boost spiking to 20 psi

[Blackcrow64]

Originally Posted by ez1286

Safely you can run about 42psi if you have balls you can set it to about 55psi.

Maybe on a built motor with the head o-ringed.


Ok,seriously though... Your stock t-25 can only produce like 16 or 17psi at the most... If you crank up your boost though, you are gonna need to log your engine sensors so you don't get knock... If you get knock then you need to turn your fuel up a little bit.

[sganc4life_4]

Well, your getting boost creep from what Ive read at posracing.net ( thanks kevin ) reason is because of the bigger exhaust is flowing too much and overpowering your wastegate. Basically you need to port the o2 housing and wastegate, then you can turn boost up or down.

[Blackcrow64]

Originally Posted by sganc4life_4

Well, your getting boost creep from what Ive read at posracing.net ( thanks kevin ) reason is because of the bigger exhaust is flowing too much and overpowering your wastegate. Basically you need to port the o2 housing and wastegate, then you can turn boost up or down.

I thought that too restrictive of exhausts is what causes boost creep because the exhaust gases can't escape the system quick enough causing pressure. And the only other place it can escape is through the turbine causing it to build more boost and thus receiving the term "boost creep"... Or have I misunderstood it all this time?

[sganc4life_4]

Well from how kevin explained it, when he put on a 2.5" exhaust on a 14b, he spiked to about 21psi...same thing happened to me with a 3".

[Blackcrow64]

Originally Posted by sganc4life_4

Well from how kevin explained it, when he put on a 2.5" exhaust on a 14b, he spiked to about 21psi...same thing happened to me with a 3".

How much boost do you have it set to?


I sure hope Kevin visits this thread, cause I sure would like to know which theory is right...

[sganc4life_4]

I had it set to 15psi before I put on the exhaust, then it jumped to about 20 after

[ez1286]

Boost creep is when te wastegate doesn't open enough (or is not big enough) therefore there is less resistence through the turbo. A bigger exhaust makes it worse cause there is even less resistence after the turbo yet it remains the same for the wastegate. I think the best fix would be to port the flapper hole, or get en external waste gate, boost spike is diferent but i'm not sure how exactly, i think it's more of a sow response from the wg cause the boost to momentarilly "spike"

[Shpyder]

Spiking is pretty normal with an MBC, and the pattern you displayed seems pretty standard. I blew my T-25 running 17psi for 2 months (ok ok...the car was practically begging for an upgrade so I kinda...helped the stock turbo...u know, lol ). Keep the boost at 15 if you dont plan on changing the turbo any time soon.

[Nayr747]

Mine is now spiking to ~18 and then decreasing to/below 15. It's wierd. Need a MBC.

[kjewer1]

EZ explained it correctly. THe thing to consider is which way will the exhaust gasses want to go (path of least resistance). With a freer flowing exhaust but the same crappy internal gate, the exhaust gasses are more likely to ignore the wastegate and go through the turbine, which produces more boost, which produces more exhaust flow, which wants to go through the turbine even more, producing more boost, and so goes the cycle.

Spike a function of the WG's but probably more so the boost controllers abililty to react quickly to rising boost. Small turbos like the t25 spool so quickly spike is very common. EBCs tend to really shine in this department

The maximum boost I Would run on a t25 is 16 psi. I found that going above that doesn't add any performance on pump gas. If it spikes to 17-18 psi but quickly falls to set boost of 16 psi, I wouldn't worry about it. MBCs are going to give you some amount of spike. To fix the creep read about the porting stuff on my site. The vast majority of it can come from porting the WG exit area of the turbine housing and not even touching the flapper hole. But, creep is extremely unlikely on a t25 for two reasons. One, the turbine is so restrictive the wg looks like an atractive option for the exhaust gasses. Two the turbo doesn't flow enough to creep over 15 psi at high rpm.

[Blackcrow64]

So a nice external wg would fix boost creep even if your dumping it back into the exhaust?... Or is it better to let the wg dump atmosphere?

[ez1286]

Originally Posted by Blackcrow64

So a nice external wg would fix boost creep even if your dumping it back into the exhaust?... Or is it better to let the wg dump atmosphere?

That's personal opinion, i don't think there is much of a performance gain with dumping, but it does sound pretty damn good.