Yes but this is all a balancing act. On the other end of the spectrum there are many turbos out there with too large of a compressor vs turbine (like 76/66) and that will result in the same problem, excessively high drive pressure.

That's why I think twins are better every time. For a given potential airflow you end up with faster response and less drive pressure compared to a single.

Agree about the balancing act, but the turbo you mention is hard to beat on a 5000 rpm v6. All caters to many variables. Testing testing testing.

IMO it's just a mismatched unit. I would rather the compressor and turbine be capable of similar power levels. So if I have 750hp worth of turbine give me a 66mm compressor instead of less response from a 76mm capable of 1000.

I would stick with a turbo that has compressor maps available, BW or Garrett. Your unlikely to find someone running a combo that will be similar, so trying to find a proven combination is not going to be GM LS easy.

Both BW and Garrett have programs, Match Bot , and they are very good. Make sure your data entered is accurate, and pay attention to where you are using the turbo in it's compressor map. I like the MatchBot because I can make changes to the formula to best make use of a combination.

I am running twin EFR 9180 turbo's with Tial 1.02 housings. Using MatchBot, this was the best compromise for staying in the efficient part of the compressor, spool time, and EMAP (back pressure in the manifold).

Makes sense @feets @TRENDZ

For those of us who are hobbyists vs hard core, you shouldn't discount the amount of fabbing and cutting. Twin T4's might be the best theoretically but be terribly difficult to package in a car that needs to maintain it's OEM inner fender wells and such for other reasons. A single might be easier to package for most cars with power brakes and power steering. A T6 is a BIG thing to fit as is a 5" downpipe. A single T4 turbo can be the easiest item to package and be successful for a hobbyist. Matching your cubic inches to a turbo size that you can package, e.g. feets' original beast may have been better served with a 383/400 making the same or better power more comfortably/economically.

I have a 383 in my Fury for a reason vs a 440 or stroker. I'm using a 5.7 in my Coronet for a reason - allowing me to more easily package appropriately sized turbos and still have the capability to make more power than I'll use/install safety equipment for.

For those reading who aren't intimately family with turbos...
Turbos are not free power.

In this world you don't get something for nothing. The same goes with boost.
Any real street car with a turbo will have more pressure in the exhaust than in the turbo. Compressing air takes work.

Oh, but it's exhaust gas you say. Your breath is exhaust gas. Ever notice you have to put a little effort into blowing up a balloon? Try blowing up a car tire to 20 psi. Think you'll get there by puffing on a valve stem?

The engine is experiencing the same issue. It has to work to build up that pressure. However, instead if a fixed container, it has to maintain that level of work until you get off the throttle.

Turbo lag? That means the engine hasn't worked hard enough to get the turbo up to speed.

Turbos can be very efficient but they aren't free.

I have not measured it, but I do have some information.

I only run a 2psi wastegate spring, and rely on the boost controller (on board air tank) pressure into the top side of the gate to make the boost. Basically it requires 1psi of gate pressure, to make 1psi of boost. If the backpressure was at 53psi, it would be blowing that 2psi gate spring open for sure. Also, the car does not like RPM regardless of boost pressure. Even at 10 or 15psi it doesn't like RPM (ET slows down if you shift it higher).

But in principal, I do agree any combo can benefit from lower backpressure. 100% agree with that. But it's not the end all, be all, of a combo.


I would think a S480 combo (80/88) at 850hp goal is a great choice for the original poster. 80mm compressor will make 850 easily, It will spool relatively quick, and the China Knock off versions can be had for $750 or so in billet wheel form. I can't see doubling the complexity and cost with Twins being worth it in a build like that.

Easy way to find out is to measure it. Probably 10 minutes worth of work if you are interested in finding out.

Twins aren't double the cost or complexity. Just depends on your goals.

Yes you can make almost any power goal with a single turbo. If at the same power level you want much faster response and the ability to hit peak boost/torque at a lower rpm on a street car, twins will make that happen.

[u][/u]I've driven Dizusters car on the street. It's hard to manage the "response" now. It doesnt need anymore. A 5 second burst gets you to where you dont need to be on the street. Racecar is a different story. We can always go faster.
Doug

Yes all preference. I feel single turbos are harder to manage as you can go wide open throttle and get a big thump of boost as it hits.

Twins can almost follow the accelerator pedal as far as response so easy to roll into it and maintain traction.

That and more so, just response during part throttle driving.

Agree. Changed over a customer car to twins from a single. Much more predictable and followed the throttle better. A bigger single gives that “2 stroke” feel of a power rush.

For sure, great analogy.