Will vacuum distributor boost my MPG?
 

Will swapping out the mechanical only distributor in my C3 with a vacuum advance unit boost my MPGs with no changes to base timing, or carburetion?

Why or why not?

Yes it will. It will also improve throttle response at part-throttle and keep the plugs cleaner.

Yes.
Why? It adjusts the timing to suit engine load.
It takes about 40 hp to maintain 55.
You can go up to 52-54* then.

40hp is a guess.

Yes. Significantly. Because it optimizes timing at light-throttle cruise.

I will not only give you a noticeable increase in mpg but the big advantage is a smoother, cleaner, snappier running engine on the street.

Yes, if you make sure you hook up to full manifold vacuum and not ported. Ported could just make things weird and dangerous.

-Stroke

And what distributor would be suggested for street performance but without points

Yes......but getting the right amount of advance is important. Pulling more advance under light load lights the charge much earlier but because there is no strain...the heat potential is lower and generally there is less charge overall in the cylinder.....under these conditions a charge can be lit earlier causing more available energy from each light off......more energy from the same amount of charge= more efficency and less fuel needed to make the same power (energy).
Read Lars papers on timing......ask him and he will send them to you.....good education :)

Jebby

If you are not using a box...the MSD ready to run is ideal because the curve can be pre set easily before installation.....but if you have a tach drive then they only make that distributor to require a box.....no internal module.

Jebby

If you don't need the tach drive, the MSD HEI Pro-Billet is a great distributor.

https://www.ebay.com/itm/Small-FEMAL...rd!19061!US!-1. Even resembles the oem points dist.

I have one of the above small cap distributors and the problem is it doesn't come even close to fitting under the stock shielding on my 69 big block. The distributor is 3/4" taller than an original Delco points distributor as you can see below. I think mine has a Dragon Fire stamp on it but they are the same. They actually said it would fit in the fleabay ad but as you can see below, it isn't possible as the cap on the stock distributor is right up against the bottom of the shielding. It does have a tach drive and works nice with a standard coil though. One other problem was that the supplied vacuum advance allowed almost 20 degrees (crankshaft) advance which is basically useless. It did come with springs and bushings so is easy to set up.
https://cimg9.ibsrv.net/gimg/www.cor...e408df0f41.jpg

They sell enough parts now to convert your original Delco to TI,. ignition. Your shielding will fit again.

Yes, I was rebuilding my original distributor and wanted something to use and keep for a spare. I thought the price was really good but same story, you get what you pay for. I had been rebuilding the Delco, converted it to electronic and was playing with advance curves, springs and vacuum cans and have it right where I want so the MSD clone now sits on the shelf. It worked fine except for the vacuum can and it's too tall for shielding. I stuck a B26 can in it to replace the 20 degree advance one with no markings and it was OK.
I found the best advance can for the 427 in the Delco was the original stock MS360-12 that I had. It measured at 0@6" and max 12@13". I run a Comp 270HR on an otherwise stock numbers matching motor and it's slightly choppy but not lumpy and no bad habits. I now have it set at 18 initial and 18 mechanical and am using 91 octane no ethanol. I can get Chevron 94 just up the street but why bother or pay the extra as it's not a race car.