Oz928BOY

Hi all and ty for the tips and help with some of my 928 issues
I have a question about the 'vacuum advance' located/attached to the distributor, Mine has been capped off and i have noticed that every1 has theres attached for use! Do i need it does it do anything and why wauld mine be capped off... not sure if i should get it working in the system?
Cheers for any help


'83 928S 4.7L 5speed

dprantl

Vacuum advance means exactly what it sounds like. It advances the ignition timing at lower engine loads to improve throttle response when cruising.

Dan
'91 928GT S/C 475hp/460lb.ft

123quattro

It is your friend...

aj986s

Here's a generic link that discusses distributor operation, including mechanical and vacuum advance.

http://en.wikipedia.org/wiki/Ignition_timing

If disconnected on your it could mean a couple of things. Either a problem with your specific distributor or vacuum advance unit. Or PO chose to bypass the vacuum advance for some reason; maybe changed the mechanical advance or opted for a static/fixed timing, which itself has pros & cons. Static timing was prevalent on very early cars, before introduction of dymanic timing, which improved drivability. Also seen some race cars/dragsters use static timing, because motor is only run at high RPM.

Oz928BOY

So it doesnt affect high end throttle/load, just low end...why did the PO do this(so not kool) , looks like i need to hook it up... any1 have a diagram as to where it leads to in the system does it attach direct into the MAF via a port of some kind?

Oz928BOY

AAAAh ok ty Tony!
I will have to get this checked out then

Oz928BOY

I dont know if this info helps! but,
I did a PowerDyno test to see what specs i get and for kW i got 190.6@171kph, & 559.2 Nm@128kph does this seem ok for my MY 928 ('83 928S(euro) 4.7L 5speed)

dprantl

The power is just slightly low (255rwhp, you should be 260-270rwhp for a EuroS) and the torque seems way too high (412lb.ft). Since you don't have the torque multiplication of an auto gearbox, I would say the measurement of torque was way off. Also, the measurements should correspond to RPM, not kph.

Dan
'91 928GT S/C 475hp/460lb.ft

mark kibort

vaccum advance should be around 10 degrees added under high rpm. most of it is centrifugal, bu the vacuum helps a little from only the venturi effect of the throttle body. under WOT, it might only ad 5-10 degrees. there is a chart in the manaul. that could be costing you 10hp or so, 1 or 3 by optimising -/+ 3 degrees when things are working well.
hook the vacuum line to the air box side port on the throttle body (not the plennum side of the throttle body, which is used for constant vacuum at idle , like for fuel regulator pressure pull back)
early cars had a vacuum retard, which retarded timing under decel or idle, that can be disconnected. check your timing, at 3000rpm with no vacuum connected, timing should be around 20 degrees BTDC
mk

Oz928BOY

aaah ok ...i wasnt to happy with the DynamicPowerDyno test that the mech did! Also straight after he did the test my Airpump failed or maybe while he was doing tests as it had locked up and the belt was fried so maybe im thinking that the belt may have made things go off a lil(maybe)!
He did the test with no MAF system fitted, i rocked up at his Workshop as he just finished the run...i wasnt to happy about not having it installed esp at such high RPM!
i also have x3 exhaust mufflers and after XMAS im ganna make that down to X1 Sports muffler and an X-pipe(cross-flow) where the large muffler (at the Cat. spot area under shifter pos.) will be remooved and a cross-flow fitted in its place so i can add a lil more HP...i have a dual SS 2.5inch system!
Also Mark im interested in the e-Ram you sell im thinking of adding x2 of those on my car...will it be able to handle it and what wauld be needed in preperation for the system install(wiring, tubing/ducting and bat. power...etc) I like the system as it is not so noticable under the bonnet...i prob should private MSG you on this!
CHEERS GUYS!!!
I will see what the situation is with this Vac. Ad. and hopfully get it hooked up and working as it should!...BTW can the Vac.Ad. be removed and replaced or do i need a whole new dizzy replacment(with Vac.Ad. attached)?

aj986s

Not sure specifically about 928's, but generally, for dedicated track driving, I think vacuum advance can be removed, and tweak mechanical advance (change weights and springs) along with the engine's static timing, to achieve optimum performance in a narrow RPM range. But for street driving, I really think you need vaccum advance to enhance drivability across a wide RPM range.

Note that late model cars use computer controls to control timing advance based upon a wide range of sensor inputs, and not just engine vacuum. Those cars can be even more finely tuned by a knowledgable tuner, with the right equipment. Computer controls are a major reason that engines of late are getting more powerful and efficient at the same time.

Tampa 928s

If you remove the cap and use a Miti-Vac on the port you can see if the advance actually moves when you apply vacuum to it.