Tuning nitrous -- a/f and ignition advance.

[Razathorn]

Is tuning nitrous basically the same as tuning boost -- needing to richen the end a/f to remove heat from the combustion chamber and using 'just under peak power' ignition advance?

Generally speaking, every resource for tuning nitrous I've found gives you the "you need to add fuel and remove ignition" shpeel, but doesn't tell you how. I have always assumed that nitrous was just 'chemical forced induction', another way to get more oxygen into the chamber, so you would probably just tune it with the same philosophy as you would a boosted motor. That is, richen things to manage in cylinder temperatures and run less timing as the mixture burns faster.

I'm specifically interested in ignition timing. With my charger, when I tuned ignition advance, I hunted for peak power, and found it quite easily. With methanol injection, I could run past best timing without detonation, but obviously I do not run like this. The tuning guides for nitrous all seem to say to retard ignition to avoid detonation and say nothing about tuning for peak power across the rpm band. I'm in a situation where I would be running water/methanol + nitrous if I added nitrous, and quite frankly, to me, it seems dumb to only retard timing on nitrous spray if detonation is encountered because my mixture will be very resistant to detonation and I could be putting unwanted stress on my bottom end being past best timing.

Am I correct in thinking that I should be able to tune nitrous just like 'additional boost' and run 'just under' best timing on the dyno?

Very interested in hearing if this is the correct methodology for tuning nitrous.

Wayne

[Hondata]

There is another factor which you need to consider - mixture burn rate.

Removing timing is necessary, not just to prevent detonation, but because a faster buring mixture does not need the same advance and also to reduce the peak cylinder pressure.

A lean mixture has a faster burn rate. Increasing the cylinder compression pressure through forced induction will increase the burn rate. Nitrous increases the burn rate.

The tricky part is determining the amount of ignition timing which you can run. Probably your method of just under best timing is good. I work of the principle of minimum timing before power drops off, but with a turbo systems you will often continue to make power as you add timing, and conversely sometimes your minimum timing is limited by the EGT.

[Razathorn]

There is another factor which you need to consider - mixture burn rate.

Oddly enough, that was the whole reason I asked about the correct methodology. I knew burn rate changed with nitrous, as that's what every nitrous tuning thing I found cited as why you adjust timing. I just drew exception to their hap hazard suggestions of "just pull a few degrees and you're good". I would always think "I'm sure hondata could do a better job of explaining this". Sure thing!

I can certainly confirm that I have observed ignition advance in a turbo rsx adding power right up to the knock limit. I tuned a revhard sc61 rsx at 9psi starting with the cn 9psi map. The last increase of 2 degrees gave more power, about 10whp, but detonated and the pull was aborted. My s/c with the methanol injection ended up having *exactly* the same timing as the s/c base maps when tuned for power, however the car accepted 3 more degrees than that map without detonation and no additional power. I was tuning in 2 degree increments and ended up one degree past the base map where I found peak power. +2 degrees was no more power and no detonation. I went back -2 and pulled one more degree to leave it right where the base map was.

Wayne