gains with exhaust cutout on low 10second cars?

[1985GN]

has anyone seen a gain with an exhaust cutout on something going in the low 10's?? im running a 3" atr single shot at the moment and was contemplating going to a cutout for making passes...anyone gain anything on a car going low 10's?? thanks

 

[nordy racer]

has anyone seen a gain with an exhaust cutout on something going in the low 10's?? im running a 3" atr single shot at the moment and was contemplating going to a cutout for making passes...anyone gain anything on a car going low 10's?? thanks

YEP.. still picked up about 2mph with it open.. not the big difference like when the car was stock but it's still a gain...

 

[VadersV6]

Ive seen posts made by people claiming that they had a greater gain with a decent catback than a dump. Is this pretty common? Im still running a totally stock exhaust with some no name cat converter thats smaller than stock (real hack job..flanges cut off so Im screwed)...I was wondering if it would be a waste of time doing a full catback when I could just go with a decent DP and a dump with electric cutout. What kind of gain have people seen going from a stock DP/cat and catback to open dump and aftermarket DP? Sure, you gain a bunch of boost which gives you a gain, but I dont plan on running around with 5-6 more psi. Whats the gain, say 20psi stock exhaust and DP to 20psi aftermarket DP and dump?

 

[andy999]

has anyone seen a gain with an exhaust cutout on something going in the low 10's?? im running a 3" atr single shot at the moment and was contemplating going to a cutout for making passes...anyone gain anything on a car going low 10's?? thanks

Its worth a gain i pick up about 2-3 lbs of boost with it open.

 

[Turbo1dr]

It's really simple to check the back pressure in the exhaust. Just run a vacuum line to a pressure port just after the downpipe. Then connect that to a second boost gauge and do a WOT pass. If it reads pressure then the closed exhaust is restrictive.

 

[ESP Products]

What about ET?

 

[bison]

Its worth a gain i pick up about 2-3 lbs of boost with it open.

Yes. 2 years ago one of my friends melted an engine after i maxed out his 50lb injectors and dual alky nozzels. It was at 24.5psi and out of fuel through the muffs. He opened the exhaust and it went to 26.5psi in 3rd and he promptly melted a piston. This was with an ATR 3". Car was going 10.90's at 126+mph before the meltdown.

 

[1985GN]

im bringing this topic back up cause i know most of you have gained some from this mod but how about same boost levels open vs closed was there a gain or was the gain form the increase in boost? thanks guys

 

[Adam Connell]

on my stock DP with a stock exhaust I gain 2-3lbs of boost with mine open... I have a 2.5in dump to match my 2.5in stock DP. You can get the dump from Jegs for 35$, and since your exhaust is chopped up like mine was then just have you exhaust shop hack it into place before the cat... Now, when I put my cap on my dump last friday I noticed the car felt peppier on the low end for around town driving. I figure this is due to the back pressure creating torque.

Now just because you gain 2-3lbs does not mean you cannot adjust your controller or WG so that you can run safe boost levels... the gain in boost really is not a gain because your goal is to run a safe boost level with whatever setup you are using... if you run 16lbs with the cap on you want to run 16lbs with the cap off...

I really did not notice that huge of a mph increase now that I think about it... then again I change a lot in my setup and picked up 1.1 seconds since installing it and a lot of other parts... I was running the same boost levels.

NOW, if you install a 3in DP then Im pretty sure you would see a bigger gain with a dump... Also Im only running 16-17psi with a smallish turbo. If I turned it up to 20-22psi Im sure I would see a bigger gain because Im flowing a lot more air... next time I go to the track I will run a closed and open dump with the same boost levels and see what I get...

damn I said now a lot in this post...

 

[ESP Products]

Look most performance "gains" on these cars, it's contingent upon your current set-up. The more restrictive the exhaust the more gain you'll have. You gain may not always be MPH, but throttle response and/or less turbo lag. In theory, if you flow more air, you must match it with more fuel - A/F ratio. If you increase your flow and don't tune for it, you may loose performance. Everyone has heard someone complain about running poorly with an open exhaust; you need to tune for it.

Merry Christmas to all ...

 

[Scott Atk]

my experience

I always opened my dump. In March, I ran in a heads up street legal event where I had to keep it closed. I ran my best E.T. ever through the exhaust. So now I leave it closed. My exhaust is pretty much straight through. 3" single through DYNOMAX race muffler. Now I'm wondering if using a dump pipe closed is adding turbulence by the exhaust bouncing off the closed dump??

 

[Turbo1dr]

I always opened my dump. In March, I ran in a heads up street legal event where I had to keep it closed. I ran my best E.T. ever through the exhaust. So now I leave it closed. My exhaust is pretty much straight through. 3" single through DYNOMAX race muffler. Now I'm wondering if using a dump pipe closed is adding turbulence by the exhaust bouncing off the closed dump??

You are not the only one that has run faster through a closed exhaust.

 

[1985GN]

hmmm now you guys have me thinking if its even worth it since im running a
3" single shot....

 

[bird]

i havent tried open exhaust. im running the 3" dual atr and 3' atr dp. i doubt i would have seen any gains.

 

[SloGN]

It's really simple to check the back pressure in the exhaust. Just run a vacuum line to a pressure port just after the downpipe. Then connect that to a second boost gauge and do a WOT pass. If it reads pressure then the closed exhaust is restrictive.

vernon here is what i came up with when i checked my backpressure @the egr port a few months ago


Mods to the engine/exhaust/turbo is in the sig. well here goes.


All the pressure reading were taken from the EGR port.

RUN 1 20 psi of boost in third gear i showed a BP of 33 psi made two runs to verify consistesy. this was thru the exhaust

RUN2 Next i proceeded to open the collecter on my test pipe. with the dump open @ the same 20 psi the BP was @ 36 psi Again to runs were made to show consistesy.

RUN3 i took the Test pipe competely off the car and ran just a open DWN pipe the boost went to 22 psi with 35 Psi of BP

Run4 i corrected the boost back down to 20 psi with the Dwn pipe and got 31.5 Psi of BP.

So from what i have noticed on my car just opening the dump on my test pipe yeilds no gains at all.


next. i'm going to check the Back pressure @ the o2 sensor location to see if there is an actual diffrence in pressure there than at the egr port. i doubt there will be any difference since the EGR port is tied in witht he rest of the exhaust system pre-turbo.

so 31.5psi/20 psi= 1.57 ratio just a open dwn pipe.

20psi/33psi= 1.65 ratio thru the exhaust

20psi/36psi= 1.8 ratio with the dump open on the test pipe.


The only thing that i can think of why the Backpressure went up by just opening the test pipe is that it is creating turbulence in the pipe by the air having turn and exit the dump collector. thus having to have more pressure to get the air to flow out or maybe not more pressure bu more engery to push the air out even tho it's a shorter way out.


The only thing that i can see that would make the Backpressure lower by opening the dump collector is the fact that the car has a real restrictive exhaust.


how this makes for some interesting info guys.

 

[SloGN]

Look most performance "gains" on these cars, it's contingent upon your current set-up. The more restrictive the exhaust the more gain you'll have. You gain may not always be MPH, but throttle response and/or less turbo lag. In theory, if you flow more air, you must match it with more fuel - A/F ratio. If you increase your flow and don't tune for it, you may loose performance. Everyone has heard someone complain about running poorly with an open exhaust; you need to tune for it.

Merry Christmas to all ...

not if you use a fuel system that can comepensate for the extra air flow. (fast,big stuff 3 ,accel)

YEAH we know the stock crap can't do that