I am running 24lb injectors with my 305(long story)

Anyways, I have a scanner and when I do n2o runs with a 88hp shot(dry) the injector pulse width is 10.2.-10.4.

At what point in the injector pulse width does it go lean, the number I mean?
12? 13?

I am wondering b/c I want to run a 100hp or 125 shot and I am not sure if I have to go to a bigger n2o jet b/c I am still running rich. I am running the leanest jet I have(82)

I guess I can just keep using the scanner and going bigger n2o jets but the info before I possibly blow a motor would be alot better!

Thanks for your help!

 

anyone?

 

You would need to post the max. RPM you intend to run in order to get an exact reponse. If you are using a stock GM ECM and the normal double fire batch mode for a TPI then the following is for 100% duty cycle.

10.9 ms inject time at 5500 RPM
10.0 ms inject time at 6000 RPM

Or you can use 60000/RPM to get the max. time in ms that the ECM has to inject at that RPM. By the sounds of it you are around 100% duty cycle with your current setup.

 

You also need to post the AFR. If your 10.2ms inject time is giving you a very rich AFR then even if you max. the inject time it is still too rich which means that you could give it more N2O because it already has too much fuel.

Post the RPM and AFR for a better estimate.

 

The injector pulse width is at 10.2-10.4 the whole rpm window

The max rpm is 5000rpm

The fuel pressue is 40psi.

These are injectors off of a 4th gen camaro(1996)

Thanks for your response.

 

Your worst case is 5000 RPM. The max inject time is 12ms.
That leaves you at 10.4/12 = 86% duty cycle.

If your AFR is right on at 5000 RPM then you can't add much more N20. If it is rich then you can add more N2O. It is hard to say without knowing the actual AFR of the engine.

Assuming that the AFR is proper right now, then you could give it a little more N20 and get the injector duty cycles up to the 90-95% range. I would do it in small steps though and watch the injector duty cycle and AFR.

Overall, you are getting close to your fuel limit if your AFRs are proper and not way rich. The only way to really tell is by using a wideband O2 sensor. What is the stock O2 sensor reading through out the RPM range?

 

The stock o2 sensor is reading about 0.8-0.85 with a 88hp shot.

When the o2 sensor reads about .5, isn't that when it goes lean?

When I was doing a 75hp dry shot, the o2 readings were 0.9.

 

A reading of .8 on the O2 sensor is about as low as you want to go and still be safe. A reading of .5 would lead to engine failure.

If the ECM PROM is stock then you really can't make it so the injector pulse widths increase like I mentioned. That is, your current 86% duty cycle can't be changed to a 95% duty cycle to add more fuel. This can only be done with a custom PROM.

If that were my setup and the injector duty cycles were 86%, the NBO2 read .8, and I couldn't re-program a PROM then I would NOT add anymore N20. If you want to go with the 100HP shot then you would need to increase the fuel pressure more (if you could.....be careful doesn't go too high). Overall, I would leave it at the 88HP shot.

If I could re-program a PROM, then I would increase the upper RPM VE table and try the 100HP shot. I would increase the upper RPM VE table by 10-15%.
Overall, I would increase the VE table and use the 100HP shot, check the results and possibly go to the 125HP shot.

EDIT - just realized your base fuel pressure is 40 PSI. You could probably get away with the 100HP shot if you increased the base fuel pressure to 47 PSI (stock is 43 PSI). At 47PSI, your injectors would act like 25#/hr injectors. That would be enough for the change from 88HP to the 100HP shot.

 

I tried the 100hp nitrous jets without upping the fuel jet.

The o2 read 0.79-0.82

I checked the plugs and there were a nice light brown color.(Brand new plugs)

The injector pulse width stayed at 10.4 the whole run, so maybe that is the max for these injectors?

I am going to try the 125hp nitrous jet and see if that leans it.

So, from a 75 hp shot to a 88hp shot to a 100hp shot only took the o2 reading down from a 0.90 to 0.85 to a 0.79.

 

ide say go down in injector go back to 19lbs and bump the pressure up you wont be able to lean those 24 lbs enough my friend went 3 tenths faster yankin the 24 goin back to 19 and he had a 350 ure way to rich

 

Or convert to a wet kit and be done with the sillyness.

 

I sprayed a 125 shot using the 100 fuel jets.
I ran a bit rich so I am going to run my 140hp n2o jet and leave the fuel alone and see.

I ran faster

See times below

 

Wait, in your sig and in your OP, it says dry. Now youre talking about fuel jets. If you have fuel jets then its a wet kit.

Do not play with your fuel mixture by changing the nitrous jets. Change the damn fuel jets. Its kinda dangerous to your engine to do that.

 

VWDave,
I have a dry system. Yes, they have a n2o and a fuel jet

If you don't know how the system works, this is how...
The 900psi off the bottle flows through a tiny orfice and bleeds a bit of pressure to up the fuel pressure using the AFPR. In that line is the fuel jet. The nitrous is sprayed though a nozzle before the throttle body.

The difference b/w a wet and dry system is that a wet uses a dedicated/extra fuel line, the dry uses the existing hardware.

Both have ad/disadvantages.
Mine actually runs really well now that I have figured it out.

As for your post, I ran the scanner on the car with the 125 shot and it is still a little on the rich side.

There is only 2 ways to lean it out
1. Use the 19lb injectors
2. Up the n2o without stepping up the fuel jetting.