Ive seen some dyno graphs of different systems (wet and dry) and sometimes the afr goes lean a lil bit right after the nitrous is activated. How is this avoided?

 

Its the nitrous being at a much higher pressure (i.e. faster) than the fuel pressure. I had a Holley Strip Annihalator ignition system on my 90 vette with nitrous...it had two window switches. I had one switch to control the fuel solenoid (active at 3000), and I had the nitrous set at 3200 or so. Gave the fuel a second to "get there first"

SDB

 

It's also the stock fuel pressure regulator location. Since the regulator is at the tank the system can't compensate quick enough when the nitrous first pulls fuel from the rails. If you eliminate the stock regulator and put one at the rails running a -6AN return line the spike will not be as bad. I don't think you can ever completly eliminate for the reasons SDB said.

 

Would a dry shot have less of a lean spike?

 

Not all the time but sometimes when the person that is operating the dyno hits the sample button and starts the run there is still some of the exhaust from when the car wasnt running WOT in the exhaust, so the first exhaust the Wideband see's is the cruising A/F, When the car is just cruising the AFR is around 14.1

 

Even on NA cars you can see a lean spike, the
MAF is very slow responding (thermal time scale)
and a big sudden air density spike / thermal dip
will not be passed on immediately. The MAP
transition may not even be large enough to
alert the PCM to the air surge and trigger the
speed density "fallback" as in throttle opening
MAP events.

 

God I love good ideas. I was just about to put some thought into this problem since I am doing my direct port now. Guess I can focus on something else now. Thanks for that fantastic tip!!

 

I cant qualify what I'm about to say, but I believe the cause is the fuel regulator being so far from the rail that it cant respond to changes in load quickly enough. That's why NX came out with the fuel accumulator.

If I am correct, then you will not have this problem if you use a dedicated n2o fuel system.

 

I have heard that as well Slart...I will try it the way its set up now with both noids on one window switch...with the stand alone fuel setup. If I still see a lean spike...ill try the dual window switch idea.

 

I have 3ft of braided line on my n20 noid to the n20 rails. Then I have the fuel noid right on the fuel rail. This gives the fuel a bit of a head start. This is on a carbd setup and the n20 has its own regulator.

 

After looking at your system, I'm having second thoughts. My system has much smaller lines (I've got the crappy flexible hose), so it didnt occur to me that the fill time was enough to matter.

I dont know about you, but I'm going to be running a FPSS in my auxilliary fuel system (assuming I can find a methanol compatible fpss).

Why not put a FPSS in the fuel distribution block, then wire the system so the fuel solenoid triggers solely off the button, but the nitrous solenoid triggers when the button+fpss both give a green light? This way the nitrous would wait the absolute minimum guaranteed safe time before engaging.

One concern I have is if there will be measurable fuel pressure in the distribution block. I dont think you'll see full fuel pressure because the nozzles let it bleed out. But there has to be some amount of pressure in there.

I wonder if it's enough pressure to trigger a FPSS?

Steve

 

How about putting a FP switch on the output of the nitrous fuel solenoid wired to the nitrous solenoid for a wet system. This way the nitrous could not inject until the fuel is first pressurized and flowing? For a dry system, set FP switch to the activation fuel pressure. I'd rather have a rich spike. Should this switch fail you are either back to where you were before (switch shorted) or no nitrous ( switch open) so no engine damage.

EJ

EJ

 

Ooops, correction to last post - this will not work with dry system due to the fact that you need nitrous first to get additional fuel pressure.

EJ

 

That is an interesting way to make a fail-safe a system. If the fuel sol ever failed the nit sol wouldn't energize. pretty cool

 

Brilliant!!!!!!!!....I love you guys

 

Back in '96 I bought a NOS dry kit (5122 I think) for my '95 SE-R. That is exactly how the kit worked. I later adapted it to my '97 Z28.

 

What if you just took the lines going from each noid to the nozzle and made the nitrous line longer than the fuel line? Or is the high nitrous pressure so much that you would need a really long line?
Just throwing out an idea

 

You guys are workin hard on a question I forgot about. I wasnt sure of how serious of an issue the lean spikes are. These are some good ideas how to avoid it.

 

Yes, this works to smoothen out the lean spike and also, especially on the higher HP nitrous systems, helpes to "soften the hit" if you are having a traction or suspension problem when nitrous activates. This softening often allows an earlier activation of nitrous resulting in better ETs, drive train reliability and fender longevity from hitting guard rails at drag strips.

EJ

 

One afterthought from my previous post - increasing line diameter, from nitrous valve to jet, has the same affect. EJ