So a friend of mine has posed a question. He has a 94 TA and is planing on building a motor for nitrous. I know there won't be any hard answer but I'm hoping to get some ideas from more experienced Nitrous users.
Basically He wants a sleeper, mild cam without much lope. It already has all the bolt-ons. Assuming a multiple stage system with a separate fuel supply on Race Gas anyone have any ideas on the amount of nitrous we can safely squeeze into the motor? I don't know how feesible it would be but in the conversation our goal was 700whp, assuming 350whp on the motor that would require approximately a 450 shot. Any thoughts?

 

Would need a 350 shot

If the bottom end will hold together this wont be too big of an issue for pumpgas. I would prefer some racegas for saftey, but as long as its jetted a little rich and the bottom holds gas wont be a factor.

Pull some timing though.

 

Many people use a guideline that limits the maximum size of the shot to 50% of the engine's NA flywheel power. If your 350rwHP motor was sitting behind an 18% drivetrain loss, it would be making 425 at the flywheel. Spraying a 350-shot on top of that would mean you are spraying more than 80% of the NA HP. The problem is that as you increase the percentage of power made with nitrous, the percent O2 in the mixture starts to climb, and as the percent O2 increases, the speed of combustion really starts to increase. To do that large an increase on a pump gas/race gas mix would seem like a bit of a stretch.

I used a similar approach.. a relatively mild 500 HP (NA) setup, with a 300-shot (60% of NA power). But that's on pure C-16. Yes, my engine builder/tuner is very conservative, but so am I.

 

ON my 408 350 was about the limit before it started being just to hot in the chamre to keep it from melting ****. but i had a tight quench . If i built the motor for pumpgas i think we could have got 450 in it.

 

Big shot on pump gas could be done. But total timing would have to be about 18*. The 2* per 50hp doesn't always work. It is better to pull extra timing and check the plugs jetting it rich doesn't really help.

 

The tune has a lot to do with it and the build a little bit as well. Nitrous accelerates combustion, so to avoid excessive cylinder pressure too early in the power stroke as well as pre-ignition, the timing has to be retarded. Nitrous also produces a lot of heat (that's why it makes hp) and can lead to local overheating which in turn can cause detonation. This is why you use extra fuel with nitrous, beyond the chemically correct amount per the mass of nitrous injected. This cools the chamber and also slows combustion. I have never done the experiment, but I think you reach a point of diminshing or negative returns if you have to keep pulling timing and making it richer to avoid detonation or preignition. I have seen big blocks live with 300hp shots on pump gas, but they were very rich with very retarded timing. I wonder if they would make just as much power in a safer and cheaper manner with less nitrous and a better tune?

I am sure people have investigated this, I know David Vizard has done a lot of dyno testing with nitrous and I am sure others have as well. The problem is finding unbiased data. It is expensive to do this kind of testing, so I think the people who pay for it keep the info proprietary unless it helps sell their product.

All of these leaves out the issue of breaking something simply due to excessive cylinder pressure. If I had a stout motor I could afford to break, I would go as far as maybe a 300 shot but I would back the timing way off and aim for 10.5-11:1 AF ratio. This is an area where water injection might really help, but this is something that I have never seen investigated. I may try and talk the boss at the shop into it. Get someone to give us a car to test it on, and they get the water injection for free? Of course, they might also get a busted engine so it they would have to a real gambler. Maybe we could get a magazine to sponsor it?

Rich

 

This is a quote from a guy that builds cars for the pump gas drags and works on nitrous kits fro the bb guys running three foggers



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"X" amount of degrees per hundred sprayed, is a useless way to figure it, does not work. If I suggest across the board numbers, and your initial is at 35*, somebody else is at 40* and someone else is at 30*, who is at the right place. While N/A, optimum timing numbers can vary greatly, that is not the case on spray. Most all motors, given similar combustion chambers and compression ratios and spraying similar amounts of nitrous, will be within a degree or two on spray, I don't care if the initial was at 30* or 40*. So as I said, I will never give you a number per hp to pull. I will just tell you where you need to end up. To spray your motor 250, on pump gas, you will likely need to be at 16-19 degrees total. If that seems low, it is because 90% of people run way too much timing on the hose and you are used to hearing those numbers. That same 90% of people that run too much timing, also run way too much fuel, which will cover timing to a point on a smaller tune, but when the tune gets bigger, the combination of the two leads to beat up motors, pinched rings and burned pistons. I will challenge any nitrous racer on this board, to show me a piston that was burned because of a lean condition, that was NOT a mechanical malfunction. Bet we won't find one. I have been using nitrous for 30 years, I personally have NEVER gotten a tune lean enough to burn a piston. Got a boatload of hurt pistons from too much fuel and/or timing.

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Just trying to get more opinions I agree with the 11:1 but have seen guys go for lower to mid tens and burn pistons from to much timing

 

Disagree about the fuel.

Rich

 

Dissagree all you want 90% of all nitrous motors hurt are form to much fuel not to little. timing is not an issue until the fueling is right. then once its right timming will bite you.

 

How many nitrous motors have you seen hurt and how did you determine that is was "too much fuel" that did it.

Rich

 

How do you determine the correct amount of timing versus Air/Fuel? I Could only assume trial and error on a dyno would only way to find out but when talking about a large shot that gets pretty expensive.

 

Enough....

Heres how it works. the extra fuel gets down between the ring lands and pops off it pushes the top ringland up. then as more fuel pops off it melts the top till you can see the bottom of the ring package. it tends to happen in the 10:30 position on ls1's especually on valve relif motors. also once the rings are compromised the oil gets in and melts the plug off.

LS1 guys need to step out of the box and ask big nitrous guys how it works.( im not one of them) We have learned the hardway to. I started to do alot of research on nitrous from guys who's been racing longer than ls1's have been around.

 

THeres no magic number. but first you will need a lean and mean motor tune. then based on lbs/hr of nitrous there are equasions to get you close. but the only way to know is read the plugs. and if your not cutting the threads off to see the bottom there is no way your doing it correct. you need to see the very bottom of the porcelin.

 

Do you have a link to the equasions? What are you looking for on the bottom of the porcelin, a consistant coloration of the plug or evidence of detonation?

 

It seems like I read that before. From the guy I quoted before. He wasn't talking about LS1's just about nitrous in general with everyone else saying to stay rich he says lean it out and pull timing.

I may make a attempt to get in the pump gas drags next year. So we'll just have to see how it goes.