Ok guys, I'm in a pickle. I've got no clue what's going on here. Last weekend I went to the track, it was mid temps and I was running a 12.4-12.8 @ 109-111with the car. I put a 150 shot on it and got a few 11.8-9's @ 116. I backed it down to a 100 shot and got a 12.1 @ 113.

I upgraded my fuel pump and called NX and got the 200 and 250 jets and tried those this weekend. 12.6 @ 111 n/a and it was hot 70-80*. I got a 12.0-2 @ 115-118 with the 250 shot. I leaned out the mixture with a different fuel jet an no real change. I tried adding timing and the mph went up to 120. I changed the nitrous jetting to a 200 shot and got a 12.0 @ 120. It was getting a little cooler then.

WTH With that much nitrous I should be getting much better times than those, shouldn't I?

It doesn't feel like it is hitting as hard as it did last year before I got the engine rebuilt.

The only things I can think of is that my exhaust is to restrictive and is holding it back, or my ecu can't handle that much nitrous and doesn't know what to do with it.

Oh yeah, bottle pressure was constant or pretty close too for all the runs. The last few runs this weekend the battery might have been running low(alternater control came unplugged), but otherwise the car was fine.

Here's what I've got

396 Fully forged bottom
9.5:1 compression using 93 octane
ported stock heads
hooker longtubes with stock catback
MSD Digital 6
Ed Write Chip
2.59 rear end with a built 700R4
close to stock stall torque converter
NX Nitrous kit

Any help or suggestions would be very helpful. Thanks. :confused: :confused: :confused:


[Modified by mn_vette, 7:12 PM 10/19/2003]

 

Brian are you sure you were not rich I saw a guy with a 540 with a 200 shot of nitrous make 970hp on the dyno then he changed the soleniods and jets to a 600 hp shot and it made 940hp. So adding 400hp he lost 30hp but A/F ratio went from around a 12.7 to 10.0 on the 600 shot or another way of looking at it is the running rich cost him 430hp. :leaving:

 

Bart,

When I called NX they gave me a rich and a lean setting for the 250 setting. I tried both with no real difference. The 200 shot has the same fuel setting as the lean 250 shot. So when I swapped the nitrous jet only I got about the same result, a tenth or so faster. I guess the only real way is to do a wideband testing. But I'm not sure how wise it would be to go even leaner than the recommended jetting that NX gives.

The jet for a 100 shot is a 33, I can try a 31 with it and see what happens. I had someone watch my exhaust as I was going down the track, and they said that there wasn't any smoke out the back like I was running really rich or anything.

 

Well I think if it was me I would get a wideband meter and install it or go to a dyno where they have one to see what the A/F is. The guy with the 540 used a NX system and he installed the recommended jets. I have a NOS system and with what they recommended for jetting mine was in the 9's couldn't even read it with a wideband it was off the scale but they jet them for 43lb. fuel pressure and I run 70lb so that throws the calibration off a mile. If you had a Gen.-7 dfi it would tell you what your A/F was but it would be what ever you had your target A/F map set for because it would automatically adjust the fuel and force it to run at the correct A/F ratio. I don't think you should use it until you get a wideband hooked to it and see what is going on. It could have other issues but I"m betting on a rich A/F

 

Well, the accel DFI was going to be one of my big purchases this winter when the car is out of the snow. I think I'll just wait until then to worry about it. I'm not going to bother blowing a few hundred dollars for one track event left for the season. Oh well, maybe next year I'll get that 10sec slip.

 

There could be several things here... Like has been mentioned quite a few times it could be pig rich... Get a wideband O2 meter or at least an EGT guage and watch it closely. Take baby steps in the fuel jet... A friend/customer of mine and Forum member, Jim Barth, took about 8 or 10 jet sizes out of the fuel side of his 150 shot to get his A/F into the 11.8/9 range. It started out SO rich that his FAST W/B O2 was pegged at 9.00:1!!

Another thing that nobody has mentioned or asked you about. Is it killing your 700R4?? Big nitrous hits and the 700 don't like each other very much... The tranny could be eating your power with slippage and since nitrous motors accelerate SO quickly you might not be able to tell.
-Jeb

 

I'm not sure if the tranny is slipping, but it's a built 700r4, or so I was told. My mechanic couldn't get my 4L60 right so he said screw it and pulled the 700R4 out of his big dually pickup truck swapped the tail housings and threw it into the vette. he said he had it rebuilt for heavy duty towing last summer so It should take the torque.

The 2-3 shift did seem like it was happening sooner than it used to, but maybe that's just in my head. To used to track shifting it at 6500.

 

i would recommend NOT RUNNING 93 WITH THAT BIG A SHOT. Your asking for trouble. With that you need some 107 motor octane. I would look into detonation as a culpret also. Do you have free scan ? If not down load it for free and monitor these runs and study data.

If you don't have a wide band, you do have the next best thing, pull the plugs and read them. I recommend going to the hobby shop and getting a magnifying glass with a light and use that.

I have 3 friends with lt-1's they all set timing to 34 with a 100 shot and 30 deg with a 150 shot. I would guess a 250 shot would run good with 30 deg and 107 motor octane. Also see what the KS is picking up.

the 396 LT-1 has gone 10.80 with a 150
( bone stock) lt-1 11.52 with 150
hot cammes, shorties lt-1 has gone 11.80 at 116 with 100 shot.

We have found all these motors prone to detonation.

 

now i know this sounds stupid but could it be something as simple as tire spin and tranny slip? i mean i did a 175 shot on my vette i ran a 13.6? and with a 150 shot 13.2's because i could not get traction?

 

I agree with Mike on the race gas. You want to run some 104 at the very least with a 200 shot or more. Could have very well been detonation.

Also a consideration with the larger shots is the 4AN feed line. I have some friends that said they picked up considerable power by simply going to a 6AN feed line over the 4AN they give you with the kits. Nitrous just can not get to the solenoid fast enough. I am still running the 4an lines though so it is just a consideration.

 

I had no issues with tire spin. None of the shots hit like they should, or like they used to last year(100, 150). I can feel it when it hits, but it doesn't feel like more than a 100 shot at most.