I do not agree with this statement. Based on my experience and everything I've seen, turbo's are capable of Increasing fuel mileage.

The turbine wheel creates virtually no opposition to exhaust gas flow at cruising speeds. On my car my MAF is reading in the vicinity of only 25gm/sec of airflow through the motor while cruising, for comparison it goes to over 350gm/sec at full boost.
But at the same time the compressor wheel is helping feed the motor fresh air, making the motor work less hard to get it, resulting in less throttle to maintain speed.
I would like to hook a gauge to my exhaust (before the turbo) to measure back pressure.

My friend drove the exact same route on the freeway before and after installing a turbo on his truck. He gained 6mpg(!!!) and was only getting like 18 or something before the turbo. Both times were on cruise control going the same speed, running a 'there and back' route.

The turbo STS uses is a 60-1 with a TO4E compressor cover and a T4 turbine housing, it flows about 60lbs/min of air; enough to produce around 550-600hp.. The upgrades are 67mm, 70mm, and 76mm compressors, and can all be had in journal or ball bearing, and I believe comes with a 1 year warranty?

 

Any piston is going to hold these power levels if tuned well. The better the piston, the more forgiving it is. Like many others I run the high silocone content SRPs with no problems on 20psi.... if something happened in my fuel system they would break before a better piston.

Gas mileage shouldn't be affected much either way really. Even with my little bitty turbo its not spinning much at 1500ish rpms. If I get to 2 or above its making a good noise for sure. The exhaust and turbine housing are going to cause more restriction than the spinning wheel inside it.

 

Does any one have any pictures of how the STS kit mounts the turbo behind the car?

 

http://www.ststurbo.com/camaro_lt1

 

Yea I had looked at that, and I was curious about how the turbo was attached, if at all. I can see the air filter is attached via the driver side hanger and the exhaust tip I assume grabs the passenger hanger, but the turbo just hangs in between them?

 

Not really sure. These guys here added a a pretty simple bracket to help support the weight (seen about half way down)

http://www.exoticperformanceplus.com...Car.php?car=32

 

Has any one tried to fab up their own version of the STS kit?

 

I made all of my own pipes except the one that loops up and over the axle, and used a huge intercooler.

The majority of the weight of the turbo is held by the exhaust pipe that's welded to the stock exhaust. The turbo is also located by the intake pipe that loops up and over the axle, the air filter pipe, and for people using an exhaust 'tip", that has a hanger as well.

Here's some pics of my install.

 

So the turbo is supported mainly by the exhaust tube?

 

umm, well you can undo everything and it'll hang by the exhaust pipe, but it'll droop a couple of inches. So everything is really responsible for kind of "triangulating" it into place.

It's not really hard mounted though, it floats like an exhaust system should.
I just went out and layed under my car. I grabbed the turbo and can only wobble it about 1/4" or so in any direction.

 

Mike,

Dicussing this may be better served as a seperate thread so as not to hijack, but it certainly seems interesting. At steady cruise: I think what you are saying is that the compressor wheel is reducing pumping losses associated with the pistons pulling in air, but I'm not sure it is actually relavent. I don't doubt what your buddy was seeing, but could that be due to a different tune or other changes?

Regardless, I think we can agree that a large object placed inside of a volute is not going to flow as well as a straight pipe. Both the exhaust and intake have to flow through such. The exhaust is certainly being restricted as it passes through the turbine & housing. The real question is if the speed of the compressor - at cruise - is helping to reduce engine pumping loss, OR is its rotational speed slow enough at cruise to also cause an intake restriction?

At steady cruise there is XX net power required from the motor which remains the same for turbo, blown, NA. So which of the three systems has the least total-loss at low flow levels? Which requires the lowest airflow (and fuel) to produce that XX net power?

During even light acceleration, additional exhaust energy is spent accelerating the wheel from rest.

At WOT, you get a significant pressure rise across the comp. which increases intake flow, engine VE, and power but at higher specific fuel consumption than NA.

In summary, my opinion is that a turbo will reduce mileage under all three of these scenarios (cruise - when at same A/F ratio, acceleration & WOT) when compared to the exact same motor (save for intake/exhaust changes) before adding the turbo.

Thanks,
Scott.

 

The tune wasn't changed, and it never went near boost during the test. Keep in mind this was a pre-conceived test, not just a 'hey looking back, I got better mileage" kinda thing.

This is a hard scenerio to speculate on, I can see it either way, I understand exactly what you mean. Sure the turbine housing creates quite a restriction on the diameter of the exhaust pipe, but at cruising airflow rates I think the restriction would be negligible. My friends vehicle also has a rear-mounted turbo, which replaces the muffler, so muffler backpressure couldn't be a factor in any way. So when his turbo was off he even had very little backpressure.

Image this... Say we have a syringe, that when pulled back rapidly (as we all know) requires quite some effort. Liken this to the piston (pumping losses).
Now if you repeat this while -slighlty- blowing into the syringe, it will be easier as it'll create less vacuum. Overcoming the pumping losses will net more power, and in an effort to maintain the same cruising speed, will require less throttle. Less throttle decreases engine load and requires less fuel, hence an increase in fuel economy.

Now this isn't a perfect analogy. I'm sure it has flaws, but it portrays the basic principle as I see it, and of course I may be wrong.

I'm going to tap a pressure gauge into my exhaust so I can monitor back pressure during all driving conditions, as I'm now very interested in gathering some data.
I may even remove my turbo since it only takes 15 minutes, just to test this myself (and of course have the intake suck air from up front again).

 

LOL well this a good read guys, I don't mind the hijack its good stuff!

 

haha sorry

 

I think measuring exhaust pressure would be a good idea to better understand how well a particular system performs. I was almost thinking of mounting a boost gauge in-car that could be swapped from a pre-turbine fitting to a post-turbine fitting.

Nice car Mike!

-Scott.