Guess my exhaust was restrictive.

[gunslinger]

I installed a Hooker cat back system last week, and finally had a chance to mash the throttle yesterday.

The system sounds great. I had to remove 10 inches of the test pipe, and had to tweak the shit out of the system to get anything to fit, but after a couple of hours to get it perfect, I gained 5lb of boost.

The system I removed was an exhaust shop built system with ATR pitbull mufflers. Granted, the old system was pretty bad, but I was shocked to see that much of an increase in flow. It will be interesting to see what it does for my ET.

 

[EVIL]

So all you did was change the exhaust and you gained 5lbs of boost?

Sounds to me like your system is more restrictive now than it was before.

Am I seeing this correctly? Boost should drop with a freer flowing exhaust?

D

 

[novaderrik]

my car spooled up faster and seemed to have more power after i put the Flowmaster crossflow muffler on my car... i didn't even have a muffler before- the stocker was blown out when i got the car so i just sawzall'ed the pipes off above the rear end and ran it with no muffler for the first year i had it.. the second year is when i got the Flowmaster kit and just slid it into the existing pipes... common knowledge on teh internets told me my car would spool up slower and slow down due to the Flowmaster sucking so bad, but the exact opposite happened..

 

[Chuck Leeper]

Exactly what I was thinking^^^^^^

 

[gunslinger]

So all you did was change the exhaust and you gained 5lbs of boost?

Sounds to me like your system is more restrictive now than it was before.

Am I seeing this correctly? Boost should drop with a freer flowing exhaust?

D

Maybe...
I was under the impression that if the exhaust system is moving more air, the turbo will spool slower, but will move more air.
The only thing I changed was the exhaust from the downpipe back. Maybe my boost controller is flaky? I was running 15lb boost with the alky system off because of some tune issues that I was having. When I got on it yesterday, I saw a consistent 19-20psi. I started getting some knock, so I turned the alky system back on, and the boost stayed at 20psi.

 

[Pittsburghkid]

What are you doing with the pit bull mufflers?

 

[TT/Ameasap]

Yes. You gain boost with free flowing exhaust. How do we still have these discussions? Remove the 30 freaking stickies in each section and put up a solid list of information for these guys. Flow master has been proven over and over to restrict turbo cars with the baffle design. Our cars need through design muffelers.

 

[gunslinger]

What are you doing with the pit bull mufflers?

They were rusted through. I junked them.

 

[Pittsburghkid]

They were rusted through. I junked them.

I thought they were stainless?

 

[gunslinger]

I thought they were stainless?

They may have been. They rotted at the rear seam where water would have collected.

 

[1KWIKSIX]

I thought they were stainless?

ATR offered their Pit Bull Mufflers in both Stainless Steel & Aluminumized Steel. I had a pair of the Aluminumized Steels & sold them when I found a NOS set of Stainless for sale years ago.

dave

 

[Pronto]

V8Killer (Al) had a similar experience with his GN when he switched from a Flowmaster exhaust to the ATR pitbull SS system. Gained more boost and dropped .5 seconds with no other changes in car. I'm running the Hooker exhaust and don't see it as a restriction.

 

[gunslinger]

V8Killer (Al) had a similar experience with his GN when he switched from a Flowmaster exhaust to the ATR pitbull SS system. Gained more boost and dropped .5 seconds with no other changes in car. I'm running the Hooker exhaust and don't see it as a restriction.

Do you think he picked up the extra .5 because of the extra boost, or because of the extra exhaust flow?

 

[Pronto]

I would say the extra boost but he wasn't getting that boost with the old exhaust so I would conclude the restrictions held back the car from better performance.

Any progress with the O2 issues?

 

[Mike T]

Excellent write up on this subject.
http://www.tercelreference.com/tercel_info/turbo_exhaust_theory/turbo_exhaust_theory.html

 

[gunslinger]

Any progress with the O2 issues?

Since I dropped the fuel pressure, the wideband is reading correctly, and the car is running much better, so I'm tuning off of that. The narrowband is still reading really lean (.550s at 15lb) at WOT, but I'm getting no knock. I WILL get to the bottom of it, it's just got me stumped right now.

 

[Pronto]

Excellent write up on this subject.
http://www.tercelreference.com/tercel_info/turbo_exhaust_theory/turbo_exhaust_theory.html

Interesting information. From his numbers our 3" downpipes are on the verge of being restrictive for 11 sec cars. It seems we should be 3.5" or more. A dual 2.5" looks like it would not be a restriction though. Wonder if anyone ever made a 4" downpipe and single out. It would be loud for sure but no backpressure.

 

[mgmshar]

If you are running the stock boost control solenoid (i.e. no feedback control), and you install a freer flowing exhaust, your boost will increase. Lower back pressure behind the turbine equals more work through the turbine, and the amount of air bleed off by the solenoid before reaching the actuator is the same. I personally experienced this when I upgraded from stock to ATR system many years ago.

If you run mechanical boost control like RJC (check valve in the line going to the actuator), your boost will not change significantly. The check valve will open and close at the same boost pressure regardless of what is happening in the turbine. This is poor man's boost control.
If you run a feedback type boost control system like MAFTPRO where a MAP sensor provides feedback to control boost, your boost will not change significantly. The electronic boost controller will control the actuator to a given boost pressure regardless of what is happening in the turbine.

The key here is that the stock system has no provision to feedback boost pressure to the ECU. It is a dumb system, it has no idea what boost you are running. It just sends a signal to the boost control solenoid that is only dependent on RPM and gear. If you lower the back pressure behind the turbine, it will convert more exhaust energy to work, and boost will increase.

Clear as mud?


Posted from the TurboBuick.Com mobile app

 

[Pronto]

That's a good indicator then that the new system is less restrictive.

 

[Mike T]

Interesting information. From his numbers our 3" downpipes are on the verge of being restrictive for 11 sec cars. It seems we should be 3.5" or more. A dual 2.5" looks like it would not be a restriction though. Wonder if anyone ever made a 4" downpipe and single out. It would be loud for sure but no backpressure.

Your suggested set up would seem to be ideal according to his write up except for his suggestion of the slight 12 degree flare after the turbine wheel.