# Help with ID and estimated HP of a 455



## billsnp5 (10 mo ago)

Its hot here in Vegas. Can't go fishing, cruising or anything else out side other than the pool and casino. So I thought I might try to find out some info.

I bought a 64 Tempest with a 455, 200R and a Currie 9" 3.25 posi. Car is not a race car by any means but runs good, looks good, sounds good, doesn't leak any fluids and will light up the tires. I do not believe the car has many miles since engine was rebuilt as I have put over 2k miles on her and oil is still full and oil looks new and so far zero leakage of any kind in garage floor. I know there are many Pontiac experts here and I would love to know exactly what engine and engine parts I have and an idea of horsepower.
I think it is a mixture of parts. Hopefully they are a good mix of parts.

First the block casting number is 483677 with a date code of H31 built in August of 71. The number on front of block is 53552 with a YC code. The 483677 and YC code do not match together on anything I have found. Pictures attached.
From what I can figure out it is probably a 72 GTO 455. Some sites states a 220HP but some say the smallest HP is 325. The site I looked at states 325HP.

On the heads there is a 9536 stamped on the front passenger head, no idea what that is. A H270 date code which is Aug 27 1970.
The heads on drivers side there is 6 on front piston, 6 6 on the middle two pistons and a 6 on the back.
The passengers side there a 7 on the front piston 6 6 in middle and a a whatF on back piston.
it looks like they were for a 1970 400 Ram Air

On the drivers exhaust manifold there is a GM8 with a 9791637 part number. I cannot see a passenger side number. It looks like they are 68 GTO 400 HO Ram Air.

I believe it has a Comp Cam #51-230-3. Doesn't look like anything special but the car sounds good..

If there is any info that I am missing that would help let me know. I would appreciate any help.
Also if I get some extra money I would like to know if this would be a good engine to bring to another level.


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## Sick467 (Oct 29, 2019)

The 66 heads seem to be from '71. They are large valve heads, which is good, but they are also large chambered heads (144 cc's). Those heads came on the 325HP 455ci engine. The compression ratio would have been around 8:1 when stock. If the pistons have been changed, block decked, or the heads modified, who knows what the compression ratio is now. That makes a big difference in horse power if pushed up to 9 or better. If it runs well on 87 octane, I'd say you are very close to the 325HP and 8:1 compression, maybe 8.5:1 with the decking that often happens with a rebuild. If you have to run 91 octane, your compression would be higher than 9:1 which means a good jump in HP. I would venture to say a 25 to 40 HP gain could be had depending on how high the compression ratio is. The cam is a step above stock which could add some power, but my cam spec knowledge is very limited to even guess the gains.

I only see one year for the 66 heads from Wallace Racing here...



Pontiac V8 Cylinder Heads



Compression ratio estimate came from here using the stock head chamber size of 114cc's...






Pontiac Cylinder Head and Engine Compression Ratio Chart


Wallace Racing Home of Pontiac Powered Firebirds,Trans Ams,Pontiac Powered Dragsters,Pontiac Power Rules!



www.wallaceracing.com


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## billsnp5 (10 mo ago)

Thanks for your input Sick.


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## BearGFR (Aug 25, 2008)

According to the Wallace Racing site, 483677 + YC with #66 heads is a 71 325 HP 455 out of an automatic transmission car. Although it's a little puzzling for a date code that late in the year (August) to still be model year 1971. My understanding is that the engine foundry usually started casting for the next model year around the June time frame. 

Those 66 heads have the larger valves, and nominal chamber volume of 114 cc's. Even on stock untouched heads the volume can vary some, plus unless you measure them there's no way to know if they've already been cut.

Compression ratio alone doesn't make as much difference as people think. For example, the difference between 9.5:1 and 10.5:1 on an engine that's over 400 cubic inches and making close to 400 hp will only make a difference of about 8-10 hp, give or take, with no other changes. So my opinion at least is that on a street engine, it's not "worth" the risk of pushing compression up to the limit for that small of a power gain. Everyone gets to make their own decisions on that, however. 

You've got a good base to start with there if you want to step it up some.

Bear


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## O52 (Jan 27, 2019)

Having a casting date of Aug 31, 71 would normally make it a 72 production item. But no 483677 blocks were cast for 1972 

53552 is an early EUN for the manufacturing year. For a 483677 block, that EUN falls in between Aug 31 and Sept 1 1970 according to the Wallace racing EUN charts. 

Take another look at the casting date, a photo would be nice. 
Not unheard of to have the wrong year inserted. 

I'll bet that the block is designated N for night shift, and this may be a possible scenario; 
coming up on midnight Aug 31, the foundry guy is getting his letter I and number 1 ready for the Sept 1 casting pour. Gets ahead of himself and inserts a 1 instead of 0 on the last pour of Aug 31. 

Strictly a guess and 'what if' on my part.


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## billsnp5 (10 mo ago)

Thanks for the info guys. I have added a picture of date code on block.


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## O52 (Jan 27, 2019)

Maybe I'm seeing things but is that a faint '0' behind the 1? Possibly stamped?


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## O52 (Jan 27, 2019)

Cast DateEUN1971WCH31483677N1034590048516Trans AmN09A455 HO"1971YE-483677N1025590050780Trans AmN-Norwood-455 HO"1971YEH31483677N1056160051624FirebirdN-Norwood 455 HO"1971WCI010483677N104010054083FirebirdN-Norwood-455 HO"1971YCI010483677P3045550068941GTOP-Pontiac-455"

EUNs were stamped as the engine was built. 
It is possible to have a earlier date block with a later EUN, but generally they were stamped within a day or two of casting. 
Blocks that were damaged during the casting process could have a later EUN as the engine block would have to be repaired before assembly.

Also note on this list that the H31 dates do not have a zero afterwards like the I010 dates. 
The EUN list isn't an official Pontiac listing, but one created by Wallace from owner input. There can be and are errors.


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## billsnp5 (10 mo ago)

It’s definetly H31 here is a little better picture.

The reason I posted this is I haven’t found anywhere the date (H31), cast number (483677), EUN(53552), and the engine code of YC match.


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## PontiacJim (Dec 29, 2012)

billsnp5 said:


> It’s definetly H31 here is a little better picture.
> 
> The reason I posted this is I haven’t found anywhere the date (H31), cast number (483677), EUN(53552), and the engine code of YC match.
> View attachment 155299


As pointed out, #66 heads are 1971. Block code YC is 1971.

1971 A-body (Lemans, T-37, GT-37, GTO) B-body (full size) & G-body (Grand Prix), F-Body (Firebird) 8.2 Compression, 325HP, 455CI, Automatic, 4-Bbl #7041262, "067" camshaft.

You should find the partial VIN stamped on the front of the block along the timing cover or it is under the timing cover. It may be possible to contact PHS services to learn what body line the engine came out of. 

The 1971 year began 8/10/70 and ended 7/20/71
The 1972 year began 8/12/71 and ended 6/30/72

H=8th month, August 1971 So August 31 is right at the transition period from 1971 to 1972 cars.
The engine shows to be a 1971 engine based on heads/block code. The distributor (if still original) will also have a ID number and date code as will many of the other parts on the engine if still original and intact. My guess would be the engines were still being assembled with "left over" heads ( they would not throw them out because of the year changeover) and the engine factory/stampings may have not yet been issued or they stamping person was just using the previous stamping code for the 325 HP 455. It could have also been a factory replacement engine for some car that did not pass quality control and was set off to the side until the factory could get to it and replace the engine OR it was a dealer replacement engine.

Many different scenarios that it "could" be seeing it was right at that transition point from 1 model year to another. Keep in mind, 1972 was the year of the long strike at the Norwood Firebird factory and it also possible that the engine shop was taking this into account and trying to get ahead on engines knowing that union negotiations were around the corner - and generally a business with union employees has an idea on how negotiations are leaning.

So if you can find that partial VIN stamping, you might be able to know exactly what year car and what body type that engine came from and that would settle it as to it being a 1971 or 1972 engine - if that matters to you.


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## billsnp5 (10 mo ago)

Thanks again everyone for the information. Been a big help.


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