Another boost drop question.

[MrBentley]

Okay i know there have been thread on this before but none of them suited my situation when i did a search.

I have a pretty much stock 98 GSX, no boost controller on it but i have a 1g BOV uncrushed in there. Now when i go WOT, my boost gauge jumps up to 15psi and then like a second later it drops to 10-12.

I haven't done any type of tuning on the engine or anything so i don't understand.

 

[romeen]

1) If you are still using the stock boost control solenoid it could be the ECU dropping boost that you normally would not be hitting because of the leaking stock 2G BOV.

2) It could be a boost leak that starts to leak above 12 psi

3) It could be your T25 just running out of steam and unable to maintain 15 psi.

4) Could be some elements of all of the above.

Since you are still on the stock fuel system and stuck with 91 octane Cali piss water you really don't want to run 15 psi anyways. I would do a boost leak test and try the BCS restrictor removal mod. Hopefully that will help you maintain 13-14 psi a little longer.

 

[T9S1i]

Thats a boost spike. Good for torque. If i read correctly, you have no mbc so you are running off of wastegate pressure alone? Stock wastegate pressure (on a 14b or 16g) is 9psi, the internal cant keep up usually so its about 10psi. A t-25 should be right there in the ballpark somewhere, so 10-11psi is right. THe 15psi is just a spike, try to make the line from your pressure source to your wastegate as short as possible to avoid boost spikes, the longer the line the longer it takes for the wastegate to react to the fast spooling stock turbo. Other than that it shouldnt hurt anything if its only when you instantly spool, then just drops right off. If you are using the line to your BOV for the pressure source, delete it, take the pressure source off of the turbo outlet j pipe and make a short piece of tubing that goes directly to the wastegate, should solve your problem.

FWIW, I kind of like a boost spike for drag racing as it gives you that initial umph of torque for the gear, then the boost will hold steady to redline.

Hope this helps, if i misunderstand the routing of your wastegate, clear it up for me and i'll try to answer any other questions as best as i can.

 

[MrBentley]

1) If you are still using the stock boost control solenoid it could be the ECU dropping boost that you normally would not be hitting because of the leaking stock 2G BOV.

Its a 1g Bov like i sated.

... so you are running off of wastegate pressure alone?

I guess so. I really don't know. I run whatever the stock T-25 can do and I was just observing the drop off and was curious on what was going on.

 

[T9S1i]

Lemme get this straight. NO MBC right? NO stock boost control solenoid? So you have a vaccum line ran from your pressure source (j-pipe, or bov line) to the wastegate?

If so, then the boost pressure is correct, and the 15psi initial spool is just a boost spike.