Your engine should have come with 6X-8s, which were smog heads and should yield 8.1-8.2:1 compression. 6X-4s would give you substantially more, but will still be pump gas friendly. Most of the pre '71 Pontiac heads of 72-75cc will produce 10-10.7:1 with a standard bore, zero deck piston.

Bill

 

Ok, wanting to get some more compression from my 78 pontiac 400. Has 6X-4 heads, smaller chamber, but only has 7.7-8:1 compression. I want to get it up to around 9.5:1 or even 10:1. (dont tell me about it not running on pump gas, I know it most likely wont)

What heads do I need to look for, or can i get these decked enough to accomplish what I want?

Also, when the heads come off, i want to put a little better cam in it. The one thats in it is a 10 year old grind, so its time to update. Wanting to get some more power/torque. Running 3.73 gears, torque converter is stock, but will be changed with the cam. Looking for suggestions.

thanks!

HERE is a chart giving estimated CR for various combustion chamber volumes. With a standard, undecked block, 0.041" gasket the 6X-4 will get you about 8:1 CR. A better choice would be another head altogether, like a #12, or #16. And to get the deck height down.

 

I always heard that the pistons in the later blocks sat way down in the block. Once I get my current project done, this engine is coming out and getting gone through. When I started it this morning a big POOF of oil smoke came out, it WAS rather cold this morning, but the engine was built 10-12 years ago, so its in need of a freshening.

Would zero decking the block get me where i want to be?

Or would that be a bad idea?

...or should I just pull my 12:1 355 out of my dirt car and stick in there *evil giggle* 415 hp with a 350 cfm 2barrel...stick a BIG deamon on it and go ricer hunting!! sorry lol, anywho...

Why dont you hear stories about finding pontiacs with good performance stuff on them for 200 bucks, like you do with sbc's? oh well...keep the suggestions coming!!

 

from my experience on pontiacs over the past 12+ years, every block ive cracked open had a 0 deck height. mabe i got lucky, or mabe they didnt make them every other way, ive built 3 engines at a machine shop and many many oki rebuilds. the slugs always come up to deck height.

if you want crazy compression, you can build a set of closed chamber heads, 58-64cc's but a 72 cc head is pretty much the limit on the street without ethonal or race gas

 

Zero decking is a move in the right direction. Fortunately, CR in the Pontiac isn't quite as critical as w/a Chevy, but having a decent quench figure is important for getting the best detonation resistance as possible. The chambers are machined- albeit a "groovy" machined- i.e. you will see the machining lines on most all Pontiac chambers if you look closely.

If you want to really get after it w/a big, long cam, you'll need more CR than you can safely get w/6X-4 heads, IMO. They'll need too much taken off the decks and you'll be going through head gaskets.

The choices then are to go w/a better D-port head, find a set of RA IV heads, or go w/a set of aftermarket aluminum heads.

The deal THEN becomes the rods- they're cast iron as you know, and aren't good for anything above 6K RPM, maybe a bit more (but who wants to find out how much more ain: :sweat: )- and that's w/ARP hardware.

So, by now you see the rods need to be replaced. For a pittance more, you can stretch the stroke of the 400 to the 455 arm- and have a smaller main journal OD to boot.

This is where most guys find themselves eventually. That is, deciding on keeping things docile enough for cast rods and crank, or biting the bullet and going w/forged rods and a quality cast crank (forged if needed) and aftermarket heads to make some power.

BTW, you want to make the CR by the chamber size, not domed slugs. They're expensive and inefficient.

Some sites for info:

Butler- http://www.jbp-pontiac.com/

Kens- http://www.angelfire.com/fl4/pontiacdude428/kensspeedandmachineshop.html

Nunzi- http://www.nunzi-pontiac-expert.com/

Rock & Roll Engineering- http://pontiacpower.com/

SD Performance- http://www.sdperformance.com/

Pontiac magazines on on the web:

http://www.pontiacstreetperformance.com/

http://www.highperformancepontiac.com/

And others, you can do a search on google for them. The magazines all have tech sections w/articles, etc.

Verify everything- Pontiac lore is flat ATE UP w/bad or misleading and/or incomplete information.

Good luck.

 

With that 78 engine it's a long way to the top if you want to rock and roll.

 

It will be brought up sooner or later, so might as well get it out of the way here and now.

Check the casting number of your block. Hopefully it will be a c/n 481988 block- it should be. They are the better of the two blocks used in the latter years of 400 Pontiac engine production.

If it's a 500557 block, don't plan on stroking it- it as made lighter (and somewhat weaker in the process) and isn't recommended for making that killer 455 with. It IS fine for a 400-450 HP street engine.

 

It will end up being a money pit, that's the nature of the beast. Too many things need to be changed.

 

It will end up being a money pit, that's the nature of the beast. Too many things need to be changed.

money pits is the name of the game!!

in the process of building a stroked 400
275 for 4.25" stroke
460 for 6.8" H beams
690 for ross pistons
3 grand for a used set of ported KRE's with new valve job new valves
560 for lifters
320 for cam
230 for rockers
150 for pushrods
100 for felpros
90 for oil pump
1900 for MFI
$7775?
and i dont have the machine work or bearings yet????

almost wanna pull a second of the damn house hahaha

 

so........the "smart" thing would be to put a sbc chevy in it...or a bbc.

 

so........the "smart" thing would be to put a sbc chevy in it...or a bbc.

It would be the "cheap" thing, but I hesitate to say "smart".

Pontiac's have their own panache, either you feel it or you don't, IMO. If you don't, then by all means, go w/a Chevy. Cheaper per HP, no doubt. But just so darned boring is all. At least a BBC would haul the mail...

 

Finding Chevy stuff is easy. Finding Pontiac stuff is not so easy unless you did it years ago. Now you pay much more for the Pontiac stuff. It's been over 30 years since they made a 400. Lots of them have been lost to the scrap yards and people blowing them up.

 

SBC Vortec gasket compared to Pontiac D port gasket.

 

There is also about a pound each difference between a SBC piston and rod and a Pontiac piston and rod.

 

It would be the "cheap" thing, but I hesitate to say "smart".

Pontiac's have their own panache, either you feel it or you don't, IMO. If you don't, then by all means, go w/a Chevy. Cheaper per HP, no doubt. But just so darned boring is all. At least a BBC would haul the mail...

Then im in a pickle...cause I love my pontiacs! ...great.

 

l:

Then im in a pickle...cause I love my pontiacs! ...great.

:evil: Pontacs? I see a Mopar and you mention a SBC.

 

l:
:evil: Pontacs? I see a Mopar and you mention a SBC.

huh? im confused...but that happens. please explain.

 

You are selling a Mopar.

 

Now I am confused. Where is the Pontiac?

 

oh! yeah, the mopar was my "nice" car, but im just tired of it. I havent got any pics of my pontiac up here...yet...but will here in a few minutes!!!

 

This is how you bump up the compression. The problem is they cost more to rebuild than you can find a good set of Vortecs for. And then you have to deal with the bottom end.

 

But, i have all the equipment to rebuild heads. valve and seat grinder, guide replacement stuff, the only thing i couldnt do is surface them, and pull the seats. Whats a set like those cost?

 

Don't know, I never sold a set. Pontiac owners are cheap. :thumbup:

 

I hear ya!

There is a salvage yard about 30 miles from me that has a couple pontiacs, i guess i really should go get them before they get crushed!

 

and about the bottom end, I've heard 5500 rpm...maybe 6k max!

I really don't want to rev it much higher than that, its never gonna see the strip, just the occasional showoff in town and some weekend cruising.