Brian Coles

Read many posts on the subject, but most are arguments of the saftey of spraying below the 3,000 mark. I wanted to know how 3,000 became the low mark? I keep seeing great numbers on stock drivetrain cars that are spraying at much lower RPMs. Many have done it multipul times. Is doing this a ticking time bomb or is the LS1 able to take it. What is the risk vs reward?

1redta

i have been under the impression spraying to early, low rpm, will let the fuel puddle in the intake

buzz12586

iTrader: (17)

The lower the rpm the more torque is created.

T = (5252 x HP) / RPM

So a 150hp shot at 3000rpm = 262 ft/lbs torque

Where as if you sprayed it at 1500rpm = 525 ft/lbs torque.

Its going to make a bigger difference in a manual car because in an auto the converter usually flashes higher than 3000 anyway. In a manual car you would be in big trouble if it bogged on the launch and was spraying at 1500 rpm.

jc98ss

iTrader: (13)

^^

Brian Coles

So the question is about how much torque and at what RPM is the LS1 capable of? If a kit is designed to spray up to 150 shot could you lower activation RPM if you are only sprayin a 100 shot?

buzz12586

iTrader: (17)

I don't have a number for what the LS1 is capable of handling torque wise. I don't know where the 3000rpm number came from but you can experiment with lower activation points. Spraying at a lower rpm under load is just going to be harder on the motor.

ATVracr

iTrader: (5)

If its a stick I would not spray below 3,000.
If its an auto ... spray it at WOT.

JL ws-6

iTrader: (50)

I have a small outlook on this and it depends on shot size. If you're spraying a 50 shot you probably can do that anytime, bigger the shot the more rpm that are needed, here's why:


Intake overlap. If you have a cam with no overlap at all (I don't think even a factory cam has this) then you probably can spray at a really low rpm, compared to a cam with alot of overlap.. you don't want the fire getting out of the cyl's and into the intake, and a cam with alot of overlap can allow that to happen at a low rpm.

So, the 3000 rpm mark, probably came abotu due to cam overlap, the velocity in the intake carrying the fuel/nos mixture, and the speed which the cyl's are getting filled, preventing any fire from getting into the intake.

Say on a race car, you are spraying 500 hp, you probably need to start spraying that into the 4000 rpm range due to overlap, and the overall shot size and tq creation like mentioned above, for example.

Hopefully that makes sense.

Brian Coles

Will the A/F ratio be effected by lower RPM activation. I'm using the HSW Interface to control the MAF signal to add fuel.

custm2500

iTrader: (11)

I have always understood that a good reason for the 3000 rpm mark is that by then the air flow in plenty powerfully through the motor that you won't have a backfire blowing the intake apart.
I never knew that nitrous made significantly more power at a lower rpm.

I am sure almost any motor on any shot it will handle, will easily go below 3000 rpm. Just like a chain rated for 10,000 lbs can easily pull 12,000 or more. But it is much safer to stay within the ratings of everything.

BAKED

iTrader: (14)

Let me try to explain this so that everyone understands.....

At 2000 RPM your engine is breathing X amount of air
At 3000 RPM your engine is breathing XX amount of air
At 4000 RPM your engine is breathing XXX amount of air
And so on and so on....

When you spray a 150 shot, it is spraying a set amount the instant you activate it weather you are at 2000 RPM or 5000 RPM and it does not change. At 2000 RPM's that 150 shot is a greater percentage of what your engine is breathing than it is at 5000 RPM's threfore creating more torque at lower RPM's.

3000 RPM is just a rule of thumb because your engine is starting to pick up RPM's pretty quickly by that point. People do spray at earlier RPM's but they are taking a risk. Sometimes a calculated risk but none the less, still a risk. Different engines will respond differently to spraying down low, alot of things come into play when you start spraying as soon as you go WOT. Things like cam, converter, gear, tranny, etc.

I spray mine as soon as it goes WOT but with my converter It really isn't that low of a RPM. As is the same with ATV's car I'm sure.

BTW, I have sprayed a 100 shot on a stock 01 SS right off the line at WOT and not had any trouble.... Probably wasn't smart but it worked LOL.

ShiznityZ28

iTrader: (11)

the tighter the convertor the less rpm it will get and the more load on the motor. if you bog it on nitrous bad things happen. there is no magic number since each convertor,gear ,tire, car weight the number would be different. most not stock auto's can take it at wot casue the convertors going to flash enough to never be an issue.

LSxPwrDZ

iTrader: (4)

Like stated above, the lower RPM you spray the car the greater cylinder pressure you create (torque). And on a stock motor those hypereutectic pistons are only going to take so much pressure. If not the pistons, the rods or even the cylinder head, gasket and bolts/studs. I've sprayed a 150 shot as low as 2000rpm before and when it ran this way could pull a 150 yr old stump out of the ground launching at the track but it was not good on the motor. I later had some backfires that I eventually found that cracked my intake! So I bumped the window up to 3000rpm where the airflow is already moving and the engine is more capable of handling that extra airflow!

NHRATA01

iTrader: (10)

Exactly as above. The mass of nitrous entering the cylinder is way, way more at a lower RPM since your nitrous system is always flowing the same amount of gas regardless of what speed the engine is turning. So your cylinder pressures are far higher because of a much stronger explosion taking place. That makes it more likely for a piston or rod to fail from the stress.

MPM IV

iTrader: (3)

Thanks for the posts. I was under the impression that it had to do with distribution based on air speed, but see that was wrong. 1st time I've realy understood it.

Brian Coles

I second that!!! I love the "which kit should I get" posts as much as the next guy , but its nice to see some tech on Tech.

It also sounds like I will be searching about a progressive set up, if I want to spray smaller shot at lower RPMs!!

WS6 Canada

I have a 3200 stall (yank) a Rossler th400 w/t-brake

Can i set the two step at 2600 rpm, activate the window switch a 2700 and then the converter flashes to 32-3600 rpm. Will the work. I use a 200 shot now. (vic jr intake)

ATVracr

iTrader: (5)

Yes but I would put it on at 2800 ... 100 rpm is cutting it close with the 2 step.

minytrker

iTrader: (13)

I used to have my nitrous come when I let go of the trans brake, same rpm as 2-step, just had a relay killing the nitrous while on the brake. If traction isnt and issue is there any down side to this?

ATVracr

iTrader: (5)

No, its fine to have it that way but he didnt say he has another relay to the Tbrake to kill the N20.

Our 2 step jumps around alot and 100rpm might be close enough to turn on the N20 if it jumped a little high once. We did it before, had the nitrous on when on the 2 step and it made ALOT of noise and left real hard. LOL