Nitrous Jetting Rule of Thumb

[fastTa]

Ok, most say you should only setup your jets to spray about 50%-60% of the hp that your motor would make NA.

Now since most nitrous kits rate their various jets at RWHP levels, would that be 50%-60% of the NA RWHP?

So if you are making around 620 at the tire NA, is that to say you should feasibly only be able to spray about a 350-375 shot?

[MN6WS6]

NO!! Jetting has a lot of factors, and half of the NA HP is just a "shot in the dark" guess. It has to do with compression ratios, quality of internal components, flow numbers of the heads, octane ratings, timing, lots of things. The general "guess" on a stock motor is 50% of it's flywheel HP, but that is just a guess. That figure works on f-body's we know, but you go throw 100 shot on an S2000 and you'll be picking up parts for a month. Then again, there are overbuilt guys running 1000 HP NA motors with 750 shot of nitrous.

Those figures above are just for the engine. You also have to determine if your drivetrain can handle it. Do you have traction, stong enough clutch/tranny/rearend/chassis, all kinds of factors go into how much nitrous you can run without spreading parts over the track like the Exxon Valdez. Check around on big boards like CZ28 and LS1, and see what people with similar setups as you have are running on their rides.

[KnightFire]

I agree with MN6WS6 there are SO many variables when it comes to jetting its not even funny. MN6WS6 covered most of them, but on the safe side I would say that you should never jet for more than 1/3 of your RWHP numbers...at least on a non-nitrous prepped motor.

Oh, the only N2O kit producer I know of that uses RWHP numbers for jetting is TNT the rest use FWHP.



KnightFire

[Injuneer]

He's talking about a "serious" build - top level parts, a drivetrain and chassis that can handle it... that's a given. And the 50-60% guideline is based on "chemistry" more than anything else. As the % of O2 in the air/fuel mixture goes up, combustion speed increases and combustion temperatures increase. Go too high on the O2 % and you simply can not reliably control the combustion. Try and spray 750HP on a 1000HP engine and it will self-destruct.

The "mix" of fuel and oxygen that you get when you are fueling for both the "NA" portion of the charge and the "N2O" portion of the charge reaches that limit (rule of thumb) at about 50%. I've heard this as long as I've been playing with nitrous. Yes, you will find some fool claiming he is spraying 200HP on a stock engine and it is surviving.... but its just a matter of how long. Its pretty much the way they built my setup.... a relatively mild "street" engine that will pass emissions (less than 500HP) limited me to about 250 FLYWHEEL HP for the nitrous. They were very happy when they found they could spray 275 flywheel (56%) on my engine. It was only after I pushed them for a little more and we had a talk with the people at VP Fuels that they were willing to push it a little higher, to 300 flywheel (61%). They are now using the same fuel blend on their 7.0-second Pro 5.0 car... and based on the engine dyno numbers, they are only spraying in the 50-60% range.

I'm more confused about the claim that the manufacturers rate their jets for "rear wheel" HP.... how do they know if you are running a 12% manual tranny loss, or a 25% super loose automatic?

Additionally, the actual flow through the system is affected by virtually every component in the nitrous setup, and the length and size of the lines. Change one item, and you can totally alter the tune. Nitrous flow depends on the pressure loss in each piece of the system. The solenoids are the next limiting factor after the jets. You aren't going to jet a Super Powershot the same way you jet a Cheater solenoid. Add a filter, switch to a bottle with a super high flow valve, etc.... and you better check the jet size.

The best way to understand the jet sizing and the fuel calculations is to get the Joe Pettitt nitrous book that I have listed in my reference list. He goes into quite a bit of detail. But even that is no substitute for a shop that specializes in nitrous setups.

[fastTa]

Yes as Fred stated, only the best internals and drivetrain will be used. Callies Dragonslayer knife-edged cross drilled crank, 12.5:1 JE custom cut lightweight coated nitrous pistons, oliver billet rods.

TH400 reverse pattern full manual tranny built with straight cut front and rear planetary gears, oversized input-output shaft. Built to withstand alot of abuse! And a slightly overkill 9" out back.

And the LT1 block will be filled to the plugs with a mixture of hardblock and something else (I forgot the name?).

I will be making an estimated 620 RWHP NA so I was just trying to get a feel what I was going to spray on top of that. I was thinking of jetting the setup for a 400 shot to do the nitrous tune.

*EDIT* That would be about a 64% spray over NA increase.

We are looking at going with a cam around 282/292 @ .050", .703/.713" lift with 1.6 rockers.

The limiting factor here will not be the rotating assembly but more likely the weak LT1 block unfortunately.

Thanks for the book info Fred, I will have to see about getting a copy!

[fastTa]

BTW all of the major manufacturers of nitrous kits advertise their kits at REAR WHEEL hp levels not fly.

I am also a little confused about the generalized RWHP advertisements. I seem to remember talking to someone about this a while back. I will see if I can dig up an answer to this!