Crankshafts for Pontiac 400 history? - Pontiac GTO Forum
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post #1 of 7 (permalink) Old 04-27-2019, 08:53 PM Thread Starter
 
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Crankshafts for Pontiac 400 history?

Doing some self-education on 400 Pontiac motors. Specifically, trying to learn about the crankshafts that came in the 400 (production). Can't find a good source! Is there a difference in the crankshafts as Pontiac left the 1960s and went into the gas saving 1970s? What do you look for to find a good/the best production crankshaft for a Pontiac 400?
Thanks!
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post #2 of 7 (permalink) Old 04-27-2019, 10:16 PM
 
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Never heard anything bad about Pontiac 400 cranks. Have heard that the later cranks that used a flexplate/flywheel with the smaller 2 1/2" center hole are not as good as the older cranks.

Some tout an Amasteel crank or a nodular iron crank as being better. But they're both cast cranks, not forged.

Most say that just about any of the '60's & early '70's Pontiac cranks are plenty good for high power builds.

This article may have the info you're lookin for.

https://www.pontiacdiy.com/pontiac-v...ormance-guide/

Just curious, are you planning a big power, high rpm 400 build, for which you think a factory crank won't be strong enuff ?

The quickest Pontiac Stocker ever built used a '71 nodular iron 400 crank. It probably saw 8000 rpm many times.

https://www.hotrod.com/articles/hppp...tiac-firebird/

If you're shootin for 600 + hp & 8000 + rpm, you can buy a forged crank.

https://butlerperformance.com/i-2445...tegory:1234870

Last edited by bigD; 04-27-2019 at 11:03 PM.
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post #3 of 7 (permalink) Old 04-28-2019, 09:25 AM Thread Starter
 
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bigD,
Thanks for the info. Nope, not planning on anything other than a great production engine rebuild. But as conversations at the cruise in (or at the bar) usually go, there's a lot of know-it-alls. The horsepower from the 400 over the years varies greatly. You want 335 hp? You want 180 hp? All can be done with a build up of a basic 400 block. Obviously, this is due to all parts of the engine so I'm trying to nail down what the crank contributes to the that variance. Do all 400 cranks have the same throw? Are there other design variances in the crank that would affect performance (not just strength)? Or all 400 cranks the exact same except for materials or production process?

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post #4 of 7 (permalink) Old 04-28-2019, 12:10 PM
 
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Originally Posted by Shooter View Post
bigD,
Thanks for the info. Nope, not planning on anything other than a great production engine rebuild. But as conversations at the cruise in (or at the bar) usually go, there's a lot of know-it-alls. The horsepower from the 400 over the years varies greatly. You want 335 hp? You want 180 hp? All can be done with a build up of a basic 400 block. Obviously, this is due to all parts of the engine so I'm trying to nail down what the crank contributes to the that variance. Do all 400 cranks have the same throw? Are there other design variances in the crank that would affect performance (not just strength)? Or all 400 cranks the exact same except for materials or production process?

Shooter
They are all basically the same and depending in year, can have a different metal composition with some claiming to be a better material than others when used for hi-performance applications - meaning HP you are probably not going to see on the street.

The stroke & dimensions are all the same, 3.75" stroke to include the 389, 350, and 400. Not all will have the hole drilled at the rear of the crank for the use of a pilot bushing when using a manual transmission - seems this would be some of the later 1970's cranks. Most do, but a few did not, so something to check if using a manual transmission. And as bigD pointed out, the flywheel register where the flywheel bolts on can be different with some of the mid-to-late 1970's cranks.

I have read that the snout on the 389CI cranks are a bit shorter, but never personally confirmed this. It does appear they are shorter on the earlier 1963 and older cranks. Many will upgrade the 1964-1966 389 to the later and more available 11 bolt timing cover and water pump which would indicate these years having the same snout length as the 400CI.

I have read that the 350 crank is lighter than the 400 crank. Again, never confirmed this and if it were lighter, then I would think many Pontiac builders would be jumping all over the 350 cranks as the 350 engines go for peanuts and are often just junked because no one wants them. So may be another Pontiac arm chair myth.

Most all Pontiac cranks are cast. Forged are found in the the early Pontiac's of 1955- 58, Super Duty engines, and Ram Air V. Forged cranks are also heavier than cast.

Armasteel cranks are said to be the better cranks for high HP drag engines. Found in the 1964-1966 389 engines. I found this reference, "Armasteel cranks were Pearlitic Malleable Iron (PMI), with enhancements, are not drop cast poured, but are centrifugal spin cast. Armasteel is less prone to cracking and pounding damage from detonation, not much, but a little more, and is more dense in its basic structure. After the main casting process is done and the basic machining is completed, the fillet radius and main/rod journals are rolled in a hydraulic former, to make those areas stronger (about 10 to 15 percent stronger) than either drop cast or machined areas of the cranks."

Next is the Nodular Iron cranks produced in the 350/400 CI in the 1960's. The Ram Air engines are said to use a crank with .001" more clearance than standard cranks.

The Nodular cranks are good cranks up to about 1976 when they are not as desireable with thinner counter weights.

Check out this chart - Wallace Racing - Crankshaft numbers

So don't listen to the arm chair engine builders who are the experts on Pontiac engines and crankshafts. Pontiac cranks are some of the best in the industry.
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post #5 of 7 (permalink) Old 04-29-2019, 06:18 PM
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I'll add that the '65-'66 326 used the same Armasteel crank as the 389's in those years. The nodular iron '67-up cranks have a big 'N' cast on them. All are bulletproof.
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post #6 of 7 (permalink) Old 04-29-2019, 10:06 PM
 
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Just assuming that the 326 & 350 cranks would have more material taken off at the balance holes, since the bore size is much smaller than a 400. Assuming the pistons/rings would be lighter, requiring that more weight be taken off the crank, for balancing.

But, if you go with lighter forged pistons and/or rods, a 326 or 350 crank might be closer to the correct balance than a stock 400 crank. Anyhow, the balance would depend on the weight of your rods/pistons/pins/rings.The machine shop should be able to take care of that.
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post #7 of 7 (permalink) Old 04-30-2019, 02:11 PM Thread Starter
 
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Wow! You have answered my question in no time! My biggest concern was to identify the difference in the stroke. Now I know what to look for when matching leftover parts for an engine build.
Thanks!

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