Dry kit experts out there?

Considering going with a less expensive route on the nitrous and using the Holley/NOS kit #05176TBNOS instead of a dual stage or direct port for now. I already have the TB, just need to get the nitrous side. I asked Holley why the kit is only rated at 135-150 HP, and they said that it was due to the stock LT1 fuel injectors. I kinda knew that, but wanted to verify that the TB was capable of a bigger shot, and wouldn't have any disperse pattern problem.

My problem is how do I find out what size injectors I will need to handle a 200-300 single dry shot on top of my 383. Wondering if 42s will suffice, or if I should stick with the 50s I had with the stroker/blower setup I was running? A gradual aproach in upping the shot will occur, I just want to prepare for the max, without sacraficing idle/driving caracteristics with the large injectors. If anyone can point me in the write direction it would be great. Thank you,

Mav

I don't know anything about the flow capacity of the Holley/NOS throttle body. But the 5176 kit uses two Super Powershot nitrous solenoids in series. I don't think you are going to be able to flow much more than a 150-shot through them. I run a pair of the Super Powershots in parallel, and I think about 175-185HP is the upper limit for each one. Put them in series, and they will flow less than a single one.

As far as sizing injectors, use the injector sizing formula. Put in the total crankshaft HP of your system including the nitrous, use as least 0.55 #/HP/HR for the BSFC, and always look for a duty cycle of no more than 80%.

For example, an 800 crank HP system would get you:

(800 X 0.55) / 8 / 0.80 = 69#/HR for the injectors.

You could achieve this with a 60#/HR injector, if it was rated at 43.5psi and you ran it at 58psi. The 5176 kit is capable of pushing the fuel pressure higher than that. At 80-85psi, you could get by (in theory - see comments in next paragraph) with a 50# injector.

All that said, you would be relatively insane to try and run a 300-dry shot using an NOS 5176 dry kit with its Mickey Mouse fuel pressure controller. It is fine for a 125-150 shot, where you can run it on the fat (rich) side and play it safe. But to think you could run a 300-shot off a hit-or-miss system like that is way off base.

I'm probably one of the few people that does run a 300-dry shot, but I'm using a MoTeC ECU that can control the system with high accuracy, based on tuning backed by dozens of dyno pulls, first on an engine dyno, and then in the car. And that's running 64# Bosch injectors at 58psi (78#/HR).

You might want to rethink your plans.

Wow, thanks for the help on this one Fred. Nicely indept, and it gives me much to think about.

Funny, seems like every hair-brained idea I come up with backfires on me. I've got some time to continue to "think" over my future plans, but please take it easy on me when I pop up another off-the-wall, not you average idea. I'm diving into a new realm, and I thank you for your help.

**EDIT**

From what I read, in theory, it could be pulled off with 60lb injectors at a relitivly stock 43.5psi(400hp +300shot= 700hp), but In order to use the 50lb injectors, fuel pressure must be increased to equal a 60+lb injector? Increased using an inline bosch pump in conjuction with my intank Walbro 340. Curious why or maybe how you would keep my injectors around 80% duty cycle if you up the pressure to cover the diference in injector size. Mabye it is too late(in Germany) and I'm over thinking this one. But the bottom line is you would not trust the supplied FPC, and you would suggest an aftermarket ECU setup like FAST, MOTECH...etc? Thanks again,

Maverick

Good stuff - Thanks Fred.

There was another post today and I'm interested about possibly doing this in the future as well, did you ever run the kit at 175HP (72N), and if so, what fuel pressure tee did you use?

Joe

Im with Joe. Id like to know as well. Would the 42 tee work with the 72 Njet?

The problem with running the NOS 5176 kit is that it uses the stock PCM/stock fuel pressure to run the engine when you aren't spraying, and then has to adjust the fuel pressure to compensate for the added fuel required when you spray N2O. That works fine for a stock setup with 24# injectors and a stock fuel system (+NOS inline booster pump). NOS has done the homework, and can tell you the required jet sizes, keeping in mind that they are going to run it rich, to stay on the safe side. But once you change any element in the equation, you have to start all over again.

First, your injectors have to meet the needs of the engine when you aren't spraying. If you have a 500HP "all motor" setup, you're going to want 36# injectors (at least that's what I would use.). Remember, you can meet that requirement with a 36# injector running at 43.5psi fuel pressure, or with a smaller or larger injector running at a higher or lower pressure.

Then, when you spray with the 5176 kit, the system boosts the fuel pressure by applying the slipstream from the blue pressure regulator to the FPR vacuum connection, and using a jet in the line back to the intake manifold vacuum source in an attempt to control that pressure. When I bought my 5176 kit in 1994, it only came with an 0.067 nitrous jet, and had no jet in the "tee".... it was not considered an adjustable system, and was rated 125-150HP.

So... you have to find the correct balance of injector size and one fuel pressure for "NA" operation, and another fuel pressure for "N2O" operation that allows you meet both the tune in the PCM and the "tune" in the fuel pressure system. It take dyno time. No other way to do it.

The advantage of the aftermarket ECU is that you can independantly tune the injectors you have for the "NA" case, and then have a second program in the ECU that allows you to independantly tune for N2O operation. You aren't relying on the hit-or-miss fuel pressure control using the slipstream from the blue pressure regulator. You are running two independant tunes that are correct for the single fuel pressure you happen to be running. (Just to clarify, it isn't really two independant sets of tables... its a base table plus offset tables for fuel and timing based on a digital input 'yes/no' for nitrous activation)

In my opinion, relying on the NOS 5176 method of controlling fuel pressure is not reliable. In any event, once you change the size of the injectors, or the base fuel pressure of the system, you would have to start all over again on the jet size required to control the fuel pressure. Could be done, but I would not try it without the ability to do some serious tuning on a dyno or at the track. And if you make a mistake....

As far as running the 5176 with an 0.072 jet, I believe I have seen people do it, but I don't know the exact details of the fuel pressure system. Again, if you make a mistake, you are going to damage the engine. I would put it on a dyno, do a pull, read the plugs (not easy to check all 8 plugs on an LT1 while its in the car - a lot easier on an engine dyno) then gradually increase the size of the nitrous jet while gradually decreasing the size of the fuel jet. You may get into trouble though. Just playing with numbers, assuming that the "no fuel jet" gives you 80psi fuel pressure, and meets the fuel needs of a 150-shot, you would have to go to almost 95psi on the injectors to add the extra fuel that is required to go to a 175-shot. Is your fuel sytem up to that requirement? Remember, as system pressure goes up, the fuel pump flow capacity drops. Some pumps get into big trouble at those pressure levels. You need to get a flow chart (flow vs pressure) for your specific pump. The injectors work harder to open. Getting the pressure high enough will tax your fuel system.

Thanks Fred!

If you have time, it would be great if you could add any comments you might have in the other 5176 thread going on right now.

http://web.camaross.com/forums/showthread.php?t=333280

Joe

Lemme get this str8 there is supposed to be a jet IN the tee or the tee is the jet? Or when nos merged with holley they changed the kit a lil bit right? So a 400hp rwhp engine and 30's could or could not run the 72 and 49 tee? I get confused when ppl calls the tee a jet and visa versa, but i only got one jet in my kit. and it was the 67. other ppl i talked to that bought there kits awile back says they got several jets. i really want the 175 shot but wanna be safe bout it to. And if im supposed to have a jet IN my tee, NOS shafted me.

I bought my kit last spring and I have the brass tee just like you with a 59 stamped on it. And just like you, the only jet that was in my kit was the .067 for the nitrous. My understanding though is that the earlier kits, like what Fred had, shipped with an adjustable tee that did actually have jets in it so you could adjust the fuel pressure just by popping in a new jet rather than swapping out the entire tee like what we have to do with our kit. To my knowledge NOS no longer sells the adjustable tee, which would be nice if they did since you can get a jet in about any size but appears you can only get a .059 or .042 tee.

Well i said the hell with it and ordered my tee and other jets today. The jets i got were actually a 71 jet. I will prolly hit the dyno with them soon. Man NOS knows how to make something confusing.

Awesome. Let me how it goes on the dyno.