[78MayanW87]

Hello experts! New around here and just picked up a '78 Trans Am. I have not been able to get to all the codes but I wanted to check to see if I was on the right path here... The car was sold as a non-numbers matching 400 and the PO believed that it was a 1977 engine but now I am wondering if it may in fact be a 1967 motor. Perhaps a '77 engine with '68 heads? I have attached pics below but here is what I have so far:

VIN stamp on passenger side of block by timing cover: 27?xxxxxx (the first four digits are pretty hard to make out)

Engine Code on passenger side of block just below the head: XA 8008. What does 8008 reference?

Head Code: #62
Head Date: J288

Any and all help is very appreciated

[johnta1]

The block is a 1977 400, should be a block casting code on passenger rear of block, probably 500557.

The 1967 had no partial VIN on it. ( the 67 block would have a block casting code of 9786133)

The heads were changed probably for more compression and maybe more power.

[unruhjonny]

To build upon John's post;

The XA engine code is telling;
It is an unusual code that was only used (as far as I know) for 1977 on a 400;
For 1978 that engine code was used on a 301.

All 1977 400's are '557 blocks, this is a casting that was introduced later in the 1975 model year, and used till 1977 for all 400's, and I believe it was also used in 1978 on non-W72 400's.

The number underneath the block code is an Engine Unit Number;
I suspect there are more characters there if you clean it up and look closely - this number was used for warranty purposes.

The best way to identify any block is as follows:
1) look for the block casting number (pontiac put it on a flat behind the right side cylinder head
2) look for the casting date - it will be cast near the distributor hole.
3) the stamped block code.

Those heads are 1969 "72cc" large valve heads;
I believe that they were used on 400 & 428 engines.

The date code on those heads decodes as follows:
J = October
28 = day of month
8 = last digit in calendar year
October 28th, 1968
This is firmly during the 1969 vehicle model year.

If my memory serves me, those heads need to be matched to either an aftermarket, or factory intake manufactured before the 1971 model year.
If a factory intake cast after the onset of the 1971 model year is used, there will be a pretty decent exhaust leak - assuming that nothing has been done to remedy this.

[78MayanW87]

Originally Posted by unruhjonny

To build upon John's post;

The XA engine code is telling;
It is an unusual code that was only used (as far as I know) for 1977 on a 400;
For 1978 that engine code was used on a 301.

All 1977 400's are '557 blocks, this is a casting that was introduced later in the 1975 model year, and used till 1977 for all 400's, and I believe it was also used in 1978 on non-W72 400's.

The number underneath the block code is an Engine Unit Number;
I suspect there are more characters there if you clean it up and look closely - this number was used for warranty purposes.

The best way to identify any block is as follows:
1) look for the block casting number (pontiac put it on a flat behind the right side cylinder head
2) look for the casting date - it will be cast near the distributor hole.
3) the stamped block code.

Those heads are 1969 "72cc" large valve heads;
I believe that they were used on 400 & 428 engines.

The date code on those heads decodes as follows:
J = October
28 = day of month
8 = last digit in calendar year
October 28th, 1968
This is firmly during the 1969 vehicle model year.

If my memory serves me, those heads need to be matched to either an aftermarket, or factory intake manufactured before the 1971 model year.
If a factory intake cast after the onset of the 1971 model year is used, there will be a pretty decent exhaust leak - assuming that nothing has been done to remedy this.

Thank you both for the info! That is super helpful. I was able to verify that the block is a 500557 and from the reading that I have done here on the forum, if someone wanted to build up an engine exceeding 400 hp, this would not be the block to do it with. Fortunately, I don't have plans on making this really anything beyond that 400 mark.

Regarding the intake code, it is 481733 which I believe to be a 1971 or else was used on model year '71s. There is no exhaust leak at least not a noticeable one. Perhaps you can verify the code as one that should have paired with the #62 heads.

From what I understand, those #62 heads are likely pushing the CR up near 10:1. Any advice on how to handle that from a fuel standpoint? Assuming that I am not hammering on it would it suffice to run 91 octane plus some booster? Also, not to get to far afield here but I pulled the plugs yesterday to inspect them and they are R45STX gapped at .056. From reading here on the forum it seemed that for an HEI car, it was split between folks saying .045 was good and .060 was good. The plugs all looked fairly new (likely less than 10k miles) and so I didn't change them or the gap. Thoughts? Also, the timing was at 4 degrees?!?!?! I set it at 12 at idle (800 rpm) in park. Thoughts on that?

As a side note, while I had the plugs out, I ran a compression test and it ranged from 148-152psi after 4 revolutions. I didn't see any noticeable leak off.

I have not been able to access any other block codes yet but I think from y'all's help, I feel pretty good knowing what I have at this point..

Thanks in advance for sharing all your knowledge!

[johnta1]

481733 is for a 1971 engine. The intake is good with the 62 heads. The problem is with 72 and newer with 71 and older parts.

If it has the original pistons in the block, the cr would be a little lower from the extra space from the piston bevels.

[78MayanW87]

Thank you sir!