Here are my near-future plans for my '97 LT1. I will be trying to install all of them at about the same time for tuning sake.
-- LT Headers with ORY and 3" Magnaflow catback
-- 58mm TB
-- bored out intake entry to match new TB
-- 100-125 shot Nitrous (dry?)
-- better CAI than the Ebay one I have
-- Performance fuel pump
-- PCM tune (pcmforless or Madz28)

Now in about 2 years, I do plan to install a LE2 package and a hot cam, maybe (just maybe depending how bad the bug has bit me) a Vortec SC. Hopefully you see that I'm trying to get all the peripheral mods the the LE2 package suggests for the 420RWHP rating.

I was planning to install a Wet Nitrous system until I got to thinking. Since I will have to increase my injectors to 36lb'ers, I'm thinking of getting a DRY N20 system and installing the 36lb'ers with it. Then tune the PCM for the larger injectors.

My question is this....what exactly does the PCM tune for a larger injector do? Does it limit the injector pulse to maintain that optimal fuel/air ratio, in essense making the 36lb'ers act like stock 24lb'ers until I go WOT?

I don't want to lose daily driveability of my car since I will use the N20 on rare occasions (trust me!). Will a PCM tune to the 36lb injectors make the LT1 run rich all the time fouling the plugs (and destroying the O2's)? I've read a few posts here that reported this. At the same time, I want to save some money in the long run since I'll need the 36lb'ers anyways.

On my near-future setup listed above, what will the PCM tuned 36lb injectors do at WOT, will it be too rich for the little mods I have?

 

If you put in the correct flow constant and offsets for the injector you are using, the PCM uses that data to correctly calculate the pulse widht and supply exactly the required amount of fuel. It will supply the correct amount of fuel, using shorter pulse widths, whether you are at part throttle or WOT. You'll never know there's a larger injector in there.

The problem with oversize injectors is achieving the small pulse widths required for the low fuel requirements of idle and low loads. But I doubt you'd see problems running a 36# injector on what sound basically like a mild bolt-on engine with an oversize throttle body.

A more realistic question would be "why are you changing the injector size at this time"? The stock 24's are more than adequate for your headers and TB, and you don't tune for or control a dry nitrous system with the stock PCM.

 

I got to thinking that I could save some money buying a dry N20 instead of a wet system. I could use the larger injectors and better fuel pump to deliver the added fuel needed when I spray. AM I thinking logically?

 

I wouldn't go that route. You can't get a stock PCM programmed to add enough fuel when the nitrous was on, yet not be wickedly rich when the nitrous was off.

 

How do you make the stock PCM supply exactly the correct amount of fuel when you are not spraying, then suddenly add a larger amount of fuel when you are spraying? As far as I am aware, there's no way to do that with the stock PCM, at least not in the LT1. The LS1 dry ssytems spray though the MAF sensor to add the extra fuel, but alledgedly that is only possible because of the high processor speed of the LS1 PCM. I have a 300HP dry system, but its running on an aftermarket ECU that is capable of switching between programs when I arm the nitrous switch. And the ECU is equipped with high resolution drivers to handle the 78#/HR low impedance injectors, and idle smoothly at 800rpm.

In addition to fuel, you also need to address spark timing on nitrous. There is apparently a way to use the tables in the traction control part of the PCM to do that, assuming you have done away with the real TCS system.

With either a wet or dry system, you tune the PCM for optimum performance without the nitrous. Then with a wet system, you adjust the fuel and nitrous jets in the wet system to control the A/F ratio when you spray. Most dry systems for the stock PCM add the extra fuel by boosting the fuel pressure, not by altering the pulse widths. You retard the timing externally, with an MSD box or similar.

 

The only way I could think of doing this would work if you used nitrous exclusively at the track. You'd need 2 complete programs for the PCM, one for with nitrous and one without. You'd drive your car to the track (with the standard program running), use a laptop to flash the nitrous program into the PCM, and then race. Once you were done racing, you'd reflash the non-nitrous program into the PCM, and drive home with the nitrous off. Or you could do this with 2 PCMs.

It doesn't seem like a convenient way to do it, and you'd need 2 custom programs for your car. Really, a wet system is probably the simplest way for you to go.

 

Wow, adding N20 is a lot more indepth and technical when doing it correctly! I'm glad you all chimed in...I'm learning a lot! Thanks!