# 70 GTO 455 Exhaust Manifold leak question



## 70455goat (Nov 5, 2007)

Just got my goat last week. It has lots of exhaust leaks under the hood. I checked all of the exhaust manifold bolts and they seem to be tight. On the driver's side I can actually feel the air coming out of the manifold on the forward and middle part of the manifold where it contacts the head.

My question is: Does the 455 use a metal gasket between the manifold and head or some other gasket? Or is it surface to surface with no gasket?

Thanks for any info.


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## GTOsarge (Oct 9, 2007)

Should be a gasket. I would try and putting a new set of gaskets in. Go with a higher quality set like Felpro. Also consider replacing the manifold bolts.


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## 70455goat (Nov 5, 2007)

GTOsarge said:


> Should be a gasket. I would try and putting a new set of gaskets in. Go with a higher quality set like Felpro. Also consider replacing the manifold bolts.


Yeah, I bought a set yesterday. Bad news I think. I was just talking to a local performance shop this morning. The guy who works there has a 70 Judge, 70 GTO and a bunch of others. Sounds pretty knowledgeable. I happen to mention that I didn't like how it only has one bolt in the front and rear of the manifold. He said "70s have 2 bolts, 71-72 have single bolts". I need to do some checking on my engine when I get home. I may not have a bone stock all orginal 455 under the hood, like I thought.

Dale,


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## Kevgto67 (Apr 7, 2020)

Hi, I was doing some searches and it appears you may be in a similar scenario as me. I have a 1967 GTO that someone put a 1971 455ci in but seems like they left the original 1967 400ci exhaust manifolds. There are exhaust leaks on both sides I’m trying to fix. Did you have any luck fixing the leaks? What gaskets did you end up using. There are high performance regular style, aluminum ones copper ones. Many options to consider . Thanks


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## pontrc (Mar 18, 2020)

Mr gasket copper coat spray. Spray the gasket on both sides.Make sure they are not Ram Air or HO heads?


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## Kevgto67 (Apr 7, 2020)

Hi thanks for the reply. I don’t think they are ram air or HO heads. The engine is casting number Back of block 485428

Front of engine block
(066605
“YC”

Back of engine block center
Date code H241

and on the front next to the water pump it’s 22P311526.

based on all of this it appears this 455ci it was assembled in August of 71’ and put into a 72’ Pontiac, and is a 250hp model. However the same casting number for 1971 says it’s a late production high output so I am not so sure, do you have any ideas. The prior owner stated that this engine was out of a 1971 GTO judge but I think the “22P” on the front of the block contradicts that if that was the case I think it would say 21P as for 71 instead of 72 but I am new to pontiacs.


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## PontiacJim (Dec 29, 2012)

Suggest you do some reading. Several good books out there with a lot of info. Get a factory Service Manual for your car.

August engine build means it is a 1972 engine. The casting on the heads, if still original, will tell you what you need to know. Date codes on the head will also be close to the August date.

The 455 will have a large triangle like lug on the back of the engine off to the side of the distributor - you won't miss it.

The "YC" block code is for a 1971 325HP/automatic 455, and the 1972 250HP/automatic, not an HO engine.
The 1971 455 HO was block codes, WL, WC, YE
The 1971 455 heads have casting #197 (found on the end exhaust port) have round port exhausts.
The 1971 YC heads are #66 and 1972 YC heads are #7M5.
The HO engine uses an aluminum intake #483674
The HO engine has the larger round port RA exhaust manifolds.
The HO exhaust uses 6 holes for attaching the exhaust manifold, 2- each end port, 2-for the paired center port (6 bolts) BUT I also have found them with only 1-bolt each end port like the 1972 HO head - maybe early & late manufacturing? 1972 #7F6 HO exhaust ports had 1-each end port, 2-for the paired center port (4 bolts).
The block casting #485428 is indeed for the late 1971HO, but also for the 1972 455 which is what you seem to have. It is also the same casting number for 1973 & 1974 455's - same block for 4 years.

So block codes & head type/casting numbers, aluminum intake, round port RA/HO exhaust manifolds all define a 1971/72 455 HO engine.


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## pontrc (Mar 18, 2020)

Thanks Jim saved me from looking up numbers Making sure manifolds were correct d port vs round


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