Rb30 Power Delivery, Should It Be Better? How?

[paulr33]

assuming 4th gear 183km/h is 5124rpm

[Guilt-Toy]

I cant see this being correct at all. I am pretty sure those runs were done in 4th gear hitting rev limiter 7000rpm when i backed off...

if that is true then a extra 2500rpm would mean the car would do 220km/h plus in 4th gear.. i dont think it would no way

assuming 4th gear 183km/h is 5124rpm

[paulr33]

sorry im a retard, sorry

6428rpm it is

[Guilt-Toy]

what computer is this rb30det running? can you take a screen shot of the ign map and post it ? fuel map too if you can but not really needed

[Guilt-Toy]

6428 still sounds a little too low to me... im sure i was reving it to 7000rpm

sorry im a retard, sorry

6428rpm it is

[r33_racer]

So they reckon bigger exhaust hey.. So i wonder if our knock will drop with a 4" system and power will increase?

If it really is the hotside...that could explain something....

[Guilt-Toy]

i can see how the exaust side with a small exaust could cause knock but when your talking a engine that has a top mount extractor manifold and a 3" pipe with a external gate the turbo is a bit far away from the engine plus you got the 3" pipe and the external gate pipe moving air away from the engine..... hmmmm

if this is the case then im screwed. my 3" pipe is nearly hitting the air con pipes as it is... i dont even think a 3.5 " would fit with my exaust manifold.. then again ive changed manifolds since then but still. i dont want to make it bigger i still have to pass the noise test for my engineers certificate.

So they reckon bigger exhaust hey.. So i wonder if our knock will drop with a 4" system and power will increase?

If it really is the hotside...that could explain something....

[r33_racer]

Since the oulet of the turbo is 3" anyway...you can go first 90" at 3" and then straight away taper out to 3.5" or 4" whatever way you want to go. That way you wont have to worry about the lack of room.

[kastin]

If 5500rpm is the magic number that the power noses over, regardless of power like your saying there are a few cars that nose over at 5500rpm with 200kw, then you get cars that run 320kws and nose over, then i cant see how it is the plenum because 320kw's is flowing way more air then a 200kw so i dont see a plenum restriction.. what happeneds at 5500rpm,

vvt? (when does this step up)

duty cycle?

I know youve been around for ages cubes, i think it's a bit to wierd.

[Cubes]

kastin,

A plenum and its runners aid in tuning a motors power band.

Short runners are known for high rpm, long runners low/mid range torque.

[DennisRB30]

Anyone got pics of these plenums? Do they just use the stock bottom half joined to a sheet metal plenum chamber?

I don't like the way power is only shifted toward higher RPM without actually increasing it. Sure, you get more high RPM power, but you loose it in the mid range. You would get the same on road feel at similar speeds by fitting taller gears.

[Guilt-Toy]

The plasmaman plenum uses the stock standard bottom half its just the top that you buy

www.gtr.com.au has them for sale.

Anyone got pics of these plenums? Do they just use the stock bottom half joined to a sheet metal plenum chamber?

I don't like the way power is only shifted toward higher RPM without actually increasing it. Sure, you get more high RPM power, but you loose it in the mid range. You would get the same on road feel at similar speeds by fitting taller gears.

[aphid]

EDIT: dammnit, wrong rb30 post

Edited January 31, 2007 by aphid

[R31Nismoid]

We put 24psi through mine (2.5ltr) so thats equiv to what, 20psi on a 3ltr (very rough stab), be that on 104, not 98/100.

I was using stock cams/plenum.

If mine was working fine, and others before me have worked fine in 3ltrs im still yet to be convinced the problem lies there.

Mine was still making power @ 8000rpm if memory serves me correct on both PULP/104

On PULP i had the issues, and guess what, i was running a 1980's R31House 3" exhaust/external 45mm gate also.

Plumbing the gate is was just a no-no (i tried it). The car lost that much power as the 3" was never going to flow enough with the gate plumbed back.

So it was obviously only "just" getting by with the what it was in the 3" + Screamer setup.

I would have loved to fit a 3.5, ideally 4 all the way, but no room left. Make do with what i had... well... RPMGTR did it cause im special :sorcerer:

And i paid him teh monies

My new setup is going to see twin 2.75 exhaust so i dont have any issues like that again.

[r33_racer]

I nearly finished the 4" system on ours and its a mission with space. But im really interested to see how it affects our knock and power.

[paulr33]

maybe exhaust pressure might give away some info ?

[Cubes]

We put 24psi through mine (2.5ltr) so thats equiv to what, 20psi on a 3ltr (very rough stab), be that on 104, not 98/100.

I was using stock cams/plenum.

If mine was working fine, and others before me have worked fine in 3ltrs im still yet to be convinced the problem lies there.

Mine was still making power @ 8000rpm if memory serves me correct on both PULP/104

On PULP i had the issues, and guess what, i was running a 1980's R31House 3" exhaust/external 45mm gate also.

Plumbing the gate is was just a no-no (i tried it). The car lost that much power as the 3" was never going to flow enough with the gate plumbed back.

So it was obviously only "just" getting by with the what it was in the 3" + Screamer setup.

I would have loved to fit a 3.5, ideally 4 all the way, but no room left. Make do with what i had... well... RPMGTR did it cause im special :sorcerer:

And i paid him teh monies

My new setup is going to see twin 2.75 exhaust so i dont have any issues like that again.

Unfortunately it doesn't work that way with the RB30DET's. 20psi makes the same power through the rb30det's as it does on the Rb25DET's. No more no less. The head is what governs the inlet restriction not the pots/stroke.

The RB30 simply spools the turbo a hell of a lot earlier and pulls up low and mid range power as a result improving 'average' power so when you snap that next gear your making more power.

The peak power figure stays the same or very similiar.

With regards to the rb30det...

'Tuning' of the inlet system for a particular motor has always affected the rpm power band. Engine manufactures have been taking advantage of this for years. Maybe opening the exhaust right up is simply 'masking' the not suitably tuned (for piston speed, runner velocity etc) inlet plenum and runner combination.

Why doesn't the RB26 head pose the same problem on the 30det's if it really was 'only' the exhaust that was causing the problem? Surley we don't need a 3.5" exhaust for 180rwkw, well maybe we do when used with the std rb25 runner/plenum combination. :S

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There's recently a little discussion over on performance forums regarding dump pipe design with the new gt30/35r iw.

Consider fitting the largest dump front pipe possible, fitting up a split dump you have to go with a smaller dump, a single open mouth dump you can fit a larger dump.

Some suggest a single open mouth design is better due to a couple of reasons:

1. It creates a larger pressure differential across the turbine due to there being a larger open area directly behind the turbine.

2. The wastegate causes interference with the 'swirling' turbine exhaust gas, this interference is good as it gets the gas flowing in a laminar fashion earlier so slightly better exhaust flow.

3. A larger pipe always exhibits less 'friction'.

4. No interference with the front pipes laminar flow when the wastegate pipe joins back in.

And for the cons.

1. Possibly worse boost control due to a slight increase in backpressure on the wastegate side.

2. Possible increased backpressure directly behind the turbine wheel at WOT, but would this be negated by improved front pipe flow due to better laminar flow?

With regards to internal gate (gt35r iw); there's the suggestion that if one can only fit a 3" dump and say a 2" wastegate pipe would it not be better to simply fit a larger 3.5" or 4" open mouth dump.

But no one really knows as no one has ran say a 3.5"+ exhaust with a smaller split and larger open mouth. lol

[discopotato03]

Hi Cubes , I wouldn't mind a link to that discussion if possible .

It may also pay to go back and look at Maximum Boost and Corky's views on pipe diametre vs turbine exducer or outlet diametre . Gas speed has a lot to do with determining pipe size obviously the larger diametre means lower velocity but its still going to be highest at the most restrictive point . The easy way to measure this is to tap into the exhaust at various points along its length and measure the pressure .

I think we all know that for maximum effort power with a GT3582R your going to be using the largest 1.06 turbine housing available for the greatest flow with least restriction and less gas bypassing going on .

IMO the easiest way to make a compact dump with a healthy tube diametre is to copy what HKS did with their dump pipe for the Pro S IW housings . This would not be terribly difficult to fabricate though time consuming , has the added advantage of keeping everything at a more uniform temperature than a totally divorced tube so less likely to crack with heat cycles .

Cheers .

[kastin]

I think we should consult the Oracle..

someone point sydneykid to this thread!

or my mrs she seems to think she knows everything..

[r33_racer]

i already asked him...just waiting for a reply. See what he thinks on this matter.