[77pontolds]

Hi, gang... I just wanted to say hello, and tell you what I'm building. I have a 77 Formula with a 403 Olds, and I'm going to put a 400 Pontiac into it.

[69 widetrack]

Good call, excellent up grade...Now that's my opinion...I'm sure some people may have other viewa. What are you going to do to the 400...what year 400?

Ray

[77pontolds]

Well, I actually have two 400's. One is an older rebuild on a 71-2-3 block. The other is one that I got with the 78 Bonneville that was a one -owner. It has 6X-8 heads and is stock. The older one runs, and is ready to put in, but I think I might put the newer heads on it first,

[69 widetrack]

Well the older one should be a stronger block as well, depending on what kind of upgrades (if any) you do to the older 400, the 6X heads can be a good move, are you planning on putting any more performance into the 400?

[69 widetrack]

What heads are on the older 400?

[77pontolds]

The 71 engine has been rebuilt, but never installed in a car. I've heard it run, and things seem good, oil press, etc. The rebuilder said it now has flat top pistons and a valve job and all the regular stuff. It has 99 heads. I was thinking of installing roller rockers to help out, but since I would have the valve covers off anyway, well You know, one thing leads to another. I wonder what, if anything I should do to the 6X heads to have aC.R around 9. to1.

[cobalt327]

Originally Posted by 77pontolds

The 71 engine has been rebuilt, but never installed in a car. I've heard it run, and things seem good, oil press, etc. The rebuilder said it now has flat top pistons and a valve job and all the regular stuff. It has 99 heads. I was thinking of installing roller rockers to help out, but since I would have the valve covers off anyway, well You know, one thing leads to another. I wonder what, if anything I should do to the 6X heads to have aC.R around 9. to1.

The 6X-4 heads have a smaller chamber. Makes upping the CR easier.

Using the -8 heads you need to remove a little over 0.050" from the head decks to get about 8.5:1. These are rough estimates- the heads have to be CC'd to know what the volume actually is. I have never tried to get 9:1 using -8s, so someone else can fill you in on the plausibility of that. My thoughts are it will take too much milling, but that's me.

The '75(?) and newer 400 pistons have a large chamfer around the outer edge, plus a dish and valve reliefs. Your earlier engine doesn't have these pos slugs, so that's a plus as long as they weren't replaced w/the later pistons or those godforsaken 8 valve relief "one size fits all" pistons.

Use straight wall studs (ARP p/n 190-4003 w/hex nuts, or p/n 190-4203 w/12-point nuts, or stock BBC studs will work) to get away from the weaker bottle neck studs.

Some Pontiac info:

• Info/sites
• Pontiac engine info

[69 widetrack]

If I'm correct the #99 heads are 1971 vintage yielding 265 HP in a 400, The 6X heads have bigger valves 2.17 intake, 1.66 exhaust, but lower compression. Milling the heads will increase compression some but to get to where you want to be might be tough. Have you looked at finding an older set of heads, or maybe a set of 4X with a smaller combustion chamber to increase compression?

[69 widetrack]

Originally Posted by cobalt327

The 6X-4 heads have a smaller chamber. Makes upping the CR easier.

Using the -8 heads you need to remove a little over 0.050" from the head decks to get about 8.5:1. These are rough estimates- the heads have to be CC'd to know what the volume actually is. I have never tried to get 9:1 using -8s, so someone else can fill you in on the plausibility of that. My thoughts are it will take too much milling, but that's me.

The '75(?) and newer 400 pistons have a large chamfer around the outer edge, plus a dish and valve reliefs. Your earlier engine doesn't have these pos slugs, so that's a plus as long as they weren't replaced w/the later pistons or those godforsaken 8 valve relief "one size fits all" pistons.

Use straight wall studs (ARP p/n 190-4003 w/hex nuts, or p/n 190-4203 w/12-point nuts, or stock BBC studs will work) to get away from the weaker bottle neck studs.

Some Pontiac info:

• Info/sites
• Pontiac engine info

See, there you go, lots of good information this site.

[69 widetrack]

Roller rockers by themselves aren't going to improve performance to any great degree. Put a good camshaft underneath them and you will notice considerable performance.

[77pontolds]

Thanks for a lot of help so soon!! Maybe I should leave well enough alone and just put the older one in as is. I know how to do a few things to improve on the ngeneral, but it involves tearing down.

[77pontolds]

Concerning the roller rockers, I was told by the rebuilder that the cam has a lot of overlap, and was probably made by COMP cams. More info as I get it.

[77pontolds]

OOPS!! I meant duration as well as overlap.

[69 widetrack]

Understood what you meant, specs on the cam would be great, more info = more help. Even a cam number that could be crossed over would help out.

[LATECH]

Dont spend money on roller rockers. They wont do anything for performance on a street build.

The 78 block is most likely the 557 block. It will be an OK block, but if your building in excess of 400 horses the older block would be better.

If it were mine, I would sell the 557 as a buildable core, and use the money to get what is needed to put the other one in the car.