Power Problems

[roba]

I have recently upgraded from a GT35r to a TO4Z, but the engine would not make any more power - just exhaust manifold backpressure...

RB30_Power_Run1.pdf

This is plot of the GT35 run. the TO4Z run is basically the same but has about 500rpm more lag.

Exhaust manifold backpressure with

GT35 is 30psi

TO4Z is 42psi

Inlet pressure is 20psi.

Any ideas that might cause this backpressure ???

Is the flow through a RB25 head likey to be the problem?

Setup is

RB30 block - built

RB25DET head - kelford cams 272deg 9.35mm lift, valve springs to suit

Custom exhaust manifold, merge collector similar to 6boost

Tial 44mm wastegate

4" exhaust, not cat

2.5" plumbing to intercooler, 3" after intercooler, 125mm thick GTR cooler.

Vh45 throttle body 80-90mm?

Jun Style inlet plemum.

720cc injectors

Autronic ecu

Hoping to make mid 400's rwkw

RB30_Power_Run1.pdf

[Al]

Have you dropped the exhaust from the dump pipe back?

Have you measured boost before and after fmic?

Sounds like you have a restriction somewhere and i doubt it's the rb25head.

My mechanic has made 485rwkw using a built rb25det and a T04Z (C16 fuel)

My car has made 330rwkw using a built rb25/30 and a GT30R (GT3076R)

** EDIT: **

Looking at your graph, the power you're making isn't bad at all

[roba]

Yes I have dropped the dump pipe, but not when on the dyno.

I have droped a tennis ball through it to check for blocks - it came out the other side so it gotta be pretty good.

Boost pressure either side of the intercooler is pretty much the same.

Dyno numbers aside, the strange thing is it just wont make any more power, we added 3psi boost and 2deg more timing - it only made 10 more kw.!

[bubba]

Weren't you having similar problems with the old turbo and the old manifold? or was that someone else..

[Al]

You miss understood.

I said to drop the exhaust from after the dump pipe, then to do another dyno run, to check if your mufflers are causing a restriction

Who made the exhaust manifold?

[GTRNUR]

Its making boost so it wont be the exhaust. My money is on a rag in the intercooler piping or hopefully not... the plenum.

Edited August 19, 2009 by GTRNUR

[zebra]

That exhaust manifold pressure is huge. what exh housing is on the t04z? and where are you measuring the back pressure from?

[Fastrotor]

Yeah what are the turbine housing sizes of the outgoing 35 and the new T04z ?? Having a pressure ratio over 2:1 is why your power has stopped increasing. Without knowing turbine housing sizes id still say you just need the next turbine housing size up.

[R31Nismoid]

Weren't you having similar problems with the old turbo and the old manifold? or was that someone else..

i was thinking exactly the same thing

[roba]

Yeh it was me, i could write a book on the issues ive had.!

The GT35r setup first started off with 250rwkw, for all that are interested - some of the issues / things changed were:

*Spigit in the new cams was misaligned creating vibration in the CAS causing a large timing fluctuation.

*The unit in the ECU that heats the A/F ratio sensor was causing timing problems also.

*The boost controller electronics were faulty.

*The cam timing wasnt spot on.

Im sure there was much more that I have forgotten, during the process we changed the exhaust manifold, the wastegate position, and the A/R of the turbine housing, set a crank trigger to run timing. (none of this probally needed doing)

I still had fairly high backpressure, but the car was running good and making good power so i just went out and enjoyed it.

That is untill the craving for more caused me to change turbos - highlighting the flow problem.

GT35 - A/R 1.06

TO4Z - A/R 1.00

You can see the hole in the manifold collector where the pressure reading were taken.

The muffler is 4" straight through.

cheers rob

Edited August 20, 2009 by roba

[R31Nismoid]

So you just pushed on when you knew you had problems last time? ugh... should have fixed it then, because now look

If you have backpressure in the maniold its only going to be coming from a few places.

Do you see boost climbing as if the gate is not venting enough?

It could be manifold

wastegate not passing enough air (due to manifold)

exhaust causing blockage (a tennis ball is not a test)

[zebra]

whats the I/D of those manifold runners. They look quite small in the picks

[roba]

Boost control is perfect, manifold runners are 1 1/4 inch steam pipe.

[Fastrotor]

Retarded timing can cause large increases in exhaust BP. Perhaps you still have a timing issues. Checked timing under load on a dyno ?? (keep your head out of the way of belts incase they let go !)

And a simple way to rule out the exhaust system giving trouble is to move the pressure sensing out of the runner and into the dump for a few runs, or hook a boost gauge to it for a couple of runs. Then you can definatley rule it out.

As R31Nismoid said, tennis ball isnt a good test. You need to see the actual pressure. And when your this deep with problems, don't leave anything to chance.

Gary

[roba]

Have checked timing on dyno, and after we converted to crank trigger it rock solid.

Its not the exhaust - it's 4" straight through. http://www.skylinesaustralia.com/forums/po...98-IMG-2942.jpg

My engine builder thinks it is the cams as the duration at 0.05" is 216 and 216 (intake & ex). Advertised duration is 272 with 9.35mm lift

I dont know much about this area - can someone confirm this maybe the issue?

[r33_racer]

not a 100% sure, but i think advertised and what they are at .050" are never the same. I believe the standard measurement is always at .050" though.

check the cam card though to be certain!

Edited August 26, 2009 by r33_racer

[roba]

Sorry Just to clarify,

The cams i have are 272 / 9.35mm - 216 at 0.05"

My engine builder thinks these are to small.

Anyone agree/disagree with explanations.

Cheers

[r33_racer]

you guys havent messed up the cam timing by any chance? Have you tried playing with the exhaust cam timing?

Maybe put the belt on a tooth out or something silly?

[bubba]

272's too small?? you trying to rev the thing to 10k or something??

[Guilt-Toy]

my car did this. i spent months and months chasing the problem. Cams are not too small, i am making 375rwkw with STOCK cams.

I think the issue is cam timing. Getting the cam timing right on a RB30 is quite tricky. I would first start by setting both cam gears to 0 and then tuning it and see what power it makes. Dont be suprised if the power sky rockets. on my RB30DET the car makes the most power with the ext cam gear set to 0.

Set them all back to stock and try again - report back with results