Nitrous on 2.5 Drag

[CI STV]

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.

I have a lot of personal experience with nitrous, but the only time I’ve run it before on a 2-stroke/boat was about 24-25 years ago was on an old Monty-built 3.0L OMC. But that was a kit that Nitrox (Chuck) did for me, so all I had to do was bolt it on and hang on.
I had that motor on an 18’ Action at first and sold that hull before it could kill me, then bought Gordon’s old Mirage and put the motor on that, and man that thing ran, except it had a terrible bog off the line that killed my ET. It could hit ~115mph in 1/4 , which was a big deal for me back then.
Here’s a picture of it on the run, back in 1999:
Attachment 538505
BTW: The Triad ahead of me was Larry Smith’s APBA Hall of Famer, then owned and driven by my buddy Dale Crighton. That thing was quick as hell, especially when he loaded it up with a mixture of Klotz Coxoc and Nitro. Unfortunately, that ended badly when he blew the motor one day at the end of a run and the boat caught fire and burned down to the waterline.

[donmac]

I'm running pyrometers and a/f ratio gauges with alarms on my sled, wondering if those could be tied into the ignition system for shutdown before meltdown occurs! I realize racing in a final , win at all cost and meltdown is okay, but pleasure riding having a limp mode would at least allow you to get home! sometimes your just watching for trees and the gauges are non existent!

[LakeFever]

I don’t believe anyone has ever attached a fail safe that responds fast enough to stop the carnage. Boost or spray when it starts to go wrong it goes from trouble to disaster in a millisecond.

[CI STV]

I'm running pyrometers and a/f ratio gauges with alarms on my sled, wondering if those could be tied into the ignition system for shutdown before meltdown occurs! I realize racing in a final , win at all cost and meltdown is okay, but pleasure riding having a limp mode would at least allow you to get home! sometimes your just watching for trees and the gauges are non existent!

I already have my AiM dash programmed so that if:

- Water pressure drops below 15 psi at 7000+ RPM;
- Fuel pressure drops below 53 psi;
- EGTs exceeds 1175* F;

then the whole dash flashes red. The minute I see that, I’ll lift.

And, as I said before, I’m going to now use a low fuel pressure shutoff switch to shut off the nitrous of fuel pressure drops below 54 psi. I will also eliminate the vacuum hose on the regulator because I can see from previous logs that when I ease off at the end of the run, the instant high vacuum pulls the fuel pressure down by about 2-3psi, which is a little more than when it’s idling at 1500rpm. Don’t want it going even slightly leaner at high rpm when I lift.

I’m also looking at the fuel curve in my Brucato and I see where there are a bunch of cells in the 8,000 and 8,250 rpm columns and high vacuum where the fueling is about 25% less than anywhere else adjacent in the graph. I’ll probably start another thread about this and post pictures to explain better what I’m referring to. I have a couple of tunes that were done by a reputable tuner where those cells have been adjusted upwards to match the surrounding cells, so I think I may be on to something here.
The idea here is to make sure that when I lift at the end of the run, the fuel curve doesn’t go lean (high rpm/high vacuum from the closed throttle). I’m betting that’s killed a few motors over the years. Might even be the reason someone came up with the “wash down” feature.

[CI STV]

I don’t believe anyone has ever attached a fail safe that responds fast enough to stop the carnage. Boost or spray when it starts to go wrong it goes from trouble to disaster in a millisecond.

I hear you, but not sure I can fully agree. It’s certainly the case that there are far less nitrous failures than back in the good old days, and some of these boys are spraying BIG volumes. It’s all about maintaining solid fuel pressure (on a wet system), and most of all, not overdoing it on the timing.

[LakeFever]

I hear you, but not sure I can fully agree. It’s certainly the case that there are far less nitrous failures than back in the good old days, and some of these boys are spraying BIG volumes. It’s all about maintaining solid fuel pressure (on a wet system), and most of all, not overdoing it on the timing.

I definitely agree with that. The one certainty that the digital age has brought us gear heads is the ability to connect and share what works, and what doesn’t work. The tuning control of digital ecu’s is also incredible. That aside, in the two stroke world I’m still reading plugs lol

[tlwjkw]

did ya ever see tha front (motor) of Logans Q-ship way back when?!!! i'll see if i can find a picture of it..

[CI STV]

I definitely agree with that. The one certainty that the digital age has brought us gear heads is the ability to connect and share what works, and what doesn’t work. The tuning control of digital ecu’s is also incredible. That aside, in the two stroke world I’m still reading plugs lol

I hear you, and I don’t think anything will give you a better idea of what’s going on in a 2 stroke motor than reading plugs and piston tops.
We don’t have the luxury of using wide band O2 sensors (although I’ve seen where a pretty smart fellow on here named Ronnie from the Netherlands did that on a 2.5) or knock sensors nor can we read crankcase vacuum and watch for spikes like the pros do with nitrous motors that have vacuum pumps on them.
So, we’re stuck with reading plugs. And watching EGTs, once we’ve established what the motor likes.
I suppose I could install some pressure transducers to measure cylinder pressure like I read somewhere that a certain badass outboard company does, but that could get expensive in a hurry…
So, yeah, I guess reading plugs is what I’m stuck with, lol.

[CI STV]

did ya ever see tha front (motor) of Logans Q-ship way back when?!!! i'll see if i can find a picture of it..

I’ve seen that picture, I think. The one with all those lines running everywhere, right?
That boat was nuts. I’ve seen thing run in person, back at Jasper back in the early 2000s. That sucker was violent!

[tlwjkw]

it really was... marty has a set for sure.. think it had 24 (12 each) solenoids and nozzles with very big pills..

[108]

I’ve seen that picture, I think. The one with all those lines running everywhere, right?
That boat was nuts. I’ve seen thing run in person, back at Jasper back in the early 2000s. That sucker was violent!

The good ol' days! Was a blast down there back then. Now I just go for the river run and to see friends.

[25two.stroke]

I have ab early silver SVS that has two tubes drilled in it; I assume for nitrous and additional fuel. It wasn't hooked up to anything on the boat when I go it. Does anyone know if there was a company offering that service on the SVS at any time in the past...or were all those kinds of drilling/adding tubes to carb manifolds, horns and SVS all a complete DIY deal by racers?

I don't have bits that small or any way to measure the orfices...or any idea how to figure what pressure they were running on it. So I am kinda scared to mess around and find out...

[CI STV]

I have ab early silver SVS that has two tubes drilled in it; I assume for nitrous and additional fuel. It wasn't hooked up to anything on the boat when I go it. Does anyone know if there was a company offering that service on the SVS at any time in the past...or were all those kinds of drilling/adding tubes to carb manifolds, horns and SVS all a complete DIY deal by racers?

I don't have bits that small or any way to measure the orfices...or any idea how to figure what pressure they were running on it. So I am kinda scared to mess around and find out...

Does it have solenoids attached? If not, do the spray bars themselves seem to be designed to carry jets? Some of the old Nitrox kits simply used the size of the holes in the spray bar for calibration.
The big advantage with direct port, one nozzle per cylinder systems is that you can even change the jetting on problematic cylinders to take some heat out.
Most of the big nitrous companies will still build and install custom spray bars on just about any manifold you send them. That wasn’t an option for me as I wasn’t letting my Diamond manifold out of my sight, let alone shipping it overseas.
In any event, most folks don’t like using spray bars anymore, especially where they’re fairly long, as the nitrous distribution can be inconsistent, as it tends to flow more on the holes nearest to the dead end of the spray bar.
My manifold has vertical holes holes drilled through all the intake slots, which I was at first thinking of using with a custom spray bar kit, but the holes are behind the slider plate and very close to the reeds:

[CI STV]

One thing you might have noticed is that I’ve moved the inlet air temp sensor from the crankcase and mounted on my homemade solenoid bracket. I actually just left the original one in the block and installed a new one.
The reason for relocating the sensor is that in the stock location, when the nitrous mixture hits the crankcase at subzero temps, the sensor will tell the ECU that the boat is in northern Siberia, and it will add fuel accordingly.
In short, the extremely cold nitrous mix will make the motor run pig rich. Now, that’s ASSuming that the ACU actually uses the air temp sensor for fueling at WOT and not just fir starting/idling/cruise. That I’m not sure of. One thing I’m sure if is that there is no table in the Brucato software for IAT calibration or fueling adjustment based on temperature. Would be glad to know if anyone knows for sure how that works.

[AlliStan]

Michael Dixon ran nO2 on some of his drag STVs and won a lot of races. He was an innovator at the time and used a progressive system that injected it in stages, as opposed to all at once. But, i don't think he ever ran a slide. If I'm not mistaken he injected it into the horn. If you could get a chance to talk to him you could get a lot of questions answered on the tech side. He's out of racing now but hasn't forgotten much.