T-25 boost drop off, when and how much

[DSM-Talon-John]

Can you guys tell me on your t-25 turbo when and how much the boost drops off, mine will hit full boost and automatically drop down from 15 to 12 down to 9-10 by the time i shift.

 

[DGajre777]

My T25 goes from about 15psi to 10psi by redline. This is caused by the internal wastegate not staying closed due to change in engine's VE.

 

[DSM-Talon-John]

Im not sure if its not spiking to 15 though cause it goes instantly to 12 then drops to 9 by redline. What causes boost spike and how would i fix it.

 

[DGajre777]

Im not sure if its not spiking to 15 though cause it goes instantly to 12 then drops to 9 by redline. What causes boost spike and how would i fix it.

A search in the Tech Guide would have answered your question.

Boost Spike: Boost spike is when the boost level initially "spikes" up to higher than the preset boost setting, and then quickly settles back down to where it should be. As most people with turbos know, once the boost pressure in the intake starts to rise, the rate at which it rises quickly increases until the pressure is increasing at a phenomenal rate. This means that, if your boost is set at 12 psi, when it reaches that point it will be increasing so quickly that it will go higher than 12 psi and then drop back down once the boost control system can correct it, which is within a half second or so.

Some causes of spike are bad boost controllers (only ball-and spring type MBC's should be used, and only proven electronic boost controllers should be used), long boost source or wastegate activation hoses, and the lack of any boost controller at all. It's basicially an effect a t slow response time of the boost control system.

http://www.dsmtuners.com/forums/showthread.php?t=96678


What do you use for boost source on your boost controller? If you have it T'd off your blow off valve, it can cause a boost spike. The correct way to do it is to use the compressor nipple on the T25 as a boost source for the boost controller.

http://www.dsmtuners.com/forums/showthread.php?t=237982

 

[my98GST]

It doesn't matter the t25 is going to drop off anyways. the turbo is not designed to handle revs. It doesn't matter even with the WG... I had the FP 17lb WGA on mine and ti would spike 17, hold 17, and by 5 it had already dropped to 11-12

 

[DSM-Talon-John]

What about boost creep, i have a stcok exhaust, could it be that.

 

[DGajre777]

What about boost creep, i have a stcok exhaust, could it be that.

Link on post 4.

Boost Creep: While boost creep also refers to an unwanted rise in manifold pressure, its cause and effect are totally different from those of spike, as is the way it manifests itself.

As you know, boost pressure is controlled by the wastegate, which allows exhaust gasses to bypass the turbine wheel. In effect, it creates an alternate route for the hot exhaust coming out of the motor to take, which means that any gas passing through it will not spin the turbine wheel.

Now, if this wastegate cannot flow enough to bypass the required amount of exhaust, then that means that too much of the gasses are going to go through the turbine wheel, meaning that it will have too much energy imparted on it (it will be spinning too fast). As the excess exhaust gas amount gets greater and greater, the turbine wheel spins faster and faster, and the boost level rises.

Creep happens ANY time when the wastegate cannot bypass enough exhaust gas to keep the boost under control. This can happen when the wastegate is too small in diameter, or when the design of the wastegate doesn't allow it to open enough, or when the wastegate simply doesn't have a good enough flow path to divert a lot of exhaust. It can also happen when you increase the amount of exhaust coming out of a motor (running more boost/airflow, making more power).

Since this tends to get worse and worse as the engine speed rises (more cycles per second is more conducive to more exhaust gas, to a point), that means that one will see the boost climb to the preset level on the boost controller, and then it will gradually creep up past that line to a "minimum" given the circumstances.

That minimum can be 2 psi above the set boost level, or it can be over 30 psi, depending on how the wastegate is designed, how big it is, the car's setup, and more.

It is also important to not that you certainly can have spike AND creep at the same time, which would result in the boost level jumping up, settling to the preset level, and then slowly climbing back up again as you approach redline.

I have a 2.5" RRE downpipe (no cat) and a 3" Apexi N1 and I get no creep. Check your boost controller and see how it is installed (if you have one).

 

[CanadianTSi]

The simple fact of the matter is the Motor is flowing more Air then the T-25 can move, theres nothing you can do about it.

 

[olmytsi]

Get a 14b.

 

[nightspeed87]

get a 16g

 

[Glliw]

Get what you think will be good for your goals. Personally, both of my T25's held 12-13 psi from 2700-redline. stock wastegates.

 

[calreef18]

When I had my t25 it would go 15psi then down to 12-10 around 5k with a mbc.

 

[ILLiCliPSE]

get a t28 and look stock


t25's are junk. Worst turbo ever. Before I had my T28 installed, the T25 would spike to 16-17 then drop to 10 by redline...and never pulled at all. With the T28 @ 15psi, it pulls real nice all the way to redline.

 

[DSM-Talon-John]

so it doesnt matter that it hits 15 and instantly drops to 12 then lower, thats normal?

 

[calreef18]

That's pretty normal from what I've seen, depending on the boost controller, there is sometimes a little spike in psi, and with the t25 definitely a drop in psi towards redline.

 

[t25fury]

just some fyi, with my stock intercooler pipes and stock b.o.v, i had the exact same readings everyone else had, spike to 15 then drop to 10 or so psi,depending on the weather,now still on the same t25 but with greddy pipes and a better b.o.v it will spike to 18 and settle to 14/15 (have even seen 21 psi but on really cold days)

 

[welfle18]

I have an SBR MBC with the t25 and hits about 15 psi at 3000 RPM and at 5000 RPM its already down too 11-12 psi. Good initial pull but after the boost starts falling off its downhill from there....

 

[CanadianTSi]

The more efficient your setup (Higher Volumetric Efficiency) the more your boost will fall.

 

[DGajre777]

The more efficient your setup (Higher Volumetric Efficiency) the more your boost will fall.

What ^^^ said. If a car has 3" catback, aftermarket downpipe, blow off valve, bigger intercooler pipes, aftermarket intake, etc to increase VE of the engine, the boost drop off will be more. At the same time a car with stock exhaust and stock intake might only have drop off of 1 or 2 psi.

 

[DSM-Talon-John]

Thanks guys, theres alot of helpful info in here.