RB20DETT TwinTurbo2Litre

[R32 GTSTT]

Hi guys, After blowing a turbo gasket, I’m in the process of fitting 2 stock RB20 turbos to my Nissan Syline R32 GTSt. All the work is been done at a engineering firm in Bunbury WA where my dad works.

We are making 2 separate manifolds one for each turbo. Front 3 exhaust outlets to one and the back 3 to the other turbo. There is going to be a balance pipe that goes between both manifolds to equalise pressure into both turbos. We see there is no need to have 2 wastegates so one will be blocked off. All water and oil lines are been ‘T’ . There will be 3” pipes coming off the back of the turbos converging into a 4” exhaust system. Air intake for the turbos will consist on the 1 pod filter, splitting into 2 pipes after the afm then to the turbos. The outlets for the turbos will converge into one tube entering the front mount intercooler then engine.

This project is well underway, and if all goes well will be completed in a month. Before starting this project I had 200bhp running a stock turbo with 13psi, with the intercooler and a 3” exhaust. I have had it down the drag strip with a time of 13.7 @ 167km/h.

I was interested if any one had any comments on how laggy it will be, the power output I might achieve, or any concerns about what im doing. All comments will be appreciated. thanks, Ewan.

[rev210]

the stock RB20 turbos are a tad larger than the factory gtr ones and will come on boost and make full boost at approximately a tad over double the rpm they would as a single (probably add another 500rpm or so).

So thats about 5500-6000rpm?

[rev210]

You will need 'two' wastegates btw. If the wastegate's a factory one it isn't going to cope by itself.

[R32 GTSTT]

OH NO, i hope not the late, it will be lag city, is there any mods i could do to help overcome the lag, cams??

[rev210]

cams will help a tiny bit.

Increase the capacity to 2.4L with the stoker kit availible from JUN and others. Put an RB30 bottom end on the motor will be much cheaper.

[Ronin 09]

Yep, keep both wastegates. If you block one off, that turbo will overboost well before equalizer pipe has done its bit

[Steve]

Did some reading on twin turbo setups. Where twins will help, if run in parrallel, not talking about sequential, is if you are aiming for xxx amount of flow (power), rather than fitting one large turbo, two smaller ones with a combined flowequal to the flow of the larger one will spool up quicker - that is if the turbine wheels are half the size etc. Its not exact in the real world, because of so many other variables, anyway starting to digress....

This has to do with the energy required to move the wheel varying exponentially, rather than linearly, as the radius increases - so two smaller wheels (turbine) require less energy to spin at the same speed as one larger wheel.

So, where the advantage will lie, is if you were wanting to fit, for exampe, one 500 hp turbo, two 250hp turbos of half the size exactly, will come on boost quicker than the one bigger turbo.

Perhaps it would be worth seeing if you cannot find a couple of smaller turbos to fit?, second hand GTR ones or even smaller if possible? This would give you boost alot quicker. Remeber that while the rb20 turbo isnt huge, it is designed for a 2L engine, so if you put 2 of them on, you probably have a car that would be good for the drags, not so much of a streeter.

For wastegate, perhaps it would be possible to run one wastegate on the crossover pipe between the manifolds? but probably alot better to just use the stadard wastegate on the turbos - these could be controlled by one boost controller, with the line t-ed no probs.

As rev suggested, exhaust cam, also a good manifold design, decent dump pipes, good exhaust, 'high' flow cat etc will all make boost earlier.

[Warpspeed]

I saw the other thread on the same topic first, but rev210 is exactly right. Each turbo will have to spin up to the original shaft RPM to generate the original boost, but with only half the exhaust volume to do it. As a result boost threshold RPM will double, and rate of boost rise will be just about half.

It will be pretty awsome at the very top end though. Some smaller a/r exhaust housings would be what I would be looking for, or a couple of stock GTR turbos at a friendly price.

[Warpspeed]

Further to Steve's comments on large single versus twins has to do with the relative needs of airflow and boost pressure for various engines.

If you look at any flow map it leans to the right, with the most efficient operating islands in the middle somewhere. Now this means a given sized turbo will give you more available flow as the pressure increases, and you operate higher on the flow-map.

It also means that at low boost levels, there will be a far lower efficient flow available.

Now suppose you have a fairly large capacity engine and you only want to run low boost. You could either fit a huge single, or two smaller turbos, each supplying only half the flow.

Ford on the XR6 have gone the huge single way with a monstrous GT40 turbo, which everyone thinks is oversized, but almost certainly is not. Or Nissan with the GTR have two very small turbos to do much the same thing. In each case there is pretty high airflow requirement at fairly low stock type boost levels.

On the other hand if you have a small capacity engine and you want to run very high boost, a large single is going to be better because it will fit better onto the flow-map. High flow and high boost go well together with a large single.

So as Steve says, if you want 500 BHP it really depends on the boost level you need to make that power. If it is going on an eight litre monster that only needs 4psi boost, go multiple turbos.

If its a one litre engine running 50 psi boost or something, a single will get it done best.

[iluvewan]

i dunno its gonna be nice cause i know your car sorta and im sure once its finished if you eva finish it it will kick ass

lu

[R32 GTSTT]

Very interesting, Do you think that i will need a bigger afm to support the larger airflow meter

[Steve]

AFM will be dependant on how much air flow, ie, how much power you are making - no point forking out dollars if you havent had the car on a dyno. Lots of other things to consider, like fuel system, clutch, ECU, gearbox (perhaps) etc - more important than doing an AFM straight up.

What other mods do you have already?

[R32 GTSTT]

Well i have a cermanic clutch, stock R32 GTSt gearbox, The ECU has had something done to it, dunno wat thou, has no boost cuts , or speedlimiters on it, will be running to stock R20 turbos

[rev210]

my friend you are soon going to find out how expensive power is to chase

There is as they say 'no free lunch'.

[Gradenko]

R32 GTSTT, what sort of power are you looking for? RB20/25 afm's are good for ~370bhp (thats at the engine). If you want any more, you'll need a Z32 or better afm. Whats your power goal? Chasing power without setting a power goal is always going to end in disaster.

A twin turbo RB20 is a different way to go about things and I like it. Twin RB20 turbos is the wrong choice though. Look for twin RB26DETT turbs (T28 flange) or twin VG30DETT turbs (T25 flange), they'll be a better match.

[Nismodified]

is it me or is there like 2 other threads about this same topic and from the same author?

[Cubes]

Just slap a RB30 bottom end in there. Set of forged pistons and you will be enjoying 500+ bhp... with full boost around 3000-3500rpm

[hawks]

i would get a aftermarket computer and ditch the airflow meter completely for a map sensor.

[Gradenko]

Originally posted by broken

i would get a aftermarket computer and ditch the airflow meter completely for a map sensor.

Why? A 80mm pipe with filament running down the centre isn't going to be a physical restriction, and afm's are much better at measuring engine load than map sensors. Work with the ecu you've got R32 GTSTT. Its more than capable.

[Steve]

Save a few bucks for other mods.

The R32 ecu can be modded to accept a z32 or infinity AFM cant it? Alot cheaper than going to full map.