Ignition Advance ?

[PaulProe]

I have chosen to use a Mallory Unilite distributor on my FE 3x2 setup. The unit had vacuum advance but when I sent it in to have the crab cap conversion for air cleaner clearance, the vacuum advance was history. Not enough room/metal for both.

I intend to use the car for road trips. Knowing the FE isn't going to win any awards for fuel mileage, I am still after all I can get.

I've had the thought of adding an electronic timing adjuster to allow "dialing in" a few degees advance when cruising. Will I improve mileage any amount by doing this or am I chasing dreams?

The timing adjustment would run about $120 and allow about a 15 degree adjustment from the cockpit.

? ? ?

Paul

[blykins]

I don't think it would be worth it IMO. I would rather spend that $120 on a good chassis dyno session where the a/f ratio could be mapped and the carbs tweaked.

[Cobrabill]

A "road car" without vacuum advance isn't a good idea.If you're after all you can get-get a distributor with vacuum advance.After that,you're looking for 34-36 total(ballpark-depends what your motor likes) and get it all in by 2500rpm.

[Barry_R]

Their both right. The fuel mapping would be worth a bunch on one of the old 3x2 setups. An electronic timing control can be used simulate a vac advance - depending on how sophisticated you want to get. More advance under light load will improve mileage a bunch.

[c6ae]

I have played with this timing detail quite a bit, (428 w/ CJ specs)
Adding a vacuum advance and using the factory specs for a 390-4V as a benchmark to start tuning I increased my mileage from 11 to almost 14... that’s better than 25%!

The advantage of the vacuum set-up is that when you increase engine load the timing automatically retards. With a dial type electronic control if you forget to do this severe engine damage may result.

The stock specs (in distributor degrees) are;
Mechanical centrifugal advance 11-1/2° at 2000 with a vacuum advance of 10°. These are added to a static crankshaft-timing advance of 10° for a total of 51° crankshaft degrees at 4000 rpm

My set-up is like this- in crankshaft degrees;
Static 10°, plus 25° centrifugal all-in at 3000 plus 15° vacuum advance. Total is 50°

The vacuum control is connected at the timed port so that the vacuum advance comes in at about 1000 rpms (idle speed is 800)
My car has a “tall” gear so to be drivable at slow speeds (5 –10 mph) I need to keep the initial advance and idle speed low to avoid excessive clutch slipping. A different engine may want completely different timing specs

[CHANMADD]

I have run my car both ways, and for sure "with" the vacuum advance is definately way better on the street. A smoother ride and better gas mileage,
John

[Excaliber]

I have vacuum advance, there is no question it improves the mpg. But Blykins makes a very valid point for a dyno tune. Assuming limited funds where to spend the money? Depends largely on the miles of driving anticipated, this is a tough one.

One way to calculate it: How much GAS will a $120 buy and how many miles will you have to drive to get pay back? When the 'numbers' are in the 10-11 mpg range (thats what I get, up from SIX) even a modest increase has a reasonable pay back time frame. With a car all ready getting 25 or better mpg it's tough to get pay back if you spend very much.

I used to work on 18 wheelers getting 5 mpg. Buying radial tires gave us 6 mpg. Number of miles driven, 'X' and it was a no brainer. The tires MORE than paid for themselves.

NOTE: On my car to improve the mpg it was a radical change even to the point of rebuilding the motor! New carbs, distributor, cam, pistons, vacuum advance etc. Pay back won't happen for me. Street driving dramatically improved, more RANGE on a tank of gas is pretty cool. There are benefits beyond a simple mpg calculation in some cases.