smokeshow

iTrader: (16)

I figured since that last thread got a bit heated when the debate had nothing to do with the OP's question, we could bring it to a thread just for turbo theory

The main argument before was whether or not a turbocharger can assist the engine in efficiency or power-making ability out of boost to help mileage. I believe a lot of the confusion came from not understanding how a turbo behaves differently during part throttle vs wide-open throttle.

If anyone wants to chime in with their thoughts about turbo power capability with T4 vs T6 exhaust housings, please do. That's also up for debate.

kostelacd69

iTrader: (4)

I was reading along in the last one and justed wanted to say somethin. My brother (cheap ***) has recently turboed his honda (b18c LS) and he calls and tells me that fuel milage went from 23 to 35mpg. He just added the turbo. He checked 3 or 4 times and kept getting that number. When I was home on my break we went to the track with mine and his. Well he made 3 runs and the car no longer runs. Took it home took it apart and found all 4 pistons are melted. We all know why that happen. All Im getting at is it has alot to do with the tune. Crusie or WOT. When I had a 5.3 vs 5.3 with the turbo I lost 2 mpg on the freeway with the same loads (A/C ect).

cjg454ss

iTrader: (27)

no debate really, a T4 housing is for kids(j/k). a t6 housing has much more volume flow than a T4, i ran a pt88mm t4 on a 365cu ls motor, back pressure at 23psi was 50-60psi. that means that to get 23 psi in the motor you have to push out 50psi of exhaust. my setup now has a t6 91mm on a 418cu. backpressure is 25-30psi at 20psi.

t4 turbos are ok for low hp builds(800rwhp). also my t4 88mm would lock up from the bearing seizing due to the back pressure.

just for comparison my pt88mm 365cu made 1000hp at 22-24psi(maxed out the turbo) and my 418cu 91mm makes 1000hp on 10psi of boost. i have been as high as 26psi so far.


i had a supercharged corvette, it picked up 2-3mpg
my supercharged srt8 jeep picked up 1-2mpg.... but i do all my own tuning

tarinitup

iTrader: (11)

00z71 gained over 100rwhp going from 76mm t4 to 91mm t6 at same boost level. On a sidenote I need one of you 1000 hp turbo guys to max out my setup.

cjg454ss

iTrader: (27)

was your spool up any slower, i noticed on mine the t6 seemed harder to spool, my t4 was very quick but also was half the size. are you running an S91 BW airwerks turbo on your truck?

op- it will increase efficiency. if you can cram more air in and do more work at a lower rpm than you have gained efficiency.

http://www.youtube.com/watch?v=-x0GXq5K0No

kalikid06

iTrader: (6)

Speaking from experience here. I went from about 19 MPG to about 21 MPG after I put my turbo on. I base this off the same route, driving conditions(just cruising down the highway at about 75MPH), and calculations.

tarinitup

iTrader: (11)

I have always had t6 but I did drive the set up I reffered to before and after. The t4 was instant boost whereas the big turbo let's you control it with throttle position. It has a bit more lag but moves nicely out of boost and never stops pulling under boost where the t4 flatlined.

00Z71

iTrader: (2)

I would never go back to a t-4.. lol
I actually had a TC78 T-4 setup... boost was to easy and came in hard and instant, then choked up top.
My new set up has a Garret GT-91 T-6 with 1.08 exh housing..
Its laggy compared to what I had (instant) But in my opinion its perfect, let your right foot control it and it just keeps pulling up top!

TURBHOE

iTrader: (4)

I think the turbo increases efficiency. My mpg has been basically unchanged over the years from non turbo to turbo. But I had a very good tune before the turbo. But as far as the engine doing work it comes with great ease now. Cruising through the hills I no longer have to down shift or unlock the tcc. It's not often I even have to go about 33% throttle. I think just because there is no boost shown on the boost gauge doesn't mean the turbo isn't at work.


I missed the other thread though.

smokeshow

iTrader: (16)

That's what I like to hear, makes me glad I went with a T6 setup

What sort of efficiency are you referring to?

That's important to note too; changes to the tune when adding a turbo will have an effect on mileage as well.

There is a fine line here though, and that's the point where different loads on the engine will produce the same fuel efficiency. For example consider your Tahoe pulling a 5000lb trailer up a hill. On a smaller grade of incline, you can keep it in OD with a locked converter and creep into boost a bit to maintain speed. But as the grade increases, there will be a point where its no longer more efficient to use boost in a high gear. At that point it is wiser to downshift a gear to create less load on the engine because of the transmission's mechanical advantage, and build less boost in the process. If the grade (simulated load) is high enough, the engine will be more fuel efficient at a higher RPM/lower boost level.