2.2E: converting to vacuum advance distributor
 

gents

wanted to revisit this post. my current 2.2E distributor has been recurved for ALL mechanical advance. there is no advance/retard diaphram on the side.

is anyone running a similar motor with webers? where do you tie in the vacuum to the carbs/intakes?

(original post)

on a 2.2E with webers, is it possible to use a vacuum advance distributor? application is a steet car. looking to help out the MPG...

what year distributor could i use?

what would the curve look like for the mechanical portion?

how much vacuum advance?

i read some of the other articles that talked about pulling vacuum off of the #1 and #4 intake manifolds and using a T-line. what size tubing?

appreciate any insight.
matt

I don't think there is a dist that will work. The only vacuum advance I know of was on the later 3.0SC motors. These dist will spin backwards of your current motor. There are others that have vacuum retard mechanisms which were only for emissions at idle. They will do nothing to help your gas mileage.

I am just curious why you think more advance will give you better gas mileage. too much and you will just start pinging, especially with a 9.1:1 on pump gas. You should just set the dist to have max advance of 30 BTDC at 6K rpm. This should leave you at about 12 BTDC at idle (1000 - 1050rpm). That's how mine is set on my engine, same as yours. runs great and gets about 24-25mpg on the highway when just cruising.

I concur with Jamie. The only vacuum units available for the mag engine bosch distributors retard timing. If you feel you really must change the characteristics of the distributor you should have it re-graphed to suit your application, however if it is the original you'll probably find that if set correctly it is as good as it will get.

If fuel efficiency is the issue, I'd begin with an assessment of your weber's settings. It is all a compromise though...

Buy a 2.4 or 2.7 distributor and take it, along with your 2.2 distributor to a machinist and have him lathe the 2.4/2.7 dist. down to the same diameter as the 2.2

Then machine off the little stand, and you're done.

The vacuum retard (they are retard not advance, but we know what you mean) distributors work better, since the mechanical only units tend to have issues with a hanging idle. You set them up correctly, and once they get hot, the idle either sticks high, or takes too long to come down.

anyone have any additional info. the questions stem from running chevy's with a conventional vacuum advance distributor, and knowing the importance of 1) retard under load and 2) max advance during cruise.

thanks
matt

The Marelli distributor used in '68-69 T engines used a vacuum advance unit.

Vac. adv. takes advantage of lean part-throttle A/F mixtures which burn slower. Advancing the spark timing takes advantage of this characteristic and provides increased PT fuel mileage.

Vac. adv. does not work at WOT, thus reg. mechanical advance only during this condition. However, the Marelli distributor was setup to maximize the reduction in engine emissions and not performance. Some parts are NLA.

I've got a Marelli dist. in good condition if you want one, btw.

Sherwood

sherwood
so on this marelli dizzy, is it 15deg mechanical, 15 deg vacuum? how is it split up?

last i checked on my car, i'm about 7 deg at idle and 36 at 6000. at 3500, i think it's only 28ish. this cruise PT scenario is what i'm getting at. it should be max advance at cruise, then retard when under load.

why is the vacuum advance setup considered "not performance"? couldn't you run the VA and simply limit Total Advance to 36 deg? that way under PT, you were always maximizing efficiency...

on the "brain" ignition systems (eg crankfire setups), is there a way to add in a vacuum port? or is it strictly mechanical?

thanks for entertaining my thoughts.

Matt,
I never plotted the Marelli vacuum advance curve and I couldn't find it in the repair manual. However, the specs are typically 5ºATDC (initial setting) and 35º total mech. adv. @ 6000 rpm. The retarded ATDC timing spec is for emissions.

"couldn't you run the VA and simply limit Total Advance to 36 deg? that way under PT, you were always maximizing efficiency..."

Yes, that's how the Marelli works, but certain parts (e.g. dist. cap) are NLA. The factory mech. advance limit (40º total) is a little too agressive for non-emissions engines - when the timing is set before TDC, you're going to add that amount to 40º and probably create a detonation situation.

Adding more advance at PT is doable depending on the engine control system you have. You would need a vacuum sensing switch as an input to the ECU to kick in more advance (assuming the ECU has that programming functionality).

Sherwood

got it.

these questions all stem from my old chevy days and from VW applications. Mallory and MSD have off the shelf applications available for flat 4s (including 914/912s) that are completely tuneable. when i spoke with Mallory, they said there was not enough interest in the 911 community, and so they never made a 6 cylinder model. additionally, you have to drill a port hole in one of your webers...

this is aircooled.net's info on this mallory 47 unilite:
http://www.aircooled.net/new-bin/viewproductdetail.php?keyword2=IGD0003&cartid=

i guess i'm caught somewhere between long hood purists, and 3.6l converts... maybe i can get a prototype!...

thanks
matt