Join Date: May 2002
lilscreamer is offline
this should help, this info is all directly from the Chevrolet
Power catalog from GM
1978-84 v6/90 where 200 and 229 cid, these motors had a
"semi even" firing order with a rod throw of 132degrees/108deg/132deg/108deg and so fourth throughout the firing order of 1-6-5-4-3-2.
the 4.3 was introduced in 1985 and is a true "even fire " engine.
Its rod throws are offset 30 degrees which produce 120 deg. of crankshaft rotation between cylinder firings.
Then there is a heavy-duty "common pin" crankshaft that was developed by Chevy Special Products for v6/90 racing engines. There is NO offset in the rod journals of a common pin crank.
So this design produces an "odd fire" sequence with alternating
150deg and 90deg intervals between cylinder firings. NO PRODUCTION V6/90 CHEVROLETS HAVE BEEN MANUFACTURED WITH ODD-FIRE COMMING PIN CRANKSHAFTS, however most of the v6/90s used in COMPETITION are equipped with a common-pin
odd fire crank.
Thus there are three possible firing sequences for a v6/90 engine
as determined by the crank shaft. EACH FIRING SEQUENCE REQUIRES A SPECIFIC DISTRIBUTOR AND CAMSHAFT TO PRODUCE THE CORRECT SPARK AND VALVE TIMING FOR PROPER OPERATION.
The firing order is the same on all v6/90. 1-6-5-4-3-2
91 43:comp cam,early 200/229 headsw/pocket port,headmen headers w/ true duals,edelbrock intakew/holley600 and ram air,driveshaft loop,mini-spoolw/3.42's,lakewood slapper bars and bfg drag radials.