Vacuum Line Check Valve

[65Cobra]

I just noticed the original Mr Turbo setup for my 99 Busa added a vacuum hose from the throttle body vacuum line to the IAPS (Intake Air Pressure Sensor). In that line is a Tee and the extra fitting on the Tee runs to a small plastic check valve.

Since everything under the tank has been replaced (fuel pump, fmu (Begi), plenum, wastegate, bov, etc) this is no longer a Mr Turbo setup. So now I'm wondering (a) what the vacuum line to the IAPS does, (b) what the check valve does, (c) if this is a common mod on all Busa turbo setups, or something only on the Mr Turbo kit, and (d) do I leave it be, change it, or remove it all together. Thanks.

 

[texas-buzzard]

the vacuum line to the IAPS on a stock busa provides the necessary manifold pressure to allow the sensor to adjust the fuel injector timing for a correct mixture. the pressure is very low due to no boost from a turbo. on a boosted setup the sensor is not designed to handle boost and will give a false reading and can also be damaged. the check valve bleeds off the boost while also allowing it to see vacuum off boost. to answer your question, leave it there.

 

[65Cobra]

I think I understand, but one thing confuses me. If the check valve bleeds off boost, the way it's connected implies it would reduce boost throughout the maze of lines coming off the throttle bodies, thus affecting anything else connected within that maze. For example, my vacuum/boost gauge is connected to those lines via a Tee fitting because my understanding was the gauge would be less erratic that way. But that means in one area the check valve is bleeding boost to keep the IAPS from receiving a false reading, but not far away is another line leading to my boost gauge which might be receiving a false (low) boost reading. I connected my BOV and the two connections on my Begi Multi Role Regulator the same way. Should I be separating some or all of those connections by using the unused fittings on the throttle bodies?

 

[OZBooster]

yes. keep the bleed circuits seperate to those that need accurate readings

 

[65Cobra]

Thanks for the help. I just finished remapping my vacuum lines and was wondering if the vacuum/boost gauge would be stable enough connected to only the center two throttle bodies instead of all four. If so then I'm good to go and can move on to something else.

 

[cdhoroho]

be sure the aip sensor has all 4 TB's hooked to it or youll not get the bike to run right down low

 

[65Cobra]

The sensor is connected to all 4 TB's as originally intended. In fact the sensor has sole rights to that set of lines so it should be fine. The BEGI is connected to the spare vacuum fitting on the leftmost TB. The spare fittings on the three other TB's are tied together and connect to the BOV and vacuum/boost gauge.

 

[mcbusaturbo]

my system has the AIP vacuum lines set up as it was stock all four throttle bodies and just the sensor with the exception of the check valves to bleed off boost, then I have a line connecting both outer cylinders and that is the line I put the tees in for the boost gauge and the BOV.

 

[dubious]

Why do some systems have the check valve oriented in line so it closes blocks boost, to prevent over pressureing the IAP,

while others put the T inline so the check valve blows the boost off to atmosphere, but closes on vacuum?

Which way works better? Why?

Thanks,
Lyle

 

[OZBooster]

FMU that has an open end will have a check valve inline ...but a map sensor that has no outlet if connected this way will get a vacuum lock on the sensor side and not react correctly , so these are tee'd and vented to atmosphere

 

[dubious]

Not sure about FMU's but my regulator is an Aeromotive 1:1, there isn't any check valve in it, so should I vent with checkvalve to atmosphere, or simply use a check valve to block boost to my closed end IAP?

Thanks,
Much appreciated!

 

[mcbusaturbo]

for the IAP sensor, vent the check valve to atmosphere, blow through it so you are sure which way air passes through. and then for the FMU you use the check valve in the same orientation but connect the outlet side of the check valve to the vacuum line that goes to your FMU.... so now you will not build boost on the line going to the IAP sensor, but you will see boost and NOT vacuum on the FMU

 

[OZBooster]

Aeromotive 1:1, put it on a different vac line to the vented iap and don't use a check valve (FMU should be on a different vac line too for those with stg 1 kits)
You have a secondary injector kit or stg 2 ??

 

[dubious]

secondary injectors.
Thanks!

 

[GPW]

Run everything that needs to see boost through a multi-port mini vacum manifold and keep the lines that need a vacum signal seperate i/e AIP and Blow of Valve. This way everything needing a boost signal, Wastegate, FMU (use one-way check valve), Boost Gauge, Boost Controller, 3 Bar MAP sensor all get the same strength signal makes tuning a breeze. Vent the AIP sensor check valve to atmosphere works for me..

 

[dubious]

Thanks Greg, that made it much easier to picture!


/Lyle

 

[mcbusaturbo]

I got a smoother vacuum/boost fueling transition when putting a restrictor (from a boost gauge) in line going to the AIP sensor. don't know if any one else has done that but it cleared up a a little cruising speed richening hichup. Now when cruising in 6th gear and I start up a big hill wear I have to increase the throttle enough to keep speed there is no transitional change problem from vacuum to boost just smooth.