[MarkS57]

Originally Posted by hurryinhoosier62

As a retired ASE Master Engine Machinist( and crank grinder) I wholeheartedly agree. The most critical part of the process is welding the thrust flange and regrinding it to the correct width. IMO, a nodular factory 3.25” main crank that been correctly welded, re-cut to the proper width and nitrided is superior to a Chinese cast crank of dubious metallurgical origin

I was looking into doing this and still might at some point. I did find a shop that said they can do it; cost was about $500 to "cut & weld" my 428 N crankshaft.

[hurryinhoosier62]

Originally Posted by MarkS57

I was looking into doing this and still might at some point. I did find a shop that said they can do it; cost was about $500 to "cut & weld" my 428 N crankshaft.

As long as the shop is reputable they should be able to perform this work successfully.

[Douglas Willinger]

typo correction

A 455 has a 4.21" stroke, while the 421 and 428 has a 4" strole.

Did Pontiac ever make a block suitable for a 4.255" bore, needed for a 455 if designed with a 4" stroke?

Originally Posted by Douglas Willinger

excerpt:

THE STROKER QUESTION

Another misconception that must be cleared up is what happens concerning the stroke when performing this mod. Cutting down the mains of the 421/428/455 crank has no effect on its original stroke, which remains the same as it was in the crank’s respective original block. When you install a larger stroke crank in a 400 block, you are not building a ‘stroker’ per se. (Although many guys just LOVE saying the word “stroker,) Rather, you are simply building the same engine on 3-inch mains. Let me explain.

A 400 has a standard bore of 4.120 inches. A 455 has a standard bore of 4.150 inches. By using a standard bore 455 piston in a .030-over 400 block, you end up with a standard bore 455 on 3-inch mains.

Similarly, a 421/428/455 share a 4.00 inch stroke. A 428 engine shares the 4.120-inch bore of a 400. You use a standard bore 428 piston when using a 421/428 crank in a 400 block, so you can end up with the proper deck height, just as you do when using the 455 piston on a 455 crank.

I haven’t singled out the 421 engine because most guys use the 1967 or later 14-degree valve angle cylinder head. If you’re going to use a 1966 or earlier set of heads with the 20-degree valve-angle heads, you must have custom pistons built. I can do that for you.

end quote

A 455 has a 4" stroke, as do the 421 and 428?

Did Pontiac ever make a block suitable for a 4.255" stroke, needed for a 455 if designed with a 4" stroke?

[25stevem]

4.255” x 4.00”, not in a production block but who knows what they where toying around with in the era of the DOHC 2-4 barrel motors and others that we never heard about?

[Formulajones]

Seems to me Pontiac was already stuck with that small bore block architecture and possibly backed themselves into a corner by 1970 when other manufactures were building over 400 cubes with their production blocks with much shorter cranks.

As an example the BBC 454 ci was a 4.250 bore and 4" stroke, and GM didn't change it's architecture to get it there. Hard to say if they were thinking ahead in 1965.

Pontiac was somewhat stuck with that small bore size block, so the most cost effective solution to keep up with the others was to just make a longer crank. Seems Olds had that same approach.

[25stevem]

I would love to know what some designers had in mind on some things and how they justified doing a certain thing with there upper management.

Like with the Olds 403 motor.
That nice big bore motor that could’ve made terrific use of big valve sizes, yet the heads suck!

You can’t really knock the Pontiac motor because it was very very well conceived!

Since it’s introduction in 55 at 287 cid it was able to be stretched 59% up to 455 cid with no major external redesign!

I know of no other passenger car motor that can lay claim to that !

[MarkS57]

Originally Posted by 25stevem

I would love to know what some designers had in mind on some things and how they justified doing a certain thing with there upper management.

Like with the Olds 403 motor.
That nice big bore motor that could’ve made terrific use of big valve sizes, yet the heads suck!

You can’t really knock the Pontiac motor because it was very very well conceived!

Since it’s introduction in 55 at 287 cid it was able to be stretched 59% up to 455 cid with no major external redesign!

I know of no other passenger car motor that can lay claim to that !

I agree. I still question the 3.25" mains they felt were necessary on the 421. I've read the reasoning but eh? Take that out of the equation and sheesh what a great set of additional options arise.

[25stevem]

Yes, Pontiac engineering seem’s to have gone way to the extreme for safety once they went from the 370 motor with its steel crank over to cast iron ( Armasteel) for the then new 389 motors.

Both the 370 and the 389 had the same stroke of 3.750” yet they enlarged the crank mains from 2.623” to 3.00”.
That’s a gain of .377” or a crazy 14.5% increase in diameter!!!

In comparison when the 421 came along with its 4.00” stroke they only increased the main size by 8.5% over the 389.

I think the fact that Pontiac stuck with the 3.250” mains when they took the stroke up to 4.210” for the 455 is because they realized they had plenty of reserve strength with that 3.250” main size regardless of the fact that it was a cast crank.

If Pontiac would have been able to afford to produce enough steel cranks for 4.00” stroke motors back then I don’t think the main size would have ever grown bigger then 3.00”.

One things for sure no post 1959 motor with a cast crank that had no casting flaw’s in it ever broke when used as intended in passenger car format!

[gavin]

I don’t know why the cast 455 after market cranks don’t offer a 3” main version with the Pontiac journal size. They already have the casting it’s just a mater of making the mains 3”. This would make for a very cheap upgrade for a basic 400 low compression late model rebuild. With the amount of companies using the same basic casting I am surprised no one has done it. It seem to me an arrangement were they want to force you to use aftermarket rods and pistons for a bigger profit. For the guy on a budget the ability to use cheap cast pistons and rods when you want torque not horsepower would be great.

[25stevem]

Good good point! Plus I have never liked the unneeded extra rod side clearance in terms of oil control that takes place with the usage of BBC rod’s these cranks kits are using.

[b-man]

Originally Posted by 25stevem

Yes, Pontiac engineering seem’s to have gone way to the extreme for safety once they went from the 370 motor with its steel crank over to cast iron ( Armasteel) for the then new 389 motors.

Both the 370 and the 389 had the same stroke of 3.750” yet they enlarged the crank mains from 2.623” to 3.00”.
That’s a gain of .377” or a crazy 14.5% increase in diameter!!!

In comparison when the 421 came along with its 4.00” stroke they only increased the main size by 8.5% over the 389.

I think the fact that Pontiac stuck with the 3.250” mains when they took the stroke up to 4.210” for the 455 is because they realized they had plenty of reserve strength with that 3.250” main size regardless of the fact that it was a cast crank.

If Pontiac would have been able to afford to produce enough steel cranks for 4.00” stroke motors back then I don’t think the main size would have ever grown bigger then 3.00”.

One things for sure no post 1959 motor with a cast crank that had no casting flaw’s in it ever broke when used as intended in passenger car format!

The 1957 347 and the 1958 370 both used a 3.5625”’ stroke crank with a 2.623” main journal.

The 1959 389 was the first to use the 3.75” stroke crank and 3.00” main journals, however the 370 and 389 did share the same 4.0625” bore.

Pretty cool that the 1955 287 grew by 102 cubic inches to a 389 by 1959.

[25stevem]

Yes, I screwed up !

Sorry!
That’s what I get for on this long overdue nice day having a extra beer with my pizza.

[tom s]

FYI,not all 57-58 are forged!I have run into a couple of them doing my 303 stroker RA V short deck builds!Slso when I tried to help Kasse with one of his Engine Master builds,found him a crank and when he got it the thing turned out to be cast.Tom

[Douglas Willinger]

IIRC Pontiac went with the 4.21" stroke for the 455 for supposed emissions reductions, and that there was a prototype RAV block in aluminum capable of a 4.3ish bore.

Would like to know more about any such prototype creations.

Originally Posted by 25stevem

4.255” x 4.00”, not in a production block but who knows what they where toying around with in the era of the DOHC 2-4 barrel motors and others that we never heard about?

[hurryinhoosier62]

Originally Posted by 25stevem

I would love to know what some designers had in mind on some things and how they justified doing a certain thing with there upper management.

Like with the Olds 403 motor.
That nice big bore motor that could’ve made terrific use of big valve sizes, yet the heads suck!

You can’t really knock the Pontiac motor because it was very very well conceived!

Since it’s introduction in 55 at 287 cid it was able to be stretched 59% up to 455 cid with no major external redesign!

I know of no other passenger car motor that can lay claim to that !

Not just the heads. A 403 bottom end cannot survive repeated high RPM use (5,000+) without the use of a main stud girdle. The late Joe Mondello absolutely hated the 403.

[25stevem]

Yes, I have heard him comment on such.

[hurryinhoosier62]

Originally Posted by 25stevem

Yes, Pontiac engineering seem’s to have gone way to the extreme for safety once they went from the 370 motor with its steel crank over to cast iron ( Armasteel) for the then new 389 motors.

Both the 370 and the 389 had the same stroke of 3.750” yet they enlarged the crank mains from 2.623” to 3.00”.
That’s a gain of .377” or a crazy 14.5% increase in diameter!!!

In comparison when the 421 came along with its 4.00” stroke they only increased the main size by 8.5% over the 389.

I think the fact that Pontiac stuck with the 3.250” mains when they took the stroke up to 4.210” for the 455 is because they realized they had plenty of reserve strength with that 3.250” main size regardless of the fact that it was a cast crank.

If Pontiac would have been able to afford to produce enough steel cranks for 4.00” stroke motors back then I don’t think the main size would have ever grown bigger then 3.00”.

One things for sure no post 1959 motor with a cast crank that had no casting flaw’s in it ever broke when used as intended in passenger car format!

The only forged cranks during the early 421 era were the legendary 990 cranks of the 421SDs. Smokey tried to warn PMD engineers that the 3.25” main was too large for continuous high RPM service. The 1961 NASCAR season proved him correct, when the new 421SDs were failing at alarming rates. Smokey took the bull by the horns and created his own 421SD based on the 389SD NASCAR block and a welded and cut down 990 forged crank. It worked, but PMD dictated that ALL Pontiac sponsored teams would use the 3.25” main engines for the 1962 season. In reality, a proper prepared, machined and nitrided OE Pontiac nodular or Arma-Steel crank is more than strong enough for street service

[hurryinhoosier62]

Originally Posted by Douglas Willinger

IIRC Pontiac went with the 4.21" stroke for the 455 for supposed emissions reductions, and that there was a prototype RAV block in aluminum capable of a 4.3ish bore.

Would like to know more about any such prototype creations.

It is a fact that under square engines (stroke longer than the bore diameter) produce fewer emissions.

[tom s]

I have owned a coule of the Alu RA V blocks and they could not go 4.300.Tom