Buying 455 Edelbrock heads w/068 cam - Pontiac GTO Forum
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post #1 of 32 (permalink) Old 07-24-2012, 10:22 PM Thread Starter
 
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Buying 455 Edelbrock heads w/068 cam

So, I'm buying a fresh 71 455 with edelbrock performer RPM heads with and 068 cam, never ran. The bottom end is a fresh rebuild with .030 stock pistons, so the seller says, but I believe him, friend. I'm assuming stock for 71 is 9.5 compression but I don't know the CC of the stock heads, so the E heads should up that. I don't know the head gasket width, but can fix that with some good advice.. Any experts out there with a guess on power? Should I upgrade the rods? Also, what is the best cam for a 2000 stall, cruiser/torque over the 068. I am considering a roller cam and new rods, but I won't really be beating on it, so this motor should live fine in my 70, the Jury. And give it street cred were the judge couldn't finish the deal, lol..
I have a turbo 350 with a shift kit, and a 3.36 open rear, posi coming next. I have a turbo 375 in the garage to bolt in, how much do I have to cut the driveshaft to bolt the long shaft Pontiac 400 in it?

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post #2 of 32 (permalink) Old 07-25-2012, 05:43 PM
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I can help with a little of this. Stock for '71 455 was 8.2 compression, done with 111cc and 114cc heads. The Edelbrock heads at 87cc will give you over 10:1 compression,which will be fine because they are aluminum......will need the same fuel that a 9-9.5:1 iron headed engine would need. No issues there. An 068 is pretty small for a 455....it would give you a lot of low end and run smoothly and well, though. Absolutely upgrade the rods....new forged are less than $300 a set, and cheap insurance. Others will chime in with more info, hopefully..............
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post #3 of 32 (permalink) Old 07-25-2012, 06:40 PM
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Depends on which heads they are - the round port E-heads come in two finished chamber sizes, 72cc and 87cc. I'd recommend either going a-head (ar ar ar) and pulling one of the heads to measure for sure, or checking for part numbers. I *think* mine have the part number stamped into the ends of the heads by the Edelbrock name, but don't remember for sure.

To really get an exact figure for compression you'll need to know the piston deck clearance anyway, and the heads have to come off to measure that.

Just "rough guessing it", 72 cc's with "usual" dimensions on everything would put you at 11.3:1 with 72cc heads, 9.9:1 with 87cc heads. (.040 gaskets, 4.18 gasket bore, .020 deck volume, 6cc's in the valve releifs)

I'd never recommend building a Pontiac that's ever going to see any 'spirited' driving without putting forged rods in it. Consider them relatively cheap insurance.

I love my solid roller cam, but they're on the pricey side so get ready - also if you go that route you'll want to put oiling restrictors in the lifter bores. Its not hard, I did mine myself, but you do have to thoroughly clean the block afterwards to make sure all the thread cuttings are removed.

How are you planning on driving it? --- Highway? Street? etc.

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post #4 of 32 (permalink) Old 07-25-2012, 09:58 PM Thread Starter
 
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They are performer RPM heads, it's stamped on the front of the head, so I assume these are them. Edelbrock 60599 Edelbrock Pontiac Performer RPM Heads
.575 max lift, so could be hard on a stock cam. 72 CC heads, so 11:1 compression, assume he did something to address this. I want to buy the motor, pull the pan and drop it in. But I know more, so I could put a couple grand more in and have a sweet motor. Funds being tight, throwing it in and upgrading later is a better idea. It has 10 10 crank and plastigauged. I'm doing it as a cruiser/show car, aluminum heads don't burn the paint off. It is an upgrade to a car that sits in the garage, it shouldn't ever see the strip, lol.. Dougs headers are in the future also.
What kind of torque/hp will the motor make as is?

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post #5 of 32 (permalink) Old 07-25-2012, 10:38 PM
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You say it's got the 068 hydraulic cam now? 1.5 rcokers? Factory intake and a QJet?

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post #6 of 32 (permalink) Old 07-25-2012, 10:58 PM Thread Starter
 
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No, edelbrock performer intake, no carb. But seller has a couple 750 Demon double pumpers in the Corner I'm going to try to work in the deal. Stock rockers on it now, no nuts on them, just holding pushrods in. I need to talk to the builder to see why and what. Price is right, but need to ensure it was built to Pontiac specs.

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post #7 of 32 (permalink) Old 07-26-2012, 09:27 AM
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I think 11:1 CR will be marginal and probably too high for pump gas with aluminum heads. The 87cc head would be a much better choice for a street driven car on pump gas.
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post #8 of 32 (permalink) Old 07-26-2012, 11:42 AM
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FYI - both the 72cc and the 87cc heads wear the name "Edelbrock Performer RPM" - you have to use the actual part number (or measure) to be sure what you've got.

I agree that 11:1 is pretty risky for pump gas. You will find people doing it successfully by running the "right" cam ("big and rowdy" enough to manage cylinder pressure), but everything's got to be dead nuts on.

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post #9 of 32 (permalink) Old 07-26-2012, 11:56 AM
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The problem with big and rowdy cams bleeding off cylinder pressure at idle and low rpms, is that it makes up for the lost pressure in spades at mid range and full power. You can cheat a bit at light throttle and get away with it, but when you nail it, you pay the piper. Best to adjust CR to the fuel available, IMO. BTW, Bear, I for one appreciate your 'pocket protector' humor (a-head)!! LOL
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post #10 of 32 (permalink) Old 07-26-2012, 12:07 PM
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Quote:
Originally Posted by geeteeohguy View Post
The problem with big and rowdy cams bleeding off cylinder pressure at idle and low rpms, is that it makes up for the lost pressure in spades at mid range and full power.
'Dat be true and is also another reason why Bear doesn't push the envelope. Right now the Beast is at 10.02:1 with aluminum heads.

In a conversation I had with Jim once I asked him about that very thing (high compression with a nasty cam), and he explained that the idea behind it all is that once the engine gets up into the power band and volumetric efficiency (VE) kicks in causing the pressure to jump, you're at an RPM where eveything is happening so fast that the motor tends to not have 'time' to get into detonation. Detonation is most likely at low rpm under heavy load, like going up a steep hill or pulling a trailer. That's the theory anyway and apparently some people apply it successfully, if they're being truthful.

Regardless, the point is that pushing compression ratio to the limit in a street engine is a risky proposition for at best a low to moderate benefit.

(Oh, and thanks for the kind words about my lame joke.. )

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