Brake servo and itb's

Post Tue Oct 23, 2012 1:09 am

I've been looking at itb set ups for m20 engines. I don't see any brake servo vacuum connection on the ones I've seen. Is the servo not connected if itb's are fitted or am I not looking hard enough? Would the servo work properly if only connected to 1 intake runner? If a servo can't work properly using the vacuum produced from one intake runner, could a vacuum pump from a diesel engined car be used?

Post Tue Oct 23, 2012 7:13 am

On my S50 I'm sure the vacuum pipe from the servo was connected to all 6 TBs via a runner connecting all 6 together. It ran along the top with the fuel rail.

Aftermarket ITBs may not have this, so one would need to be added.

Post Tue Oct 23, 2012 10:10 am

Im pretty sure all the late S14 TB's only have one port on cylinder 4 TB for the servo. But they are 48mm, however I don't think the size of the throttle is what matters, just seems that the over all bore size would play a larger role in producing more vacuum.

Post Tue Oct 23, 2012 7:32 pm

Well, mine is going to be a home brewed effort using a chopped 325i inlet manifold and gsxr 600 throttle bodies. Judging by the ones I've seen that have used a chopped manifold there doesn't look like there's room for a fitting on the inlet runner. Looks like I'll have to graft a vacuum pump from a diesel onto the motor.

Post Sat Oct 27, 2012 12:04 pm

Demlotcrew wrote:Im pretty sure all the late S14 TB's only have one port on cylinder 4 TB for the servo. But they are 48mm, however I don't think the size of the throttle is what matters, just seems that the over all bore size would play a larger role in producing more vacuum.

^^ Yep - absolutely right...

No need to go to the hassle of a vacuum pump - just make a hole the same size in one of the runners to accomodate the servo and you are good to go - you will definitely get enough vacuum that way...

Post Tue Oct 30, 2012 5:09 pm

yep, a single throttle take off works fine, you'll need a decent one way valve in the system though or you can get a pulse through the pedal.

Post Wed Oct 31, 2012 6:02 am

harry_p wrote:yep, a single throttle take off works fine, you'll need a decent one way valve in the system though or you can get a pulse through the pedal.

keep in mind how big the S14 brake booster is!

Post Wed Oct 31, 2012 11:39 am

Is an s14 brake booster/servo a lot bigger? I would've thought that using a vacuum take-off on only 1 inlet runner would produce a weak vacuum or not keep up with demand if the brake pedal is pressed repeatedly.

Post Wed Oct 31, 2012 12:41 pm

No its not, the point Uwe is making is that the OP might have to run a smaller Booster for clearance etc.

I have never experienced any vacuum relates issues and mines only has one take off.

Post Wed Oct 31, 2012 4:20 pm

Thank's for everyones input. I think I'll probably include a servo take tooff in one of the runners. And fit a 1 way valve in the vacuum hose.

Post Wed Oct 31, 2012 4:36 pm

UweM3 wrote:
harry_p wrote:yep, a single throttle take off works fine, you'll need a decent one way valve in the system though or you can get a pulse through the pedal.
keep in mind how big the S14 brake booster is!

i only had the pulse thing on my metro when i first swapped the engine and had to bodge a hose (with no one way valve) temporarily.

my only experience of the m3 setup was when the union popped out of the throttlebody and my scrawny legs struggled to give any noticeable braking effort