Poor first dyno testing 150 nitrous shot

[Snakester]

I did my first dyno today at APEX with .46/.24 jets (150HP?) and only got 508RWHP/585RWTQ.

But my main problem was jetting because the car's A/F almost immediately went to below 10, flatlined the dyno until the window switch cut it out at 5800RPM. So it's running really rich now.

I was happy to NOT be too lean, but I didn't have any extra sets of jets to swap out and tune the A/F mix to get the proper power out of the car.

It was a hot day and so I was running about 15RWHP/15RWTQ under my last recent dyno normally aspirated (421HP/448TQ), but the strange thing was that my N/A A/F mix was also rich, being under 11 with a dip to 10 around 4.0K-4.6K RPM.

The total gain was 87RWHP/137RWTQ.

I could go up to .52 N2O jets, or maybe down to .20 on the fuel jets.

I'll have to play with getting the proper mix.

-Dean.

 

[Ben Gratt]

Dean,

I would stick with the stock jet combinations as detailed on the card that comes with the kit as they are purposely rich in order to be safe. When I had my 2000 GTS (making about 423 rwhp on the motor), the NX kit with the 200 jet combination would also send the air fuel ratio right off the chart (under 10:1). However, you can still make plenty of power even with these rich ratios. I made 565 rwhp / 736 rwtq with the 200 jets.

In my opinion, bottle pressure is far more important than worrying about your a/f ratio (once again, I believe pig rich is playing it safe). Did you have adequate bottle pressure on your runs? With the 200 jets, this is what I observed on the dyno:

900 PSI: 523 rwhp and 659 rwtq.
1050 PSI: 565 rwhp and 736 rwtq.

So, you could be off as much as 40-50 rwhp due to bottle pressure alone.

I don't have my jet card anymore, so I'm not sure what your 46/24 jet combo equates to, but 508 rwhp might not be too far off from normal if you had low bottle pressure. (The NX 150 jets don't really produce a 150 rwhp gain - more like 150 flywheel).

Sure, you could mess with the jet combos and tune the a/f for more power, but I prefer to keep it rich and safe. You could always go to larger jets. Once I put the 300 jets in, and dynoed with around 900 PSI and made 607 rwhp (I didn't want to try it at 1050 PSI since I figured I was getting close to the limits of the stock creampuff pistons).

Ben.

 

[Snakester]

I don't have the NX jetting card, and I'm not sure that it would help if I did as it seems to be different for different cars. I had this NX N2O system on my previous Corvette, and was just adapting it to the Viper. Adding an extra pair of jets, nozzle, and having the MSD window switch modified for the Viper.

I can find tons of info on jetting for single intakes like the LS1 V8 and 5.0 V8, but not for the dual throttle body Viper jetting. And the more that I read, the more that it seems that jet tuning is almost always done on a dyno to optimize the A/F mix.

The difficulty is that there are no local shops that seem to carry NX nitrous parts, and ordering from out-of-state takes some time.

Mostly I wanted to get the Viper setup with the N20 install to run at the dragstrip this weekend. And I was much more concerned with NOT running lean, so the dyno test today accomplished exactly that. And I do feel safer knowing that it's too rich instead.

I'll have to double-check my bottle heater and PSI level, as that was one of my least concerns before, but it certainly could be a big factor. It was a full N2O tank, and a warm day so the tank pressure should be up. But I'll need to look at it more closely tomorrow.

Thanks for your input Ben,
-Dean.

 

[TOOOFST]

Ben,If your going racing this weekend and want to go fast with some MPH(with your existing set up),here's what you do.After getting to the track and having the viper cool down,toss the bottle in the floor of a friends truck for 15min with full heat on.Get the tank to 1100PSI.You'll have 550-580rw.Remember at the top end you'll be coming back rich as bottle presure drops through the 1/4.After your solid 11sec stock tire run,pull out #1,#3.#1 usually gets blown away 1st.PS. bring and extra plug.
My jetting is NOS and will be different with the VEC-1.Good luck
TOOOFST dynoed same #'s N/A.

 

[treynor]

Ohhh boy, Dean got his Nawwwssss for this weekend's racing. It's going to be "pick on the Benz" day, it seems

 

[Snakester]

Ben,

I'm just hoping to get into the 11s (and probably get promptly kicked out).

I know it can be done, I even saw a big Mercedes sedan hit mid 11s once at the track (believe it or not) so it should be no problem for a Viper with Naawwws right?

Who knows, it still depends on if I can get the power to the ground.

See ya,
-Dean.

 

[Snake Bitten]

Dean,

As I previously posted, I did 513 rwhp and 665 rwtq with 41/22 jets...I was lean on the low end and rich on the top end, just like yourself...Bottle pressure was 1050 psi...Did this with a heat gun, but running around town, I can pretty much maintain that in the summertime...

I am tossing in the 46/24 jets when they get here, I am also installing the VEC1...to richen the low end and lean out the high end...I am hoping for a fairly consitent 575 rwhp and 675 rwtq @ 1050 psi of bottle...

Back to the dyno in a week or so...

Keep us posted on your tuning...

 

[Jack B]

As indicated each car is different and it is difficult to use a cook book approach. Another thing that is also important is repeatability. You want a consistent A/f not just great power for a short time. Just to repeat an ealier comment, a 150 hp shot is really 150 X .85.

I used the VEC-1 and liked it when NA, however, I found it was slow to react or learn when dynoing on the bottle. On my Gen 1 it actually showed less hp, because it pulled out to much timing (timing and a/f are changed together), I haven't tried it on the Gen 2, because I feel you can get the proper a/f by jetting alone and that equates to consistency. Only run the bottle at a temperature that you have dyno'ed at and one that gives you an A/F of 11.0 to 11.5. There are a couple of good NOS books and the common thread between them is safety and it is only achievable through repeatability and consistency.

 

[Snakester]

I dynoed again today, and hopefully, some of you nitrous savvy guys can help with my latest puzzling dyno results that I got today.

As mentioned above, I was running really rich before, and today's runs were to try and get my A/F mix dialed ina bit better.

My first run was baseline and I got 426RWHP/450RWTQ, which is pretty close to my previous N/A dyno run.
Then I ran with my existing 46/24 jets and got 510RWHP/488RWTQ compared to my previous 508RWHP/585RWTQ run (almost 100RWTQ lower!).

Then I put in .52 jets because the A/F was well below 10 as before, and I pulled 541RWHP/501RWTQ, and with .52/.24 jets the A/F was still pegged somewhere below 10.

So I swapped out the .24 jets with .22s and I ran 571RWHP/518RWTQ, and I could see the A/F just peek-out a touch over 10 after 5400RPM.

My pressure gauge is not working, but these runs were done with a just-filled N2O bottle, with the warmer on all of the time. It seems to me that if it were a low pressure issue, then I would have also had lower HP figures as well

If I can arrange it, I am going to go to another dyno shop tomorrow to double-check if it's an anomoly with the dyno or my car.

But if you guys have any suggestions or ideas, I would love to hear them.

-Dean.

 

[Tom Welch]

A couple of questions;

1. What rpm are you starting the pull? Reason I ask is because your torque is way down, while your HP on the last pull seems to be close for your mods.

2. What spark plugs are you using?


Peak torque on a good nitrous set up will be at around 3400 RPM. If you start your pull too high in rpm, you will never realize the torque potential. Also, to pull to 5400 rpm is useless on a nitrous set-up. You should see peak HP at 4800-5000 with a stock type engine.

In a nutshell, I suggest starting your pull at 2500-2800 rpm in 4th gear. Run up through the gears as normal driving, hold steady at 2500 in 4th for a moment to allow the computer to stablize, start the dyno sampling with the green button and floor it. Hold till 5000 rpm and release.
Let us know how that turns out.

Best of luck,

Tom

 

[Snakester]

For all of the runs I started in 4th at around 2000RPM and they started measuring at between 2400RPM and 2800 RPM.
My pills in the MSD window switch trigger the solenoids on at 3000RPM, and off at 5800RPM.

On my last dyno (the rich one) there was a mountain of torque right up front, hitting peak TQ at 3600RPM and slowly tapering off from there. HP mirrored N/A power with about a 85RWHP gain across the rev range.

On these latest runs, the N2O power actually starts out making about 25RWHP/50RWTQ less than the N/A run at 3000RPM, then it steps up, matching the N/A power at around 3700RPM, and shoots up to 500RWTQ by 3800RPM and mostly stays flat until 5800 RPM. Meanwhile the RWHP shoots past N/A HP by about 25RWHP at 3800 RPM and then builds increasingly to a 150RWHP gap over N/A, peaking at 5750RPM or so.

On my previous N20 run, the HP peaked at the same RPM as the engine did N/A (5500RPM).
I have S&B filters, Archer airbox, smooth tubes, roller rockers (stock internals/cam) high flow cats, and a Corsa cat-back.

Sorry, I don't have a scanner handy to show you.

The sparkplugs are stock.

Thanks for your tips and suggestions.

-Dean.

 

[Snakester]

So I went to Apex and dynoed the car with the same settings as on the Mustang Ranch dyno on Tuesday.
The only difference being that we dialed in the VEC-1 a little better power for the N/A runs.

So running between 11.5 and 12.0 A/F on just the engine it ran 435RWHP/460RWTQ, and with the N2O it ran 10.0 with a little rise to 10.5 A/F at 5000 RPM and had a corrected output of 546RWHP and 607RWTQ. Which is pretty good.

The missing element right now is the bottle pressure.
My N2O gauge got messed up, and needs to be replaced. But it was a pretty much full bottle (5 dyno runs done) and I had the NX bottle warmer on, so the pressure should be OK.

I'll swap the gauge out next and check the pressure.

But at least today's dyno runs confirm that there isn't something really messed up wit the car, soaking up all of my torque.

I might still look at getting 0.20 fuel jets (0.22 now) to gain a bit more power and have the N2O A/F around 11.0.

-Dean.

 

[Jack B]

Your problem is that the NOS volume is not normal. Possible problems could be: low bottle pressure; bottle filled with wrong concentration of NOS (pressure gauge will not show this condition, weigh bottle); nos filter at solenoid dirty; crimped nos line; low voltage at solenoid causing chattering; low volume sprayer used.

 

[Snakester]

Thanks for the troubleshooting tips Jack.
I'll check those things out.

-Dean.

 

[V10TT]

Tom, what AFr's do you shoot for on the juice?

 

[Snakester]

In another thread Tom said that he likes to tune for around 11:1 A/F because running at higher speeds on the track leans out the A/F a bit, so it allows a safe margin to maintain reliability.

-Dean.

 

[WESTCOAST JASON]

Tom is right about the car running leaner on the track/street than on the dyno. (especially if you are doing the dyno on a dynojet) The load of the dyno is lighter than pushing the car down the road. (about 2200 lbs. vs. 3400 or whatever your car weighs) Tune a bit rich to be safe. The A/F should go richer during the pull when using the nitrous and being in the low 11's or even high 10's by 5000 RPM is a good idea.

A working bottle pressure gauge is of utmost importance, you can easily find a 25% power difference between 700psi and 1050psi.

 

[Snakester]

Thanks Jason.