Nitrous on 2.5 Drag

[CI STV]

Anyone with hands on experience care to share or at least discuss nitrous tuning for two strokes on here?

There’s lots of discussion and a ton of data on jetting and tuning nitrous on 4-stroke cars, but almost nothing on two strokes.

A few forums I’ve come across have referred people to this forum, but there’s not a lot (except one great thread on nozzle placement, etc) on here either.

I get it that most competitors want to keep their tune ups to themselves, especially since they probably had to learn it the hard way themselves.

BUT, surely we can have a general discussion about some of the basics on here, no?

Just speaking for myself, I’ve had to take educated guesses at things like:

(1) Nozzle/injection placement: In front of reeds (outside of crankcase), but not directed at the reeds (to prevent the nitrous stream from working against crankcase pressure) seems to be the consensus?

(2) Timing: Do we need to retard timing using the commonly accepted 2 degrees per estimated 50hp (based on jetting) of nitrous injection? There’s been a paradigm shift in the thinking on timing and it’s relationship to fueling, which we can discuss in due course.

(3) Jetting: can we follow the jetting charts on the major nitrous companies’ websites, or do we need to add some fuel jet size to compensate for oil content (assuming that one is using the same fuel supply for nitrous-fuel enrichment. Here, for four strokes at least, there’s also been a major change in the old mindset of “richer is safer”, and we’ve generally gone from having bigger fuel jets than nitrous jets to using fuel jets that are much smaller than the nitrous jet, to the extent that on high fuel pressure systems, the fuel jet is roughly half the size of the nitrous jet.

Those things should get us started and I’m happy to expand into to anything else anyone may think we need to discuss.

I do understand that there’s a lot of variables involved and there’s always going to be more than one way to skin the cat, so to speak. But there doesn’t seem to be any company around that specializes in nitrous kits two strokes (at least not that I know of) and a lot has changed since the old days when you could buy a spray bar or twin nozzle kit from Chuck Goodman/Nitrox, since he’s passed. I had one of his kits and it worked great, but that was 20 years ago, and a lot has changed since then.

This is not a “fishing expedition” intended to provoke argument or a pissing match. I’m just trying to get as much help as I can setting up my system so that I don’t blow it up. I’m happy to post up everything I’m doing, unless someone shares something they want kept confidential.

[donmac]

Marv Jorgenson , did a sled with 2.4 on nitrous years ago thinking they were squeezing 420hp out of it in a 500lb. sled!! you might try looking if Hypersports is still around! not sure if they were nitrous or nitromethane engine builders!
We tried fuel mechanical fuel injection back in the late 70's on 235omc's which worked but drivability was tough and turboing a 2 stroke was unheard of but it works today!

[BUZZIN' DOZEN]

I don't know if he still would be any help but, Earl Moorman was hands down the best nitrous man in the day, they LEFT THE LINE on nitrous and added 1 or 2 more stages with their drag hydro

last I know of contact, [COLOR=rgb(var(--color_15))]Lightning Performance Group / Ph: 309-562-7271 / Easton, IL [/COLOR]

[LakeFever]

I’m not a nitrous guy but I have seen quite a few set ups. The ones I like the best are wet and treated entirely independently from the engine fueling. There’s some math calcs out there on how big of a shot needs so much fuel using such and such jet at whatever psi. Add a small stand alone tank with electric pump and put some hi test ultra rich premix like 20:1 or something like that. Stuff the nozzles in the intake tract somewhere after the engine fuel delivery area like the carb boots or a tapped bung. Have at it. Start rich and dial back as needed

[CI STV]

I don't know if he still would be any help but, Earl Moorman was hands down the best nitrous man in the day, they LEFT THE LINE on nitrous and added 1 or 2 more stages with their drag hydro

last I know of contact, [COLOR=rgb(var(--color_15))]Lightning Performance Group / Ph: 309-562-7271 / Easton, IL [/COLOR]

Thanks. I’ve heard of him. Pretty sure I read somewhere he was the guy that did David Carver’s setup. That was a monster. Basically the same setup I’m going to be running, except mine’s gonna be much slower, LOL.

[CI STV]

I’m not a nitrous guy but I have seen quite a few set ups. The ones I like the best are wet and treated entirely independently from the engine fueling. There’s some math calcs out there on how big of a shot needs so much fuel using such and such jet at whatever psi. Add a small stand alone tank with electric pump and put some hi test ultra rich premix like 20:1 or something like that. Stuff the nozzles in the intake tract somewhere after the engine fuel delivery area like the carb boots or a tapped bung. Have at it. Start rich and dial back as needed

Thanks. For now I’m running it off the otherwise blocked outlet port on the regulator. I have so much fuel volume that there’s no way I would need a standalone system. I’m logging fuel with an AiM Datalogger and fuel pressure is rock solid. Will have a low fuel pressure shut off switch on it anyhow.

I only run C12 or Sunoco 112 anyhow, so octane won’t be a problem. Will use Reline Racing 2-stroke oil at either 25:1 or 32:1.

Was running 17cc pockets in the heads but switched back to the 21cc pucks yesterday, just to get more chamber volume and less quench area to prevent detonation.

I’m starting with some 0.020 jets on the nitrous. N.O. recommends a 0.009” fuel jet for a 20 N jet @ 55psi fuel pressure, but I’m going to start with a 0.012.

[CI STV]

[LakeFever]

Very nice work! Clean and tight. Wet system port per each exactly how I would do it. I would say the only tricky part left is shutting down at speed to read the plugs. I’m not sure if you have done that yet but it’s hairy and the transom gets swamped.

[25two.stroke]

I do know the guys who used to drag race 2.4 and early 2.5L out here on the west coast used a solenoid that mechanically retarded the timing whenever the nitrous was activated. 18 or 19 degrees was preferred over 23-25 or whatever your preference without nitrous. Since the timing arm is spring loaded they just hooked and extra arm on a solenoid that pulled it back. I believe this could be done more easily by influencing the bias circuit to ground with a resistor...

If you haven't already done this you should consider it at least during initial setup. I know it worked.

[CI STV]

Very nice work! Clean and tight. Wet system port per each exactly how I would do it. I would say the only tricky part left is shutting down at speed to read the plugs. I’m not sure if you have done that yet but it’s hairy and the transom gets swamped.

Thanks. I’ve put a lot of time into figuring out where everything goes. This is a V8 nylon/shower-head direct port kit that’s good for 400hp, but I’m not going anywhere near there. Maybe 150. But I’ll test it at 75-100hp first.

I still haven’t finished everything up yet, so no testing as yet. Need to swap out my 2:1 L/U to the 1.78 otherwise I’ll be out of prop long before the 800’ mark. Last pass I made with it before I installed the nitrous, it went 10,350 in about 800’, so I know I need more gearing.

Don’t need to worry about it swamping. This old STV can glide without power for hundreds of feet before it settles down. I’ve shut it down by accident (hand hit the ignition toggle) at high speed a couple of times and it just keeps going for a couple of hundred feet before it even starts to slow down.

I also have a test prop, so I might give it a couple of quick hits with it tied on the trailer just to make sure everything works, before making a test pass.

I’m triggering the nitrous via the WOT button on my pedal that triggers the timing computer, and I’m using an rpm Window Switch so it only activates at >3500 rpm and shuts off at like 10,400.
I’m going to set the limiter at 10,750 or so, and avoid running it past 10,500 as best I can.

It took me awhile to figure out how to get the right RPM on the Window Switch. For those who want to know, you have to use the “Distributor” type ignition setting and then use that with the 12 cylinder (four stroke) setting.

[CI STV]

I do know the guys who used to drag race 2.4 and early 2.5L out here on the west coast used a solenoid that mechanically retarded the timing whenever the nitrous was activated. 18 or 19 degrees was preferred over 23-25 or whatever your preference without nitrous. Since the timing arm is spring loaded they just hooked and extra arm on a solenoid that pulled it back. I believe this could be done more easily by influencing the bias circuit to ground with a resistor...

If you haven't already done this you should consider it at least during initial setup. I know it worked.

Now there’s a hell of an idea! And electric servo that moves the timing arm…
The timing has been set at 25 degrees since I got the motor back from Diamond. I was planning on dialing it back to 20 or 21 degrees, just to be safe. I can do that, since this is not a pleasure boat.

But from experience and what I’ve researched over the years, it’s actually too much timing that kills nitrous motors, not lean mixtures. A motor just doesn’t need as much lead time on spark when the fuel is oxygenated. But for many years we all thought that jetting it rich was “safer”, because that slows down the burn rate, and then when it starts burbling because it’s too rich, you throw a little more timing in it, and then it barbecues your pistons, rips off ring lands, etc.

Now that’s on 4 stroke motors, so I don’t know whether and to what extent the oil mixture affects a nitrous motor and consequently, what the jet spread needs to be on a 2 stroke.

That’s going to be absolutely key to this whole 2 stroke nitrous adventure, IMV.

I’ve seen some say that you need more fuel jet with premixed fuel, since the oil changes the viscosity of the fuel. That actually makes sense to me. Would be good if someone tested and published specs on a known fuel with and without oil in it, just to see how it affects the stoich, octane, RVP etc. But I guess since 2 strokes are in their way out, no one is going to fund that kind of testing.

[aj06bolt12r]

Now there’s a hell of an idea! And electric servo that moves the timing arm…
The timing has been set at 25 degrees since I got the motor back from Diamond. I was planning on dialing it back to 20 or 21 degrees, just to be safe. I can do that, since this is not a pleasure boat.

But from experience and what I’ve researched over the years, it’s actually too much timing that kills nitrous motors, not lean mixtures. A motor just doesn’t need as much lead time on spark when the fuel is oxygenated. But for many years we all thought that jetting it rich was “safer”, because that slows down the burn rate, and then when it starts burbling because it’s too rich, you throw a little more timing in it, and then it barbecues your pistons, rips off ring lands, etc.

Now that’s on 4 stroke motors, so I don’t know whether and to what extent the oil mixture affects a nitrous motor and consequently, what the jet spread needs to be on a 2 stroke.

That’s going to be absolutely key to this whole 2 stroke nitrous adventure, IMV.

I’ve seen some say that you need more fuel jet with premixed fuel, since the oil changes the viscosity of the fuel. That actually makes sense to me. Would be good if someone tested and published specs on a known fuel with and without oil in it, just to see how it affects the stoich, octane, RVP etc. But I guess since 2 strokes are in their way out, no one is going to fund that kind of testing.

Not only does the oil change the viscosity of the fuel but it actually creates a leaner mixture for a given jet size... Whatever oil you are flowing through the jet is taking up volume that would have otherwise been gasoline. So 32:1 would require a larger jet size than 50:1 to maintain a given AFR.

[CI STV]

Not only does the oil change the viscosity of the fuel but it actually creates a leaner mixture for a given jet size... Whatever oil you are flowing through the jet is taking up volume that would have otherwise been gasoline. So 32:1 would require a larger jet size than 50:1 to maintain a given AFR.

Thanks. That makes sense to me. So, it sounds like I need to figure out how much more fuel jet I need to replace that shortfall of fuel?

EDIT: So in a 25:1 mix, that would equate to 4% of the fuel mixture being oil, so in theory that should require 4% more fuel than a tuneup for a regular gas kit. The thing is, looking at the jetting charts and given the size nitrous jet and fuel pressure that I’m using, it’s going to be impossible to jet up by 4% on the fuel side. 10% maybe, but not 4%. BUT, given the added viscosity, lower octane, etc. I’m just going to start out with a fuel jet that’s a size or two bigger, such as what’s recommended for E85, which typically requires about a 30% increase in fueling (on an N/A engine tune) compared to gasoline, and go from there. For the .020” N2O jet, at my fuel pressure, that’s only one size difference on the fuel jet (.010 vs .009”).

[donmac]

looks like you guys have knowledge and talent already!
DNE performance Hawkstone, Ont! thats about 20 miles from here! they play with 2 stroke n2o , not sure how much info they'd hand out but might give some hints on tuning!
watched one dyno vid and they were 533hp out of 1.7ltr.

[CI STV]

BTW: Since I realize that running a high fuel pressure (56 psi) requires a really small jet, I/m going to install a small Russell 40 micron inline filter right at the fuel solenoid inlet, just to avoid a small piece of junk plugging up a fuel jet. I’m waiting to get some more parts to finish that.

I’ve already installed a 6AN nitrous filter in the nitrous supply line.

I already installed two fuel filters inline so that all of the fuel going from the tank to the pump with a 10AN 10 micron stainless element filter, and then downstream from the pump I have a 8AN Aeromotive 40 micron “Microglass” filter before to gets to the fuel rail.

So the fuel going to the fuel solenoid will have three stages of filtering. That may seem like overkill, but I’ve had a piece of junk plug a fuel jet before on my Vette. Luckily I was pulling enough timing that it didn’t grenade, and all it did was run like crap because the nitrous mixture went totally lean. There’s a lesson there…