Rb30det - Missing 100kw

[roba]

I have finally got my RB30 going despite a few stupid faults with the plug in autronic.

Problem is at 18psi its not making the expected power - (around 330-360 rwkw).

By my seat of the pants estimation (feels similar to last engine) it feels no more than 250rwkw - this is backed up by the injectors which are 720cc and running at 55% duty cycle.

The specs are:

CP pistons / eagle rods

rb25 head with rb20 cams

GT35r turbo .82r

115mm gtr style intercooler

Jun style inlet plenum

custom exhaust manifold

4" exhaust

44mm wastegate - plumbed back

autronic SM-4 ecu

I guess the restriction is between the inlet plenum and the turbo. namely the cams or the exhaust manifold.

I have used non vct RB20det cams which i believe are similar specs to RB25det ones . 240in 240exh 7.8mm lift.

The cam timing was set using the RB30 pdf which states, lobe centre angle (in) = 115, and lobe centre angle (ex) = 120

The exhaust manifold is a custom 3into2into1 design. The fabricator has had great results for 4 cyclinder engines using this design but im not sure he has used this design on other skylines. I have installed a pressure sender in the collector and it gets up around 30psi at full boost. (18psi)

Any ideas would be greatly appreciated.

[den001]

dude, i recon its your cams.... if you were to upgrade the cams youd be looking at the power level you are expecting

[paulr33]

without a dyno plot its just guess work

it could be cams, exhaust backpressure, other leaks in on inlet side, etc etc etc

there could be dozens of reassons and so much has changed

without afr plot, pressure and power/torque plots its all guess work - take it to a dyno or the tuner and get a power run plot

[roba]

A couple of pics...

[1TUF33]

i figured it out dude... your motor isnt completed LOL sorry man, poor humour

[R31Nismoid]

well i ran over 350rwkw with factory RB25 cams/24psi and a GT30, so not too far from what your using.

What didnt you use the RB25 complete head?

What happens when you use more boost? No more power?

[SirRacer]

id love to hear what the final problem is, as thats pretty much exactly the same setup as mine and i hope to make similar figures to you

[rob82]

Was it on a chassis dyno - if so what were the tyres like and what was the tractive effort for the run?

[NYTSKY]

Nice gate setup!

[dangerman4]

just wondering on what the manifold cost you?

a merge collector would have been a nicer

[roba]

without a dyno plot its just guess work

- dyno booked for sat, but i dont see how that will help me diagnose the problem it will just prove the power is down,

-Im hoping to get from this forum a range of ideas and comments, esp on the ex manifold design as im sus on its design, but in saying that - its got to flow better than a standard one, and plenty of mid/high hp cars use them

dude, i recon its your cams.... if you were to upgrade the cams youd be looking at the power level you are expecting.

- Plenty of people have made good power on these cams. but will be rechecking the cam timing sat.

What didnt you use the RB25 complete head?

What happens when you use more boost? No more power?

-The head came with some locally reground cams that had a terrible profile, so i threw in some rb20 ones i had.

-Didnt add more than 1.3 bar as didnt see much point, from 1 to 1.3 bar was not much improvement.

just wondering on what the manifold cost you?

paid for all fabrication work in one go so dont kno exact cost - prob around 800-1k.

cheers for the comments, hopefully i can get more of a clue to whats going on after the dyno run on sat.

[SirRacer]

Here is my custom one for a few comments. Feel free to criticise

Paid 800NZD for it in steam pipe

I agree re the collector, have you got any pictures of that?

You have also routed your hoses a long way (just noticed). Why didnt you put the water return straight into the radiator instead of pumping it round the engine again.

Edited February 21, 2008 by SirRacer

[sky30]

Id say definately look at your exhaust manifold, from that last pic it looks like all 6 cylinders merge into a hole about 50mm in diameter. You need a propper collector.

[R31Nismoid]

If you went from 1bar to 1.3bar and didn't get any return - you have massive restriction.

Manifold is my bet too... sorry... but it shithouse in design.

RB's are not the same a a SR, not is a 4G the same as a SR... manifolds for the motor, not the generalisation

[roba]

Spent a bit of time on the dyno this morning, checked / adjusted a few things incl cam timing and gained 10-15 rwkw at low boost.

Still couldnt find any significant power, so checked manifold back pressure, ended up being 27psi compared to boost pressure of 11psi.

Everything starts to happen about 3700rpm - torque falls through the floor as manifold back pressure goes through the roof.

My manifold fabricator is going to replace at no cost, ill let you kno how we get on in a few weeks...

ps Thinking of a tomei solid lifter kit so i can run some 272deg cams, do I use RB26 cams with this kit in my 25 head ?

Whats the max lift i cn run without machining...?

cheers rob

[R31Nismoid]

Dude - just buy a decent manifold from someone that knows what they are doing.

[6BOOST]

So what ended up happening with this?? I haven't been on here for a while and just got your PM. Did you find the missing power?? OR find any other problems on the dyno?? Give me a call, 0410 730 598. If you haven't found a solution yet, I'd be happy to build a manifold for free for you to try and back to back test, just send it back when your finished, that way I get feedback and results and you get to check if that was the problem. Altho at this stage, I'd be thinking cam timing.....

6BOOST

[Pun4N1]

Id say definately look at your exhaust manifold, from that last pic it looks like all 6 cylinders merge into a hole about 50mm in diameter. You need a propper collector.

I agree 10000% this hole is about what i would expect to have for 1 pot not 6

[swanny180]

I agree 10000% this hole is about what i would expect to have for 1 pot not 6

+1

It looks about half the total area of the flange itself?! Thats terrible?

[Mr. Untouchable]

yeah thats just no good mate. that manifold is shithouse, not going to cut the mustard.

i'd be tempted to say a stock manifold would flow better.

6Boost's offer sounds fantastic.

if you have already paid for the work, thats fine, and he's offered to make you a new one at no extra cost, i'd get a chinese one off ebay or borrow one thats proven in design them get him to make one as close as possible.