Question for engine builders

[Kevin Johnson]

Have you ever switched the firing order on a V8 engine and experienced a problem with the crankshaft?

To be clear, I am assuming you are using the same crankshaft when making the change.

I understand that many other things will likely have been changed that could affect the crankshaft. I am simply wondering if you had a suspicion that changing the firing order brought out a difference/problem. I am curious if the effect of millions of cycles stressing the crank in a particular sequence while still within the elastic range of the base material imparts a "memory" or type of hysteresis.

[Walter R. Malik]

Have you ever switched the firing order on a V8 engine and experienced a problem with the crankshaft?

To be clear, I am assuming you are using the same crankshaft when making the change.

I understand that many other things will likely have been changed that could affect the crankshaft. I am simply wondering if you had a suspicion that changing the firing order brought out a difference/problem. I am curious if the effect of millions of cycles stressing the crank in a particular sequence while still within the elastic range of the base material imparts a "memory" or type of hysteresis.

I have had customers run many several small block Chevy engines in oval track cars with the 4,7 swap and seen nothing abnormal anywhere in that engine when refreshing them ... crankshaft and bearing wear seem to be no different.

[Kevin Johnson]

Have you ever switched the firing order on a V8 engine and experienced a problem with the crankshaft?

To be clear, I am assuming you are using the same crankshaft when making the change.

I understand that many other things will likely have been changed that could affect the crankshaft. I am simply wondering if you had a suspicion that changing the firing order brought out a difference/problem. I am curious if the effect of millions of cycles stressing the crank in a particular sequence while still within the elastic range of the base material imparts a "memory" or type of hysteresis.

I have had customers run many several small block Chevy engines in oval track cars with the 4,7 swap and seen nothing abnormal anywhere in that engine when refreshing them ... crankshaft and bearing wear seem to be no different.

They were using the same crankshaft before and after the swap?

[engineguyBill]

From what I have seen, firing order change does not have any adverse affect on crankshaft, nor bearing, longevity.

[swampbuggy]

EngineguyBill---What are absolute known positive results that are gained by going from 1 8 4 3 6 5 7 2 to 1 8 7 3 6 5 4 2 or the LS F.O.

Anybody else is welcome to comment as well, thanks Mark H.

[Walter R. Malik]

EngineguyBill---What are absolute known positive results that are gained by going from 1 8 4 3 6 5 7 2 to 1 8 7 3 6 5 4 2 or the LS F.O.

Anybody else is welcome to comment as well, thanks Mark H.

The 4.7 swap on a small block Chevrolet will have a minor effect of making all the cylinders run at a closer combustion chamber temperature ... heating up number 2 and cooling number 5 a bit more.
There are probably some other effects but, I haven't witnessed any of them.

[Kevin Johnson]

Maybe another related question:

Assuming the rotating assembly is kept the same and the same cam grind etc. -- JUST changing the firing order. If BHJ came in and graphed the torsional dynamics to fit a custom damper, would they notice a difference?

If Jon is reading this, would there be a different optimum counterweight design?

[rebelrouser]

EngineguyBill---What are absolute known positive results that are gained by going from 1 8 4 3 6 5 7 2 to 1 8 7 3 6 5 4 2 or the LS F.O.

Anybody else is welcome to comment as well, thanks Mark H.

Reher Morrison engine book says .5% improvement in horsepower for the 4/7 swap, and the nitrous guys say they don't burn pistons as bad, and hold up better. Never did any back to back testing, just repeating what I have read and heard through the grapevine.

[Tom Walker]

Very interesting question Kevin. Looking forward to more discussion about this as it relates to the possiblity of different harmonics in the crankshaft with different firing orders.

[peejay]

This is a neat line of thought to go down.

VW played with firing orders on their W12 engines. I know they had a near 100% crank failure rate with the first generation 12s. Bear in mind that these are dang near a worst case scenario, with 12 cylinders on 6 SPLIT PIN crank throws in an engine the length of a short V8. Crankshaft looked like a collection of journals stacked Jenga-style with dinner plates in between.



Highest-resolution pic I could find.

[engineguyBill]

Thanks Peejay,
That is one ugly-ass crankshaft . . . . . . . . .

[MadBill]

Have you ever switched the firing order on a V8 engine and experienced a problem with the crankshaft?

If I was looking for FO-induced crank problems, I'd fire two cylinders at a time; sort of an adaptation of the Moto GP "big bang" philosophy to a dirt series...