boost falloff.....

[gixxer750]

k....this is probably a normal thing. Its happened ever since I upped the boost.

I'm running a 57 trim ct26....ported manifold... all that good stuff.


I can hold 16-18 psi from about 3200 rpm until about 4800 rpm, then the boost starts to fall off. At 6000 rpm, the boost has fallen to about 9 psi...

Is this the weakness of the wastegate actuator spring? If so, will shimming it slightly help?

Oh yes, BTW, I'm running a greddy profec B Spec II boost controller.

 

[GrimJack]

Yes and no. Shimming the spring will help for sure, but it is unlikely to make the problem vanish entirely.

 

[IHI-RHC7]

Yeah, I have a DDP, so I KNOW when the gate is open. and it stays closed past 4500 and boost just falls. The CT just doesn't enjoy high rpm.

 

[bigaaron]

Its not a normal thing and the ct26 has no problem holding 20+psi all the way to redline on my car. That ProfecB II is a pain in the ass to adjust correctly. That is your problem, not the turbo. There is a specific way to adjust it and it will not hold boost until you get it exactly right. I honestly think the older ProfecB I have is a better and more user friendly unit.

 

[malloynx]

shim the wastegate wth 3 washers. that should help. also i use to have the profec b spec2 and i hated it. you need to paly with the gain forthe boost to hold. i sold mine and went with a mbc

 

[IHI-RHC7]

Bigaaron, what Ct26 do you have? and how many miles?

 

[bigaaron]

50 trim with 10 degree clip, with about 20k miles on the turbo. Makes 370whp at 21 psi and 395 tq. I have a 60 trim i'm going to put on this weekend and once I fix an exhaust issue, it should be over 400whp at a lower boost setting.

 

[jaydm16]

Im going to leech onto this topic. I have the same problem but not as drastic of a fall off. I used to have my wastegate shimmed until i got my boost controller, then i removed the shims and installed the controller. Is it possible that i have stretched the spring or something?

 

[IJ.]

Just wondering if it's not a weak BoV that's causing this?

 

[GrimJack]

I don't think so. I used to get this on my stock CT setup - as soon as I switched to my upgraded CT, it virtually went away. Same BOV.

 

[IJ.]

I was thinking more in Gixxer's case Dave!

He's got a modded CT.

 

[bigaaron]

Or boost leak?

 

[gixxer750]

well, I've got a greddy type S blow off valve, and its wound pretty tight.... It won't even blow off under 6 psi(like if I barely get into boost around town.) I'm also running an upgraded turbo. It could possibly be a boost leak....I still hit fuel cut around 17 psi when its cool outside, and around 15.5 when its hot outside. That is with the lex afm and 550's. The screw is backed completely out to the lip on the lex afm(supra sport lex afm replica with some kind of different adjustment screw with about 2" of travel)

I've always thought I had a boost leak, but I have yet to track it down... I've got hardpipes by the way, and a new 3000 pipe to TB coupler....

 

[thesupraman]

I have a 60-1 upgraded ct without a clipped turbine wheel. It holds 19.5 psi till redline with no problem. The only difference is that my turbo came with a turbonetics made exhaust housing which has a larger wastegate port and swing valve. If anything that would cause the w/g to blow open easier, but it holds fine...

 

[suprahero]

When I Had My Car Dynoed Shawn (autolabz Tech) Told Me That My Car Was Boosting At 11 Pounds Shortly Then Leveling Off To 6 Pounds. I Cant Remember Where I Read It, But Somewhere I Read That The Supra Turbo Would Not Hold It's Boost But For A Few Seconds Then It Would Level Off. I Didnt Try To Fix Mine Because I Thought It Was Normal. Now I'm Reading That Everyones Doesnt Do It And I Want To Fix It Now. What Would Be The Best Way To Fix This Problem?