B18B1LS1

iTrader: (12)

Is it normal to make "only" 1490 rwhp with twin 91's at 35 psi? Just curious on the rest of the combo I guess!

Jeffrey

engineermike

That kinda' surprises me that the backpressure is that high with those two huge turbo's. Usually, the bigger the turbo in relation to the engine, the lower the backpressure (see also Old Geezer's data). Maybe it's a huge engine or spinning really high rpm. . .

Mike

B18B1LS1

iTrader: (12)

Ha ha! That didnt take long! Its the only turbo vehicle I have running at the moment.

engineermike

Folks, keep in mind that the cold-side is just as influential on backpressure as the hot side. Restrictive piping, restrictive intercooler, small TB, small compressor, or even a small air filter will a) reduce boost in the intake plenum and b) make the turbine work extra hard to spin the compressor in an effort to reach wastegate setpoint. Both of these make the E/I ratio worse.

Mike

DrTurbo

iTrader: (3)

Very true....also the fuel used. Meth and Alky will have a definite effect on backpressure reading as well.

MADMAN

iTrader: (4)

No its not normal. After disassembling the motor we found we only had 7.3 to 1 compression and the cam selection was wrong. We are changing some stuff up to make it 9 to 1 and a new cam and we should see some changes.

MADMAN

iTrader: (4)

You need to come by and put your "engineer" eyes on it!!!!

engineermike

I'm afraid I'd get "turbo envy".

DrTurbo

iTrader: (3)

We plan to bring to the market a special "Blue Turbo pill" just for that. Turboagra

HydroStream6

iTrader: (16)

I assume this is measured after the turbo correct? Where would be the best place to check backpressure on a rear mounted setup?

DrTurbo

iTrader: (3)

BP should be measured after and before the turbo.

B18B1LS1

iTrader: (12)

Thats cool, I wasn't questioning you guys, just wondering what was up with it!

DeltaT

iTrader: (5)

How about 'Psiagra" instead?

Boost goes up and stays higher longer? Sign me up, but no SPAM!

Jim

Phil99vette

iTrader: (11)

Is there a general rule of thumb for exhaust sizing to get a back pressure ratio of 1:1?

DrTurbo

iTrader: (3)

We use 1.25 X turbine exducer.

Phil99vette

iTrader: (11)

So if the turbine exducer is 5" than you need something equal to ~6.25"?

DrTurbo

iTrader: (3)

Correct....of course thank goodness their is no turbo currently out yet that has a 5" exducer turbine....hehe

Fireball

iTrader: (21)

they would need one helluva v-band outlet too...that would become a restriction at that point since most thumpers use a std 5" setup...

Phil99vette

iTrader: (11)

I know, just using round numbers so for a turbo with a 4" exducer you would need a 5" Exhaust, would that number assume the wastegate is vented internally or externally? How would that change the calculation?

hellbents10

iTrader: (10)

Depends on how soon the gate pipe is coming into the down pipe. Certainly there is a difference though because of the extra exhaust gas in the down pipe.