[69 widetrack]

Originally Posted by 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.

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

[WDCreech]

Originally Posted by 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.

Pontiac, having had block failures, went back to the #488986 block in early 1977, I believe. This block would be fine for a build-up. I would recommend checking the casting number befor doing anything.

[beertracker]

Since you are talking 6X-8 heads and a 400 engine these heads cannot be milled enough to achieve 9:1 because of their large chambers. I have been through this exercise before with my block\head combo (same as yours).

You will have to get smaller chamber heads or zero deck the block then start shaving your chosen head to achieve your CR. You will need to verifiy all this with a CR calculator.

If you mill heads or zero deck the block this will change the push rod length and resultant valve train geometry. I ended up using longer push rods because of this. If you mill the head you must mill an equal amount from the intake side of the head otherwise the ports may not match up. Your machine shop can tell you more about this.

If you change to a cam with a different base circle diameter this will affect push rod length.

See my photo gallery for a picture of stock 400 piston with chamfer. This chamfer lowers CR. Same is true with a valve job, it lowers CR. bt

Originally Posted by 77pontolds

I should do to the 6X heads to have aC.R around 9. to1.

[LATECH]

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.

[beertracker]

Originally Posted by WDCreech

Pontiac, having had block failures, went back to the #488986 block in early 1977, I believe.

Creech, I want to make sure I read this right. Do you mean Pontiac dealerships\service centers saw block #557 failures in stock engines? Or were these #557 blocks hot rodded up then failed?

HP numbers back in 77 was pretty low for a stock 400 block I believe 220 hp or so.

[WDCreech]

Originally Posted by beertracker

Creech, I want to make sure I read this right. Do you mean Pontiac dealerships\service centers saw block #557 failures in stock engines? Or were these #557 blocks hot rodded up then failed?

HP numbers back in 77 was pretty low for a stock 400 block I believe 220 hp or so.

I don't know for sure, but I understand that the factory went back to the earlier block before production stopped in 1979.

Bill

[77pontolds]

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

[cobalt327]

I thought I remembered something about the earlier, stronger blocks having been stockpiled at some point when they went to the 557 casting. When the 557 casting was used up/phased out or whatever happened to it, the earlier blocks came back on line.

[77pontolds]

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?

[MouseFink]

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.

[69 widetrack]

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

[LATECH]

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.

[cobalt327]

They were around 72cc nominal, but NHRA allowed 65cc so they- like all heads- need to be cc'd to know what the volume really is. The 670 head has the later valve angles.

[MouseFink]

Originally Posted by LATECH

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.

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.

[77pontolds]

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.