Hey guys,
I am looking to get some inputs on a strategy/approach for setting up/tuning my less than optimal (mechanical advance) street performance motor. Need to try and improve for drive-ability with possibly a less than optimal ignition set up and over cam for an automatic.
Ideally, I would just de-cam the motor and add a vacuum to the billet MSD dizzy (but that is not an option according to MSD) therefore change out the entire new distributor (not sure which one but one with a vacuum advance that can work with the 6AL).
However funding is to limited to replace these new components and or rip at the motor and replace the cam at this time.
So I am looking to get advice on the things I can tune, timing advance, AF, advance curve, jetting etc. At this point I have not done anything to the carb and just played with he advance and curve. I need a a more clear approach as I feel I am just shooting in the dark by myself. I have read articles on this and understand that vacuum secondaries are better for a street automatic not just for better burn efficiency but better drive-ability since you get the boost of advance at idle and cruise which is needed since the AF is lean. This lean condition takes longer to burn and more advance is needed. I get this. I do hear that people have solved or greatly improved this situation I am in but I have not located any threads as to how.
I have access to an AF meter/sensor that I plan to use to see where I am at.
The Problems:
- Idle, needs to be >1100RPM out of gear which equates to roughly 500RPM in gear. Typical issue for high cammed motors right?
- Not great vacuum 12in
- Cold idle is very poor and takes a while to warm up even here in AZ.
Needless to say I regret not running a vacuum advance set up originally as that would have been the right choice for a more street-able set up.
Current set up:
- 1974 block, 340 with unknown but very aggressive cam at least 10:1 compression
- Factory heads (1973)
- 650 CFM Holley Double Pumper 4150 with mechanical advance manual choke
- M1 high rise
- MSD6AL
- Billet MSD Dizzy
- Its a TF904 auto 2400 stall
- 355 rear end (not yet installed)
- Full length headers
Currently Tune:
- 14 degree advance stop distributor bushing to limit all in timing help with detonation
- Slowed the advance down to help with detonation using the largest springs
- Base timing is currently set to 17 degrees and 31 all in at around 3800-4000. No detonation with this setting.
Thanks for taking the time to red this and for your comments.
