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View Poll Results: Nitrous Activation: Would you spray below 3,000 RPM?
Hell yeah, no question I would! 102 18.99%
Yes, but you're playing with fire and she may blow! 53 9.87%
Maybe, but it depends on the system and safety additions. 121 22.53%
No way, you're asking for broken stuff! 261 48.60%
Voters: 537. You may not vote on this poll

Nitrous Activation: Would you spray below 3,000 RPM?

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Old 08-21-2006, 11:28 AM   #1
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Default Nitrous Activation: Would you spray below 3,000 RPM?

PLEASE READ THE THREAD/POLL 1ST POST BEFORE YOU VOTE!!

Okay, the majority of opinions I've heard are do not activate nitrous below 3,000 RPM or major damage can result (blown intake, etc). I'm looking for those with LS1 experience with a car you own/owned, or a car you have worked on or know fairly well with nitrous. Please share your experiences (good or bad) and whether you’d activate a nitrous system below 3,000 on a stock stall converter (or even a mild stall 2500-3000 converter). I'd like to stay away from hearsay (for example: "I know this guy posting on this board that has done this blah blah...") because that's how general opinions are created, which I already know. I want actual experiences from people that actually worked on or raced these cars.

The thread about the nitrous system I’m using and results is here: http://www.ls1tech.com/forums/showthread.php?t=560804

Thanks for the help!

Derek
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Old 08-21-2006, 11:48 AM   #2
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You already know my answer

Again GL with your car.


Jon




EDIT: My actual experience (since you asked) is this. Started out with a 150 shot on a completely stock car. At first I didn't even use a WOT switch, just a button. Technique was leaving off idle. That worked fine but I would usually roll out 5-10ft before hitting the button. I knew that if I wanted to see really gain in my 60 and ET that it needed to be hit instantly off the line. I switched to a WOT switch and the end result was awsome. It took a few practice runs to get it right because you've got to be very quick about getting your foot to the floor fast, or else there will still be some hesistation. You'll actually start to roll out before the nitrous engages.

Before my WOT switch I would general 60 in the 1.7-1.8 range. My best after the switch was a 1.63 with norms in the mid-high 1.6's. This on a stock conv. 2.73 car leaving off idle.

Ran the car at the track every weekend and drove it daily during the week for over 2 years with no problems.
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Old 08-21-2006, 11:49 AM   #3
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Quote:
Originally Posted by COMNBYU
You already know my answer
Again GL with your car.
Jon
Yep, and that's why I'm asking. Never hurts to find out if more people with the same opinion exist. Thanks again!

Derek
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Old 08-21-2006, 11:55 AM   #4
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i just want to know why your engine would ever be below 3000 at WOT???
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Old 08-21-2006, 12:28 PM   #5
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3000 isnt a magic #. Its not like at 3000 youll be fine and then 2999 youll blow up instantly.

Your dealing with multiple issues here. Each is probably just as inportant as the next and youll need to understand every scenario that may happen.

1st issue is the lower you go with a wet kit the more the likelyhood of backfire in the intake. I dont care wether you think intake backfires are from puddling, or going lean or whatever the reason. The fact remians the lower you spray the higher the liklyhood. Thats not to say activation rpm is the ONLY factor. But its very high on the list of factors. Why is this? Couple things I can think of of the top of my head.

Nitrous/fuel density VS air velocity is probably one factor.
The other is intake velocity vs intake lenght from point of spray to intake valve.

Obviously the first one is universal to any car. The second one is dependant on the type of car/intake and location of wet nozzle. The second one would be a huge factor in getting on/off the throttle rapidly too.


The second issue is cylinder pressure and massive Tq spikes and its toll on part and likleyhood of detonation at that point. The lower you spray the higher the Tq the more detonation prone you are. And when you get down in the lower rpm ranges....small changes have HUGE effects. Going from 4000 as an activation point dow to 3000 is not too big a deal. But its a difference of 1000 rpm. Going from 2800 to 1800 is a HUGE deal. If you have a dyno graph of a 150 shot at 3000 rpm..and the Tq shoots to 650 rwtq at 3200 rpm and starts to taper from there....just trace that line back at the same angle to whatever rpm activation point you are thinging about and that will give you an idea of what Tq you might be seeing. The difference between 3000 and 1500 could be staggering. Especially if you were in a higher gear than 1st and ESPECIALLY if you were in a manual car or a stock stalled car. The likleyhood of engine killing detonation goes way up at this point as well. And detonation has been flagged here in previous dicussion as another likley cause for intake backfire.

So if you want to spray in the lower rpms..for whatever reason. i would just say you need to plot your goals and go over your plan with a fine tooth comb. You should be able to predict the outcome pretty closely. Then you need to think about wether that will work with pump gas and what tune. Because ultimately the octane requirements are a function of peak Tq and never peak HP. You need octane to cover your highest peak Tq since that is generally your most detonation prone area with nitrous (unless you have too much timing in another area).

In other words...if you were running a 175 shot at 3000 rpm....on pump gas and stock tune and made 575 rwtq and 525 rwhp and where just fine. Then you change the activation point to 1500 rpm...your peak Tq will go WAY up but HP will remian exactly the same. Tq would probably go over 650-700 rwtq and may well put in into an area where detonation start right at activation. and if you were on the edge before...that intital detonation at 1500-1700 rpm may continue throughout the rest of the rpm range...dooming your motor.


So if you want to spray lower than 3000 rpm....just think about the size of the shot, wet or dry, cubic inches of the motor, M6 or big stall auto, etc etc. And estimate what you think you could get away with.

75 dry on a 6.0 truck at 2000 rpm...sure..why not.

A 200 wet on a stock LS1 with a t56 in 3rd gear at 1800 rpm....not very wise.
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Old 08-21-2006, 12:38 PM   #6
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i voted maybe.

i spray a 150 dry shot, in an auto which comes on at 2800.

i have a stock stall and come out of the hole at 1800rpms, originally i had it at 3200 rpms, but it just took forever.

i think its fairly safe, using a fpss, and it being on a WS.
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Old 08-21-2006, 12:40 PM   #7
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383LQ4ss, your posts rule!

I've backfired so many times at low RPMs I can't even count them. Fortuently I have an aluminum intake manifold, and nothing really happens. I just drive through it.

If I had a plastic LS1 manifold, I'd be a lot more carefull on that lower limit. It totally sucks when a plastic manifold gets blown to pieces, damaging everythng including the hood.
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Old 08-21-2006, 01:46 PM   #8
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It is not a matter of if it will back fire at lower RPM's as much as when. The lower you activate it the more chance you have. I set my window switch at 3k. You have good velocity around that area. Reduces pooling like what was mentioned in above post.
Everyone pretty much uses that rule. IT works. I always say if it aint broke dont fix it. Get a stall and utilize your spray to its fullest potential then. Being greedy now will ultimately cost you more. Oh yeah, get a fire extinguisher.LOL
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Old 08-21-2006, 02:13 PM   #9
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Quote:
Originally Posted by CuNfUzEd
It is not a matter of if it will back fire at lower RPM's as much as when. The lower you activate it the more chance you have. I set my window switch at 3k. You have good velocity around that area. Reduces pooling like what was mentioned in above post.
Everyone pretty much uses that rule. IT works. I always say if it aint broke dont fix it. Get a stall and utilize your spray to its fullest potential then. Being greedy now will ultimately cost you more. Oh yeah, get a fire extinguisher.LOL
So having a stall would be considered a safety precaution on N20? I have a 3600 that foot stalls to about 2200... would that be safer than spraying out of the hole with a stock converter?
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Old 08-21-2006, 02:35 PM   #10
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383LQ pretty much covered it. Mine is set at 3K RPMs, and it is staying there!
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Old 08-21-2006, 05:26 PM   #11
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Damn Villain it has been 8 years or so since I even owned a rigg with a stock converter.

Get off your wallet and get one

I have torn down an engine or two that was 'sneezed'. One of them was just 'Sneezed' once. It had four bent rodd's
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Old 08-21-2006, 07:24 PM   #12
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Quote:
Originally Posted by MrDude_1
i just want to know why your engine would ever be below 3000 at WOT???
Stock stall converter is your answer. By the 60 foot it's barely at 3 grand.

Quote:
Originally Posted by TwoFast4Lv
Damn Villain it has been 8 years or so since I even owned a rigg with a stock converter.

Get off your wallet and get one
I do have one. It's in an aerodynamically challenged green car

The Formula will get upgrades once she needs an engine overhaul, including a converter. But right now she's a DD, and I don't need to tear apart something when it's working fine with 116,000 miles on it

Derek
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Old 08-21-2006, 08:20 PM   #13
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i'm one for the hit it as soon as you get it guys. i've hit it as low as 1500 rpms at the track with DRs and stock converter. it spun the tires. hooked at 1800 rpms. this was a 150 compucar kit. on a 99TA i have for about a month. (long story)

this car was all stock with 3.23 gears. got the car and immediately transferred the n2o from my 86TA to it. here's the timeslips all the same day one after the other.

Click the image to open in full size.

i did it in both of my other cars as well. now, with the 3400 converter, the soonest i've been able to get on it is 2500 rpms. that was with 315/35-17 nitto DRs.
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Old 08-21-2006, 08:25 PM   #14
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now, this also needs to be qualified with a what gear are you in question. in first gear, with the rpms climbing approximately 1000 rpms/second, the air is moving pretty darned fast to be an issue. now in drive and at 2000 rpms, it can be an issue.

another thing to consider is transmission. with a manual transmission, if you launch and the motor bogs to the point where the motor can't rpm upward fast enough, you might be having a problem.
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Old 08-21-2006, 08:51 PM   #15
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so what would you all recommend on my stock 305tbi motor with the 700r4 and stock converter because my car redlines at 5k rpms which only gives me 2k rpms to spray with could i start at like 2500 and get away with it?
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Old 08-21-2006, 08:55 PM   #16
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your car, most likely, has the even worse 2.73 gear in it. still, if it was my car, i'd go with 2500 as a starting point. then go down from there as your heart and wallet allow. the NOS system for TBI cars comes with jetting up to 125hp.
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Old 08-21-2006, 09:40 PM   #17
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I'm spraying 100 wet at 2700, alot of posts I've read and magazine articles, tell you to shy away from spraying below 2500 rpms. I've had my A/F mixture checked with the spray and am as safe as you can be with using the spray. If your gonna play with the spray, your gonna most likely end up someday having to pay.
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Old 08-22-2006, 06:07 AM   #18
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above 3,000 only
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Old 08-22-2006, 10:20 AM   #19
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its all dependant on engine load. Spraying at 1500 on a stock convertor is not the same as 1500 in a car with a higher stall as it will simply flash right up to stall speed with minimal load on the motor. Spraying that low is very risky with a stock stall but has been done by many with no problems. But even a stock stall will flash higher somwhat when sprayed that low, a stick shift car will not flash at all and that is probably the worst type of car to spray that low in.
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Old 08-22-2006, 10:37 AM   #20
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Quote:
Originally Posted by QUASAR
its all dependant on engine load. Spraying at 1500 on a stock convertor is not the same as 1500 in a car with a higher stall as it will simply flash right up to stall speed with minimal load on the motor. Spraying that low is very risky with a stock stall but has been done by many with no problems. But even a stock stall will flash higher somwhat when sprayed that low, a stick shift car will not flash at all and that is probably the worst type of car to spray that low in.
thank you.
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