Best suited turbocharger

already have a 3"down pipe just need a different exhaust housing now aaahhh so many things to do and so little time

Well, no..

Its not like you can play around with it on a rolling road to get the best results, which is the only way you are going to know if the modification actually reaps any benefits..Other than that its just hoping its correct..

When I used to take customers Rover Turbos to my local RR, just setting up the inlet and exhaust cam timing by a couple of degrees either way could increase power by up to 15bhp, and bring the turbo in earlier by altering the exhaust cam..

Remember, on the PRV, we can not play with exhaust and inlet timing independantly which would give you maximum torque and power, as its a SOHC motor. All we can do is advance or retard the whole cam timing..

So as I said, we can't bring the exhaust valve timing in earlier with out advancing the inlet side too..

Absolutely - didn't realise the 5 and 21 were twin cam engines. however the PRV does benefit massively from accurately timing up the cams to 108 degrees on the Atmo's anyway.

Martin

Depends what the turbos are. Small turbos will spool up quick, but then not give decent top end power. If you find the equivalent match in twin turbos to my GT single turbo, it would be twin T3s with 0.48 housings and 50 trim compressors, which will take longer to spool than my single GT3235X.

Hold on, hold on, hold on..... First off, that was my point - that the point to twin turbos is that you have a lower inertia and they spool up faster. The right twin turbos will have no problem shifting the same amount of air as a single large turbo and have the added advantage of being closer to the exhaust valves (on a v engine) and a lower rotational inertia. A *properly set up* twin turbo WILL spool up faster and provide the same power as a single turbo in the same application, all other things being equal. I went on to point out that in the case of the twin turbo I've worked on, and indeed most modern turbo engines is that the turbo is placed on the end of a tight cast manifold so it benefits from the turbulence created in a manifold. This helps with spool time even more (and therefore torque) but hurts top end power. If the turbo is carefully selected for the application (as all should be), you will get the optimum result. As to your specific figures, I'd have to see the data but a pair of T3's is a lot of metal for a 2.5 litre engine to spin!

It helps low end torque, but not not make a higher torque figure than an unrestricted large turbo setup with minimal exhaust restriction (which is what you would have with smaller turbos to decrease lag)

Not quite sure what you're saying but I disagree that twins will be more restictive - happy to be shown data to the contrary though

http://www.nissanperformancemag.com/oct ... ask_sarah/

Basically, as the turbo is fed by a gas pulse at a time from the engine, on a traditional turbo, that one pulse has to fill and travel down the turbo housing in order to spin the turbine wheel. With the twin scroll divided flange setup, the housing is divided into two,

Errrrr - really not convinced there either because ti would appear from the article you linked to, that it's all about separating the exhaust outlets on the same bank. Specifically the words "When coupled with a pulse converter manifold" - basically a cheap way of getting close to the effect of equal length headers. You can't really apply that logic to the GTA's engine because you're dealing with two seperate banks that are out of phase anyway, and you aren't doing anything to separate the ports on ecah bank

so the pulse (from one cylinder head bank) has to fill a void only half the size of the normal housing, before it hits the turbine wheel thus getting there faster and with more energy..

Ummm..... okay this is where I'll post a link

http://www.dsm.org/menu.epl?item=363

In a nutshell, you want the pressure differential from turbo inlet to turbo outlet to be as large as possible. But you want the exhaust flow from head to turbo to be as unrestricted as possible (for maximum power). I see what you're saying about the chamber in the turbo inlet, but whether it makes a measurable difference at high rpm's is something I'd have to see figures on.

*disclaimer* I've still learning this stuff and am more than happy to be proved wrong on any of it - but I think we can all argue theory till we're blue in the face, it's figures that count so lets get some of these engines finished, Dave (speaking for myself as well!)

Martin

Nice disclaimer***
We all like to learn something new,
and we all make mistakes, some big, some small, and others we won't admit to.

Good to see someone else putting their views up for debate.

Hold on, hold on, hold on..... First off, that was my point - that the point to twin turbos is that you have a lower inertia and they spool up faster. The right twin turbos will have no problem shifting the same amount of air as a single large turbo and have the added advantage of being closer to the exhaust valves (on a v engine) and a lower rotational inertia. A *properly set up* twin turbo WILL spool up faster and provide the same power as a single turbo in the same application, all other things being equal. I went on to point out that in the case of the twin turbo I've worked on, and indeed most modern turbo engines is that the turbo is placed on the end of a tight cast manifold so it benefits from the turbulence created in a manifold. This helps with spool time even more (and therefore torque) but hurts top end power. If the turbo is carefully selected for the application (as all should be), you will get the optimum result. As to your specific figures, I'd have to see the data but a pair of T3's is a lot of metal for a 2.5 litre engine to spin!

No, as I said, I would require two 50 trim T3s to match the flow output of my GT3235X. But a T3 50 trim on a 1.5 l engine (half of the 3.0) wil be in surge at 3000rpm, where as my single is in efficiency. The turbine wheel and shaft of the T3, is the same size as my GT3235, but there are two of them, only fed by 1.5l each, so they do not have a lower rotational intertia. Thats irrelevant anyway, as spool is more a function of turbine housing size more than the inertia of the shaft and wheels..

Simple rule of thumb, the 50 trim T3 is good for around 250bhp, my turbo 500, but the spool and response will be faster on my single..

I could get less lag with say two T2's or T25,s but only have a max limit of say 160 to 220bhp per turbo.

Capacity of the engine has nothing to do with turbo requirements. Its all CFM related, against the volumetric efficiency of the engine and the pressure ratio. Just pull up the compressor map for the turbo you want to chose, plot the points against airflow and work out if the compressor can fill the requirements you are after. Even 50 trim T3's are borderline for 2.5l and 500bhp..

Not quite sure what you're saying but I disagree that twins will be more restictive - happy to be shown data to the contrary though

Because as above, I can use a larger a/r housing, and turbine wheel than on two small twins. If I use the two T3s for twin turbo, there is no restriction, but then you are back to the problem up above of lag and response...

Errrrr - really not convinced there either because ti would appear from the article you linked to, that it's all about separating the exhaust outlets on the same bank. Specifically the words "When coupled with a pulse converter manifold" - basically a cheap way of getting close to the effect of equal length headers. You can't really apply that logic to the GTA's engine because you're dealing with two seperate banks that are out of phase anyway, and you aren't doing anything to separate the ports on ecah bank

Ignore the 'pulse convertor' bit. Basically, just by having one bank feed each relevent side of the scroll, lag is reduced without increasing backpressure. The a/r of the exhaust housing I am using is a 0.78, over double the 0.36.

In a nutshell, you want the pressure differential from turbo inlet to turbo outlet to be as large as possible. But you want the exhaust flow from head to turbo to be as unrestricted as possible (for maximum power). I see what you're saying about the chamber in the turbo inlet, but whether it makes a measurable difference at high rpm's is something I'd have to see figures on.

It is, like I said, Im not using a small twin scroll housing, Im using one twice the size of the original.

As for the pressure differential, you only want the maximum difference to aid spool up, not for maximum power, otherwise we would all run tiny turbine wheel, and have a huge differential. This is why the twin scroll works, as for the inital pulses from the engine on spool up, the pressure against the turbine is high thus making it spool up quickly, but the overall size of both scrolls combined coupled with a larger than normal turbine wheel, means that top end flow and power is not hindered.

None of this is theory. This is all tried and tested, jeez, twin scrolls have been around for about 30 years in T4 footprints, its only now that Garrett have introduced it in a T3 footprint in journal and roller bearing fitments.

I'll take one!!!

I'll take one!!!

One what
I'm so now, I don't know what my name is or where I live

T3 sized twin scroll turbo thingamy!

T3 sized twin scroll turbo thingamy!

Do you want fries with it sir

T3 sized twin scroll turbo thingamy!

Do you want fries with it sir

that'll be 3 grand thingamy please

i thought you have a stage 2 turbo peter personly i would spend my money else where (head,cams,manifolds)and then change the turbo when it starts to run out of puff well thats my plan anyway

No, Pete has a previous version of the 'stage 2' upgrade, larger compressor wheel and turbine housing etc, but not as large as yours Steve..

As for the pressure differential, you only want the maximum difference to aid spool up, not for maximum power, otherwise we would all run tiny turbine wheel, and have a huge differential. This is why the twin scroll works, as for the inital pulses from the engine on spool up, the pressure against the turbine is high thus making it spool up quickly, but the overall size of both scrolls combined coupled with a larger than normal turbine wheel, means that top end flow and power is not hindered.

Okay, I know there was a lot more in that last post that I wanted to reply to but it would appear that Dave has read more on the subject than I have so will bow to his greater theoretical knowledge...

BUT I think you're beign a bit sweeping in your statement... the whole point of a turbo is to regain energy wasted in the combustion process.

"It is a common misconception that the exhaust turbine half of a turbo is driven purely by the kinetic energy of the exhaust smacking into it (like a windmill) While the kinetic energy of the exhaust flow does contribute to the work performed by the turbo, the vast majority of the energy transfered
comes from a different source."

Which is...

" As the exhaust passes through the diffuser and into the turbine housing, it moves from a small space into a large one. Accordingly, it expands, cools, slows down, and dumps all that energy - into the turbine that we've so cleverly positioned in the housing so that as the gas expands, it pushes against the turbine blades, causing it to rotate. "

I like to understand things from a "first principles" viewpoint, and that article does give a very good grounding in physics I can understand (I am a trained engineer, just not in this stuff) but what your talking about is clever engineers over many years developing umpteen different ways of increasing the efficiency of a certain design. Putting those design tweaks into practice on an engine the turbo wasn't designed for is a minefield of not getting it "just right". I do encourage anyone reading this to read the articles I linked to. That link is quoted all over the internet as "the" article to read about turboing.

And anyway, Dave still can't understand how you -can- put even fire camshafts into an odd-fire engine and vice versa, just by swapping one sprocket

(not trying to argue either Dave, just discussing )

Martin, there is no point copy pasting articles on turbo 'physics' when the what you need to know to design a good turbo setup is about a/r ratios, compressor maps, and airflow and volumetric efficiency of you engine at certain load and rev point..

Great, 'the exhaust gasses go from a small to a large space', but that doesnt help any body choose which size compressor wheel they need to fit, coupled with what turbine housing area ratio, to get 20psi from 3500 to 6500, on a 2.0 engine, from around 90% VE at peak torque, to around 75% at peak revs, without running into surge on initial full boost, or going past 70% efficiency on the compressor map...

I think were all past 'how a turbo works'

i thought you have a stage 2 turbo peter personly i would spend my money else where (head,cams,manifolds)and then change the turbo when it starts to run out of puff well thats my plan anyway

As David said my turbo can go one better.....AND..the set up I have now and some huge injectors will really unlock the twin scroll turbo. I do fancy the cams, (didnt buy them last year because they are no use on the Renault ECU) but I dont really want to move my power band up the rev range for what I do, they are also a load of hassle (engine out again!!! ) the same goes for heads...engine out and to bits.....need a year off taking the bloody thing out before I can face that!!!!! My bank also needs a year to recover....wedding, CC, ECU, speed season, Isle of Man and 4 other weddings!!!!!