Turbo Size Restiction, Good For Responce Or Will The Back Pressure Choke The Engine?

[REDMAN8]

Hi guys,

I've got a question for you all.

A friend and I were having a discussion the other day about manifold back pressure vs turbo spooling.

And the possibility of running twin T2's on a 6into1 topmount manifold vs dual gtr manifolds.

If you were to run twin N1 High Flowed turbos in series.

(mounted T4 topmount manifold with 50mm waste gate,T4 to T2 adapter, 1st N1 Turbo with int w/gate,custom dump pipe to T2, 2nd N1 Turbo with int w/gate)

Would there be too much restriction of the exhaust gasses exiting the engine?

[jangles]

Assuming rb26, yes, depending on what you plan on doing with it.

My question is, why?

[Blackkers]

That hurt to read, next time draw a diagram.

So you are thinking essentially running a compound twin turbo set up with identical turbos?

[Ben C34]

Bad plan.

[Dose Pipe Sutututu]

Convert to a single BW EFR turbo for amazing spool.

Also draw a diagram

[GTSBoy]

Most people have a hard time correctly sizing a single stage turbo system. Once you try to do compound compound/sequential yada yada yada type stuff, the chances of even an expert getting it right the first time fall to nearly zero.

[REDMAN8]

Thanks for the replies guys,

Yes we were talking about a rb26.

I acutally have a rb 25/30 in a r33 gtr with a compound setup.

The engine was built by a friend in japan and the breathing designed by a friend in the states.

It runs a Borg Warner S400sx3 467 with a 1.10ar turbine housing, Mounted on a 6BOOST feeding a gt2860.

The car has been shedded for the last 8 years.

It was an animal to drive, boost from 2300rpm right up to 7000rpm.

Torque kept breaking 3rd gear.

[GTSBoy]

Yes, so you should already be aware that compound systems require a bigun and a littlun and you have to share the pressure drop from the ex manifold to atmosphere between 2 turbine stages. How much power you need to extract from the gas at each stage to run the compressor for that stage is the million dollar question and sets the fraction of the total pressure drop you allocate to each stage.

Inevitably, unless it's intended to be some constant speed mega power engine with no response, in order to have any response at all you'll end up with a higher exhaust manifold pressure than a single turbo stage system would have. But you compensate for that by having monster boost to balance it. If you don't have monster boost, then you're wasting your time building a compound turbo system, because monster boost is really the only good reason to stage compressors*. And monster boost and petrol engines don't go together too well. It's great on diesels.

* most of the time anyway. I know about the Pike's Peak truck and so on and so forth. Let it lie.

If you really really want to make a responsive compressor system with boost from nothing, then the smart money is on using a positive displacement blower as one of the stages. It allows you to only have one turbine stage in the exhaust path, and that turbine stage can have a really relaxed housing, resulting in less ex manifold pressure than other similarly powerful engines. The pos disp blower gives you boost from nearly nothing, the relatively low pressure ratio at each compressor stage helps to keep temperature rise under control and limits the extremity of design of the compressor wheel and so on. It's all good.

[REDMAN8]

We were just chatting about running them on his rb26.

And I thought about the possibility of running them this way and feeding the airflow into my S400.

Instead of my current configuration where the S400 feeds air to the 2860.

[GTSBoy]

Hang on. So you weren't talking about using the 2 x T28s in series with each other? They'd be a parallel pair and they'd work with another bigger turbo? Well that's different. It's sure to be a clusterf**k, but it's different.

[jet_r31]

If you do it..i want pics!

Actually pics of your borgy /2860 setup would be cool aswell

cheers

darren

[hypergear]

Here's what happens. When you joins two compressors together and run off two exhaust wheels in series. It works out as you have one massive compressor running off the first turbine wheel in the series. You must blank the larger turbo on initial spool, as pressure always "leak" from the weaker exist. It might work with a complex gating system, you will be fighting to get room to fit them all.

I found smaller and very responsive single turbo surge badly under partial load on Rb26 engines. You might need use aftermarket cams and VCT system to get around this problem if you are going to make above system work.

[REDMAN8]

Will try to track down some pics of the old setup.

GTSBoy and hypergear

Yes, This is what I was thinking of doing.

Running one N1 off of the 6BOOST manifold with the exhaust gasses then passing through the other N1 and then into the S400.

With both N1 turbos suppling boost straight into the 4" inlet of the S400,

for it to compound and supply to the engine.

Or do you think I should run the S400 first then into the N1's.

[Super Drager]

Compound systems work VERY well and monster boost is NOT the only reason to do them .
Have a read of this : http://www.yellowbullet.com/forum/showthread.php?t=216811


Lots of compound systems out and working very well on petrol engines, best part of a compound system is to spool a turbo you normally wouldnt be able to, Kevin Jewers 2L DSM had a T3 50 trim and a S475 compounded and made full boost at 4500RPM (compared to NEVER with a single S475) and ran 8's. Although doing it i nthe way OP has mentioned it wont work at all.

Edited April 10, 2015 by Super Drager

[GTSBoy]

I think that 45 psi IS monster boost for a petrol engine. You ain't running that on 98.

[Super Drager]

I think that 45 psi IS monster boost for a petrol engine. You ain't running that on 98.

Ofcourse not, however you can get the total boost to a lot less than that. Pressure ratios multiply between compressors so what some guys have done is have it compound till the large turbo comes onto boost, then a bypass valve opens and flows as much air around the small compressor as possible. Boost Logic do it that way on their supra kits.

GT35R/GT45R Compound kit, 24PSI by 3500RPM.....runs mid 10's at 140+mph