I'm running a 150 wet shot thats supposidly rated at the flywheel (63/35 jets). My car has a dyno tune as well, full boltons, heads/cam ect... Some people say 2 degrees ever 50hp, so that would be 6 degrees but that seems like alot to me.

 

dyno tune FOR the n2o or for the heads/cam. if it was a motor tune i wouldn't even spray it at all till you got back on the dyno, who knows what type of timing/fuel curve it has.

 

As the gent above me said I would see what it is doing on the motor first and then address the timing for the N2O. If your A/F ratio is straight on the motor runs and there is no knock then I would pull out 6 degrees and add it back over a couple of pulls to see how it likes it while spraying it. You may find that you are able to run it without pulling any timing but depending on your cam and heads it may require that you either A) Add some octane, B) Pull some timing or C) Both. Just take your time, check everything twice and don't be afraid to ask. Good luck to you and I hope this helps.

Jim C.

 

I agree with the above posts. The pull 2 degrees per 50 hp shot is a blanket safety statement for those which have no access to dyno or tuning programs.
Robert

 

I run stock timing with a 150 shot. I do have it tunerd for AFr though, no issues here.

 

guys, sorry he hasn't responded, but he's running the mallory 685 ignition box which allows him to retard timing ON THE FLY when the nitrous is activated

so his dyno tune is for motor, then the 685 does it's thing when the nitrous is on.

hope that clears things up a tad.

oops, posted under a buddies screen name
<---HybridZ28

 

Like he poted above me I have the mallory 685 box. When I had a mail order tune I had 43 degees total timing and my car wasn't pinging, but after the dyno tune he kept pulling timing until it started to lose power, and ended up pulling 5 degrees and gained me 5 peak rwhp, and 30ft lbs of torque down low. So it is dyno tuned on motor, and I have an ignition box to pull timing on spray. On the 125 jets the a/f was high 11's, so I know its fine on the 150. I am going to get it on the dyno again, probably within the week since a shop where a couple of my friends work at just got a dyno put in. My friend was spraying his tuned LT1 with a 175 shot and was only pulling 2 degrees of timing and it lasted 2 years. It didn't blow up from detonation though, he dropped a valve seat. I also have a scanmaster in my car too, so I can see if I get any knock retart at all on spray. So what would be a good amount to pull, 3 degrees, mabey 4?

 

dont' really know on lt1's, but i'd go by what it runs as stock timing and then maybe bump 2* off of that to be safe. unless lt1's are REALLY conservative on timing.

if you got ***** go out retard like 6* or whatever, and start adding timing till it pings a tiny bit, checking plugs as you go, then you know where you are. otherwise there really is no way to tell. probably go through a couple bottles doing this also but that is pretty much what i would do. watch the kr like a hawk, any spec of knock you know you are at the limit and knock out 1-2* and you are good.

 

You don't just pull timing to keep it from detonating you need to pull the timing to compensate for the increased burn rate of the nitrous. You want to have everything burned by about 15-17 degrees after TDC by adding nitrous you are increasing the burn rate which is what requires you to pull the timing back so that you are still burning everything and generating peak cylinder pressure at the proper time. If you had the car tuned and had the timing set to were the engine liked it best then you want to pull about 2 degrees per 50hp. So on 175 you may want to start at 7 degrees. This is a fairly conservative number and you might be able to ad a degree or two back into it and pick up a little more power.

 

Good post SRS you are correct