closed dump vs open dump tuning

[pwr6kid]

Last Friday I went down to the track. After 3 passes and some tuning the car was running 11.7. A buddy mentioned that my dump plate was still on, so I took it off and logged a pass with no other changes. Went 11.6, but the wide band showed 12.1 the previous pass was 11.1. The O2 sensor logs look the same on both passes, didn’t have any knock. The sensor is 24” upstream from the dump. I verified fuel pressure isn’t dropping off, 2 5/8” gauge on the hood. I did add some fuel on my final pass 128 to 134 and the car picked up a little (.1 and .5 mph) Wide band was at 11.8 with the dump open. I was running 93 and alky. The passes were within 15 minutes of each other.

Has any one ever seen this kind of change from just opening up the dump?
Should I tune the car dump open or closed?
Any suggestions on my tune up, or if you need any more info just ask.

What the car has:
A street turbo tweak chip with a base timing of 20/18 for 17 psi[I did bump the timing up to 23/21 in before I mad these two passes
Lc-1 wideband
26” et drags
3.5 gn1r down pipe 2.5 hooker cat back
Te-44
Stock heads with lt-1 valve springs
218/218 Erson cam
3200 pro-torque converter
Maf translator
Here are the two logs
ATTACH=CONFIG]147748[/ATTACH]

 

[meanchicken]

Subscribing...but
Some will disagree most likely but IMHO...If you tune properly for a closed dump....you can go just as fast as you would with an open dump...and any difference could be made up with a better 60' approach...

Personally, I wouldn't open my dump without adding some fuel at the same time because it will lean you out if you don't, especially at the top of the track....you're removing a restriction and moving more air...so more fuel is needed to compensate...

Open dump definitley sounds cooler tho....

 

[garyk1970]

i gain about three psi with dump open..maybe youre running leaner because of the extra boost.

 

[Chuck Leeper]

Depends on the quality of the exh system to begin with.
Poor design, then bypass it, and the car should pick up some.
My dynos b2b, showed 3RWHP pick up open vs closed...Mandrel bent 2.75" pipes w/ Dynomax ultras..Out behind the axle.

 

[jasjamz]

On my Pypes system it loss 4psi when I capped it up. 62mm Turbo. I can't seem to make more than 21psi capped. I will incapable it for the ride home from work and see if it allows me to crank it past that. It will use more fuel uncapped. I records this on my old timeslips when the scanmaster was my only tuning device. Made back to back runs with no other changes and it got leaner even at lower boost levels.

 

[Sweet6]

On my TTA with a single 3" pick up about 3lbs of boost opening the dump. It uses about 10% more fuel. It picks up 3MPH or so with it open.

 

[pwr6kid]

The boost was at 25-25.5 on the cap pass and 25.3-25.7 with out it. I would under stand if it was 1-2 or more psi but with in a half pound did it make that big of a difference?

O2 with the cap were 740 and 720 with out it. So the car did lean out some, but a full point on the wide band?

I understand that the narrow band isn’t great, but can be useful since its pre turbo and the possibility of clean air getting that far up under boost is slim, in this case where the car goes from 11.1 to 12.1.

I’m wondering if fresh air is getting into the dump since my sensor is only 24” before the dump pipe. Has and one made passes and noticed a difference with out any other changes like this?

And i will be adding more fuel to the car since it started to pick up more later in the night with just that chance.

 

[Sweet6]

I would say could be a wideband issue. I had a problem with mine that was just before the open dump. It read a lot leaner than it was. If your boost did not go up then nothing should have changed much.

 

[GNICETRY]

I thought that the general consensus was to tune with the dump open. If you run a little rich with it closed that is better than running lean with it open.

 

[Razor]

The boost was at 25-25.5 on the cap pass and 25.3-25.7 with out it. I would under stand if it was 1-2 or more psi but with in a half pound did it make that big of a difference?

O2 with the cap were 740 and 720 with out it. So the car did lean out some, but a full point on the wide band?

I understand that the narrow band isn’t great, but can be useful since its pre turbo and the possibility of clean air getting that far up under boost is slim, in this case where the car goes from 11.1 to 12.1.

I’m wondering if fresh air is getting into the dump since my sensor is only 24” before the dump pipe. Has and one made passes and noticed a difference with out any other changes like this?

And i will be adding more fuel to the car since it started to pick up more later in the night with just that chance.

These O2 numbers are low. Especially if your running meth of any kind which you didnt specify. If your on Race Gas then you can get away with those O2's

 

[pwr6kid]

Razor I did forget to mention I had your kit in my parts list.

Ok, so the car is running lean, I will fatten it up this weekend when the rain stops and do some more back to back test to see if there is a big change still with the dump open vs. closed. I will not have any track data till spring unfortunately there are only a few test and tunes left all weather permitting.

 

[Razor]

Razor I did forget to mention I had your kit in my parts list.

Ok, so the car is running lean, I will fatten it up this weekend when the rain stops and do some more back to back test to see if there is a big change still with the dump open vs. closed. I will not have any track data till spring unfortunately there are only a few test and tunes left all weather permitting.

Then you need to add fuel and fatten it up. Start rich and work your way lean. Dont start lean adding a little at a time.

Also when you open the dump.. depending on how restrictive the exhaust is.. boost can jump up big time. This was technically a big no-no in your scenario as the car was already on the verge of being lean and you could have leaned it out further killing it.

When it gets cold outside.. jack up the fuel.. When you turn boost up.. jack up the fueling. And LM1's are known to have to be "re-calibrated" so that may be another issue your dealing with. Me.. I like my wideband up in the passenger compartment. Like a 12-18 inches away from the turbo. but thats just me

 

[pwr6kid]

Razor, I think I’m going to move the sensor and add 20% fuel and work back from there. I will also recalibrate the lc-1 again. Since my butt dyno isn’t reliable I may try and sneak in another track day to see if the car picks up. I’ll post some more data after I move the sensor.

 

[Steve]

I had similar problems when I had a LC1 sensor. Many run the LC1's with no issues but mine always had problems. Innovate sent me a new LC1 and it worked great for a while then started to act up again. I later switched over to a AEM unit using the same bung and it worked perfectly with no issue.

 

[bison]

My $.02. You will gain little power at that level at the same boost open or closed. You will probably see an increase in boost and maybe a little quicker spoolup but dialing the boost back after opening the dump will not show much for power. I had a POS flowmaster on my blue car and i picked up about 6whp at the same boost (25-26psi) when i opened it up and got some clean pulls in at the same boost level. It spooled a lot faster. About twice as fast. This was around 460whp. At lower levels the gains are less and less noticeable.