Firing order question

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needsaresto

needsaresto

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Has anyone used a different firing order on thier small block?

I know the Hemi guys can do this.Makes more power and torque.

Are there any drawbacks?

Did you make more power?

Run faster?
 
not sure for mopars but i know that comp makes a 4/7 swap cam for smallblock chevies. supposed to be good for 20-30 free horsepower. i'm building a 302 sbchevy for my 65 van right now and i'm gonna use the swap cam so we'll see. changes the firing order to a ford pattern, so my chev motor is gonna sound like a ford but oh well, keep em guessing i suppose.

you'd probably have to get an extremely custom cam ground for the mopar but i'm sure it could be done.

-tim
 
I saw an article a while back where they did the comparison back to back with conventional and 4/7 swap on a 350 Chevy motor. The cams were identical other than the 4/7 swap and they did not see anymore than a couple of ft-lbs and 2-3 HP difference.
 
Ran across this back in 1978. Put a see thru dis. cap and moroso blue max plug wires on my 304 Gremlin engine. Crossed a couple of plug wires unknowingly. It didn't idle quite as smooth so I adkusted the timing just a tad. Screwed around with the carb a bit too. It still refused to idle perfect but ran like a scalded dog. A couple months later it was in a local shop for trans rebuild and the mechanic there pointed out my crossed wires and said "fatest damn little car I've ever driven so just leave it that way I spose."
I out ran a lot of local stuff with that Gremlin, 327 Camaro, 302 Maveric grabber, etc...
 
it helps get rid of what chevys and mopars have in common, the 5 and 7 firing right after one another. the later style (genIII?) sbc have an updated firing order. wouldn't the crankshaft have to be changed to, to bring the piston up at the right time?
 
redfastback said:
it helps get rid of what chevys and mopars have in common, the 5 and 7 firing right after one another. the later style (genIII?) sbc have an updated firing order. wouldn't the crankshaft have to be changed to, to bring the piston up at the right time?
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The cam is ground so it matches the piston at TDC. 99% of all V8 cranks have the rod pins at 90 degrees. Also the piston is at TDC twice in the cycle, once for the power stroke and once when the valves are at overlap. It is up to the cam at which time it will be the power stroke. Marine engines have cams ground backwards so the engine will run backwards. In twin motor applications you want your motors counter-rotating so as to alleviate torgue steer. If you want to change the firing order, you have to change the cam.


Chuck
 
As a practical joke we used to switch the 5 and 7 plug wires on each other's smallblocks. They idle almost normally then run like crap when you drive off. Got a lot of laughs out of it.
 
340mopar said:
The cam is ground so it matches the piston at TDC. 99% of all V8 cranks have the rod pins at 90 degrees. Also the piston is at TDC twice in the cycle, once for the power stroke and once when the valves are at overlap. It is up to the cam at which time it will be the power stroke. Marine engines have cams ground backwards so the engine will run backwards. In twin motor applications you want your motors counter-rotating so as to alleviate torgue steer. If you want to change the firing order, you have to change the cam.


Chuck
Click to expand...

yeah i figured that you could change it to only when it is at tdc, not just choose your firing order. but to do what needsaresto said, a hemi can be changed? i don't think so, its the same 18436572.
 
I haven't heard of it but possibly at one time someone was grinding cams that would change the firing order of the Hemi to get a slight edge on the competition. In the 60's and 70's cars raced heads up in classes so any edge you can get over your competitor was the game.


Chuck
 
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