race engine timing..
07-11-2001, 06:28 PM
#1
Racer
Thread Starter
Join Date: Jul 2001
Location: Torrance ,Ca
Posts: 416
Likes: 0
Received 0 Likes
on
0 Posts
race engine timing..
I have a 3.4 liter race motor with 10.5:1
compression, GE 80 cams, 46 IDA 3C Webers, headers, and open exhaust. I've modified a 3.0 distributor to work by swapping the drive gear from the 3.2 distributor. Also, I've locked out the advance and installed an MSD ignition set-up with a Vari-Curve unit for timing adavnce. If I use factory settings,(5 degrees BTDC at idle and 26 degrees BTDC at let's say 5K rpm, it runs terribly, currently it is set at 15 degrees BTDC at idle and 35 degrees between 3k and 7K rpm and it runs rather well. Any suggestions on the proper timing? The British method is out( you can't hear any pinging or knocking with a race exhaust), Of course I could Dyno it, but I'm concerned with any possible damage at this point with incorrect timing.
Thanks !
compression, GE 80 cams, 46 IDA 3C Webers, headers, and open exhaust. I've modified a 3.0 distributor to work by swapping the drive gear from the 3.2 distributor. Also, I've locked out the advance and installed an MSD ignition set-up with a Vari-Curve unit for timing adavnce. If I use factory settings,(5 degrees BTDC at idle and 26 degrees BTDC at let's say 5K rpm, it runs terribly, currently it is set at 15 degrees BTDC at idle and 35 degrees between 3k and 7K rpm and it runs rather well. Any suggestions on the proper timing? The British method is out( you can't hear any pinging or knocking with a race exhaust), Of course I could Dyno it, but I'm concerned with any possible damage at this point with incorrect timing.
Thanks !
07-11-2001, 06:58 PM
#2
RL Technical Advisor
Hi Howard:
You didn't say whether your engine is single or dual plug but from your symtoms, I would venture that its single ignition.
Assuming that you are using race gas, I would set the timing with those cams and compression at:
About 10-12 deg idle (Everything is BTDC)
About 25-28 deg at 3000
About 35-36 deg at 6000
Never more than 35-36 total at 6000 for single plug engines,......
As you so noted, do not ever use the "British" method timing on any air-cooled engine. These things are subject to sub-audible detonation which is a phenomenon that you cannot hear, but spark plugs will show it, if you know what to look for.
Fact is, the threshold of detonation changes with outside air temperature, cylinder head temperature, mixture, and load so timing anything by ear is very dangerous to the pocketbook.
Optimal ignition timing is determined on an engine dyno or a load-type chassis dyno using specific instrumentation and many plug cuts to read the plugs.
Hope this helps a little,
You didn't say whether your engine is single or dual plug but from your symtoms, I would venture that its single ignition.
Assuming that you are using race gas, I would set the timing with those cams and compression at:
About 10-12 deg idle (Everything is BTDC)
About 25-28 deg at 3000
About 35-36 deg at 6000
Never more than 35-36 total at 6000 for single plug engines,......
As you so noted, do not ever use the "British" method timing on any air-cooled engine. These things are subject to sub-audible detonation which is a phenomenon that you cannot hear, but spark plugs will show it, if you know what to look for.
Fact is, the threshold of detonation changes with outside air temperature, cylinder head temperature, mixture, and load so timing anything by ear is very dangerous to the pocketbook.
Optimal ignition timing is determined on an engine dyno or a load-type chassis dyno using specific instrumentation and many plug cuts to read the plugs.
Hope this helps a little,