turbo question. HELPPP

okay, is it true, that you will get better acceleration off the line if your running a single turbo opposed to running a twin turbo, because a tt takes longer to spool up? i was discussing this with a friend and i thought id bring it up here to see if that is true.

Hmmm... it's debatable. Personally, I think singles spool up faster.

so there is no deffiniate answer?

twins spool up faster actually, because they are smaller.
the only thing that will give you better acceleration I beleive is more boost.
so if you have a twin setup that makes more overall boost than a single, you'll have more power, and if they are individually smaller than the single, they will spool faster.

Smaller turbos have lower inertia, but in this case, the turbos in a twin setup have to run on half the amount of exhaust gas.

that depends on the engine type.
on an inline, yes.
on a V setup, no, they will each have equal exhaust. ex. a V8 twin setup will each get 4 cyl worth of exhaust, but an inline 4 single turbo will have 4 cyl of exhaust too.
granted, thi depends on the size of the engine as well.
It's complicated, but to put it simply, the twin setup will spool faster.
I don't know of any twin turbo inline 4 setups.

What are you talking about? I was mentioning the difference between single/twin turbo setups. Why would you think I would talking about usage on different engines?

well, on a dual exhaust V8, how would a single turbo get all the exhast from the engine?
That's why I thought that a twin setup would be good, one for each header.
sorry.

You run the turbo off the merge pipe.

Yes. Although it's not very practical - sorry, as practical as one turbine per bank.

Right. But you could run a massive turbo (T88 for example) with lots of boost and get almost instantaneous response.

Or go even bigger and get the biggest turbo I have heard of the street, the T-105, and just go all balls out. You may get some lag with that, but really, how much more off the line power do you need with a V8? And after you get traction and the turbo spools, you are gone.

Instantaneous response from a T88, even hooked up to a V8, is a bit of stretch.

Ok. But there sure won't be ahrdly any lag at tall though. Considering that Supra's run T88's and get full boost at 4700 RPM on a 3.0L engine. Now with a 5.7L engine, that would roughly half the spool time so full boost would be around 2300. Your right, instantaneous full boost is wrong, but that turbo will begine to spool up as soon as you press the gas.

How do you figure turbo lag is linearly related to engine displacement?

exhaust volume is increased linearly with displacement.

Not always. There are many factors that affect exhaust flow, especially headwork.

And even so, volume isn't the only thing that drives turbines.

when the engine dosen't have any load why dosen't the turbo produce boost? you still have the exhaust gases pushing against the turbine.

Yes, but the gases flowing thru the turbine do not speed up the compressor wheel enough to get more pressure than the ambient air pressure.

when the engine dosen't have any load why dosen't the turbo produce boost? you still have the exhaust gases pushing against the turbine.
The spooling of the turbo depends on the temperature of the exhaust gases and the frequency of the exhaust pulses. In short, full throttle spools up fastest.

It depends, whether the twin turbos are sequential or parallel. Usually parallel twin turbo setup uses 2 turbos of the same size and spoolled at the same time. Where sequential twin turbo have 2 turbos that are different in size. A smaller turbo is spool first and the bigger turbo kicks in at a later rpm.

A twinturbo setup will not spool-up faster, it will however have a lower boost threshold but it will also have reduced peak power.

This is so since two turbochargers will run with half the exhaust energy, with inertia proportional to the square and the flow proportional to the cube, which means that the lag can stay the same. Since in general one large turbocharger is more efficient than two smaller ones power will be greater from the single one.

Turbine power, which is needed to produce boost and overcome the inertia of the turbine/compressor assembly is defined by the enthaply change of the turbine (temperature*Cv or Cp) multiplied with the massflow where the maximum temperatures are inlet temperature and ambient temperature (this is why a higher inlet temperature is better).

There are twin turbo inline four engines, even twin turbo inline twin engines.