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Rb25det Overboosting

13thracer
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13thracer Rising Star

13thracer

Posted
Posted

hello people i have an overboosting problem in my 25 powered silvia after about 5000 in 3rd 4th and 5th the boost just keeps climbing up slowly to the point were the factory ecu hits fuel/boost cut at 14psi.

i have rb25det series one engine with series 2 turbo on it, front mount intercooler, split dump pipe the type that loks like a screamer but is plumbed back in full three inch exhaust all the way from the dump pipe cat has been bashed out, k&n pod, standard exhaust manifold, am running an rb20 wastegate (10psi) which i got a off a mate a work was working fine on his rb20 so i know thats not the problem, and finally a set of hks cams not sure how big they were allready in the engine when i bought the car, they are pretty lumpy and only offer about -10 vacumn at idle. And the factory r33 boost solenoid is no longer being used.

Initially i thought it was my stock dump pipe not getting the gas out so bought the new one tried it last night made it alot better controlled it more and pulled alot harder but still started to climb after about 5000 rpm.

have moved the wastegate line off the plenum and plumbed it into the intercooler pipe just after the turbo outlet and used new silcone hose and plenty of zip ties so its not leaking and as i said the acutator is also fine.

would something like an avcr control this (i cant see how but i might be missng something) or am i going to have to go aftermarket manifold and external wastegate

any ideas would be greatly apprecitated i would like to see how this car goes all the way to redline

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https://www.sau.com.au/forums/topic/124894-rb25det-overboosting/
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DennisRB30 Community Regular

DennisRB30

Posted
Posted
weird

just get a ebc then it will never go above setting

um. No.

Any form of boost controlers can only be used in increase boost above stock. The lowest boost you can get is having the boost signal from the turbo acting straight on the actuator.

Are you sure the actuator is opening all the way up? Maybe it opened far enough on the RB20 but it isnt opeing far enougj for the RB25? You might need to bore out the wastegate.

Liz Grand Master

Liz

Posted
Posted
Are you sure the actuator is opening all the way up? Maybe it opened far enough on the RB20 but it isnt opeing far enougj for the RB25? You might need to bore out the wastegate.

I agree with you (not that I know alot abuot the topic) but given the avenues that 13thracer has been down this might be the next thing to try... perhaps find a stock rb25 wastegate and bung it on and give it a whirl.

13thracer Rising Star

13thracer

Posted
  • Author
Posted

well that didnt work just gave me alittle more leway before it starts to climb can get to about 6500 now looks like its time for an external wastegate and aftermarket manifold or get the wastegate bored out.

ellie Proficient

ellie

Posted
Posted

Hey mate, I forgot to say at work, have you tried wiring the wastegate fully open and giving it a run? because if it still over boosts with the wastegate fully open with a direct pressure feed to the waste gate, you'd have to draw the conclusion that the wastegate port is insufficient!

just a thought :D that hurt!

ellie Proficient

ellie

Posted
Posted

Might be worth a try reading your last post as the greater opening of the wastegate gave you an extra 1000rpm!

You might have a sticky wastegate. Unknown history!

Time to buy supplies for origin! C U next week sucker! :laughing-smiley-014:

Links Veteran

Links

Posted
Posted (edited)

Almost like the wastegate isn't opening enough.. try what ellie says.. could be an issue with the line from the compressor to the wastegate (could it be too restrictive).. Try holding it open and seeing how it goes..

Wastegate is opening.. but not fully.. so it's unable to vent all the excess gas @ a high air flow (6000rpm)..

Check that it is opening fully and easily.. not sure how to test though..

Edited by Links
mad082 Grand Master

mad082

Posted
Posted

i find the -10 vacuum a bit odd. should it be that high, as my stock motor runs about -22.

have you completely removed the stock r33 solenoid, or just unpluged the wire?

also you may have a problem with the wastegate hitting the dump pipe, which is stopping it from opening the whole way.

13thracer Rising Star

13thracer

Posted
  • Author
Posted

it has -10 vacuum due to the cams in it (greater overlap) the solenoid is totaly remove and did what ellie suggested and tied open the wastegate so it seems the stock wastegate can not get rid off the gas my engine is creating. but i may double check that the wastegate isnt hitting the dump pipe doesnt feel like it when i open it with my fingers it doesnt get stuck and i can actually open it further than if it was connected to the acutator rod

R31 POWER Mentor

R31 POWER

Posted
Posted

If it's one of those shitter "XS POWER" split shitter dumps id say thats the problem. I got one that was modded to screamer pipe spec and if i had my boost set at 16psi it would go to 20psi later in the rev range.

I chopped the small screamer pipe off and added a 2inch pipe, it creeps no more :D

DennisRB30 Community Regular

DennisRB30

Posted
Posted
If it's one of those shitter "XS POWER" split shitter dumps id say thats the problem. I got one that was modded to screamer pipe spec and if i had my boost set at 16psi it would go to 20psi later in the rev range.

I chopped the small screamer pipe off and added a 2inch pipe, it creeps no more :D

LOL. Yeah rice over function. The "high performance" twin dump might be creating backpressure in the wastegate section.

  • 2 weeks later...
13thracer Rising Star

13thracer

Posted
  • Author
Posted

thought i might just post to help others in the future. i have my overboosting under control i removed the turbo on the weekend and attacked the wastegate with the die grinder gently of course. manged to open it up roughly 15% more in size and made it all smoth to try and encourage the gas to go out the wastegate, wacked it all back together and and no more overboost has the usual initial spike to about 12 or 13psi but then settles back down to 10psi and holds nicely.... yay i can finally rev it out to redline looks like it out to willowbank for me this weekend.

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