Was reading from another thread how much retard to be adding for a given HP shot of nitrous. What's the rule of thumb? I was running 4* retard with a 125 hp shot and it was still pinging (could hear it in the exhaust, but not in the car). Total timing is set at 32*;running 91 pump gas;10.25:1 compression. I know it needs valve seals, so oil might have been a factor. That will be remedied with new heads this spring.
2 degrees for every 50 hp of nitrous.But thats dependent on the combination if its detonating you need to pull out more timing or put more fuel in it.If you are getting oil into the chambers that is deadly you will hurt it.Was that 32 deg on motor and your pulling 4 more out.I would run a minimum of 6 deg retard on pump gas its safer on the wonderful gas they are selling us these days.
Rule of thumb is 2-3 degrees for every 50HP. So for a 125 shot, I would retard by about 6 degrees. Also, on 10.25:1 compression, I would use higher than 91 Octane! Sunoco used to offer 94, and even that would be borderline in my opinion, depending on your cam design. You might need even more than the 6 degrees retard because of the low octane. (Are you at a high elevation?) Keep in mind that with nitrous, it is fairly common to make more HP with even more retard than you need to get away from detonation. If you run 30 degrees with no pinging, you might even make more HP at 26-28 degrees of timing. That's because you get a different combustion than you do without nitrous. Play with that and see. And, get some more octane in there. If you can only purchase 91 octane, maybe a toluene/xylene combination will be your ticket (especially if you don't want to spend the money on race fuel). Also make sure it is a high quality fuel, don't buy it from Joe's Corner Gas Station and Laudromat- buy a reputable name like Exxon/Mobil, etc. -Bob Cunningham
Oil greatly increases detonation. On a race motor, oil blow by will burn or break a piston. If its only your seals leaking and it doesn't use much oil or smoke under WOT you should be ok. What size cam are you running? How large of cam compaired to your compression can change how much or how little you take out compaired to the rule of thumb. Intake duration under 230 can be sensative to octane and timing with 10.25 comp.
Hemi Killer Cam (241-2411 @050. I'm also at ~4000-5000 feet. I would have fixed the seals, but I knew that heads were going to be swapped withing a month or so. No smoke at WOT, just on decel. All plugs look OK except 1 cylinder. 91 Octane is the best I can get at the pump, however I did mix 30% xylene in the nitrous fuel tank. I rechecked and was running 36* total with 4* retard. Then changed it to 32* total with 4*. I haven't had a good opportunity to power-time it but suspect I'm not gaining any power over 32*. I want to make sure to pull out enough timing as I jet above the 125 hp tune-up. Adam Whitman (My old ID got nuked)
As for timing, if you can get away with more, almost always the more power you will make. Kindof odd to be pinging with what you are spraying??? The best firing nitrous system in my area is my buddy's 10.5:1 chevy 427. He runs a 300 shot gasoline conventional stage 6 with 32 total timing. (He does not take any out for the nitrous). Plugs look perfect and he has been spraying this shot on the same motor for about 2 years. Valves seals you say? What ring gaps are you running?
I disagree, especially when using nitrous! I think he will go FASTER if he retards 2-4 degrees more. Just my opinion (and experience). -Bob Cunningham
I'm guessing he's no running 91 octane? The engine smokes on decel is why I strongly suspect valve seals. That and 10% leak-down. Higher than I'd like, but not terrible. Also, chvies generally like more total than Buicks, that might have something to do with it too? I don't remember ring-gaps, but pretty sure I set them with nitrous in mind. I'll have to look through my paperwork on that as the engine is 4-years old. I kind of agree I shouldn't need that much retard, hence my thinking that oil is a factor.
Timing at altitude Adam: Most of what is said above is true, so I won't rehash it. At altitude, I race at 5800 ft, timing can be a little advanced over sea level, 3-5 deg. I run 41 total on the motor, 4.5 inch bore Chevy, and a fairly hot plug. On nitrous, I take out between 12 and 14 deg. for a 300 hp shot, depending on the DA (air). I use 114 octane fuel whenever I run nitrous, even at this altitude. I also run dead cold plugs, with a racing style (thicker) ground electrode and regular tip (not extended at all), this takes the plugs out of the equation as a starting point for any detonation. I have had plugs burn off the entire ground electrode from being too hot, I have had the engine go into detonation because of the wrong plugs and melt .200 in off the domes. (its hard to hear this with an uncapped engine turning 8000 rpm) The point is: I feel that to run ntrous and go home in one piece, it is better to be conservative and under time, under heat range the plugs, over octane the fuel and under spray. I know the last one is the hardest. :grin: As far as the oiling, what buicks4speed said is true, but get it fixed soon!!! :eek2: Good Luck, Jim
It sounds to me like he already has timing pulled out.Most bbc's like alot of timing to make the big lazy combustion chambers work 38+ on motor alone.I agree with Bob take more timing than recomended in most cases you will run more mph threw the lights.More timing at launch will allow the car to run better early if traction is available then retard the timing more down track to run it out the back door.Of course you can pull a lot of timing out at launch to help a traction limited situation then adavace it to your desired timing for down track performance.Experimenting is the only way to figure out what works for you. Adam your leak down is not to far off as long as all cylinders are even and none are past 10%.We average 7-8% leak down on our ford with 50 plus 300hp nitrous passes since we fixed it in june.I think you are on the right track with the valve seals or maybe the guides are getting loose and taking out the seals.I would hold out on spraying it until you change your heads or at least find your oil problem.
OK, I'm going to keep the total at 32 and retard 6-degrees on the juice. This is s true street drier (I drove it 180 mi to the last race I went to). That's why the 91 octane and not race-gas. I will try to plan more ahead and put some race gas in the nitrous fuel tank next time. Since the snow is going to fly here any week, It's pretty much parked until spring, when the new heads will go on, if not this winter. I've got to get my other car running before I want to pull this one apart. Rick and Bob, I should mention per your advice a while ago, the system is still working well with no hobbs switch or pressure problems. I am still planning on uprading the pump though.
What temp are you running the motor at? Over 180 with compression and pump gas can be a problem. Street Motors with alot of cranking compression can run hot.
Back when I had an engine that liked to detonate, I found Exxon's gas to be the best "street gas". I use to think Amoco was the best, but it did not help as much with minimizing detonation like the Exxon did.
