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Boost Creep

l_uk3y

By l_uk3y,
in Engines & Forced Induction

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l_uk3y Proficient

l_uk3y

Posted
Posted

Hey Guys.

Hope someone can help diagnose a problem for me.

R33 with Rb25 with Full exhuast (with compliance cat), Pod, Cooler, Splitfires, untuned at this stage. And boost controller.

I was running a Catback exhaust and a turbotech. Set at about 11psi. Boost levels were as

Stable as ANYTHING. good as gold.

Sent the car in to mechanics get the Split Dump with custom front pipe installed. When i got the car back the first night i blew an intercooler hose first time i gave it any (previously never a prob). Anyways next day i found that i was boosting WAY over the mark. Screwed the controller which was a TURBOTECH back as far as possible. and was getting about 9psi until 5000rpm. then it is creeping upwards with revs marginally over what im willing to let it go to.

From here i proceeded to swap out the turbotech and installed an electronic Blitz spec S controller.

Set at its absolute lowest setting im still getting the same response of creeping once the revs hit roughly 5. and it is telling me Peak boost im getting is 0.80 bar. (I want to aim at about 0.7 straight off the bat as it used to before the trip to the mechanics).

Ive been through making sure all my vaccum lines are connected properly and theres no splits. And i cant find anything wrong. Could the dump pipe be causing this maybe? Maybe im missing something? For 2 diff boost controllers to be doing exactly the same thing something must be wrong elsewhere. Im running out of ideas.

If anyone has any thoughts how i can level the boost out so i can turn the boost up a bit to hit my target and not overshoot, then please share.

Thanks for any help

Luke

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black_gtst Proficient

black_gtst

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because your factory dump and front pipe are really restrictive you will always get around a pound or 2 boost creep by installing a less restrictive exhaust. I got a turbotech on mine and set at about 9 lower in revs will creep out to 13psi on a cold night. sucks

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Al Grand Master

Al

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You dump pipe could certainly be the cause.

A poorly designed split dump pipe may be interfering with the internal gate, not allowing it to open fully, thus making the boost creep.

To check unhinge the boost actuator off the gate arm. and open/close the gate through it's full 90deg motion, make sure it doesn't interfere with anything and is very loose and smooth to move.

Another problem is: If the split pipe is too small or doesn't merge cleanly with the exhaust pipe, you'll also get boost creep.

I heard too many problems with split pipes (but i heard just as many without faults) and can not justify the gain for the trouble, i have always stuck with a "bell-mouth" dump and have never has an issue.

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Al Grand Master

Al

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Posted
because your factory dump and front pipe are really restrictive you will always get around a pound or 2 boost creep by installing a less restrictive exhaust. I got a turbotech on mine and set at about 9 lower in revs will creep out to 13psi on a cold night. sucks

A gain of a pound or two is acceptable 7psi (std) + 2psi = 9psi

His boost is creeping well past his desired 11psi so that's at least a 5psi increase, something else is causing it. From his accounts it keeps creeping with rpm and even has blown his ic hosing off his ic pipes, that doesn't happen at 12psi :blink:

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l_uk3y Proficient

l_uk3y

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When i fixed the cooler hose i found that it was boosting too the moon (guage said almost 20 before freaked and took the foot off) thats when i wound the boost back as far as i could without the nut falling off. Which was when i was getting the results of roughly 0.5 bar from about 3000rpm to 5000rpm. then from 5000rpm moving upwards with revs to 0.8

What i find interesting about this is i have no idea why the controller (turbotech at the time) would have been turned up. I have faith in my mechanic that they arnt fiddling with that.

I might try turning up the boost tonight on the controller and seeing if it hits my goal earlier in the revs then creeps to the exact same level or whether it hits a higher point.

As a quick question. On a Stock RB25 turbo. 0.80 bar boost as absolute maximum in short bursts shouldnt cause any problems? I know its getting pretty close to the limit.

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  • 2 months later...
l_uk3y Proficient

l_uk3y

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Hmmm. update to this thread. Standard Boost Control is back, was creeping upto about 0.80 bar after install. All was well.

Just installed the new Cat convertor. Pick up is noticably improved. Except now even the stock boost solonoid is managing to slip out to around 0.90 bar (Definately too much) and that is without totally winding the revs out.

To check unhinge the boost actuator off the gate arm. and open/close the gate through it's full 90deg motion, make sure it doesn't interfere with anything and is very loose and smooth to move.

Can you elaborate on that. i.e Is that the bracket looking part that is attached to the turbo with the rod connected to it?

My other thought is maybe reinstall the stock dump pipe. Hopefully the stocky will fit with the new front pipe. Should do as they welded the flanges on. as long as the length is the same.

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