Danger of spraying below 2500 rpms?
06-18-2002, 06:17 PM
#1
Danger of spraying below 2500 rpms? What can actually be damaged doing this? It seems that there are a number of people spraying well below the magical 2500-3000 rpms and not seeing any problems. I REALLY want to make ONE pass with a stock stall spraying right off the line but I can only stall up to 1800 rpms.
Thanks!
Thanks!
06-18-2002, 06:45 PM
#2
Re: Danger of spraying below 2500 rpms? Jeff, below 3K cylinder pressures aren't at optimum conditions for nitrous. I am not very good at explaning this one because I can't remember all the technical names, but all the big nitrous guys with tell you this is a big no no...
Josh
Josh
06-18-2002, 07:27 PM
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Re: Danger of spraying below 2500 rpms? Well...it depends. 3000 is just a general rule of thumb. Theoretically..if you can get away with a 150 shot at 3000 rpm you should be able to spray a 75 at 1500rpms and have similair cylinder pressures. The problem is due the static flow rate of an on/off nitrous system. A 150 shot flows the same at 2500 rpm as it does at 5000 rpm. So twice as much nitrous/fuel is packed in each cylinder event at 2500 than at 5000. Hence the huge Tq jump at low rpm as seen on the dyno that tapers down with rpm.
As far as spraying off the line...that would be your call. Ive seen people do it with a 125 shot and no problem, although they may have had a higher stall...but youd be walking a very fine line IMO and it would be a crap shoot. Youd be better off getting a progressive controller and dialing in half your shot or so for off the line and ramp up to %100 quickly. Brook(99Redhawk)...who took his stock shortblock very far finally blew his stock shortblock spraying like a 300 shot off the line. He shattered a few pistons and bent half his rods into the shape of a Z. Basically completely destroyed his motor. Of course he knew the chance he was taking beforehand.
<small>[ June 18, 2002, 07:29 PM: Message edited by: 383LQ4SS ]</small>
As far as spraying off the line...that would be your call. Ive seen people do it with a 125 shot and no problem, although they may have had a higher stall...but youd be walking a very fine line IMO and it would be a crap shoot. Youd be better off getting a progressive controller and dialing in half your shot or so for off the line and ramp up to %100 quickly. Brook(99Redhawk)...who took his stock shortblock very far finally blew his stock shortblock spraying like a 300 shot off the line. He shattered a few pistons and bent half his rods into the shape of a Z. Basically completely destroyed his motor. Of course he knew the chance he was taking beforehand.
<small>[ June 18, 2002, 07:29 PM: Message edited by: 383LQ4SS ]</small>
06-19-2002, 05:18 PM
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Re: Danger of spraying below 2500 rpms? On Brooke's motor the #6 piston was Gone when they pulled the motor apart, and as stated above many of the rods were bend this way and that. From my understanding he was trying to blow the car up that day. lol <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
06-19-2002, 05:53 PM
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Re: Danger of spraying below 2500 rpms? Think about using a Jacob's Electronics Progressive Controller. As a result you COULD start spaying at say 1800 rpms to the extent of 50% and progressively increase the shot to 100% at say 6000 rpms. This should result in optimum performance in terms of hp/torque, traction, and yet be safe for your motor. Obviously, this assumes you take all other common sense precautions such as fuel, retard timing, plugs & gap, fuel pressure, n2o pressure, a/f ratio, etc. As a bare minimum, I'd consider using higher octane fuel (preferably 110), retard about 6 degrees, and insure that your fuel pressure is more than adequate. That'll give you some "insurance" against detonation. Then, "take it easy" by programming the Jacobs at say a 9 0r 10 setting, meaning at 6000 rpms you'l only be utilizing 60% of the n2o shot (6000/10000). You can work up the n2o from there if all is well, and reading the plugs indicates no early signs of detonation. Best of luck.
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06-28-2002, 08:04 PM
#10
Re: Danger of spraying below 2500 rpms? DONT SPRAY AT LOW RPM, FOR ONE N20 ADDS A HP THRU A JET WHERE 100 HP IS 150 TORQUE AT 3500 BUT YOU ADD 100 HP AT 1500 ITS LIKE 400 TORQUE YOU TRY TO INCREASE POWER THAT MUCH IN .1-.2 SECONDS YOU'LL START BENDING RODS OR CRAPPIN GASKETS, AND AT LOWER RPM THE CYLINDER PRESSURE IS HUGH COMPAIRED TO 3000-3500. 1500 RPM LAUNCHES ARE NOT WORTH THE ADDED TORQUE-VS THE COST OF VERY LIKELY ENGINE DAMAGE, I RAN A 250 -350 SHOT IN A SMALL BLOCK MY LOWEST RPM EVER WAS 3000 GOING FULL THROTTLE 1ST. DON'T LISTEN TO ANYONE WHO TELLS YOU TO SPRAY THE CAR AT 1500 THERE RETARDED
07-03-2002, 11:03 PM
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Re: Danger of spraying below 2500 rpms? I've seen an LT1 car launch a little to easy while on the bottle. The car bogged and the induction was blown off. Luckily there wasn't any other damage but there was a small flame that shot out that looked pretty interesting. I always recommend a minimum of 3000 RPMs before spraying.
Tom
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07-04-2002, 06:36 PM
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Re: Danger of spraying below 2500 rpms? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by RAGENZ28:
<strong>DONT SPRAY AT LOW RPM, FOR ONE N20 ADDS A HP THRU A JET WHERE 100 HP IS 150 TORQUE AT 3500 BUT YOU ADD 100 HP AT 1500 ITS LIKE 400 TORQUE YOU TRY TO INCREASE POWER THAT MUCH IN .1-.2 SECONDS YOU'LL START BENDING RODS OR CRAPPIN GASKETS, AND AT LOWER RPM THE CYLINDER PRESSURE IS HUGH COMPAIRED TO 3000-3500. 1500 RPM LAUNCHES ARE NOT WORTH THE ADDED TORQUE-VS THE COST OF VERY LIKELY ENGINE DAMAGE, I RAN A 250 -350 SHOT IN A SMALL BLOCK MY LOWEST RPM EVER WAS 3000 GOING FULL THROTTLE 1ST. DON'T LISTEN TO ANYONE WHO TELLS YOU TO SPRAY THE CAR AT 1500 THERE RETARDED</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Retarded huh <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" />
Like I said..3000 rpms is just a general rule of thumb. If we want generic info we would all run generic kits and follow generic rules. Theres alot more variables that will determine safe rpm to spray than just saying 3000 rpm is good and 2999 you blow up. The two main conditions that could be unsafe with spraying at a given rpm are obviously:
1) nitrous backfire which will damage various intake parts and is a fire hazard and
2) very high cylinder pressure which could exceed load limitations of engine parts
Variables that could lead to condition #1 are mainly:
1) size of shot
2) wet or dry
3) intake design
4) flow rate of intake charge (RPM)
Variables that could lead to damaged parts as a result of condition #2:
1) size of shot at given rpm
2) rpm shot is introduced
3) detonation (can occur at any RPM)
Yes theres more...but those are the basic variables.
So....first question...what are we talking about...wet or dry? Lets talk dry kit first, and we are talkin LS1 only here. I have never seen an LS1 dry kit have a backfire through the manifold. Never! Even 99Redhawk sprayed a large shot right out of the hole with no problems of backfire and I have sprayed 200 on many occasions. I think if the car is in good running order a dry nitrous backfire isnt a consideration. So then for a dry shot we are basically only worried about inducing high cylinder pressures by spraying too low in the rpms. What would be the safest shot at given RPM? There is no "magical" rpm number. If its ok to spray a 150 shot dry at 3000 rpm (as has happened many times) then what would be the lowest rpm you could spray a 50 shot dry? Certainly lower than 3000 rpms. Get my point? My new nitrous setup will be RPM based, and nitrous will start flowing below 3000 rpms..probably 2500. It will be a dry shot and ramp up from 0% at 2500 rpm to 100% at 5800 rpm and stop flow at 6400 rpm. It will likely be a 250 shot dry. So between 2500 rpm and 3000 I will likely see no more than a 40 shot or so ramping up from 0. Not unsafe IMO. Especially with a forged bottom end.
Ok...lets talk wet kits. Wet kits have all the consideration discussed above...but have the added problem of nitrous backfires. The LS1 manifold is not really that bad for spraying a wet shot. Its not the greatest...but people have regularly sprayed a 150+ with very few backfires overall. In this case the 3000 rpm recomendation is probably a good general rule of thumb. Just not worth the risk IMO.
If your just going to add an off the shelf nitrous kit to your car and not modify it then by all means...follow all the basic guidelines that came with the kit, nothing wrong with that. But there are lots of people out there that tweak and build and use progressive controllers and dual dry/wet stages and tweak shot sizes as well as activation points at 100 rpm increments and do all kinds of other stuff. In this case having a good understanding of the dynamics involved will come in handy. I dont want my knowledge of nitrous use limited to generic statements that come in the instruction pamphlet. I want to continue to learn so I can apply some knowledge to getting the most out of nitrous while doing so safely.
Al
<small>[ July 04, 2002, 08:55 PM: Message edited by: 383LQ4SS ]</small>
<strong>DONT SPRAY AT LOW RPM, FOR ONE N20 ADDS A HP THRU A JET WHERE 100 HP IS 150 TORQUE AT 3500 BUT YOU ADD 100 HP AT 1500 ITS LIKE 400 TORQUE YOU TRY TO INCREASE POWER THAT MUCH IN .1-.2 SECONDS YOU'LL START BENDING RODS OR CRAPPIN GASKETS, AND AT LOWER RPM THE CYLINDER PRESSURE IS HUGH COMPAIRED TO 3000-3500. 1500 RPM LAUNCHES ARE NOT WORTH THE ADDED TORQUE-VS THE COST OF VERY LIKELY ENGINE DAMAGE, I RAN A 250 -350 SHOT IN A SMALL BLOCK MY LOWEST RPM EVER WAS 3000 GOING FULL THROTTLE 1ST. DON'T LISTEN TO ANYONE WHO TELLS YOU TO SPRAY THE CAR AT 1500 THERE RETARDED</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Retarded huh <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" />
Like I said..3000 rpms is just a general rule of thumb. If we want generic info we would all run generic kits and follow generic rules. Theres alot more variables that will determine safe rpm to spray than just saying 3000 rpm is good and 2999 you blow up. The two main conditions that could be unsafe with spraying at a given rpm are obviously:
1) nitrous backfire which will damage various intake parts and is a fire hazard and
2) very high cylinder pressure which could exceed load limitations of engine parts
Variables that could lead to condition #1 are mainly:
1) size of shot
2) wet or dry
3) intake design
4) flow rate of intake charge (RPM)
Variables that could lead to damaged parts as a result of condition #2:
1) size of shot at given rpm
2) rpm shot is introduced
3) detonation (can occur at any RPM)
Yes theres more...but those are the basic variables.
So....first question...what are we talking about...wet or dry? Lets talk dry kit first, and we are talkin LS1 only here. I have never seen an LS1 dry kit have a backfire through the manifold. Never! Even 99Redhawk sprayed a large shot right out of the hole with no problems of backfire and I have sprayed 200 on many occasions. I think if the car is in good running order a dry nitrous backfire isnt a consideration. So then for a dry shot we are basically only worried about inducing high cylinder pressures by spraying too low in the rpms. What would be the safest shot at given RPM? There is no "magical" rpm number. If its ok to spray a 150 shot dry at 3000 rpm (as has happened many times) then what would be the lowest rpm you could spray a 50 shot dry? Certainly lower than 3000 rpms. Get my point? My new nitrous setup will be RPM based, and nitrous will start flowing below 3000 rpms..probably 2500. It will be a dry shot and ramp up from 0% at 2500 rpm to 100% at 5800 rpm and stop flow at 6400 rpm. It will likely be a 250 shot dry. So between 2500 rpm and 3000 I will likely see no more than a 40 shot or so ramping up from 0. Not unsafe IMO. Especially with a forged bottom end.
Ok...lets talk wet kits. Wet kits have all the consideration discussed above...but have the added problem of nitrous backfires. The LS1 manifold is not really that bad for spraying a wet shot. Its not the greatest...but people have regularly sprayed a 150+ with very few backfires overall. In this case the 3000 rpm recomendation is probably a good general rule of thumb. Just not worth the risk IMO.
If your just going to add an off the shelf nitrous kit to your car and not modify it then by all means...follow all the basic guidelines that came with the kit, nothing wrong with that. But there are lots of people out there that tweak and build and use progressive controllers and dual dry/wet stages and tweak shot sizes as well as activation points at 100 rpm increments and do all kinds of other stuff. In this case having a good understanding of the dynamics involved will come in handy. I dont want my knowledge of nitrous use limited to generic statements that come in the instruction pamphlet. I want to continue to learn so I can apply some knowledge to getting the most out of nitrous while doing so safely.
Al
<small>[ July 04, 2002, 08:55 PM: Message edited by: 383LQ4SS ]</small>
