Re: Timing & Vacuum Advance 101
I did post recently about a knocking noise I experience with my camaro, after distributor and carburator setting changes.
Now as a return of experience I want to post for reference for similar engine configuration people may use....
Engine is 327 ci vortec heads comp cam 268HE straight propane impco 425 edelbrock perfomer intake and tri Y headers. with T56 and 4.11:1 posi rear end.
As tuned now the car is pretty fast, certainly 2-2500 rpm untill 5500 with very good throttle response, which correspond to the cam installed.
Under 2000 rpm I guess I could have better respons still maybe with more advance but as now with the 6° speed can have high load on engine and I didn't want to experience and play with more advance...
- AEM wideband lambda gauge is installed and working.
- I could then test drive the car and tune it.
So here it is :
12° mechanical starts at 1400 full at 2500 (so total = 23°)
10° vaccum advance
1.02-05 acceleration under 2200 RPM
0.95 acceleration at WOT higher RPM
For the understanding of my research and coming to these numbers after having these knocking issues :
- CR 10:1 high compression --> less advance
- vortec L31 heads are fast burn heads with high quench chamber design --> less advance needed. On vortec heads we have numbers on gasoline as low as 28-29 total with very good performance
- propane rule compared to gasoline: +3-5° initial and -5° total, with curve coming in faster.
Camaro 1968, propane 327ci, Big Brake, Hotchkis, T56