About $500. He's also going to blend the ports where the factory casting is rough. He doesn't do porting jobs which is ok, I cant afford that anyways.

He has concerns that the standard rocker arms may not like the cams lift and could damage the *****, so maybe some roller tip rockers or roller rockers are in my future too.

As for the TV cable, I'm wondering if the Holley geometry corrector will work on the QF carb. It really does look like a Holley so maybe it will.

I really would like to have a go at rebuilding my own auto but there's a 90% chance that it will end up in a shop after I make a mess of it. Just not sure what to do there yet. I'll probably go ahead and buy all the replacement and upgrade parts, maybe buy the how to DVD and manual and see how difficult it looks

loopy

iTrader: (1)

YEEHAWWWW

My 350 has turned up, HR-680-VS carby has been delivered.

New air-gap RPM manifold is in the post, as are the new valve springs

All that remains to be brought is Headers, flexplate, screw-in studs, rod bolts, dizzy, cam and gaskets and maybe roller rockers.

Getting there slowly as funds permit. It aint cheap down here in the land of the long white cloud

Still toying with cam choice but pretty keen on the comp Xr270HR.

Can anybody tell me, is the vortec's sump an ok fit in a 3rd gen or do I need to add that to my shopping list too.

Cheers

Geoff

skinny z

Sounds like you'll be taking the engine apart so you'll have the opportunity to determine what piston is in there and what the piston to deck clearance is. Once you've calculated your static compression ratio, you'll be better prepared to make your cam selection (Something that's been discussed already but worth repeating).

A word to the wise: Read up on valve train geometry for your new setup. ANY changes you make to an OEM configuration will require readdressing the push rod length you'll have to use. I've been down a damaging road in that regard and it's cost me (and a couple of my racing friends) several sets of valve guides until we educated ourselves and EXACTLY what's needed. Something as simple as swapping out rocker arms may require a different length pushrod to keep everything BOTH centred and compact.
This article is lengthy read but it explains in great detail what you're trying to achieve and how to go about.

http://www.aera.org/ep/downloads/ep1...2010_20-30.pdf

In all honestly, the crap that the manufacturers crank out on their web sites doesn't nearly cover the subject well enough and they all stop short of getting the job done properly. Even the enlightened few here, judging by what they've related through their own posts, don't follow through. (This is all Gen 1 SBC stuff here. With an OEM arrangement of individual rockers, guide plates, studs, etc.)

loopy

iTrader: (1)

Thanks skinny.

I really appreciate you taking the time to educate me in this stuff.

skinny z

I'm happy to.
As far as the cam selection goes, there are a lot of opinions and any one of them may get you the results you're after. You just need all of the data.
As for the valve train geometry, there's only ONE result you're after and anything else is a compromise. Problem is, with poor geometry, you can run an engine and it may perform very well but eventually, the engine starts to use oil, the valve train becomes noisier (despite repeated lash adjustments) and the guides end up unservicable after a while. The length of the "while" depends entirely on how the geometry was compromised in the first place. Most that have overlooked this part of engine building will assocoiate the worn guides with something else, never connecting the two together.
Keep in mind that many things will affect the VGT.
Head gasket thickness.
Rocker arms (both style and manufacturer)
Valve stem height.
Block decking or head milling.
Lifters (both type and manufacturer).
A change in any of these will require a revisiting of the valve train relationship.
Good luck.

vortech2

Hi Loopy, Sounds like all your Christmas's have come at once!
The standard sump that comes with your motor will fit into your engine bay perfectly (mine did)
I have done around 15000 miles with my motor and so far no problems at all. Apart from the auto burning up!
Keep us all posted.

loopy

iTrader: (1)

Tis kinda like xmas here today mate.


Hey, why don't you head down to the regional boards and introduce your self in the kiwi's thread. Theres a few I have seen around here and it would be cool to get together and maybe get a local chapter happening.

https://www.thirdgen.org/forums/paci...all-kiwis.html

I'm not being pushy mate but get yo *** down there lol.

will keep ya's posted with updates.
Skinny's given me a bit of homework to do in the meantime

loopy

iTrader: (1)

Skinny z

That's interesting reading, and when you sit down and think about it, makes sense.

the trick will be (for me) getting hold of one of those adjustable pushrods.

I assume with a split lift cam ( .495in / .502 ex) such as what I am looking at I am going to end up with intake pushrod a little shorter than exhaust, maybe .035"/1.5 (rocker ratio)?........ that's the way I read it or am I over-thinking this?

I'm guess I better go back to re-read this over and over until I have it clearly understood.

Z28NZ

Geoff, I have a pushrod checker
Simon

loopy

iTrader: (1)

Cheers Simon, that's good news. One less thing to have to worry about mate.

I'm still a ways away from needing it, got heaps of parts to buy 1st.

Once I have the heads and block CC'd I can get my actual comp ratio, then buy the correct cam ( or have machining done) and then hopefully borrow your checker. By then I'll be on the home stretch hopefully.

skinny z

There are several checkers out there but I highly recommend the Comp adjustable.
http://www.summitracing.com/parts/cca-7702-1
It's goof proof and what's more is that since different manufacturers measure pushrods in different ways, this eliminates that variable as well if you buy Comp pushrods.
You may find a difference in the requirements between intake and exhaust however what you may find is the difference is so slight it may be very difficult to measure.
Once you get into the actual measurements you'll soon discover some of the limitations that we face because hydraulic roller lifters cams we use. The best bet is to use a checking spring (from any hardware store) and do your testing with that.
More on that when you're ready.

loopy

iTrader: (1)

Things are moving slowly here.

I have just brought some hedman shorty headers, will send them away for coating when they arrive ( I have been unable to source the coated ones).

I am going to leave the cam until I have everything else sorted, would prefer to leave the engine sealed up until ready to disassemble and will CC the engine and order cam then.

I'm a bit worried all the overtime at work is going to dry up before I have all I need so leaving the engine intact means I can install it as is if work slows down. at leas I'll have the use of it then.


Whats the best distributor for my application? I can get MSD stuff or is there a better option?

Cheers

skinny z

Leaving the engine together isn't a bad idea. Heck, even installing it as is and adding speed parts as you get them is about as basic as hot rodding gets.
If should decide to install it as is, you can get a reasonable assessment of the compression ratio via a simple compression test. From there, with a few well made assumptions about the engine architecture (piston dish, head cc, gasket thickness, gleaned from a little research) your next steps could be planned accordingly. One thing I've learned is that maximum operating compression pressure isn't nearly as important as having the ignition timing spot on. If you're off a full point on compression, that is to the low side, you're potentially giving up somewhere around 4% of peak hp. If you're ignition timing has to be compromised because the compression ratio is too high, then you'll leave a lot more than 4% behind. Not to mention the resulting drop in fuel economy. Something to consider.
As for a distributor, the HEI setup is a simple as it gets. Whether it's the MSD brand or not, a top notch ignition module and quality coil are that's needed to provide a reliable spark. I have a full MSD ignition but skipped the HEI style in favour of a small cap distributor and remote coil. To me it was more of an appearance thing as I'm a bit old school. Be absolutely sure that you get a unit with vacuum advance. Better still is a vacuum advance unit that has full adjustability for both amount of advance supplied and the vacuum set point for the advance to begin. That will have to be purchased separately from the distributor as I'm unaware of any manufacturer that supplies a vacuum can with both adjustments.

loopy

iTrader: (1)

Hey Skinny, can you point me in the right direction where to purchase this vacuum module?
Are the MSD street-fire any good? (I believe you cant use adjustable weights on these), Or should I go with the pro-billet for its adjustability?

Thanks Man

skinny z

While I don't have direct experience with the Street Fire model from MSD,

http://www.msdignition.com/Products/...stributor.aspx

I'm sure it's as good as any and probably better than most. Simple installation too. It looks to be that a quality module and coil are included. It has a mechanical advance mechanism that can be modified using one of their spring/bushing kits so that's not a problem. It also includes a semi-adjustable vacuum advance can which may suit your needs entirely. In the event that it doesn't or you find that you really want to get into the advance curve tuning (as I have) then you can always upgrade to the Crane fully adjustable unit.

http://www.summitracing.com/int/sear...m-advance-kits

obliovionox09

I personally really like the XE268 from comp cams, part number 12-242-2, it works great with vortec heads and can be used with stock stall. It creates great torque and hp. also you might see how much it would cost to get the heads milled to increase your CR since you're planning on having them put screw-in studs in. also using the right gasket will help here too, just make sure you double check to math before going ahead, i'd hate for you to break all your valves from being .001 off on measurements. Good luck

loopy

iTrader: (1)

Hi Oblio

The 268 is another option.

I'm playing it by ear until I get the heads off and CR established. Then I can decide which way to go.

Cheers

Geoff

skinny z

I've been noodling around with cam possibilties based on the info I can pull off the net regarding piston dish volume and few other things I (dare way) assume.
http://www.jegs.com/i/Chevrolet-Perf...30283/10002/-1
To get the advertised 9.4:1 SCR out of the standard bore 350 with a 64 cc head, a piston dish of 12cc (which seems to be a popular value) , GMs own .026" x 4.100" head gasket and a production piston below deck of .025", gets you close. My calculator (the one included in the link in post no. 2) gets 9.26:1.
Take that combination of parts, add something like Comps XR270HR cam with your new Comp 1.6 ratio Pro Magnums (how do I know that ?) and you get a tidy 7.6:1 DCR. Chances are you could run that on regular grade fuel.
The subject of piston quench had been brought up however with the factory dished piston, there's no quench pad to speak of so I can't see a critical value being targeted there one way of the other.
Keep the carb size small, like a 600 cfm vacuum secondary with your RPM Air Gap intake and you'll have a crisp little performer. Max power is probably all in by 5400-5500 so the bottom end is stout enough (unless you want to go endurance racing) and there's no need for anything more on the induction side. Use a decent set of headers and an exhaust that breathes and that's about it.
Of course a well spec'd torque converter will go a long way too.
Just thinking out loud here...

loopy

iTrader: (1)

Hiya skinny

Just to get a good quench figure while keeping comp with-in sensible parameters, what do you think of these KB Hyper D relief pistons.
Advertised SCR with 64cc heads and 5.7" rods comes in at 9.6:1

https://www.uempistons.com/index.php...fce18eb02f015d


http://www.ebay.com/itm/SBC-350-CHEVY-Keith-Black-D-Cup-Hypereutectic-Piston-Ring-Kit-KB193KTM-STD-/161114792368?pt=Motors_Car_Truck_Parts_Accessories&hash=item258330a1b0&vxp=mtr
Just playing with options is all

skinny z

As good as any I would think. How did you arrive at 9.6:1? What did you use for piston height relative to the deck or head gasket volume?
Do you intend to re-piston your new engine or will you run it as is for a while?

loopy

iTrader: (1)

I just used KB's advertised comp ratio from their web-site. They don't mention gasket thickness or deck height on the site

I would prefer to have the engine fully built before install rather than change stuff out later.

I am happy to use the standard dished pistons (saves me $500) but if the lack of quench is likely to be an issue would prefer to deal with it now rather than later.

Our fuel octane ratings are RON which means our 96 octane is closer to your 92 or 90.

I'm hoping to use 91 RON in this build as the local fuel pod doesn't have 96 available, that's why I am worried about getting the best possible quench which with the std dished pistons will be almost non-existent.

skinny z

Like you said, they don't mention deck height or a gasket (as they are variables) however with a 12 cc dish, you can speculate to a certain degree.
Consider the need for a re-balance job if the new pistons aren't a reasonable match for your originals.
For what it's worth, if your target compression ratio is low enough (and not so low as prevent any decent power production), then an optimal quench isn't as vital. 9:1 SCR with a DCR less the 7.5:1 isn't likely to give you any trouble with low octane fuel even with iron heads. Keep in mind that the reduced engine efficiency with the lower compression ratio will impact your fuel economy.
Check this out. It's the "Agent 87 (Octane)" build from several years ago.
http://www.superchevy.com/how-to/47075/
The cam specs seem a little dated to me however the combination of the other components may be relevant to your build.

loopy

iTrader: (1)

Hi Kevin

That's one of the chaptors in the HP1400 book isn't it?

I got the book last night on Kindle. Its an interesting read

skinny z

Yes. HP1400.
Remember that a full point in SCR is arguably worth about 4% in power production. So a maximum compression ratio isn't the be all and end all. Build with low engine speed torque in mind and the total hp numbers don't count for much. Small tube headers, small carb, well developed spark curve, a cam that helps to build cylinder pressure, will all make for a more enjoyable drive than one that only concentrates on peak hp.
That's my experience anyway.

loopy

iTrader: (1)

OK, thanks

That still leaves the quench question.

The guys in the above article used D pistons and 0 deck height with .040" gasket to get the correct quench at .040".

My L31 block has dished pistons therefore quench is negligible to non-existent.

I figured, based on figures used in this thread and using KB D piston............

.025" gasket
.015" piston to deck

That gives the optimum quench at .040"

The KB D piston gives an excellent flat surface for quench while the dish helps keep the SCR OK at 9.6:1.

I realise that in the real world there are manufacturing tolerances at play and my .015" deck figure may be much different.

The cam I end up purchasing will need to be happy at 50-60MPH open road with 700r4 and 3.73 gearing but, at the same time, I want to be able to frighten old ladies and jap cars with it as well as the odd trip around a track.

I want to do it right and only want to do it once lol

That's why I am chasing this quench / SCR issue around and around and.........

Thanks for your patience mate!

skinny z

It can't be denied that getting the engine specs right will yield dividends. A tight quench will stave off detonation and give you a hedge against having to run premium fuel. It's the DCR you need to focus on as that is the predictor of cranking pressure and it will ultimately determine your octane needs. That's taking into consideration that you'll keep engine temps in check, both coolant and induction, and have a sensible spark curve. Remember that timing trumps compression every time.
While your approach is 100% the jury is out until you measure the piston to deck height. I won't be surprised if your piston is .025" or more down the bore. That said, at that spec, a .015" shim gasket would get you to where you want to be (.040"). You have a fresh block with a smooth deck and new heads so sealing (as it can be with a shim) shouldn't be an issue.
When are you going to take it apart?

loopy

iTrader: (1)

I been thinking mate............ maybe I have been going about this the wrong way, putting the cart before the horse so to speak.

I wonder if I may be better to decide what cam I want to use 1st based on its characteristics, power figures , driveability etc.........

And then build the engine around the cam eg.......

XR270HR cam

If it needs 9.5:1 SCR. I will buy suitable pistons/rings if mine are not up to it

Then have block/heads machined as necessary to obtain correct comp + quench. I'm tempted to anyway just for optimal quench for our low octane gas here.

DCR can be adjusted by playing with cam duration and overlap cant it?

I will still buy the cam last, once The SCR has been determined accurately as until SCR is figured we have no numbers for DCR.

Am I thinking this through correctly?

I already have a 3 row aluminium radiator and electric Water pump setup ready to install

As for cool air induction I have nothing, although I have been toying with the idea of opening up the hood vents, but that was mainly to create a low pressure area behind the radiator.

I'm not really very keen on most of the hood cowls I see on third gens but if I could use the existing hood vents for induction would be happy to fabricate something there.

I haven't even thought about pulling down the engine yet as I don't want parts lying around for months waiting for me to finish buying parts and save up for machining etc.

Now if I have got this all **** about face I hope you will tell me

Thanks

skinny z

There's nothing wrong with being thorough. If you have time on your side, then put it to good use and continue on with your research.
The XR270HR cam is a great choice for a solid street build with all of the attributes you're after. The regular grade fuel variable WILL limit your power production to some degree as well as impact your fuel economy but a strong and well thought out timing curve, including a well developed vacuum advance curve, will help produce the most power and economy that you can get.

loopy

iTrader: (1)

Fella's like myself too. I'm just a vineyard tractor driver and have been doing 60-70 hr weeks for the last 8 months to pay for this. If I don't have to spend the money I wont and in fact prefer not to but it would be a bigger disaster if I got it together and found that timing advance has to be limited due to being a couple of tenths too high in compression, or conversely compression too low for the cam. That's why I keep talking about quench and higher comp pistons with good quench surfaces. I see it as insurance against low fuel octane and high comp.


Can you expand on this a bit more Kevin? Do you mean because of the low SCR?

feilds

Hey Loopy, just a thought on your quench stuff, when i built my 355 vortec engine i mocked up the crank and a piston and had a quick measure with feeler gauge and straight edge at TDC, got a place in town to hone bores and deck my block by 15thou they also powerwashed it all for $200 cash!!!

Was totaly worth it then i knew it was right and i could use the cheap standard felpro blue gaskets (39thou) with pistons 5thou down the hole. Man that motor runs just as smoth as and is very flexable with timing and fuel 34degrees total will take either 91 or 95 etc.

Also i reckon go for that 270 cam it will sound sooo good, i went mild with a lunati 262 it has strong torque but will still rev out, however i wish i had a little more aggressive idle.

PS vortec heads rock!!

loopy

iTrader: (1)

Hi Fields

Thanks for that. Do you have the L31 dished pistons in yours?

Do you know what your final compression ratio came in at?

Cheers
Geoff

feilds

Hey loopy, nah mine got new speed pro flat tops and came out at just a tiny bit under 10:1 compression, probably the max with my mild cam. Hmm if you got those dished pistons you should still be alright, just did a quick compression calc on summit website with 12cc dish and 25thou deck you might be 9:1.

Heres the link
http://www.summitracing.com/expertad...ion-calculator

skinny z

Got to like the sounds of that. Have you done a DCR calculation based on your SCR and cam specs?

skinny z

[quote=skinny z;5838318] The regular grade fuel variable WILL limit yourpower production...

Yes. Precisely that. The low SCR, or more specifically the lower DCR, willbe needed if regular fuel is your objective. Compression pressure is directlyproportional to torque all else being equal. From most accounts it's best toerr on the side of low compression and keep the timing optimal.

http://www.contactmagazine.com/Issue54/EngineBasics.html

Now to get around to your question, at what point does achieving .040"(give or take) quench stave of detonation? I can't say for certain.

As an example, and I realize it's magazine orientated, Agent 87 has a fewspecs. I've run the SCR/DCR numbers for that build as compared to what yoursmight be with your stock short block.

For a few real world examples, check out some of the L98 builds here atThirdgen. Factory dished pistons and Vortec heads can make for a verysatisfying combination.
Also, Fields has what seems to be respectable combination built around your availabe fuel.

loopy

iTrader: (1)

Hi Guys

I though today to get out of this guessing situation I am in I would take the top of the engine and do some measurements, as follows

I measured the deck/piston height in 3 places on the piston as there seems to be some inconsistencies due to (I guess) piston rock depending on which way I turned the crank to find TDC for that piston.
I don't have a dial indicator so had had to go by touch rocking the crank till I had it right.

Measurement was taken at front of piston and at 90* to crank centreline on both sides of piston.

1st number is front centre, 2nd is 90*closer to crank, 3rd 180*opposite 2nd.

#1 .028", .028", .025"
#3 .028", .028", .0245"
#5 .028", .028", .025"
#7 .025", .028", .028"

I used a straight edge and feeler gauge and looking at the numbers maybe the consistencies are mine, dunno.

I will CC the head as soon as I have had the chance to go to town and grab a spark plug as I don't have any here at the moment.

skinny z

Ha! Couldn't stand the suspense any longer eh?

Well, the .025" deck height is the OEM spec (more or less) so your measurements seem reasonably close.

As for the head, it'll be interesting to see your results. The Vortecs have been variously spec’d as being anywhere from 62 to 66 cc depending on who does the measurements.

Post up pictures of your pistons if you can. Maybe cc the dish too.

loopy

iTrader: (1)

LOL! Pretty much.

Heres the pics you wanted.







I just took a run into town and had the detonation due to heat demonstrated quite well. All winter this car hasn't detonated at all and overtaking a car today in the 1st real warm day we have had and the engine was detonating quite badly as soon as the vac sec's on the carb came in.

I haven't timed this engine so I will probably need to back off a couple of degrees I suppose.

Just to clarify, Kevin, you say that its better to sacrifice compression than timing......

How many points of compression lost is equal to 1 degree of lost advance, in terms of power and economy?

Tricky question?

I cant CC piston dish at the moment as I don't have enough Perspex to cut a piece for the piston top

Back soon with some Head CC figures

skinny z

While it's difficult to slice the timing vs compression question that finely, this excerpt from the paper I posted will give you an idea of what is expected:

"Now our engine was initially designed for premium fuel and was calibrated for 20 degrees of spark advance. Suppose we put regular fuel in the engine and it spark knocks at 20 degrees? We back off the timing down to 10 degrees to get the detonation to stop. It doesn't detonate any more, but with 10 degrees of spark retard, the engine is not optimized anymore. The engine now suffers about a 5-6 percent loss in torque output. That's an unacceptable situation. To optimize for regular fuel engine designers will lower the compression ratio to allow an increase in the spark advance to MBT. The result, typically, is only a 1-2 percent torque loss by lowering the compression. This is a better trade-off. Engine test data determines how much compression an engine can have and run at the optimum spark advance."

Now consider that the traditionally accepted hp loss is about 4% per point of compression ratio reduction. 4% for a full point vs 6% for 10 degrees. My current engine would knock at 8.5:1 DCR (SCR of 10.4:1). I had to pull at least 10 degrees out of it. With the DCR now at 7.9:1 (SCR of 9.8:1), I can run a full complement of advance. Not sure exactly how those numbers stack up but I know now not to get too close to the compression edge. I would counsel anyone to do the same.
Personally, I would leave your short block intact (and save some money), optimize the quench as best you can via an appropriate head gasket and select a cam that keeps the DCR on the low side. You can enjoy the savings of running regular fuel and know that you can put a full timing curve to it without breaking anything. With optimum timing, remember that fuel economy will be better too.
Just my 2 cents.