SPRAYED 01

iTrader: (22)

Just wondering if anyone has done their own testing of back pressure.
If so post up a quick review of your setup and boost pressure #s along with backpressure #s.

Thanks
Alex

Rusted40

350 SBC with two .81A/R p-trim t-64s into 3" dynomax bullets
15 pounds at the compressor, is 20 in the exhaust.
I'm sure backpressure/boost ratio would worsen as boost goes up.
I use two boost gauges with recall to check pressure in different places.

1:1 is ideal. anything past 2:1 = effeciency loss.

SPRAYED 01

iTrader: (22)

Thanks anyone else.

engineermike

I really wish more people would do this simple exercise and post results. It's a very good way to determine the true efficiency of a turbo system.

My basics: 388 LT1, AFR 210 heads, LT4 intake, 224/236-114 cam, T-76GTS (3" downpipe, 3.5" exhaust), Bell water/air intercooler.

With a 3.5" Hooker Aerochamber muffler, it made 680 rwhp at 21 psi boost and 48 psi backpressure.

With a 3.5" Magnaflow muffler, it made 695 rwhp at 17 psi boost and 34 psi backpressure. Set up like this, it ran 9.92 at 146 mph at full street weight.

I believe someone dyno'd a T76GTS versus an ST80 and posted the backpressure for those also.

Mike

engineermike

Found it:

"76GTS at 20 psi did 771rwhp with 42psi backpressure.

ST80 at 20 psi is 882rwhp with 37psi backpressure. "

whiteghost

iTrader: (2)

What is the best way to measure back-pressure? I'm guessing a fitting and some stainless line connected to a boost gauge? Will the high temps hurt a normal boost gauge?

engineermike

90% of the line and the boost gauge do not see the high temperatures. You have to have flow in order to carry the heat to the gauge and, since it's closed-ended, there is no flow. It's like putting a garden hose end in a fire. One end and most of the hose never gets hot.

You do, however, have to isolate the hot end from exhaust heat. I simply use a 6" piece of 1/8" pipe, then adapt to the small plastic tubing. The 6" piece of pipe isolates the tubing from the heat.

Mike

SPRAYED 01

iTrader: (22)

I really want to test mine also. I just ordered the new tc78mm from drturbo so im hoping that lowers my back pressure compared to the pte67mm. Oh ya and hopfully another 100hp or so.

DrTurbo

iTrader: (3)

The TC78 is a DEFINITE improvement over that PTE67.

Photochop

iTrader: (74)

Interesting read. Wish there was an easier way for me to route my downpipe...it snakes thru the stock k-member theres not much room for more than a 3"...guess I'll step it up to a 4" pipe after it clears the firewall and run a cutout or a 4" straight thru muffler turned down at the axle to help reduce the backpressure the closest I can.

Websy21

iTrader: (34)

I too am using an electric cutout just after the dp from the k member on 3'' pipe

Old Geezer

iTrader: (3)

26# boost, and 21# back psi, dump open. Closed, the BP went up 2 psi. 3" DP, and Dynomax muffs w/ 2.75" tailpipes out the back.
But, this is on a PT74GTQ, on a v-sicks Buick.. Only made 840 FWHP, 830 TQ...
The BP gauge was hooked at the base of the turbo, using a 3' length of copper tubing as a heat sink, then 2' of hose.

Websy21

iTrader: (34)

Do you know the difference in power b/w the open and closed cutout that had that 2psi increase of back pressure?

Old Geezer

iTrader: (3)

We saw a 3HP difference in open vs closed dump. About all it made was noise! We saw no 1/4 mi performance differences, either.

MADMAN

iTrader: (4)

On our twin turbo mustang is made 35 lbs of boost and 48 lbs of back pressure at 1490 rwhp. This was on twin 91mm with true 4" exhaust dumping 4 ft from the turbos.

MIGHTYMOUSE

iTrader: (59)

only time i ever checked mine it was 25# exhaust on 17# boost

364ci, pte-88 with 3.5" downpipe and 4" bullet muffler at the time

Zombie

iTrader: (2)

Checked mine several setups ago with 3" DP T76 R trim exhaust wheel .81 a/r, boost was 15psi back pressure was 45psi. Haven't measured it since but trap speed went up about 3mph (130 to 133)with the swap to a 4" DP.

Websy21

iTrader: (34)

Holy ****, 3:1 ratio can't be good but your track times concurr

B18B1LS1

iTrader: (12)

At 55 psi of boost I'm getting 57-58 psi of back pressure.

DrTurbo

iTrader: (3)

Diesel doesn't apply here....