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Hey guys,

New here so I'll give you a quick run down of the car then I'll outline the issue. Car is an S15 Spec R with quite a few mods done. To name a few, it has a built bottom end (pistons, rods etc), BC 264 cams with upgraded springs/ retainers, a Precision 5858 high mount turbo on a china manifold, Turbosmart 38mm ultra gate and a Eboost street controlling the boost. Other than these it has all the usual supporting mods, 740cc injectors, nistune, Bosch 040, front mount and HPX AFM.

Now to the problem: I recently got the injectors installed and the car tuned. It had a run in tune on wastegate pressure due to the recent engine rebuild (done prior to me purchasing the car). All was well until I collected the car and the tuner mentioned that he had some trouble making the boost hold steady. I've attached the dyno graph to this post, which shows the low (red line) and high (blue line) boost tunes. The tune on wastegate pressure was fine, albeit some boost creep in higher rpms (likely due to crappy china manifold), but the high boost tune can't seem to hold a consistent boost pressure. The boost comes on fine but once its up there it will fluctuate 1-2 psi.

The tuner suggested it may be due to the wastegate. I contacted Turbosmart enquiring if the fluctuation could be caused by a torn wastegate diaphragm, to which they responded that if it was that I would be experiencing boost spiking. They suggested it looked to be because of the sensitivity setting on the boost controller, to which I found to be 0. So evidently the tuner saw the fluctuation, and turned the sensitivity down (the obvious solution) which didn't correct the issue.

If anyone has any thoughts on the problem please contribute, I'm completely stumped as to what is causing it. Also I'll be happy to answer any questions regarding the matter.

Cheers, Ollie.

post-14395-0-03742700-1486112565_thumb.jpg

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low boost was done on gate pressure only? no interference from EBC? whats springs did you have in it, the 12psi? after 6k rpm the boost starts increasing

- this to me would suggest that your gate not large enough to let out enough gas to slow the turbo down?

- whats the design of the manifold? if the gate pipes not mounted correctly, gate could be missing the exhaust gas all together.

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Cheers for the reply,

Current low boost tune is with the duty cycle on the Eboost set to 0, so I assume thats gate pressure? But prior to that the boost controller wasn't connected, just a vacuum line from turbo to gate and the boost curve was similar from memory.

Yeah, I haven't checked but I think the spring inside is 12 psi. I also thought the gate may be too small (tuner also suggested that), but then I see other cars running the same gate with larger turbos running fine so it has me confused.

Manifold was already on car when I bought it, but from the looks of it, it may be the JJR SR20 high mount manifold (attached picture of the one it looks like), honestly looks like a pretty poor design.

Thanks again, Ollie.

post-14395-0-96560900-1486114003_thumb.jpg

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Cheers for the reply,

 

Current low boost tune is with the duty cycle on the Eboost set to 0, so I assume thats gate pressure? But prior to that the boost controller wasn't connected, just a vacuum line from turbo to gate and the boost curve was similar from memory.

 

Yeah, I haven't checked but I think the spring inside is 12 psi. I also thought the gate may be too small (tuner also suggested that), but then I see other cars running the same gate with larger turbos running fine so it has me confused.

 

Manifold was already on car when I bought it, but from the looks of it, it may be the JJR SR20 high mount manifold (attached picture of the one it looks like), honestly looks like a pretty poor design.

 

Thanks again, Ollie.

 

 

 

That manifold has the gate right in the merge point, so in theory it would be sufficient.

when the gate pipe reverse flow of exhaust is when it would be a problem.

 

sounds like your have a pretty decent build and some quality part's tho, why did you settle for china exhaust mani?

there is some fairly decent NZ made ones going around pretty cheap.

 

personally id take the springs out of the gate and just inspect the diaphragm, then put the gate back on with a spring around 7psi (or whatever you have).

take it for a run and see if it still overboosts in the higher rev range.

 

if it does your exh manis either a super bad design and somehow the flow get interference on the gate line (unlikley if its on the merger) or the gates bad/to small.

thats how id see it anyway.

 

Turbo-smart, or somewhere decent like GCG should be able to tell you the waste-gate vs turbo size you need...maybe hit them up.

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That makes sense, well I bought the car recently with the mods done to it, my best guess is the previous owner blew the budget on the engine build and had to settle for the crappy manifold haha. Haven't heard much from the NZ made ones, what ones are decent?

 

I'm going to give GCG a call on monday, in the meantime I might pull the gate apart and change up the spring to see whats going on. Supposedly these 38mm gates are okay on this size turbo (will call GCG to get their thoughts) so I'm inclined to think the gates gone bad.

 

I'll let you know what I find, cheers again for the help.

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  • 4 weeks later...

Update:
Well I found the problem, it became pretty obvious when I kept getting a sound which sounded like an exhaust leak which got louder. It eventually led to the gate flange snapping off the manifold and a vacuum line holding on the gate and screamer as I drove along haha. On taking off the manifold I've seen someone has had a stab at repairing it with a mig and done a crap job to say the least. Well at least I know what was causing the boost issue, now the hunt for a 6boost mani begins! Cheers for your helps guys!

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