brake servo and throttle bodies

Mon Dec 04, 2006 9:04 am

i am fitting a fet of m5 throttle bodies to my m30.

can i take the brake servo vacuum feed from the plenum, or does it have to be after the throttle plates?

easier to take from plenum, but it seems to me that this area will mostly see atmospheric of positive pressure thanks to the turbo

Mon Dec 04, 2006 10:32 am

Even without a turbo, the area before the bodies will see mostly atmo pressure.
Vacum can only exist between the intake valves and the thorttle bodies. And only when the bodies are partially closed.
Same goes for a single throttle body, the only differance is that on the single setup the plunum is after the body as opposed to before it on the multi throttles setup so it has vacum.

Avner.

Mon Dec 04, 2006 10:36 am

the vac pipe on my engine is in the same place,sits after the throttle butterflies.It looks like a fuel rail but is obviously an air rail.

Heres a couple of pics :

you can see it next to the fuel rail.

cheers
andy

Mon Dec 04, 2006 1:36 pm

The air rail on the S50 has the IACV underneath it too doesn't it?

Mon Dec 04, 2006 2:53 pm

Turbo-Brown wrote:The air rail on the S50 has the IACV underneath it too doesn't it?

yeah i think so .

Mon Dec 04, 2006 5:13 pm

Gotta copy that next time I make a set of TBs, that or the throttle jack Tee showed me yesterday.

Fri Dec 08, 2006 5:15 pm

oops, forgot i asked this

cheers for the input all, i'll take the feed from after the throttles. the s38 bodies do have an air rail, there was just a convenient stub on the plenum near the servo and i was in a lazy mood...

O/T, Buster what master cyl/res is that?

Fri Dec 08, 2006 5:43 pm

i used a 1.3 Mk 2 golf servo with an Audi 25 mm master cylinder.I used the bigger mastercylinder becasue its supposed to be better with bigger brakes,there is a 23mm one available from an Audi (e30 ones are 23mm).
The reservoir was an after market one from rally design. pictures below :

cheers
andy