[Guest]

I emailed ChriSS and George the following, but am posting also to see who else may have some advice on what else to consider. A new fuel filter will go in tonight:

I did a couple of tests yesterday evening and the results have me a little concerned.
I ran the 35/20 jet combo (50 shot), and O2's started in the high 800's and ended up in the low 800's after 10 seconds. On motor only, they stay in the high 800's.
Next, I stepped up just a hair, running 38/22 jetting (75 shot recommended is 41/24). O2's started around 910 and ended up in the low-to-mid 800's after 10 seconds.
I pulled 1 deg of timing for the 50 shot and 2 degrees for the 60? shot.

Looking at DataMaster, and assuming 10 samples per second, NA time from 55 to 100 mph is 7.8 sec. With both jet combos I tried, 55 to 100 was 6.3 sec. That sounds too good to be true - what's up with that?
The 2 degrees was probably too much to pull for the 60 shot. Bryan has me running only 34 degrees total timing NA.

I pulled the #3 and #4 plugs after the second run and after driving about 5 miles home - The porcelain insulators are WHITE! If you imagine really hard, you can see a hint of gray/brown on the #3. Scary!

Tell me what you think.
I'm running the Walbro 255 and the NX 30 psi fuel pressure switch. My fuel pressure is set at 42 psi.
Now I wish I had a place to plumb a gauge in there. It sure seems like the fuel pressure is dropping. It does not drop even a fraction of a psi on NA runs.
I'm going to replace the fuel filter today.
Bottle pressure was between 1000 and 1050 at the beginning of the runs (full bottle).

 

[Guest]

Let me guess, you just missed being the first bolt-ons car in the 12s, so you're gonna shoot for the first bolt-ons + adder in the 11s?

 

[Guest]

Originally posted by AdioSS:
Let me guess, you just missed being the first bolt-ons car in the 12s, so you're gonna shoot for the first bolt-ons + adder in the 11s?

That's the plan

 

[Guest]

Pat,

I don't think the color of the insulators is going to stay the same for five miles. My guess is they're white from normal driving. Try it again and check the plugs right away after the run. What plugs are you running? You might also use a magnifying glass to look for metal imbedded in the insulator.

Did you check the fuel cutoff switch setting or did it come set from the factory?

Did you get more than normal knock retard?

To check to see if your fuel pressure is dropping, I'd set the fuel pressure switch to about 37 psi and make a run. Then if the fuel pressure is dropping, it will cut the nitrous off and on.

 

[Guest]

Thanks for ringing in, Stone.
I got no knock counts, no audible knock, and no retard.
The fuel pressure switch is the standard one for FI cars in the NX kit (supposedly at 30 psi). I don't see any way to adjust it.
I'm running TR6's gapped at .030.
I looked at the two plugs with reading glasses under a bright light and could not see any specks of aluminum.

I tried those same jets last night with the new fuel filter and the results were bad:
O2's bounced between 200 and 800 and the power surged on and off pretty badly. I think I have a blocked solenoid, line, or jet on the fuel side.
Could have even been a piece of filter media or something else in the new fuel filter. I guess I should have done a quick flush of it first just to make sure. I'll troubleshoot when time permits!

 

[Guest]

Good luck, Pat. I'll print this thread and run it by a couple of the local sprayers.

 

[Guest]

On my way home last night, I thought I figured out the problem: an empty filter plus the void left by all the fuel that drained from the line had to create an air bubble and I thought there was a good possibility that air went right through the schraeder fitting and to the fuel solenoid (high point of the system). I didn't purge the fuel prior to making that run, so I'm sure that was a factor. In fact, the O2's did come up to 800 at the end of that run.

BUT.....a more likely reason for the problem:
It appears I'm not getting enough voltage to the solenoids - they're buzzing instead of just clicking open. Prior to last night, I had only tested them individually and they opened fine, but the voltage drop with the existing wiring/relay with both of them operating is not cutting it. So my next step is to rewire and shorten leads as much as possible, and maybe run larger gage wire to the solenoids.

EDIT: Voltage was not the problem. Whizkid here was trying to do the electrical/solenoid checks without a jet in the end of the fuel line. Naturally, the resulting huge fuel flow and pressure drop upon solenoid opening caused the FP safety switch to cycle. Anyway, now I have a more robust wiring configuration!
That one lean run WAS because of air introduced into the fuel lines with the filter change. Subsequent runs have been OK.

Pat

 

[Guest]

Pat,

Sounds like everything is coming together. On the FPSS, there is a rubber cap on the end opposite where it screws into the fuel block. There is an adjustment screw under there. What you do is set your fuel pressure to the desired pressure, then use a multimeter to set the pressure switch where it just closes at the given pressure.

Rather than keep screwing and unscrewing the fitting near the schrader valve, I'd find a fuel block with multiple ports and put the FPSS in one and a fuel gauge in the other. I've managed to break the schrader valve off my fuel line, and you need a whole new fuel rail if you do that ($400+ from Dal) or make a trip to a junque yard.

 

[Guest]

Thanks, Stone.
Things are indeed coming together.
Since my fuel solenoid is too far away from the nozzle, I found that if I engage the system with the bottle closed to do a fuel "purge", and then open the bottle and purge the nitrous, my O2's immediately go to their steady state readings and stay there.
I've worked my way up to the 150 shot (running 62/41 jets) and O2's are 910 to 920 mV.
I believe with the smaller shots, fuel and nitrous flow were so low that it was just taking more time to reach steady state.

It feels GOOD

Pat

 

[Guest]

I've noticed something like that as well. If I purge the nitrous line before I stage, the car is actually slower than if I don't. I'm guessing the fuel takes a little longer to reach the nozzles.

 

[Guest]

Here's the update folks:

The bugs are indeed worked out!

11.91 @ 112+

It appears I missed understanding just how sensitive the mixture is to bottle pressure.
With my initial runs on the road, I was dealing with very cold ambient temps and was warming the bottle without letting the pressure transducer for the heater do its job. I was warming it to about 1050 psi. At the track, I just let the engine run with the heater on, and it seems to stabilize about 975 psi. I found I was running very rich at the lower pressure (950-960 O2's).
The numbers above are with this rich mixture.

After getting the car on the dyno with Bryan at SSHS3, we dropped down 2 sizes on the fuel jet to get the O2's down to 920-ish. I didn't better my ET due to deep staging on the ProTree with the Big Dawgs at SSHS3, but picked up almost a mph at a higher altitude track.

 

[Guest]

Dang, man, how do you run so fast? I've got a cam and stage 1 stock heads, and we're almost equal!

 

[Guest]

Originally posted by stonebreaker:
Dang, man, how do you run so fast? I've got a cam and stage 1 stock heads, and we're almost equal!

Randy,
I'm a fanatic for attention to detail, but then I believe you are too, so I won't attribute it to that. My car is very light (4150 with me in it when I made that run), so that's probably the biggest factor. But, it also has a beautifully flat powerband - Friday on the dyno with open exhaust and belt off, it was above 300 rwhp from 4650 to 5750 rpm NA, and above 400 rwhp from 4100 to 5750 on the 150 shot (belt on, open exhaust).
Peak numbers were 309 NA and 425 on spray (Std correction).

 

[Guest]

So what have you done to lighten your car? With me in it, the car tips the scales at 4460. Well, I guess it would be 4340 now, since the weight loss surgery.

 

[Guest]

No sway bars, Centerline Telstars in rear (15 x 8, I think), 15 x 6 Weld Rodlites in front, no airpump, Brantley front bumper support, no secondary cooling fan. That's it. Needless to say it was a light car to begin with. And I weigh only 165 right now.

 

[Guest]

OK, that makes sense. I'm still running street tires on the front and I'm keeping the stock bumpers till this ceases being the daily driver. What about other stuff? electric windows, things like that?

 

[Guest]

Full interior, the secondary fan and the air pump are the only pieces of equipment removed.
I removed the front passenger seat at SSHS3, but it was in for the 11.91 run the weekend before.

 

[Guest]

Well, whatever you did, you've got a fast car. Keep up the good work.