henry172

iTrader: (2)

So my uncle is trying to build a 73 Pontiac 400. The block he has is a 73 400 block, he has a set of 1965 #15 heads 72cc with larger valves installed. What he is wanting to do is build it with the factory crank and rods possibly upgrade the rod bolts. He is thinking about running this cam http://www.lunatipower.com/Product.aspx?id=2355 and is undecided on the pistons. What piston and cam would be his best option for CA 91 octane; his previous build with a 270h comp cam and other 64cc heads detonated and destroyed the rings of the stock pistons. He is used to building sbc's and I know my way around the newer lt1s but neither of us know a lot about these old Pontiac engines. I appreciate any help.

RevGTO

iTrader: (12)

You'll need a dished piston to get to a 91 octane compatible compression ratio on a 72cc head. Most of the available ones give you about 9:1; using stock style flat tops will give you 10:1 which will still give you detonation.

I have a Lunati cam that's has less intake duration and more exhaust (220/230) and a little less lift, also on a 110+4. Idle is rough, but it makes power throughout the rev band. You will need BBC rocker arm studs for a cam with that lift.

henry172

iTrader: (2)

Thanks, and yes I have been telling him he needs dished pistons, other less knowledgeable builders have been telling him he will be fine with the flat tops and 72cc heads. He is thinking about the .030 Icon 891 14cc dished forged pistons; I am thinking it will still be pushing it on the compression. The other issue is the cam, I am thinking it is too much cam for what he wants along with the stock stall. Also we had no idea he would need the BBC rocker studs, what would be the best cam choice for the factory stud and 1.5 rockers? I am thinking something more like this http://www.lunatipower.com/Product.aspx?id=2354&gid=297

cambirdracing

iTrader: (4)

You nee to jump on this board:

http://forums.highperformancepontiac.com/index.html


I personally can tell you that 72cc heads are going to have to much compression, personal experience. I could change head gaskets on the side of the road. Tell him to find some 6x-8 heads. They have a larger cc and will end up around 8.5 c/r pump gas friendly.

And don't apply any Chevy knowledge to a Pontiac, it doesn't work. Another personal experience.

DO upgraded the rods bolts. Or better yet if he has extra change laying around. Get a 455 crank that the mains ar turned down and bore the block .030 and throw in a set of 455 pistons. Very easy to do, all bolt in stuff. Ohio Crank does this. All Pontiac rods are the same length, so you can still use the 400 rods, just polish the beams and you should have a reliable engine.

But go to the HPP message board and those guys will help you a lot and not steer you in the wrong direction.

Oh yea, and the BBC rocker stud, all it does is make your rockers adjustable, but you will need to get the nut also as Pontiacs use a 3/8 bottle neck stud. It uses a 7/16 ball, but a 3/8 nut and not adjustable.

henryz28

My uncle and I talked to a local builder and he is saying a cast 4 valve relief piston will work fine with his 72cc heads and 91 octane.

henryz28

He says 8 valve relief flat tops will work not 4 valve. I need to sign him up on that Pontiac site.

Bob@BruteSpeed

iTrader: (16)

I didn't think they used a #15 for a head number on the 389 heads? Are you sure they're not 68 400 heads? Bob

VandykeT/A

15s shouldn't have came on the 389s. I wouldn't run a 72cc head with the stock pistons. I've got the same dilemma which leaves me stuck with 7.6 to 1. If I were him I'd find some 6x-4s and mill them some. 15s came on the 400s and the 455s. If it was a 455 head they aren't the 72s they're 87. You don't want to go over about 9.5 to 1 on that thing or he'll be doing it all over again. If you do stroke it make sure its not the 500557 block. I've read they aren't the best foundation for a stroker.

RevGTO

iTrader: (12)

Yes, those 8 relief cast pistons work ok on 400's; the reliefs are deep enough. I had those in a GTO engine with no detonation problems.

The #15 heads are 1968 400 small valve heads with pressed-in studs. Not a high performance head.

IIRC, the BBC stud shaft is 7/16 while the Pontiac is 3/8 and hence stronger. My builder replaced them after the Lunati cam caused a broken stud. Of course, that's not an option with pressed-in studs unless you tap the stud bosses.

01tam6

iTrader: (1)

A pontiac engine will not take the higher compression ratios like the sbc the chamber design is different. I would stay with a 9:1 cr and don't go crazy with the duration on the cam pontiacs are not easily built into a 7500rpm screamer they are great on torque and there are setups making good hp and tq keeping it under 6000rpm.

MrElectric03

iTrader: (71)

Id try this site also, lots of good ol poncho info. They have all tried different combos and know what works.

http://forums.performanceyears.com/forums/index.php