[sphynx88]

'78 Pontiac Firebird with a stock 400. 6x-8 heads. 2.56 posi gears.

Thinking of opting for the Edelbrock 72CC RPM heads as (as opposed to the 87CC which I hear is better suited for 455's but someone please tell me otherwise).

Currently I have a stock stall converter and the Comp XE262H cam. Would this cam be okay with the higher compression heads or would I be better suited with something else. No problem to swap out of for a higher stall if I need to.

I'm also looking at the Edelbrock Total Power Package which includes heads, a cam and an intake, however I'll need to also acquire a drop base for my shaker which just adds to the overall cost.

Just based on this thread, it seems like with my gears, I may benefit from my smaller cam than the power package one, but just looking for validation:
https://forums.maxperformanceinc.com...d.php?t=423212

Lastly, is there much else I'll need for this project aside from checking/ordering pushrods and potentially a higher stall converter? Seems like I can use stock rockers, but maybe a good time to also jump onto some roller rockers.

Thanks!

[78w72]

Will let others suggest a cam, but if you use the 72cc heads it will raise the compression a lot vs the 6x-8 heads that have ~103cc. Use a calculator to confirm the compression with the E-heads.

With higher compression you can use & definitely would want a bigger cam to work with that higher comp... & that will require a higher stall converter, they should be matched to each other for best performance, the 2.56 gears will limit how big the cam & how high the stall can be. Hopefully some of the cam experts here can suggest the best combo for that.

A factory intake ported or unported wold be the best intake with any street type cam you pic, dont need the RPM intake to create problems with the shaker or hood clearance. Even a holley street dominator or torker2 if you use a holley type carb wouldwork better than the RPM intake... & there are much better cams than the edelbrock options. Definitely need to check pushrod length when changing the cam/heads.

[Steve C.]

https://butlerperformance.com/n-1287...alculator.html



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[JB Eng Wis]

Just my thought..... Save all that money , from not buying the power package...
#1 change your rear gearing... see how you like it.... then #2 look for a Torque Conv...

[scott06]

Originally Posted by JB Eng Wis

Just my thought..... Save all that money , from not buying the power package...
#1 change your rear gearing... see how you like it.... then #2 look for a Torque Conv...

probably the cheapest way to wake it up vs 2.56's can run a sedate 3.08 or 3.36 ish and still have low highway rpm

[steve25]

A agree with post four 100%!

With your 2.56 gears Bolting on the RPM heads with there greater port area even with a gain in compression and without a swap to a tad bigger Cam will sacrifice around town drivability.

[Jay S]

If it has the stock 78 pistons in it yet with the big bevel on the piston top the compression with the 72cc heads would only be in the low 9s. That would work fine with that small XE.

[Tim Corcoran]

With 2.56 gears you don't really want to put in a high stall torque converter. Those gears are great for MPG and highway driving not so much for drag racing. If you want to keep those gears put in a small cam that makes big torque and keep the stock converter. And if you put eheads on, it will have tons of power and easily go 150+ MPH. Use the factory iron intake and a well tunes Q-Jet nothing will work better. Make sure you port match and blend in the intake to the new eheads.

This cam would work well with your gears and a stock converter

https://butlerperformance.com/i-3164...tegory:1234796

[Skip Fix]

Waste of head flow with that small cam if you do that! Heads and cam change as well as an intake change the 78 intake unless massaged will kill flow to E heads.I ran a 72 HO intake on some for awhile .
Having swapped out my 2.56 I agree a gear change will make the most change. Too much convertor and a 2.56 it will never lock up and create too much heat for your trans.

[Skip Fix]

But with 2.56 gears you can run 130 mph just turning 4000!

[Tim Corcoran]

Originally Posted by Skip Fix

Waste of head flow with that small cam if you do that! Heads and cam change as well as an intake change the 78 intake unless massaged will kill flow to E heads.I ran a 72 HO intake on some for awhile .
Having swapped out my 2.56 I agree a gear change will make the most change. Too much convertor and a 2.56 it will never lock up and create too much heat for your trans.

If you put a large duration cam in a car with 2.56 gears it will be a dog. My recommendation for a cam is what a car with those gears would need for best performance. It doesn't matter if its taking full advantage of the airflow or not.

[tom s]

Run what you have and just put like a 3.30ish rear gear in it.After that then decide if its enough for you.JMHO,Tom

[carcrazy]

Change those gears!!! (first)

[phil400]

Please before you do anything else or spend anymore money Find a copy of Jim Hands how to build a high performance Pontiac for stock stuff or Rocky Rotella newer version for big $$ stuff.

[Cliff R]

If you install 72cc heads the compression ratio goes from about 7.5/7.7 to 1 up to at least 10 to 1. That is a HUGE increase in static compression and with that tiny little XE262 cam dynamic compression will be high, maybe even past the threshold for pump gas even with aluminum heads and "modern" combustion chambers.

The increase in compression is opening the door for more camshaft. At a minimum I'd move up to something around 222-224 @ .050" and wider LSA. At least you'll start to take advantage of the improved head flow as Skip mentioned and make more power at every RPM.......

[Skip Fix]

Originally Posted by Tim Corcoran

If you put a large duration cam in a car with 2.56 gears it will be a dog. My recommendation for a cam is what a car with those gears would need for best performance. It doesn't matter if its taking full advantage of the airflow or not.

All depends how big you go. Even in a low compression 400 6X head mine was fine with a 228/228 @ 0.050 once I got a carb with a better idle circuit

[Jay S]

Originally Posted by Cliff R

If you install 72cc heads the compression ratio goes from about 7.5/7.7 to 1 up to at least 10 to 1. That is a HUGE increase in static compression and with that tiny little XE262 cam dynamic compression will be high, maybe even past the threshold for pump gas even with aluminum heads and "modern" combustion chambers.

The increase in compression is opening the door for more camshaft. At a minimum I'd move up to something around 222-224 @ .050" and wider LSA. At least you'll start to take advantage of the improved head flow as Skip mentioned and make more power at every RPM.......

I come up with 9.57 SCR if it has the stock pistons.

[sphynx88]

Thanks for all the replies everyone! Looks like I'm going to be looking into regearing in the near future. I don't drive the car long enough distances to warrant these gears! I'd prefer to keep my current carrier and run the spacer/shim. I dont think I make enough HP for it to be a big problem. Am I crazy for that thought?

[Tim Corcoran]

Before you do anything make a plan. What are your performance goals and how much do you plan on spending on the upgrades. Your car will run fine keeping your 2.56 gears it just won't accelerate as fast as it would with lower gears. My point is if you stick with the 2.56 gears don't over cam it or it will perform worse than stock. You have to look at the complete package. If you get eheads and a big cam now you need lower gears and headers too, oh now you need new 2-1/2 exhaust pipes and turbo mufflers. Now you need suspension and brakes to be up to the increase in power, will your trans now take the power and will that 10 bolt rear hold up to the increase power. Don't forget about the high stall converter too. How much will all this cost what have you got yourself into and when your done will you still enjoy driving this loud gas guzzling machine and maybe you will blow up the short block because it's old and tired and not up to all these upgrades. Just giving you some things to consider before you start buying parts. Good luck

[Skip Fix]

Remember with a gear change you will need a different posi carrier. 2.41 and 2.56 used on , 2.73 up take another. Having ripped all the ring gear bolts out of my high school Impala not knowing it had a spacer plate I'm a little gun shy! I probably have an extra factory carrier but an Eaton 28 spline is stouter and probably better shipping . Check with Tom's Differentials.