open downpipe hurts my performance?

[Race Jace]

I still do not think it is an A/F ratio issue. gennerally if you lean your car out a little then you always pick up mph.... that is if you are not overly lean to begin with as dave mentioned.


Shane, that avatar is pretty flashy!

 

[SloGN]

I would say that by opening the dump you are causing a disruption in the flow of gases through the pipe and actually causing a little more back pressure. That is the only reason i could think that you could get a reduction in power by opening the dump.
the change in A/F ratio would not be significant enough to cause a 1 mph loss.

Jason i done some real world testing on this

here is my info

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.

 

[Race Jace]

very good info!!!

It should not make any difference checking it at the EGR or at the 02 sensor location.

Good work!

 

[SloGN]

very good info!!!

It should not make any difference checking it at the EGR or at the 02 sensor location.

Good work!

well when i researched it kenny duttweiller(sp) was checking backpressure there also.

i also think the backpressure would be the same in the egr port as the o2 location.

I'm wondering if a venturi effect will happen at the o2 port with the air rushing by the port. i guess the only way to truly know is try it out.

what i'm also wondering is if your 5" DP will make a sigafiagant difference on my current combo to the back pressure in the engine pre turbine

 

[UNGN]

How a full exhaust could possibly have less backpressure than an open dump at the drag strip:

As the exhaust is traveling rearward, the pipes are taking heat out of it, condensing it. This reduction in volume lowers the pressure in the tube, helping to draw the exhaust rearward.

As the exhaust heats up, this effect would be reduced.

A dump would not generate this effect.

 

[SloGN]

How a full exhaust could possibly have less backpressure than an open dump at the drag strip:

As the exhaust is traveling rearward, the pipes are taking heat out of it, condensing it. This reduction in volume lowers the pressure in the tube, helping to draw the exhaust rearward.

As the exhaust heats up, this effect would be reduced.

A dump would not generate this effect.

well the test that i conducted was at a friends shop located in greensboro that is a 25 mile drive for me there.

so the exhaust was about as hot as it could get for a 85 degree day with 75% humidty


i'm really thinking that opening the test pipe disrupts the lamiter flow in the pipe.

 

[vader87]

I had the same problem with my old setup. I opened the dump, the car "loaded up" at idle. Then leaned out at higher RPM. I changed to a TT chip and 60lbs. Motrons and the problems disappeared. It did have 42 injectors and a Red's Chip.

 

[bilt2run]

Maybe

IN my two GN's the open dumped wreaked havoc on the knock sensor and effectivly cut the balls off through the loss of timing. I recently purchased a T type with huge KR all the time, I switched to a new quiet exhaust from the open pipes the previous owner had installed and the car has zero KR ....and no, the pipes were not vibrating it was the resonance (tone) and volume of the exhaust.

 

[Under Pressure]

o2s

My car seems to run better (smoother at least) through the free flowing exhaust. It may just seem that way, however, because the open dp has a very coarse sound by nature. I dont have times to verify yet though.

Whats are your 02 counts or if you have a wideband your air to fuel ratio?The car will run alot leaner when you uncap it this is my .02 cents