Turbo exhaust flow

[gusszgs]

Ok I have a question regarding exhaust flow and boost.

I run a TE 60 on a stock motor with just bolt on's. Last year at the track I ran approx 23-24 psi with the dump closed through Hooker CB 2.5" exhaust. The car was running low 12's high 11's. Then, I decided to open the dump and make a pass or two to see if it made any difference, and it didn't. No gains in mph or decrease in ET.
Toward the end of the year I was running the boost up a few lbs more to around 26-27psi THROUGH the exhaust running mid 11's. I'm just wondering if now, opening up the dump will net me any gains. Is there a point in boost where this my be beneficial to open the dump? Anyone pick up by opening the exhaust on a similar combo and how much boost?

 

[TurboTGuy]

Please tell me you have a Scan Master and are watching closely for knock.

 

[gusszgs]

oh ya........and PL

 

[Gene Van Horn]

How are you running 23 - 25 pounds of boost on a stock engine?

 

[achalmersman]

How are you running 23 - 25 pounds of boost on a stock engine?

I ran 36 at the track last time. 28 on the street for a year and a half

No trees were harmed in the sending of this message, however, a significant number of electrons were terribly inconvenienced.

 

[forcefed3.8's]

Doubtful that you will gain any power, but dumping it might help spool up.

 

[TurboTGuy]

I ran 36 at the track last time. 28 on the street for a year and a half

No trees were harmed in the sending of this message, however, a significant number of electrons were terribly inconvenienced.

On a stock motor? Fer reals?

 

[achalmersman]

On a stock motor? Fer reals?

Yea on 93/alky. And monitoring FP, AFR, and using a TT 6.1. 10.99 @ 122

Sorry didnt mean to hijack thread. I run open dump and always have. Even on the street.

No trees were harmed in the sending of this message, however, a significant number of electrons were terribly inconvenienced.

 

[gusszgs]

How are you running 23 - 25 pounds of boost on a stock engine?

I run Razor's alky control.......see sig

 

[dank GN]

I remember when I opened my.dump I gained 2 MPH on the big end

 

[gusszgs]

I remember when I opened my.dump I gained 2 MPH on the big end

dank, how much boost were you running?

 

[dank GN]

I believe I was right around 26-27

 

[gusszgs]

I believe I was right around 26-27

Thanks

 

[Nigel]

So here is a little food for thought.

Some of this reply is based on an understanding of compressible flow and some on reading Bison’s posts on turbochargers and the limits of the T-31 exhaust wheel.

I believe forcefed is correct in that opening the dump would help spool up, but once you reach full throttle at high boost, especially as the rpm’s increase, opening the dump on a good flowing exhaust will do nothing. My guess is that the 3” down pipe is probably more than you need at this point with a T31 exhaust wheel. The exhaust housing has a radial nozzle that has a small flow area, additionally the turbine wheel is partially a reaction wheel and takes an additional pressure drop. Once you start pushing the turbine close to it’s critical pressure ratio so it is close to, or at the point of choking, further reductions in downstream pressure will not show any improvement. The only way to get more flow through the turbine/restriction at that point is to increase up stream pressure, which means additional downstream exhaust flow area does nothing.

If you are not operating the turbine near the point of choking, and your downstream exhaust is a restriction, you will see an improvement by improving the exhaust flow. I have seen multiple posts by board members stating no improvement below 500 HP with a 3” down pipe, and with a 3” down pipe, no improvement up to 800 HP with a larger than 3” down pipe.

My personal experience running a TE-44 with a stock converter, is the dump does not help MPH, but has helped spool up on a stock elbow and 2.5" down pipe.

 

[blklt1z28]

My cutout was worth a solid 3mph on my setup. Stock motor, 30+ lbs, running 10.70's-10.80's.

The exhaust is a magnaflow 2.5" catback. Was surprised it was that much of a choke.

Running a bigger turbo now and I'm sure it's an even bigger difference.

I think at your level it won't be much but you're getting close to it being a restriction. IMO.

 

[Mr.Spool]

Ok I have a question regarding exhaust flow and boost.

I run a TE 60 on a stock motor with just bolt on's. Last year at the track I ran approx 23-24 psi with the dump closed through Hooker CB 2.5" exhaust. The car was running low 12's high 11's. Then, I decided to open the dump and make a pass or two to see if it made any difference, and it didn't. No gains in mph or decrease in ET.
Toward the end of the year I was running the boost up a few lbs more to around 26-27psi THROUGH the exhaust running mid 11's. I'm just wondering if now, opening up the dump will net me any gains. Is there a point in boost where this my be beneficial to open the dump? Anyone pick up by opening the exhaust on a similar combo and how much boost?

It depends on your ex and muffler setup,with a good ex and muffler setup you will see no gains except in the weight department if it's removed