My bad. Reading comprehension>me. 3,200 is still a bit low though.

Some nitrous facts.
BMEP = ( HP * 13000 ) / ( L * RPM )
L = Displacement in Liters

Hypothetical: 6L engine makes 200hp at 2,500rpm, BMEP = 173psi. Add a 200hp nitrous shot at 2,500rpm and BMEP = 347psi. If the same motor makes 350hp at 6,000rpm, at that rpm with the 200 shot, BMEP = 199psi.

That is a simplified explanation of why nitrous at low rpm is dangerous. BMEP calculated this way is only an estimation, but the relative numbers are accurate and illustrate the point.

Rich

 

I can tell thats pressure, but what does BMEP stand for?

I've always heard 3k as the rule of thumb, but with my car my progressive starts at 3500 and is 100% @ 4500.

The problem to me still seems like the fpss, that would make sense everytime the system fires it pulls the fuel pressure down and kills the switch, pressure back up, it fires again.

I have had my wide open throttle switch do this, but mine is tied into the tps, not a micro switch. It was adjusted a little low and was on the borderline and if system voltage dropped at all it would cut off.

 

Brake Mean Effective Pressure: Brake Mean Effective Pressure (BMEP) is another very effective yardstick for comparing the performance of one engine to another, and for evaluating the reasonableness of performance claims or requirements. For completeness, the definition of BMEP is: the average (mean) pressure which, if imposed on the pistons uniformly from the top to the bottom of each power stroke, would produce the measured (brake) power output. Note that BMEP is purely theoretical and has little to do with actual cylinder pressures. It is simply an effective comparison tool.

In a drag car with an auto, if grip off the line is not a problem, the nitrous should come on just under converter stall. On a street car, thish might be too low an rpm and lead to broken parts.

Rich

 

I have a Mallory 685 box in the car. The timing has been advanced 2 degrees by MadZ28. I was running about 900 to 950 psi everytime I tried it. Is the popping detonation in the motor? I am stumped at what it might be. My friend has the same nitrous set-up on his Z except he has a Walbro 255 and his runs just fine. I am sure it is cutting off b/c of fuel, but I cant seem to figure out why when it spray it is popping so bad.

 

How many miles on the car? stock opti?
To me, sounds like fuel pump.

 

Another vote for the fuel pump. I had a stock one in my 100,000 mile car and was spraying a 100 shot and the car did the exactly the same thing. It would cut on/off throughout the whole run. I replaced it with a Walbro 255lph and had no problems what so ever with it while spraying a 150 shot.

 

The popping is not pinging, all though it may be loud enough to cover up the pinging if it is occuring. A ping sounds like marbles inside a diesel motor.

Factory bottom end? Because if you were detonating on the stock bottom end and spray it would probably be in pieces.

Popping out the exhaust? Probably going super rich -> super lean or the other way around really quick when the system fires then cuts off again. (Also your fuel psi may be low at this point since something cuts the system)
-- Or is it popping while accelerating and the system is spraying?

Even another idea. What about your opti and what plugs at what gap do you have? If its popping out the exhaust it could be you are blowing out the spark and the fuel is burning off in the exhaust.

If its popping through the intake you may have n20 or fuel puddling somewhere in the intake. If this is the case and it ever pops big enough its going to do some damage.

 

I am running on a stock bottom end with 130k miles. It is popping out the exhaust only while the nitrous is being sprayed. the opti has about 35k miles on it, it was changed by a dealership right before I got the car, and I have brand new TR6's gapped at .035 in the motor, and have put about 1k miles on them, maybe less. I am pretty sure it is either my fuel pump, or my fuel pressure regulator.

 

Your base tune has advanced the timing 2*...using the 685 retard your timing 2* to return to stovk timing. There is no need to retard an additional 5*, this could be compounding your issues.

There are a few things that we need to know to be able to accurately help you.

What is your A/F ratio? If you don't know the A/F can you read the plugs?
Do you know the fuel pressure while spraying?

 

I can read plugs, but I am at college right now and have no where to work on the car. I won't be able to check it out here in a couple of weeks when I go home. I dont know the fuel pressure while spraying. I want to get an electrical fuel pressure gauge to mount on my a-pillar but they are kinda expensive and I have no money to blow right now.

 

dynotune square fuel pressure gauge, 140 or so brand new. mine is on the way. i plan on watching it along with my N2O pressure at the same time. supposed to be very accurate gauges, inconspicuous and very useful.

 

Where did you get this from?

 

www.dynotunenitrous.com