Hot Rod Forum banner

Pontiac 400

15K views 52 replies 9 participants last post by  77pontolds 
#1 ·
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.
 
#3 ·
400 Pontiac

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,
 
#6 ·
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.
 
#7 ·
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
 
#8 ·
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?
 
#15 ·
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.
 
#16 ·
LATECH is correct, the 1971 block is a stronger offering from GM, even if you don't plan on building 400 HP or more it never hurts to have a stronger building block to start from.

Roller rockers, again correct, as I mentioned earlier no noticeable power gains on "semi mild" street engines, if you venture to go to a roller cam, then a roller rocker would be something to look into.

You are fortunate that you do have a 1978 block and again LATECH is correct, get some cash from the sale and make your 71 sing.

Ray
 
#19 ·
The 568557 or 557 block was made from late 1975 untill 1979.

Like Creech said, be sure to check your casting numbers.
The 557 is good for a mild street motor, look to see if it has all 5 engine mounting pads drilled, as that could be a strong selling point for anyone with a firebird in mind.
The 1971 engine you have should also have 5 mounting pads, you might check them as well to be sure they are drilled and tapped.
Be sure the block has these for your application, firebird mount locations are different from A and B body cars.
 
#22 ·
I checked the 78 block and it's a 580557. That makes it a good core, but not much use to me. I spent $500 for the whole car, and got the A.C. mounts and motor mounts that I need for the Firebird a new radiator and plus 4 good tires and a lot of other stuff to put in my pile. Now I need to pull the Olds and sell or trade it and keep moving. Thank you guys very much for all the help. Uncle Rich
 
#24 ·
Helo again..Today I talked with a guy who has Pontiac heads. The ones he showed me were 671's and had no A.C. mounting bosses. He said they were from a 1967 G T O ,. They had pretty small chambers. He had other heads that were 4X4M, I think and they had larger chambers. Any ideas?
 
#25 · (Edited)
Those were 670 heads with the casting number on the center exhaust ports. They were performance heads that came on 1967 GTO, 428 H-O, and Firebird 400 engines. They are excellent heads and are sought after by the racing fuel crowd. They have 72 CC closed combustion chambers which will produce 10.20 - 10.5:1 compression ratio ( about 8.5:1 DCR) on a 400 CI engine. That CR and DCR is borderline for today's 93 octane pump gas. You may get by with that CR on a fresh engine but as the mileage increases, detonation will become a problem if the initial timing advance is set at 12 deg. BTDC where the engine will run cooler and better. You will need dished pistons for a daily driver on pump gas therefore you would be better off installing 1971 - 1979 heads from a 350-400 CI engine and keep the pistons you already have.
 
#26 ·
The 671 heads are a real good head, and will increase your compression ratio because of the smaller combustion chamber.

Cast Year CID Horse Power Valve Size CC Application
671 1967 400 350 2:11/1.77 72
671 1967 428 360, 376 2.11/1.77 72 Early Grand Prix 428 H.O.

Static compression, (C.R.) on a Pontiac is a function of the chamber volume and the engine displacement. If the chamber volume is increased, the C.R. goes down; if the displacement is increased, the C.R. goes up. You should be over 9 to 1 on your compression ratio though, but it should put out a bunch of power.

How much does he want for the heads?

Ray
 
#27 ·
670 were a closed chamber?
Were they also a 22 degree valve angle head?
That would mean the piston valve reliefs will need to be 66 style and back. Also the 22 degree angle heads use shorter pushrods.
Better do some more homework before buying .
The 67 326 still used a 22 degree angle head, and pistons that were reliefed for them, I am not sure about any others.
 
#29 ·
The 1967 heads was the last year of the closed chamber heads and that, along with the larger valves in the 670 heads, is the main reason they flow so well. The 1968- 1970 heads were open chamber heads with the same volume and made a little more HP at a high RPM than the closed chamber heads.
 
#30 ·
Hello again. I didn't ask him how much he wanted for the heads, but I could probably buy them for4 not much. I dont think I can use them because they won't accept my A.C. .They are rusty from sitting outside in the shed, but WOW! they have big valves (they almost touch) screw-in studs, guide plates, and round ports (?). The other ones have larger c.c., and the right mounts, but are probably the same as I have on the '71 block.
 
#32 ·
When you hear production Pontiac heads called 'round port' or 'D-port', it's the exhaust port that is being referred to. The intake ports are all shaped pretty much similar.

You might want to look at them a little closer if the exhaust ports are really round. Double check the casting number. A photo would help. Be sure the ports weren't modified by grinding.

The images below shows Ram Air (RA) V top (you will prolly never see a set of these in the wild); RA IV (round port) center (one of the best production Pontiac heads); and the D-port, bottom (by far the most common design).

EXHAUST PORTS



INTAKE PORTS
 
#33 ·
I think you boys are right. I'll put the 71 Pontiac in and enjoy it. I'm a little? too old to play around inside engines. The last one, a 350 4-bolt chevy cosy me $3600 by the time I got done, and put it in my 66 Corvette. I've got a 400 sbc in the shed that I might have to use some day, but I hope not. Thanks, Uncle Rich
 
#34 ·
400 Pontiac heads

I'm finally putting the 400 into my Firebird. Things are going pretty well, except for aligning the motor mounts, but that will happen tomorrow. Somewhere down the road, I might want to put headers on that block, and the stock manifolds don't use the end holes. I'm not going to take them off to see if the heads are tapped. No hurry, but any ideas? They are 99 heads. Thanks, Uncle Rich
 
#35 ·
Pontiac 400 motor mounts

We still can't get the engine to bolt into the body. I removed a 403 Olds, and got new rubber mounts to fit a Pontiac 400. I got the engine brackets from a 400 Pontiac engine that was in a 78 Bonneville. We are trying to install the 400 in a 1977 Firebird formula. We have tried various bolt paterns on the crossmember, to no avail.. The 400 is a 1971 block. We've been at this for four days now, and have pulled the engine at least 4 times. I have never had this much trouble swapping engines before, but I'm determined to make it work!! HELP Please. Thanks, Uncle Rich
 
#36 · (Edited)
We still can't get the engine to bolt into the body. I removed a 403 Olds, and got new rubber mounts to fit a Pontiac 400. I got the engine brackets from a 400 Pontiac engine that was in a 78 Bonneville. We are trying to install the 400 in a 1977 Firebird formula. We have tried various bolt paterns on the crossmember, to no avail.. The 400 is a 1971 block. We've been at this for four days now, and have pulled the engine at least 4 times. I have never had this much trouble swapping engines before, but I'm determined to make it work!! HELP Please. Thanks, Uncle Rich
I had a Pontiac 455 in a '81 Camaro. I used all stock parts from the B-body wagon the engine came from and it fit. I don't recall details on the holes, though. IIRC I welded the motor mounts to the crossmember and left it like that.

What you can do is mount the rubber mounts to the engine brackets using the through bolts an nuts but not tightening them. Then set the engine down onto the crossmember and see if anything lines up. If nothing does, you can mark and drill new holes. I have spot welded them directly to the crossmember, then remove the through bolts, pull the engine back out for drilling/bolting (did this when I put a 455 into a 4X4 Chevy Blazer).

If you do this you have to be sure the engine is square and not sitting too high or low, etc. due to any differences in the B-car brackets vs. the F-car brackets.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top