# Pontiac GTO/LeMans engines



## mrvandermey (Jun 15, 2011)

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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## Rukee (Feb 8, 2007)

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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## jetstang (Nov 5, 2008)

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


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## facn8me (Jul 30, 2011)

Yep 301's a basterd. 
here's a link to what's what. 

Pontiac Engine Codes


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## Instg8ter (Sep 28, 2010)

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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## facn8me (Jul 30, 2011)

Instg8ter said:


> 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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## Instg8ter (Sep 28, 2010)

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??:rofl:


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## mrvandermey (Jun 15, 2011)

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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## Thumpin455 (Feb 17, 2010)

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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## Rukee (Feb 8, 2007)

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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## BearGFR (Aug 25, 2008)

:agree Externally and visually, all Pontiacs look the same. Internally there are some differences. There are two "families" - one that includes 326,350,400 and another that includes 421.428,455. The difference between them (other than bore size and stroke length) is the diameter of the crankshaft main bearing journals. 326/350/400 are 3", 421/428/455 are 3.5". Since dimensionally all the blocks are the same everywhere else, that means that the 421/428/455 blocks don't have quite as much "meat" in the main webs as the 326/350/400. That can have implications for high horsepower builds. Also some blocks have additional differences in the main webs. Some of them have provisions for 4-bolt main caps, some don't. One of the anomalies about Pontiacs is that for some reason the factory for a period of time seemed to be prone to using 4-bolt blocks but building the motors out with only 2-bolt caps. "Real" Ram Air IV's, 455 HO's, 455 SD's, and a few others have both 4-bolt blocks and caps. Generally, having 2-bolt caps isn't a serious problem until over the 600 to 650+ HP (or more) level, depending on who you choose to listen to. These aren't ::cough spit:: chevys and don't have the same strength issues. If there's a weak point in them it's the stock rods. Rods get lots of abuse due to the comparitively long strokes in these motors and they tend to be the weak link once you start making some serious power. Fortunately it's not a problem because these days there are several sources for affordable and very strong forged rods.

Pontiacs are torque motors and they make it all "down low" in the rpm range. Because of that and the relationship between torque, rpm, and horsepower that can mislead people, especially on the street. Make no mistake: a stock GTO with a 350 HP 400 will absolutely >>destroy<< a stock 350 HP SS396 - every time. By the time the 396 manages to get up into the rpm range where it's making decent torque, all it's going to see are Pontiac tail lights - in the distance. 

LOTS of ways to go with a Pontiac to make power. One of the more popular builds these days is to take a 400 block for strength, then install an aftermarket stroker rotating assembly. I've built such a motor for my 69 GTO using the original numbers-matching 400 block. It's now a 461. I'm happy with the results   If you opt for a good set of aftermarket aluminum heads and have them "worked" by someone who know's what they're doing, a streetable 550+ HP in a package that will live forever on 93 octane pump gas is a no brainer.

Bear


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## mrvandermey (Jun 15, 2011)

BearGFR said:


> :agree Externally and visually, all Pontiacs look the same. Internally there are some differences. There are two "families" - one that includes 326,350,400 and another that includes 421.428,455. The difference between them (other than bore size and stroke length) is the diameter of the crankshaft main bearing journals. 326/350/400 are 3", 421/428/455 are 3.5". Since dimensionally all the blocks are the same everywhere else, that means that the 421/428/455 blocks don't have quite as much "meat" in the main webs as the 326/350/400. That can have implications for high horsepower builds. Also some blocks have additional differences in the main webs. Some of them have provisions for 4-bolt main caps, some don't. One of the anomalies about Pontiacs is that for some reason the factory for a period of time seemed to be prone to using 4-bolt blocks but building the motors out with only 2-bolt caps. "Real" Ram Air IV's, 455 HO's, 455 SD's, and a few others have both 4-bolt blocks and caps. Generally, having 2-bolt caps isn't a serious problem until over the 600 to 650+ HP (or more) level, depending on who you choose to listen to. These aren't ::cough spit:: chevys and don't have the same strength issues. If there's a weak point in them it's the stock rods. Rods get lots of abuse due to the comparitively long strokes in these motors and they tend to be the weak link once you start making some serious power. Fortunately it's not a problem because these days there are several sources for affordable and very strong forged rods.
> 
> Pontiacs are torque motors and they make it all "down low" in the rpm range. Because of that and the relationship between torque, rpm, and horsepower that can mislead people, especially on the street. Make no mistake: a stock GTO with a 350 HP 400 will absolutely >>destroy<< a stock 350 HP SS396 - every time. By the time the 396 manages to get up into the rpm range where it's making decent torque, all it's going to see are Pontiac tail lights - in the distance.
> 
> ...


WOW, that is a lot of information, but invaluable nonetheless. I like that the Pontiac engines do have strength and torq. I am not looking to go over 500 HP, for I am not a racer of sorts, although I do entertain a friendly bout of competition from time to time.

Well I think I will work on getting either a nice year correct 400 or a nicely built crate 400 and then build it up with the right aftermarket heads, air flow and etc. I would be okay with 350-380 hp, but hope to get around mid 400's or so.


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## 66tempestGT (Nov 28, 2009)

rukee,
im not disputing what you say but if that is a fact then i would like for you to say the name. im sure other people would like to know too.


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## DukeB-120th (Oct 19, 2009)

66tempestGT said:


> rukee,
> im not disputing what you say but if that is a fact then i would like for you to say the name. im sure other people would like to know too.


+1


:agree


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