View Full Version : A Few Nitrous Questions

06-09-2014, 05:01 PM
I spent quite a bit of time searching for some answers, but I was unable to locate them. So i apologize in advance if this has been asked before.

I have a few questions about nitrous use:

What is the largest shot of nitrous that has ever been used on an SC? (the most that I've read so far is 125 shot)
Has anyone ever broke a factory SC rod with nitrous?
Are blown headgaskets more of an issue with nitrous than the strength of the internals?

Thanks for everyone's input in advance!

06-11-2014, 12:02 AM
If anyone can share their nitrous experiences, that would also be useful. Such as: Dry vs. wet, size of shot, any damage, etc.

XR7 Dave
06-11-2014, 08:26 AM
Several issues with nitrous.

1) Stacking power adders is always dangerous. If you have a lot of experience with nitrous and supercharging, then it is possible to have success with it. If you don't have experience with both independently then most likely you'll be adding your name to a long list of nitrous equipped SC's that went "boom" in a variety of ways.

2) In order of things likely to fail, 1) headgaskets, 2) pistons, 3) bearings, 4) rods. The headgaskets fail all the time anyway, even on stockers. The pistons are hyperutectic so you have little margin for error. Broken ring lands are most common. Bearings are destroyed by detonation which is pretty much guaranteed if you run nitrous. Rods will bend and then subsequently break, but usually it's preceded by a cracked piston skirt or something else first.

3) The stock tune is pretty aggressive for nitrous. If your knock sensor is functional it may protect you, but if you happen to make a pass before the EEC switches it on (it's not on until several parameters are met first), then you will have too much timing and it will blow up. This is a common occurrence at the drag strip.

4) People generally chicken out or break stuff at the 100-150hp level. This is partly because the SC intake manifold delivers air at the back of the motor which feeds cylinder #3 first. So on a 150hp shot instead of sending 25hp to each cylinder, #3 gets probably about 50hp. Since the EEC doesn't allow individual cylinder tuning, there is no way to counteract this.

5) What type of system you use depends on a variety of things. ZEX dry kits raise fuel pressure to get more fuel to the motor. In order to use this you must have a very strong fuel pump capable of operating at very high pressures. Also, the higher the HP shot, the more fuel pump, and the curve isn't linear so keep that in mind. With a wet kit the system provides it's own fuel, but if you pull fuel from the rail itself (most people do) then you will experience a lean spike whenever it energizes due to temporary pressure drop. There are things you can do to minimize this but the bigger the shot, the bigger the spike. Other dry kits require massive tuning to add in the required fuel and very big injectors.

7) If you have to ask, then you probably shouldn't do it. There are too many things that can go wrong and you probably don't have the money or experience to deal with them. If you insist then I suggest starting with a ZEX 50-75hp dry shot and leave it at that.

06-11-2014, 10:34 PM
Thanks! That response answered all of my questions. The unequal distribution of nitrous between the cylinders is especially interesting, and that explains a lot of different issues that I've read about.

06-12-2014, 06:31 AM
Dave is a Supercoupe guru and no one probably knows more about them than him. I agree with everything he's mentioned but I do want to say that I'm one of the success stories of spraying nitrous on a Supercoupe , for years. I do have a built motor with all forged internals so it can handle what I throw at it up to this point. I regularly sprayed a 100 wet shot with a MPx blower but now that I have a 2.3 Whipple I plan on spraying a 50 shot. I have yet to go down the track with the Whipple so it's yet to be determined what'll happen with the 50 shot added to it. I started with a 50 shot, then a 75 shot and finally settled on a 100 shot which gave me the best results in the 1/4 and dyno. My car gained 1.1 seconds in the 1/4 and 100+ rwhp with the 100 shot. I tried a 125 shot a few times but nothing really improved so I backed it off to a 100 shot. Nitrous is definitely not for everyone or their cars and you're absolutely upping the chance for something to break for a variety of reasons as Dave has pointed out. But when working properly it definitely ups the fun factor............:)

06-12-2014, 08:49 AM
Just to echo with what others have already stated...

I've been running nitrous on my car since 2003. I ran a ZEX dry kit, primarily because it uses a TPS switch which made a cleaner install. As Dave mentioned, the ZEX kit uses some nitrous to physically push harder on the fuel pressure regulator in order to increase fuel pressure and increase fuel delivery. Other dry kits perform the same function, but not all, so check to see how they install their systems. If there is no method of fuel enrichment, it'll take some work in order to run a safe ratio. I've typically kept this around a 75"shot", which gave me about a second in the 1/4 and about 65hp at the wheels.

I've had good luck with my set-up on stock internals, but I kept the jets at reasonable levels. When running nitrous, I use a different tune in order to command a slightly richer target fuel ratio, and then tune my fuel jet in order to match my target ratio. I believe I was targeting around 11.8 on nitrous, 12.2 without. I also pulled out some timing globally while using nitrous as well via the tune.

Having the abililty to monitor a wideband and control the ECU via a chip is a nessesity if you intent to run nitrous reliably. Again, as Dave mentioned, you'll need a fuel pump able to keep up with the added pressure demand of a dry system. I monitor and log fuel pressure so I can see any trends in pressure, especially at higher RPM's. Stock fuel pressure is about 40psi static, add on 12-15lbs of boost and that fuel pressure jumps to 55psi under WOT. Tack on the additional nitrous-demanded fuel and I've seen that pressure easily reach over 65psi, which is demanding of a fuel pump.

Just be smart with whatever you decide and you'll be OK