Boost Control

[CAT_SPEW]

I've recently installed a 6Boost manifold/tial 44mm gate/gt35/40 on my RB25 with all the bolt on mods. The car is now at the tuners and he is having troubles controlling boost. He has said that the boost is peaking at the top of the rev range whereas is should be at around 4500Rpm onwards..

He has told me that the cause of this is where the wastegate is joined to the manifold, that it is not getting equal flow or pressure or something like that..

Has anyone heard of something like this and what is needed to fix it???

[CAT_SPEW]

Any ideas?

[paulr33]

a test could be to unplug the gate signal and dyno it

it will be in unlimited boost mode so be careful and get ready to back off quickly. that will show you best and quickest possible spool up time on the turbo & exhaust combination

[CAT_SPEW]

I was told pretty much the same thing from the guy I bought the manifold off. But by unplugging the gate signal, do you mean just taking the wastegate completely off?

[paulr33]

no the gate needs a boost pressure signal

so it will have a pressure line running to the intercooler piping somewhere or turbo compressor outlet.

if you unplug this, the gate never knows how much boost pressure there is, so therefore it never opens. which gives you unlimited boost. but it also means the gate cant (well shouldnt) open for any reason what so ever.

so if you find after that its still laggy as a bitch then the gate is leaking, ie: its a tiny bit open / has gaps so the excess back pressure just flows around it, making it laggy and takes ages to get the exhaust side on full swing.

if you find it winds up at like 3500rpm and is ace its your boost controller thats sucking the wang

[paulr33]

be careful with this, its a good way to kill your engine

a few have done it in the past, in unlimited boost the boost pressure will only be regulated by how fast the compressor can spin in positivie pressure, so it should fly past 1 bar with no problems. usually detonation follows and then engine goes bang

[CAT_SPEW]

mm this is sounding like it can be a VERY bad thing. I'll have a talk to the tuner tommorow and tell him what you have told me and go from there. Will let you know how I go.

Cheers

[paulr33]

i mean it can only be a few things;

tune is bad or like afrs are spasticly wrong

some big restriction somewhere

gate is leaking or opening prematurely (or always open)

[Full-Race Geoff]

What you are referring to is called boost creep. This happens very commonly on applications which have a free flowing manifold/turbine with poor wastegate placement and/or too small of a wastegate.

If you can you post pictures of the manifold, wastegate and turbocharger I can tell you where the problem is coming from. Im a mechanical engineer, and worked on a masters thesis on this topic.

Edited February 21, 2007 by Full-Race Geoff

[Guilt-Toy]

What you are referring to is called boost creep. This happens very commonly on applications which have a free flowing manifold/turbine with poor wastegate placement and/or too small of a wastegate.

If you can you post pictures of the manifold, wastegate and turbocharger I can tell you where the problem is coming from. Im a mechanical engineer, and worked on a masters thesis on this topic.

w000t

[CAT_SPEW]

What you are referring to is called boost creep. This happens very commonly on applications which have a free flowing manifold/turbine with poor wastegate placement and/or too small of a wastegate.

If you can you post pictures of the manifold, wastegate and turbocharger I can tell you where the problem is coming from. Im a mechanical engineer, and worked on a masters thesis on this topic.

I haven't got any pictures of my setup but these are pretty much the same.

GT35/40 .82 rear,3" exhaust all the way through, Tial 44mm wastegate

What do you think?

[Full-Race Geoff]

interesting design! I definately prefer twin scroll, however that is not bad at all.

I have two recommendations, both of which involve fabrication/welding

1) using your current 44mm wastegate, make a radiused inlet into the manifold. We do this on applications which tend to creep. you can just cut out part of the manifold and put the ID of a tube over the hole, make sure you grind it to fit of course

2) put a tial 60mm gate on. these things are insane. On the PROFWD GM ecotec 1600whp methanol engines we went from dual 44mm TiALs which would creep to 18 psi to dual 60mm Tials and we could hold 7 psi perfectly

I haven't got any pictures of my setup but these are pretty much the same.

GT35/40 .82 rear,3" exhaust all the way through, Tial 44mm wastegate

What do you think?

[r33_racer]

call kyle. He will help sort it out. We had the same problem with ours not long ago and also ages ago, we fixed it by going to a larger wastegate a 48mm progate ages ago. Then not so long ago we ended up mounting the wastegate right off the turbine housing and now it controls boost perfectly. Both times we changed things which affected the backpressure and had to do those fixes so boost control was capable.

However old mate the mech eng here seems to know his stuff. Ive heard of his solution before as another way to resolve this problem. But it means you gotta take the mani off and stuff around.

Edited February 22, 2007 by r33_racer

[CAT_SPEW]

I left it with the tuner for a day and he has fixed the problem. He told me how but I didn't really undetstand but I'm happy anyway The car made 416HP@17Psi and is holding that fine:)

Thanks for everyones help