Nitrous tuning/jetting

[J DAWG]

I am about to get serious and actually tune while I am on the dyno instead of just shifting thru the gears. I wanted to get some input regarding how and what the nitrous and fuel jets affect overall hp and tq numbers as well as a/f and what is the recommended path to take when changing out jets.


For instance when I was on the dyno with my car and a 150 shot(TNT kit with 46 n2o and 25 fuel jets) I made a couple of runs:


run 1 made an additional: 116/190 a/f was 10.4

run 2 made an additional: 125/188 a/f was 10.9(I took out some fuel with the vec2)



TNT kits are rear wheel rated numbers so I am leaving some power on the table. I plan on trying different jets, but which ones should I change 1st - nitrous or fuel?


I was thinking as rich as the car was the tq numbers would be on up there and by leaning the car out some it seems the tq numbers are gonna fall(my understanding is that tq is created by adding fuel, could be wrong in this situation).


I need to go over my setup to make sure something fundamentally isn't wrong and that everything is flowing properly. My psi was around 1000 and TNT said they recommend or test at 900 to 950.


Sooooo, assuming my system is working properly should I go up on my n2o jet or go down on my fuel jet to get my a/f where it needs to be and get my hp and tq numbers up? I am not using the vec2 anymore. I want to tune with the jets and around 900 psi to try and avoid big drops in psi as I make runs at the track or street.


The one interesting or confusing thing is that my 100 shot (jets 39/22) made 80/180 with an a/f around 10.8. So why didn't my tq go up with the 150 shot? I see everyone else gaining 200 to 300 or more easily. Granted I have yet to tune the car, but wanted to know what others were doing to get those numbers.

 

[mntngts99]

J DAWG
I have found that .50 on the A/F makes a big differences. On the dyno I was able to get over 30 rwhp/rwtq more with changing my A/F from 10.8, to 11.4 . After achieving the 11.4 I also played with bottle pressure

52/29 jets, 900 psi with 11.4 A/F = 567 rwhp 717 rwtq
52/35 Jets, 1100 psi with 11.4 A/F = 594 rwhp 806 rwtq

hope this helps

 

[J DAWG]

Thanks Brad. Do you know what kinda power the 52/35 jets yielded with 900 psi or are you running the 1100 psi all the time now?


Did your a/f stay the same (11.4) even when you went up by 6 on the fuel jets?


John

 

[Jack B]

High pressure is not always good, at 99 degres bottle temp, the nitrous turns to full gas and the power should drop.

Jdawg:
A good tack is to go up on the nitrous jets, then, one step greater then posted for the fuel jet. You also have to remember that the nitrous jet increases will have diminishing returns as you go greater then .050. Also, as we discussed previously, if your supply system is prone to converting the nitrous to gas (before the nozzles), the power also diminishes.

Another issue is the turn-on point, you can take a car gaining 200 ft-lbs at a 3000 rpm turn-on, then change the sequence to a 2500 rpm turn-on and gain about 50-75 ft-lbs. The cylinder pressure is what creates torque and low rpm's with a heavy car (combined with nitrous) create abnormal cylinder pressure.

 

[mntngts99]

J DAWG
Since our move I cant find last years dyno sheets. But from what I remember 900 psi with 52/35 gave me 575/775. I shift at 5000 rpm's and like my A/F to be 11.2 to 11.4. Another owner with a ACR tried the 52/35 and it was to fat. He ended up with 52/28 but did not make as much rwtq as I did. I ran 1100 psi all year. Here's a sheet from the ACR. Funny how each car likes just a little something different. Play with it and you'll find what she likes.

 

[plumcrazy]

what is the exact best A/F i should be shotting for when i dyno?

what is the best range ? ? ?

 

[J DAWG]

Jack


from the bottle my -4 line hooks up to my -4 pressure transducer and stays that way all the way to the n20 solenoid, so there shouldn't be any reason for the n20 to turn to gas unless the orifice inside the pressure transducer is creating it somehow. So hopefully I am ok in that regards. Putting a purge on as well.


Brad


thanks. Like you say I need to get to the dyno and try several things and see what happens. To me I need to keep something constant(like the bottle psi) and make one chane at a time. Need to find a jet pack and play around with it.



John

 

[J DAWG]

Phil


I am gonna shoot for 11.0:1 to 11.5:1 a/f.


John

 

[plumcrazy]

jdawg, is that typical of what we should be shooting for? or is that YOUR number based on your mods?

 

[J DAWG]

I would say 11.0:1 is the safe number(for n20) regardless of mods.

 

[Jack B]

JDawg:

the pressure transducer is a parallel device and won't create problems. Before i did the heads, the best the car did was 630/750, that was with 53/35 jetting.

 

[J DAWG]

you just reminded me of a point that was raised. It was mentioned that my heads/cam car may not respond as well as a stocker. I know certain cam grinds work best for different applications, but I don't see why my car still shouldn't make decent torque. The grind I have is fairly mild. Only 520/535 on motor.