Hi,
I'm wondering whether I should do something to alter the timing on my car or not.
Car : 1970 Challenger, 493ci RB, Indy 440-1 heads, MSD mech distributor (no vacuum advance), MSD-Digital 6 ignition. Tremec 5-speed with 0.64 final ratio, 3.55 rear-end.
Total (mechanical) advance is 36° at 3500RPM (I don't know when full advance is in, my timing light gives funny readings below 3300RPM, with the multi-spark).

I use this car primarily for road-racing.

The thing is, I have to drive it to and from race events, and I generally drive it at around 2000 RPM on the 5th gear (around 70mph, getting 14 mpg). Which means there's probably not much mechanical advance then, and without the slightest bit of vacuum advance, something could probably be done to improve mileage.

My question is this : should I change the mechanical advance springs in order to achieve total advance sooner (around 1800 to 2000) ? Should I get a MP dizzy and use the vacuum canister?

Would an early advance curve have any drawbacks in road-racing?


Same goes for a friend's cuda, except he has a 416 and a MP dizzy (with vacuum canister disconnected) with orange box. Same transmission, rear-end ratio.

If you're really getting 14mpg on the street I'd say your doing pretty darn good! Your idea of bringing the advance in sooner is good but you may find detonation at anything except LIGHT throttle at that 2000 rpm in top gear.
You running something better than 92-93 octane??

that's 14mpg highway, at constant speed. it gets considerably worse when the right foot comes into play (6 to 8 mpg mixed street/racetrack).

What makes me think about the vacuum advance is the overheating at idle that I'm experiencing.

I'm using 98 octane fuel (or 95 in backroad gas stations, sometimes they don't have a 98 pump). I have a fairly low comp ratio (9.3:1), as I planned the engine build thinking of future enhancements...

You think I could have detonation at 2KRPM when the engine is loaded if full advance is there?
Maybe I just need a street distributor with vacuum advance then - I just read an article someone posted today about that.

I just bought the MSD timing controller to use with my 6AL. You can dial out a few degrees while you're driving.