Quote:
Originally Posted by Grubby
I know that vac advance doesn't add performance, but it certainly add fuel mileage.
An FE MSD distributor without vac advance is about $100 cheaper than one with. Would you ever make up the difference in gas mileage on a Cobra?
If a 447 gets about 15mpg with vac advance, how much would it get with?
John
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Probably not an issue for your ERA but vac advance also will result in a cooler running engine - sometimes significantly. Provided it's not on a ported vacuum outlet it will also smooth the idle out a little with the additional timing. But, if you already have your centrifugal advance limited and are running 15 - 16 degrees of initial advance, it won't make much difference.
On the downside, too much additional vacuum advance at cruise can create an overall over-advanced situation with the plug firing too far in advance of TDC and create what feels like a constant surging or light missing situation. An adjustible vacuum advance canister can be used to dial it back some.
Yes, it will improve gas mileage but I'm not sure it will be very measureable with these light cars and big motors - I would guess less than a mile per gallon but someone will probably come along and prove me wrong. I'm a believer in vacuum advance but I'm running a 427 dual point w/o vacuum advance in my ERA and it seems to be doing fine.