Twin Turbo

[BHayes_S13Coupe]

I read on this forum somewhere that there's no real benefit from twin turbo on an inline engine. I'm doing a SR20DET engine swap soon in my 90 240sx and I thought twin turbo would be better. Reason I want twin Turbo is to reduce turbo lag-a small turbo for quick spool up and a larger turbo for some serious topend boost. I want Twin Turbo but if there's no benifit then is it worth it. Question is-Is there a benefit from Twin Turbo?

Thankz

[MadSideways]

Quote »I read on this forum somewhere that there's no real benefit from twin turbo on an inline engine.[/quote]Supra TT's are inline-6's and they produce way more torque from a twin-turbo setup as apposed to a single turbo setup.Quote »a small turbo for quick spool up and a larger turbo for some serious topend boost. [/quote]All twin-turbo setups require identical turbo's. Otherwise one will back-spool the other and will die within 1000 miles. And even with identically sized turbo's, they still tend to back-spool under higher boost levels.

The reason why twin turbo setups are desirable, is because you can run 30psi of boost, (if your block can handle it), and avoid engine&turbo-killing exhaust gas tempuratures, and the turbo's are still in their efficiency range.

The reason why 4-cylinder twin-turbo setups don't exist, is because a 2.0L engine does not have enough airflow to push two individual turbo's.

But have fun spending UBER money in R&D to make custom manifold/pipes and make it fit under the hood.

[crzycav86]

Supra TT's are inline-6's and they produce way more torque from a twin-turbo setup as apposed to a single turbo setup.All twin-turbo setups require identical turbo's. Otherwise one will back-spool the other and will die within 1000 miles. And even with identically sized turbo's, they still tend to back-spool under higher boost levels.

I think he's talking about sequential twin turbo.

Anyway, a twin turbo setup on 4-bangers is unrealistic. It will cost way too much money which won't be worth it.

[IvoryJ30t]

total waste of time, money, and a turbo. [on a four cylinder, that is]

[MadSideways]

Quote »I think he's talking about sequential twin turbo.[/quote] Yes, the torque increase comes from boosting sequentially. But sequential or non-sequential they still have to be identically matched turbos.

[hayato kazami]

I have a Option Mag. and its have a twin turbo SR20DET S14, running 2 HKS GT2530, with 800hp. I'll see if i scan that picture and post it up, but it is in Japanese....

unless you are looking for a very hugh power, otherwise i don't think twin turbo is a good idea for street car......

[Dori Dori]

The reason why twin turbo setups are desirable, is because you can run 30psi of boost, (if your block can handle it), and avoid engine&turbo-killing exhaust gas tempuratures, and the turbo's are still in their efficiency range.

You are backwards. Twin turbo setups cannot run very high boost levels and they create more heat at high boost levels. Consider that with a twin turbo setup, you are generally using smaller turbochargers which inherently create more heat at lower boost levels than larger single turbo setups and are way out of their efficiency range at higher boost levels. This is why in the JGTC, when they they used I6's that were originally twin turbo from the factory, they used large single turbo setups instead of twin...higher psi at higher rpm w/ greater effieciency and lower heat levels (probably also for less points of failure too).

The reason why 4-cylinder twin-turbo setups don't exist, is because a 2.0L engine does not have enough airflow to push two individual turbo's.

They do exist. Subaru Legacy B4. Twin turbo 2.0ltr.

[BHayes_S13Coupe]

Twin Turbo SR 1:

[BHayes_S13Coupe]

Twin Turbo SR 2:

[Onizuka]

Those are both show cars. Twin turbo is not practicle on the SR from a cost, function and ease of application point of veiw. But hey, if you have a wad of cash you cant stand having, spend away, it will certainly get you alot of "wows" when you open the hood.

Do a search in this secion for "twin turbo". You will find 10-15 threads with those exact pictures with people asking the same question, with people giving the same answer.

[MadSideways]

I don't see how two small turbo's pushing 15psi, (in their efficiency range), could put out more heat than a 30psi single turbo setup. Unless you go with a monster single turbo made for drag that won't spool until 5k rpm.

Earlier when I said 'dont exist', I meant as far as kits from reputable companies.. I'm sure just about everything exists...Hell, I've seen a couple triple-turbo supra's.

That second picture is a 2.2l stroked sr engine, which puts out more airflow than a 2.0l, which to me is still not quite the amount of liters you want, but hey whatever works.

[hayato kazami]

What about KA24DE? some guy from KA24DET form were talk about this "twin turbo" topic too

[DGA]

You should look into why a lot of people with twin turbo Supras and RX-7 go with a single turbo conversion. I think that would answer a lot of your questions.

[Hijacker]

They do exist. Subaru Legacy B4. Twin turbo 2.0ltr.

But if memory serves me correctly, the legacy has a flat 4 engine, so it would make sense to have two small turbos attached to each bank.

[Dori Dori]

But if memory serves me correctly, the legacy has a flat 4 engine, so it would make sense to have two small turbos attached to each bank.

Yes it does, as does every other Subaru currently in production. The argument was whether or not twin turbo 4's exist and if a 2.0ltr could create enough exhaust pressure to spool two turbos.

[extheflow]

twins don't have to be the same turbo..the RX-7 uses 2different turbos. not very practical on an SR though. as the displacement is small. maybe a couple k03 turbos with 2 runners getting their own turbo.but it's alot of custom work.i say go for it and post a dyno in a few years when it's done.

[IvoryJ30t]

yeah, but thats a sequential setup that would be extremely difficult to duplicate in your garage for an engine that such a setup was never designed for.

even if you pull it off, i doubt it would last very long.

[extheflow]

rx-7 is sequential but, 2 similiar turbos getting independent exhaust feed from seperate exhuast manifolds would not be sequential. thats what i would suggest.it would still be pretty tricky to do with piping and all.not to mention there's not a whole lotta room on that side of the car with the column being right there.

[Nurv]

I've never delved into the rotary engine as far as the turbo setups but rotaries are more than the typical heat engine as they produce alot of exhaust energy. Single turbo conversions are great for that app..Ive seen a twin turbo rps13 when I was in Adelaide, Austrailia last year checking out JPS' Drift R33 GTS-T 600whp. hehe. anyways. Is it worth it on inline motors? Yes, especially with the smooth power delivery. But an inline 4 such as a KA24 or SR20, no. Alot of work for not a huge pay off.The EJ20 & EJ25 boxer motors found in the Subaru Imprezza WRX and Forrester are availible to extent in twin turbo but different desingn, H design or boxer.

[compression]

what about this:Twin identical turbos. One getting exhaust from the #1 and #4 cylinders, the other getting exhaust from the #2 and #3 cylinders, exclusively, no crossover. Then you have one turbo (Lets call it turbo A) blowing into the intake of the next turbo(turbo B). Then from turbo B into the intercooler and into the engine. THe boost pressure from turbo A (say 8psi) adds to the boost pressure of turbo B (say another 8psi) for a total of 16psi in a quick spooling setup (you can double check that addition theory, but I am 99% sure it is correct). Whats wrong with that setup? Besides being a plumbing nightmare and costing a fortune. Just talking theory, I wouldnt ever consider building something like this.....

[IvoryJ30t]

that is one way to do it. it would work fine.

but why would you have a custom manifold made, get two turbos, and have a custom exhaust system made, when a single turbo will do the job just as good or better for less than half the price of a twin setup.

nobody is saying its impossible. its just a gross waste of money and unneeded complexity.

[IvoryJ30t]

twin turbos are beneficial when you have a V engine, or any engine with two cylinder banks.

one turbo for each cylinder bank. it simplifies having a huge header/crossover to feed one turbo. in that case, the twins are there to make the plumbing more manageable.

if you twin turbo an inline 4, your adding to the complexity, causing configuration headaches that you just dont need.

aside from building a show car, or just so you can say "look what i did" there is no gain to be had.

your spending more than double for an overly complex setup that in the end will be equal or inferior to a single turbo setup costing much less.

[VitaminT]

what about this:Twin identical turbos. One getting exhaust from the #1 and #4 cylinders, the other getting exhaust from the #2 and #3 cylinders, exclusively, no crossover. Then you have one turbo (Lets call it turbo A) blowing into the intake of the next turbo(turbo B). Then from turbo B into the intercooler and into the engine. THe boost pressure from turbo A (say 8psi) adds to the boost pressure of turbo B (say another 8psi) for a total of 16psi in a quick spooling setup (you can double check that addition theory, but I am 99% sure it is correct). Whats wrong with that setup? Besides being a plumbing nightmare and costing a fortune. Just talking theory, I wouldnt ever consider building something like this.....

I believe that when you run one into the other it does not simply add the boost. (i.e. 8psi+8psi=16psi). If I remember right the second turbo compounds the boost exponentially (sp?) so 8psi+8psi=24psi.

Can anyone else verify this?

[IvoryJ30t]

the output pressure is dependant on input pressure.turbos compress air on a relative scale.

lets say we have two turbos spinning at the same RPM.

the intake of one is from the output of the other.

[intake-turbo-turbo-IC-throttle]

anytime you look at a compressor map, the Y axis is pressure ratio.

lets say your turbos are operating at a 2:1 ratio.

its a nice day out, and the atmospheric pressure is 14.7psia.

if both turbos are operating at 2:1, the first turbo is going to output 30.4 psia [14.7 psig, or double atmosphere]. that 29.4 psia is fed to the second turbo, which is going to output 58.8 psia [44.1 psig].

see. if we were to have say, 5 turbos in series, all operating at 2:1,this would be the result-

14.7 psia- turbo1- 29.4 psia- turbo2- 58.8 psia- turbo3- 117.6 psia- turbo4- 235.2 psia- turbo5- 470.4 psia

470.4 psia is 455.7 psig.

see how it works. the output is relative to input.

it is something very difficult to do with a turbo since the wastegate is in control. to effectively do this, you would need two turbos on a common manifold with a common wastegate set to the final turbos output pressure.

this gets very complicated very quickly.

aq twin turbo setup on an inline 4 is just asking for trouble. your digging yourself a hole for no reason.

[IvoryJ30t]

in your example [8psi +8psi] 8 psi is roughly 1.5:1

the first turbo would be fed 14.7psia [atmosphere] and output 22.05 psia. that fed to the second turbo, it would output 33.075 psia.

33.075= 18.375 psig 18.3 psi would read on the boost gauge.

it seems exponential due to the fact that the turbo deals with absolute pressure, not gauge pressure.

you start to get into thermodynamics and gas laws.

properly engineering up a turbo setup like this doesnt happen in your backyard.

you cant just say "well, this looks like it should work" because it wont.

[IvoryJ30t]

that example is using the turbos in series.

if you connect the turbos in parallel, the boost does not multiply.

if you have two turbos making 14 psig, and you connect them in parallel, you still have 14 psig, but double the airflow.