boost drop at upper rpm's

[skeen550]

I have a problem keeping boost up at around 5k and up to redline.

Down low and in the midrange of revs it actually spikes a little bit but then drops down, again at the upper revs.

I have a stock ct26, full hard pipes 2" into the intercooler and 2.5" out to a 2jz FF upper intake, 24x12x3 bar/plate intercooler with 3" in/out. Full 3" elbow mandrel bent exhaust no cat w/magnaflow muffler, lexus AFM, AFPR set at 40 PSI.

With no shims on the wastegate it hits 9psi and holds it fine, does a 1-2 PSI low/midrange spike in 3rd and 4th then drops back down to 9PSI in the upper revs in 3rd and 4th.

I put 2 shims on the wastegate and then it will hold 1 or 2 psi more but stilll same as described above ... I then have tried 2 different MBC controllers bleed type and ball/spring and a combo of both and still same story, it will spike as high as 15PSI but always drop back to the 10psi....

The 7mgte is an 88 model I dropped in my 85 supra, r154, 3.73 true trac diff.

Is the ct26 just not able to keep the boost up at the higher RPMS ?

 

[suprahero]

i dont know any thing about what the ct26 is suppose to do, but when i had mine dynoed it showed the boost falling off dramatically like you said yours is doing. i just took for granted that thats what it does. i had my boost set at 11 pounds and it would only hold there at about a second then it would hold steady at about nine pounds. hope you get yours fixed if it isnt suppose to do that. just thought i would offer my two cents worth.

 

[7M-GTE]

actually both of the ct-26's I've had in my car have done this also... but in my 87 it stayed steady... infact sometimes it would just keep climbing...

 

[MDCmotorsports]

Its a wastegate issue.

Either its cracked or failing.

 

[shaeff]

ct's run out of breath at the upper rpm range. it's a common problem. with a few shims on the wastegate, and my MBC set to 15psi, i hold 15psi right to redline in 3-5th gears.

-shaeff

 

[skeen550]

When I put the engine in the wastegate looked fine, no cracks that I could see but that was 5k miles ago and I just cranked the boost up a few weeks ago so might be ... I will be pulling the ct26 off first of next year and sending it to PT for a rebuild/60 trim upgrade so I will know then if the gates damaged.

Otherwise I will just live with it for now, its by no means slow as it is, it runs like a scalded ape.. but I will be getting me a mkiv denso fuel pump with the turbo as I imagine my stock 5m pump is being pushed hard. I do have an in car fuel gauge and it doesnt drop under boost so its ok for now.