Foward facing factory plenum mod

[Roy]

Us poor neglected RB20 owners, RB26 heads dont bolt onto RB20 bottom ends, not without the sort of work that makes it a waste of time.

[RNS11Z]

Would a gtr plenum fit with an adaptor plate?? I heard something about the water jackets creating a problem?? any one done this mod before or heard of it??

I also came across a gtr head?? could it fit onto a rb25 and is it worth the hassles for the gains??

thanks

H

[Sydneykid]

Hi guys, RB26 inlet on RB20 bottom end = less power. It is designed for 2.6 litres so all the volumes and sizes are wrong for 2 litres. I have experienced it and Zoom did a fairly big article on it which ended up with the standard inlet being better EVERYWHERE in the rpm range.

Complete RB26 head and inlet on an RB25 is a totally different scenario, works a charm.

Hope that helps

[Skyrine-Dave]

Hi guys, RB26 inlet on RB20 bottom end = less power.  It is designed for 2.6 litres so all the volumes and sizes are wrong for 2 litres.  I have experienced it and Zoom did a fairly big article on it which ended up with the standard inlet being better EVERYWHERE in the rpm range.

Complete RB26 head and inlet on an RB25 is a totally different scenario, works a charm.

Hope that helps

Sydneykid, how do you go about fitting the rb26 inlet to the rb25? do the ports line up and/or are there any problems that need to be worked around?

also how do you go about controlling the 6 throttle bodies? would that create any hassles?

thanks

Dave

[RNS11Z]

btw, the gtr plenum i can get is converted to single throttle body from 6.

[dontfeelcold]

my boss used to own a turbo workshop, he did all types of testing with custom plenums shapes, narrow at the rear cylinders this and that and found if you werent running huge boost (50psi+ like the old F1 cars used to) it didnt have problems with cylinders leaning out, since the air is being forced in and preasurising the plenum all the cylinders get the same amount of air, he said it was like filling a bucket up with water, no matter where you fill the bucket up from it will always fill the bucket up, its not like half the bucket is going to fill up more or sooner than the other side.

look at the plenum on the rb26dett, its same shape all the way along.

[FORCE]

We recently built a bolt on top half plenum for a VL turbo, and one noticeable difference was an improvement in throttle response. We did fit a slightly larger throttle body (61mm) , and I assume that could be largely responsible. The car was fitted with a front mount intercooler at the same time.

One might assume that with the fitment of a front mount, with all the associated piping and volume from the cooler that throttle response would suffer, but it definately wasn't the case.

We are working on a bolt on top half setup for a R33 GTS-T now, and I will let you know the results. If we have time, we will compare it to the stock plenum with a 120deg pipe fitted. One thing that concerns me with the stock centre feed plenums is the fact that the air blasts directly into #3 & #4 runners. Although this may not be important on a stock turbo car, you would assume that on a modified car with a larger turbo, etc. the increased air speed could turn this into a problem.

[dontfeelcold]

you are correct about pressurising of the #3 and #4 runners not being a problem on a stock motor, start running 30psi+ then its time to start looking a a properly designed plenum.

thats a sweet looking plenum. how on earth do they make those in that shape?

[dontfeelcold]

you are correct about pressurising of the #3 and #4 runners not being a problem on a stock motor, start running 30psi+ then its time to start looking a a properly designed plenum.

thats a sweet looking plenum. how on earth do they make those in that shape?

[FORCE]

you are correct about pressurising of the #3 and #4 runners not being a problem on a stock motor, start running 30psi+ then its time to start looking a a properly designed plenum.

thats a sweet looking plenum. how on earth do they make those in that shape?

When you are working with Plazmaman, making nice shapes from sheet aluminium is no problem!

Wait till you see the plenum we are building for the RB25....

[Cecam]

I'm not so sure even when stock that the factory plenum is that great, on my R33 cyl 4 has the lowest compression followed by cyl 3. Cyl 1 and 6 have the best compression. Cyl 4 is the first to detonate too. One of my R32's showed this to a lessor degree while another showed no difference, but a friends rb20det has the same results (4th lowest) and a couple of others I've tested show similar trends... I can only assume its because they run leaner?

Btw, with the air pooling problem with front facing setups, why can't they be internally baffled to deflect/slow down the air to stop this pooling without buggering up overall flow?

[Warpspeed]

Btw, with the air pooling problem with front facing setups, why can't they be internally baffled to deflect/slow down the air to stop this pooling without buggering up overall flow?

Factory plenums work fine at factory power levels. Most already have humps, bumps, ridges, and all sorts of strange internal shapes to give good air distribution.

Trouble begins when you start trying to force twice or three times as much air through a stock plenum. The air velocities become extremely high, and you are going to get uneven air distribution.

It is a bit unfair to say a stock part is crap because it starts to show some problems at extreme operating conditions for which it was never designed.

Most people have no idea how high the air velocities actually get in a plenum. Try sticking your head out of a jet aircraft at several hundred Kmh, to get a feel for what high velocity air can do. Expecting air at those sorts of speed to go around narrow right angle turns is asking rather a lot.

[Cecam]

I wanted to edit that after I had posted it to clarify a few things but got 406 errors or somesuch so gave up...

I'm not saying they're crap, I'm just saying I've noted that trend (compression = 4th lower)which maybe because of other factors, but seems abit too coincidental to me?

My R33 is indeed stock, though I'm sure it wasn't when the previous owner had it, definately had turbo work but I can't expand on that so will leave it at that as its just surmising. The R32's I mentioned are not stock however and were running larger turbos etc and follow the 4th = lower bit.

I think I have enough idea about velocities to skip putting my head out the window thanks

[51jay]

http://members.optushome.com.au/jay51/Fron...hrottlebody.jpg.

Anybody have any ideas what I can use for a throttle cable in this application. It needs to be about twivce as long as a stock R33 cable. Cable bracket will come off the bracket on the side of the head just below the oil fill cap.

[FORCE]

http://members.optushome.com.au/jay51/Fron...hrottlebody.jpg.

Anybody have any ideas what I can use for a throttle cable in this application. It needs to be about twivce as long as a stock R33 cable.  Cable bracket will come off the bracket on the side of the head just below the oil fill cap.

There is a place here in Syd. called "General Auto Instruments" that can lengthen the cables. Their ph. no. is 02 96491442. You need to lengthen it about 50cm. It costs around $70.

[Steve]

RNN14 GTIR, got quoted $40 from a wrecker, mate picked one up for $20. It looks like a silvia thottle cable might fit too, as they fit on the trust plenums. RNN14 one is a bit longer though.

[FORCE]

RNN14 GTIR, got quoted $40 from a wrecker, mate picked one up for $20.  It looks like a silvia thottle cable might fit too, as they fit on the trust plenums.  RNN14 one is a bit longer though.

The silvia cable won't fit. They are a little tight with the Trust plenum, and that is with the cable on the drivers side of the plenum.

Edit:

I think this is what you need:

[RNS11Z]

Any one heard of carbon firbre plenum's? apparently work shop x in nz makes them for skylines.

[51jay]

Thanks FORCE that looks just what I need......better placement of the cable bracket than i'd worked out too.

Steve: pulled one out of a Silvia....it was same length as the R33. Which one was quoted at $40 and bought for $20???

[Steve]

RNN14, I have one with my trust plenum, and it is definatley a bit too long for it. It came with my hillsmotorsport plenum, which has now gone. The guy I sold it to, bought the throttle cable for $20 from a wrecker, I got quoted $40 from a different wrecker.