Car runs better with dump tube capped?

[Black Box]

Went to LVD Saturday for test & tune day, and noticed that the car ran better/faster with the dump tube capped. I ran it with the street chip (20*), uncapped, at 22 psi w/alky. It was running 13.0s at 102 at this point. I wasn't getting any KR, so I switched to my 26* race chip, upped the FP 1psi (to 46 psi line off) and left the dump tube uncapped. I developed <3* of transitional KR with the race chip, but also, the car developed a hesitation at the top of each gear (shifting at 5K rpm), but ran a 12.99 @ 104. It wasn't popping or backfiring, just stumbling. So I capped the dump tube, left the race chip in it and it ran the best it did all day, 12.91 @ 105, and the stumble was gone. O2's were in the 780-810 range all day long. Unfortunately (or stupidly), I didn't check the BLM or Integrator #'s on the Scanmaster.

Could this be too much/too little fuel pressure? I always thought this was a little too much FP with 009's considering my mods, and the car is getting crappy gas mileage, but that's what I need to keep it out of KR. Car has a new coil pack, plugs and ignition wires. See sig for other mods.

Thanks

 

[azgn]

BLM & Int values mean nothing at WOT......car is running in open loop...most race chip folks lock BLM's at 128 at WOT....

if your 02's are right, you are running fat....turn the boost up or FP down and try it again.....smaller turbos sometimes run better with the dump closed

 

[Mr URL]

Both my cars run better with the dumps closed through the full exhaust systems.

 

[Black Box]

Cool, thanks for the help guys.

 

[Jimn8or]

Another thought... On some cars the boost increases as much as 3lbs with the dump cap off. If you added 1lb of fuel and 3lbs of boost, perhaps in here lies your problem. You didn't mention what octane you were running, but I can only assume it wasn't C-16 as there is no way 26° timing and as much as 25lbs boost will knock under MOST circumstances. I tend to think the opposite as the above posts for these reasons...
3lbs more boost = 3lbs more FP at this boost level, not 1.
If nothing else, you have 2 theories to check out next time at the track.
Jim

 

[Black Box]

Jim,
Thanks, I honestly never even thought of that. I think my car has a pretty free-flowing exhaust, what with the THDP, 2 1/2" pipes and Race Magnums, but I'll definitely keep a better eye out for that next time at the track....or maybe some late nite I'll make a quick jaunt down the highway.

Steve