Technical Pontiac 347 vs 370 heads

Give Tom Whilhite http://www.wilhiteauto.net/Services.html a call, he is a master with the older Pontiac engines.
https://www.facebook.com/PontiacHeaven/photos/a.164779267003747/688992324582436

 

Yes, thank you. I have been chatting with him about this. Very helpful.

 

Out of curiosity, does anyone know which Hilborn pump was used with the 347-P-8 unit?

 

OK, so I am determined to get to the bottom of the mis-aligned bolt hole issue.

While I realize '56-'60 heads are supposed to be interchangeable, I am wondering if Pontiac could have made small
changes between years, possibly resulting in my mis-alignment issue, or was this Hilborn's doing?

Now, my '58 heads have casting number 528511. I see that the '57 heads should have casting number 523298 or in the case of a FI engine 52(****) - last four stamped on O.E. install.

Does anyone happen to have a 528511 head that they could take a couple of photos of for me so I could compare the positioning of the upper-two intake bolt hole locations to my '58 heads? It would be greatly appreciated!

 

I’ll bet it was Hilborn moving the hole because utilizing the factory hole would have meant an awkward divot in the port casting (going by your photos)
It probably came with a PG-150 or 150a pump. But you won’t need one going the direction you are going.

 

I've got a 1957 motor in my hot rod and a spare 1955 motor and a couple of sets of extra gaskets so I can get a picture when I get home later today

 

I agree. I bet they moved it, but how on earth did they expect someone to install it on the engine it was designed for? I wonder if they offered adapter plates? I certainly can't find any references anywhere. Adapter plates OR the correct head is the path I am on now. If all fails, I might play around with mechanical just to frustrate myself even more LOL. I hear it is possible but not easy...

 

Very nice ride! I will keep an eye out for your photos. Thanks!

 

Sorry forgot to take the photos I'll try again tonight

 

OK, thank you.

 

Fel-Pro gasket # MS9498SH1

You can see it covers two holes on the head but matches the intake ports correctly. Using a felt marker, I scribed where the head bolt hole should be on the Hilborn base plate.

I am not 100% positive I have the correct gasket, although they claim it is supposed to be compatible with the 347 and 370 engines. Still, why would Hilborn drilled the hole where they did, when the unit was supposed to "fit" the head? I have seen two Hilborn 347-P-8 units and the bolt hole locations are the same as mine. There is some piece to this puzzle that is missing...

 

Sorry I forgot again going to make a note to remember

 

That's basically the same gasket I have just made by best. It fits my 55 Motor and my 57 motor perfect. Perhaps hilborn marked the casting wrongs and it's for a later year

 

Just a wild thought based upon another remark earlier. The holes all should be the same as others have noted.

Is it possible the engine came out of a GMC truck and they had a different intake? I've only seen a couple 370 Pontiacs in a GMC truck and I don't recall.

 

The motor that's in my hot rod now came out of a 57 GMC ramp truck. It started as a 336 cubic inch and all the heads are all the same bolt pattern

 

Thank you very much for taking time to post the photo. I don't think Hilborn stamped the number in error. I have seen a couple of these and the bolt pattern is the same. So puzzling....

 

Very weird. I've had every intake for these early Pontiacs besides a dual quad cross ram in my possession and they are all the same bolt pattern. The 6x2 that I have has the coolant Port so it'll fit early and late heads. And apparently I'm missing two air cleaners somewhere in the move

 

Thank you for the photos! The attached image is comparing your 6x2 manifold to my Hilborn. We can see that where I scribed the black circle from the gasket, is in the same location as is on your manifold and correct for the heads. Notice how high up on the flange the hole is on the Hilborn, yet all other holes and ports match - it's just the two uppers. Did the later heads have this patten? I don't have any to compare.

Cool 6x2 by the way! I hope you find those air cleaners.

 

I don't have any later stuff to compare it to. It doesn't look like the water Port would line up either

 

Only thing I can figure is maybe the F.I. heads had a different bolt pattern than the carbureted heads. Nothing else makes sense to me. I have a late [64 and newer] intake I can take a photo of. Here it is........

 

You could be onto something. I see there was also a T395A option in addition to the FI for the 370 in 1958. I bet the Hilborn unit was intended for those heads and the bolt pattern, etc. may have been slightly different. What are the chances of finding a set of heads off of one of those? Slim to none, I am thinking.

 

The Tempest 395A designation was for over the counter parts. Pontiac offered high perf exhaust manifolds, a few different camshafts, valve springs and lightweight retainers. The hottest cam along with the other parts bumped the 310
horse FI engine to 338. There were no unique ‘58 heads.

 

Thank you for the information - much appreciated.

And, supposedly, the '57 heads should be identical to the '58 heads - correct?

 

Do you have an early Olds intake gasket or head laying around?

 

I am not holding the parts in my hand, so I may not have a complete grasp of this issue, but it looks to me that if you use all the existing bolt holes in the intake, you would have to drill the two that don't exist on the head. Does the head have enough material to make new holes where you need them? If so, drilling and tapping the head is a fairly simple task.

Also, if you can drill holes in the head, does the intake water port seal the head port enough so it won't leak? If so, the mis-alignment in the port shapes is not anything to worry about. You can do some mild porting to blend a bit, but in the end, water will find a way. Particularly if this is not a "driver".

By the way, I have a garage full of Pontiac engines and they are all stupid. Just different enough to be a pain in the ***.

-Abone.

 

Unfortunately, I do not have any lying around.

 

I see why Hilborn placed the upper two holes on their flange where they did. They couldn't place it to line up with the upper holes on the heads, because the bolt head and shoulder would have been jammed against the outer throttle bores.
I wonder if Hilborn informed their customers that the upper bolt holes on the heads would have to be relocated? Unfortunately, I can't find anyone from that era that knows.
Yes, there appears to be enough material to drill and tap to match the upper holes on the Hilborn unit - like they planned it that way...

 

The upper bolt holes on your picture of the Hilborn unit look to be smaller than the other bolt holes . . . or is it just my old eyes?

 

They are all the same diameter. It was probably just the camera angle.

 

What he said.
Those pictures are worth a thousand words. Glad you posted them. Unless those heads are unobtanium, I'd carefully drill and tap them using a drill alignment tool or block and call it a day.