Boost creep over 14psi already?... is this normal for my setup?

[destrux]

I can't get my boost set below the 14psi boost cut on my 1JZ. I'm not sure if this is normal for my setup or not, so I'm looking for advice from somone who's been here before.

-stock twins with stock exhaust y-pipe and stock compressor pipes
-single MBC (currently set to the max low setting, ball inside is loose if you shake it) routed to both stock wastegates
- 3" turbo-back exhaust with high flow cat
-medium sized FMIC with 2.5" piping
-stock soarer intake tube with K&N universal filter

I checked the wastegates, they both test fine (hand pressure pump). I also checked for kinked hoses and found none.

So is it normal for the boost to immediately be over 14psi with these mods, or do I have a problem with something? I've had boost creep on cars before, and it's usually gradual and at higher RPM. This car is flying right past the 8psi wastegate pressure as soon as the turbo's spool. I don't think I improved the breathing that much... but maybe I'm wrong.

 

[Poodles]

Exhaust and IC piping will make a huge difference.

 

[te72]

I have a similar setup to you, with a 3" y-pipe, but stock IC and piping. Same problem, put an MBC on it the same way you did, and immediately boost went from ~12psi to 15-16, even on the lowest setting. I had to remove the boost controller when I got down to the lower Vegas elevation, as I was hitting fuel cut in any gear because of the thing... I've been told that the ball-style MBC's aren't the best setup for a higher flow/pressure situation like ours.

Too bad that our turbos have shorter lives at that pressure though, they feel amazing.

 

[destrux]

I never saw how big the OEM intercooler/piping and exhaust was on a Soarer, so I wasn't sure how much of an improvement mine was compared to stock.

I wonder if the little bleed hole on the outlet side of the MBC is bleeding off just enough to cause the ~3psi increase. I'll pull the MBC off and see where it's at then.

Thanks.

 

[Dylan JZ]

Try hitting 18 no matter what you do, well shy of controlling the pedal..

I always thought it must be the 3" DP/3" EX combo, but I have an upgraded FMIC and piping too. My Profec-B has always been zeroed out because of this issue.

 

[GrimJack]

My method for dealing with boost creep has always been to add more fuel and set the boost controller to more than it creeps to.

 

[te72]

Stock Mk3 JZ intercooler is pretty hefty for being stock, piping's not bad either, but it is funny shaped being mostly thick rubber. Hmm, wonder if I had replaced the intercooler and piping if I could hit a consistent 15/16..?

 

[destrux]

I got rid of the MBC and ran the wastegate hoses like stock and the car only hits boost cut when it's below about 35 degrees now. I'm still at 10.25:1 AFR, so a good tune will get rid of it completely now.

I'm worried about making more than 360hp.. that's all my clutch it rated to. Can't afford to upgrade it yet. I still have a steering wander to throw money at. :: hommer ::

 

[te72]

This thread inspired me to mess with my boost controller this weekend. Took out the gate system on my Turbosmart MBC, and voila! Problem solved, pulls a solid 15-16psi at 12:1 afr, roasts the tires at anything above 2/3 throttle in 1st or 2nd now.

 

[Marotta1]

This thread inspired me to mess with my boost controller this weekend. Took out the gate system on my Turbosmart MBC, and voila! Problem solved, pulls a solid 15-16psi at 12:1 afr, roasts the tires at anything above 2/3 throttle in 1st or 2nd now.

What do you mean you "Took out the gate system" on your MBC? If I can do something similar I could probably solve my problem. I have stock twins, upgraded Y-pipe, 3 inch downpipe, 3 inch exhaust, and upgraded intercooler. I hit around 15-17 psi and therefore fuel cut, and would like to stop the fuel cut issue as well.

 

[mk3tattoos]

Yep just tune it with an safc2 to 11.5a/f and you will not hit boost cut.

 

[te72]

What do you mean you "Took out the gate system" on your MBC? If I can do something similar I could probably solve my problem. I have stock twins, upgraded Y-pipe, 3 inch downpipe, 3 inch exhaust, and upgraded intercooler. I hit around 15-17 psi and therefore fuel cut, and would like to stop the fuel cut issue as well.

On the Turbosmart MBC that I have, there is a ball and spring inside the piece that goes between the pressure source for the turbo and the line to the wastegate tee. Took out the ball and spring, problem solved. May or may not work for your particular application. Truth be told I was just screwing around with it after reading the instructions on the TS again, and it worked in my case.

 

[Marotta1]

OK, I saw that later about the ball and spring. I don't have that. Thanks for the info.

 

[destrux]

Update on this... my boost went down to 10psi when the temps went up to about 60 degrees. So I got the MBC back out that I took off the car and put it on, same problem again. So I took a hammer and a small punch and closed the bleed hole from 1/16" down to a little larger than a pinhole. Now the MBC works and I have it set to 14psi.

I can't tune the car for a higher boost cut yet because my fuel injectors are dirty and I'm afraid I'd run too lean in one cylinder because of the imbalance, but I'm hoping to have clean 440's in there soon, which will give me alot more headroom for boost. So then I can properly break my W58, lol.

 

[honeydew]

What Wastegates do you guys run? Stock?

 

[te72]

Stock here. Stock turbos though...

 

[destrux]

Stock w/ stock twins.

 

[GrimJack]

Tial with a single 67mm turbo.