boost spiking... is it ok?

[Twinturbo2800]

Just got my hallman pro MBC on and im boostin again. My old turbo XS 130$ P.O.S took a crap on me.
Anyway i set the boost to 15psi. ( highest i can go stock turbo is 16 correct?)

when i FIRST stomp the pedal it spikes all the way to about 18lbs somtimes 19-20, And drops fast to 14-15, Then when my tranny shifts gears it drops to like 10 untill higher rpm when it gets back to 14-15. (automatic tranny) Is that normal??
Tonight it got much cooler out and it was spiking to 20 every time, droping to 15.

Is thier a way to get rid of the spike that high? I dont wanna mess up my engine/turbo


-josh

 

[Mr Peepers]

T25's are known for boost spike and it is about normal, especially with a full 3" exhaust.

There is one thing you can do but only if you have the correct tools and know what you are doing. There is a hole on the wastegate side fitting, the one perpendicular to the MBC body. It should be on one of the faces of the "nut" part of the fitting. Use a drill bit to check exactly what size it is, it should be around 1/16". This is the bleeder hole. Take this fitting out and drill the bleeder hole one size larger. For example, the next size up from 1/16" would be 5/64". Clean any chips out and put the fitting back in and hook everything else back to how it was. Turn the boost down a little bit on the MBC, as drilling thing bleeder hole will give you slightly more boost if nothing else has changed. Set the boost to the desired level again, the spike should at least clam down.

The theory behind this is the MBC will need a lower spring setting to balance the boost level back out. The MBC will open slightly sooner and more progressively, hopefully keeping the turbo from rising in boost quicker than the wastegate can respond, which is the cause of boost spike. There may be *slightly* more lag during spool up, but if you are spooling up quick enough to spike in the first place I don't believe it is anything to worry about. There will be an extra small amount of air bleeding to the atmosphere(when under full boost), but this can be taken care of by finding a way to route the bleeder hole back into the intake behind the MAS.

 

[Twinturbo2800]

But is spiking a 19-20 going to harm my motor/turbo at all?

 

[JayRolla]

Not if you A/F ratio stays good and you not getting knock. Its all about if you can tune it out.

 

[Twinturbo2800]

not sure what the A/F ratio is, no gauge for that.

 

[JayRolla]

The problem with a 2g is you cant see knock on a logger. So you have to look off the timing. Problem is the timing will drop when boost hits and you wont beable to tell if you knocking. You can add fuel and if you get higher timing than you know you are getting rid of some knock. I would get a wbo2 to be safe.

I just read your mod list. You should not be installing a boost controller without any fuel mods. Really no point. You are most likely damaging the motor. Should not boost anything over 15psi without some type of fuel mods.

 

[Twinturbo2800]

Its set at 15psi,. boost spiking at 18. its not set at 18

 

[95blackGsTurbo]

The difference in airflow on a T25 at 15 and 18 psi is too small to cause any damage.

 

[JayRolla]

The difference in airflow on a T25 at 15 and 18 psi is too small to cause any damage.

This may be true but better to be safe than sorry. Running the 3psi more is pushing the t25 out of its effeciency range and blowing hot air, which could be causing detonation.

 

[Twinturbo2800]

^^
yea, and thats why im kinda nervous becuase my last turbo blew, my turboxs MBC went bad tho for some reason that might be why, but i was running around the same... 14.5-15 Psi and spiking around 18-19.

what do you suggest i do? i dont wanna buy anything else for it, im saving up $$ for a Evo or corvette or somthing