Pontiac GTO/LeMans engines - Pontiac GTO Forum
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post #1 of 14 (permalink) Old 08-09-2011, 12:57 PM Thread Starter
 
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Pontiac GTO/LeMans engines

Hey guys, I am currious and a bit confused on the various Pontiac and specifically the GTO/LeMans engines.

Is it true that a Pontiac 350, 400 and 455 are all the same block and that the differences are the size of the bored out cylinders? So in short, visually speaking, do the block look the same?

I know in Chevy engines, the 350 (and even the the 383) are small blocks, while the 396 and the 454 are big blocks. In Pontiac engines, are the blocks technically small blocks or big blocks or both?

On the Ram Air setups, is there anything different to the blocks or is it just accessories (carbs, filters, air vents, etc)?
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post #2 of 14 (permalink) Old 08-09-2011, 05:05 PM
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You are correct. All the ponch motors are the same outside dimensions, unlike the chevy small block and big block engines.


You could have a 326 in your car and tell everyone it was a 389, 400 or 455 and without running the block #s, no one knows the difference.
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post #3 of 14 (permalink) Old 08-09-2011, 07:18 PM
 
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It's just a Pontiac block, all the same except 301? Ram air uses different heads, cam and intakes. Same bottome end, maybe better rods, but not 4 bolt or anything

Burning rubber since 1982!!
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post #4 of 14 (permalink) Old 08-09-2011, 08:44 PM
 
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Yep 301's a basterd.
here's a link to what's what.

Pontiac Engine Codes

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1966 Pontiac Lemans Convertible
389 tri power
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post #5 of 14 (permalink) Old 08-09-2011, 09:25 PM
 
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421 SD was also a bastard block...they are worthless, if you have one you can PM me and and i will send you my address for shipping and disposal...
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post #6 of 14 (permalink) Old 08-09-2011, 09:35 PM
 
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Originally Posted by Instg8ter View Post
421 SD was also a bastard block...they are worthless, if you have one you can PM me and and i will send you my address for shipping and disposal...
Would you like all them 301's also?

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1966 Pontiac Lemans Convertible
389 tri power
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post #7 of 14 (permalink) Old 08-09-2011, 09:45 PM
 
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LOL...nahhh i already have two boat anchors, although i have been watching a thread on another forum about making power with them, have also been contemplating about what i will do with the numbers 326 from my Tempest i want it to stay with the car. Stroked 326??
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post #8 of 14 (permalink) Old 08-10-2011, 10:09 AM Thread Starter
 
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On the Pontiac 400, I know it came from the factory with something like 350-360 HP (depending on which one you got), but is it realistic to to get 440-480 HP from a naturally aspirated Pontiac 400 without the use of a supercharger, blower or some kind of turbo? For example, if I use a Ram Air set up (I, II, III, IV) with the right internals (cam, pistons, crank, etc) and/or the right accessories (heads, carbs, etc), could I see over 400 HP?

On another note, what is the general opinion on getting/using a Pontiac Crate 400 Engine? I see them listed from time to time on ebay and such. Are they any good? Would it be a worthwhiled project?
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post #9 of 14 (permalink) Old 08-10-2011, 10:43 AM
 
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The 455 had a bore that is only .030 larger than the 400 and 428, the difference is made by the crank. The 400 has a 4.125" bore & 3.75" stroke crank, the 428 hasthe same bore but a 4" crank, and the 455 has 4.155" bore & 4.21" stroke. The 350 has a 3.75" crank as well, but with a bore smaller than 4".

Externally they all look the same provided the year breaks are compared. Pre 65 is one set, post 67 another for different reasons, and some of them back in the 50s had reverse cooling. But for the most part, they are very interchangeable. They all have 6.625" rods, the 421,428, and 455 have 3.25" mains while the others have 3" mains. They share almost everything except for the main bearings, cranks, and pistons. There are some variances (mostly in the heads), but for the most part they use the same stuff.

Getting 440-480hp from a 400 isnt that hard, the easiest way is to stroke it with a 4.21", 4.25". or 4.5" crank which will increase displacement to 455-496ci. Another easy way is to increase compression and airflow, get more air in and work it harder. Doing it with pump gas and not stroking it takes more effort and requires good heads, usually aftermarket aluminum heads.

If you are going to get a crate 400 get it from Mr Pbody, Butler, Kaufmann, SD in Canada, Spotts, Ken Keefer in FLA. There are a couple others too, but those come to mind easy for me. You will get a quality build that will make great power and last, plus it will be an excellent foundation for future performance upgrades. A reman will have the lowest cost parts in it, cast pistons, cast rods, and a stock replacement cam and related valve train parts. I like to order the parts, get the machine work done, and assemble them myself, that way I know what is in there, and I can pick the best parts I can afford. It takes longer but I know whats in there and its my combination, and usually I can build them far cheaper that way.
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post #10 of 14 (permalink) Old 08-10-2011, 10:46 AM
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There is a shop around here that sells crate engines on e-bay, nearly every single one has been junk and the guy has been to court 100's of times!! Buyer beware!!
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