firing order engineering.....
firing order engineering.....
(OP)
american "reg'ler" V8 engines used a firing order of 18436572 for years. now on the Gen III motors, GM has "invented" the 18726543 firing order, despite the fact that ford has been using it since '88.
GM claims 7% less crankshaft stress by "moving" 4 of the 8 cylinders 360*. same crank layout, same piston position, different cam phase.
so in my dream machine motor, i'll be using a custom crank and cam...... gets me wondering.......
is it feasible to try and beat the OEMs at their own game? i'm building a performance machine, so 100,000 miles out of this engine is not the prime directive, by any means. i noticed that the "new" GM/Ford firing order doesn't solve the problem of the old 5&7 cylinders inhaling sequentially, it just moves the problem nearer the throttle body. sounds good, but i'll be using a single plane, with a central throttle body.
i've rearranged the crankpins on paper, and found that a 14326587 firing order will solve the intake problem, but i have no way of knowing what to consider in the way of "crankshaft stress".
any experience, guys? dead horse, maybe?
GM claims 7% less crankshaft stress by "moving" 4 of the 8 cylinders 360*. same crank layout, same piston position, different cam phase.
so in my dream machine motor, i'll be using a custom crank and cam...... gets me wondering.......
is it feasible to try and beat the OEMs at their own game? i'm building a performance machine, so 100,000 miles out of this engine is not the prime directive, by any means. i noticed that the "new" GM/Ford firing order doesn't solve the problem of the old 5&7 cylinders inhaling sequentially, it just moves the problem nearer the throttle body. sounds good, but i'll be using a single plane, with a central throttle body.
i've rearranged the crankpins on paper, and found that a 14326587 firing order will solve the intake problem, but i have no way of knowing what to consider in the way of "crankshaft stress".
any experience, guys? dead horse, maybe?





RE: firing order engineering.....
I don't think it means much unless you're making a LOT of torque.
RE: firing order engineering.....
RE: firing order engineering.....
16354728
15486372
18364527
Cheers
Greg Locock
RE: firing order engineering.....
RE: firing order engineering.....
RE: firing order engineering.....
thanks for the ref's Greg, i'll play with those tomorrow when i'm not so sleepy...... zzzzzzzz.......
RE: firing order engineering.....
RE: firing order engineering.....
i.e. the old Buick nailhead engines (401 & 425) number cylinders the way chevy does, but opposite- odds on passenger side, evens on driver. their firing order is 12784563, but if you start on the driver's front cylinder, using chevy pattern, you get 18736542- different than either chevy or Ford pattern, but same crankpin layout.
basically, i haven't found a V8 yet that has a different crankpin layout, so i'm betting there's a reason for it.
i still need to "decipher" the ones Greg posted, though.
RE: firing order engineering.....
maybe they're for straight-8's?
RE: firing order engineering.....
The obvious numbering system to me is front to back, as the journals appear on the crank. It's just so easy, no one could forget.
That is how Chevrolet does it, and how almost all inline motors I know do it (some old Peugeots numbered from back to front).
The only problem is with compound rod journals like radial engines and V12 aircraft motors.
Regards
pat
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: firing order engineering.....
Getting the first right is reasonably straightforward, I think. Getting the second right can be done by hand, to some extent, but I've also seen rather complex (computer based) analyses involving working out the bending stiffness of the crank and block, and taking resonances in the crank into account.
There is a third issue here - the subjective sound quality, but I think you won't be worried too much about that.
Cheers
Greg Locock
RE: firing order engineering.....
anyway, after MetalGuy's post, i realized that i have all four front cylinders firing together, 1432, which is probably very bad for the crank.
i'll probably just use a stock-type crank, and a custom cam to use the LS1 firing order.