[1 Day]

My Model A hot rod has a 327 SBC.
-10.1 compression
-aluminum heads
-300HP Chevy cam
-600 cfm carb
-195 themostat(never gets above 205)
-I use 93 octane fuel
-Delco plugs@.55 gap
-MSD 6A box
-Blaster coil
-MSD distributor, no vac can, comes with 21 degrees advance stop bushing from MSD
-new Pioneer balancer, verified TDC, timing marks
With the 21 degree bushing and two light blue springs I can put 18 - 20 degrees initial timing in it without any pinging. (19 inches of vacuum). I'm looking for economy over performance (10 gallon fuel tank). My cruising RPM's are around 2650. Is that too much initial timing? Should I be changing the advance stop bushig to a 25 degree and then cut back on the initial? My fuel mileage is about 16.5 mpg.

[techinspector1]

Every engine combination is different and in my opinion, the optimum spark lead can only be determined by experimentation and verification. If the motor is not kicking back against the starter with that much initial, then who is to say it's too much?

I think I would closely document the mileage (you said ABOUT 16.5) with the combo you have now to establish a baseline, then change it and see what happens.

[ericnova72]

I think you should have bought a distributor with vacuum advance. Besides carb adjustments to the idle fuel feed restrictor and the idle air bleeds, and the cruise RPM level, the vacuum advance has the largest impact on fuel mileage. It adds advance at light throttle opening levels, which is where you are at when you are at cruise speeds. Your initial and mechanical advance sound in the ballpark (38-40 degrees total), but best fuel mileage at cruise will come with the vacuum advance adding another 12-18 degrees at your cruising speed. My best results have been with the advance hooked to manifold vacuum, I have never gotten good results with ported vacuum. My 11-1, solid lifter, Dart headed 406 smallblock gets 18+mpg on the highway turning 4.56 gears in an all-steel 3300 lbs 72 Nova. Car runs 11.50 sec @ 116.5 mph in the 1/4 mile. It took several days of adjusting and testing to get the Crane adjustable advance kit dialed in, but it was really worth the effort IMO . I figure I picked up 6+ mpg and the plugs stay cleaner to boot! Good luck with your combo!

[techinspector1]

Excellent response Erik.

[automotive breath]

I would not be concerned about the 18-20 degrees initial advance, this will
improve idle quality. I agree with ericnova72 on the vacuum advance, some
benefit can be found with a inefficient chamber by additional advance at light
throttle. The thing to focus on is A/F ratio of all carburetor circuits. If you are
serious about fuel economy consider a wide band O2 sensor. Cruse AFR should
be in the 15:1 range.

I have been helping with a 4000 LB Ford Lightning pick-up , dual purpose street
strip. The truck recently averaged 20 MPG on the high way during the Hot Rod
power tour and high 13 second performance at the local track, he is running FI.

[tomthecomic]

I think it would be a dog with 18. I think 10 and give the distibutor 24. For fuel I would run all in at 2,500 but performance 3,000. The vacume would help.