Nitrous on 2.5 Drag

[Instigator]

Sounds good to me.

On oil content, when I ran the ‘50’s era Mercs in kneel down, I ran 8:1 oil.

As in, 1 qt oil to 2 gls gas!

In 9 yrs, never fouled a plug!

Had no access to dyno testing for power loss as RBT spec’d but know it has to happen somewhere.

I always looked at oil like insurance.

W/them it was hard to find parts.

W/your stuff, it’d be, hard to pay for parts!

Im a carb guy but your theory on going lean at shut down is real and we have fought it forever and has burned down many motors.

[CI STV]

Just to illustrate what I’m talking about with this high rpm / high vacuum situation at the end of a run, here’s a snapshot of a datalog from a run it did recently with the “ECU Vac” reading highlighted. This is data from the MAP sensor, so the higher number means lower vacuum or closer to atmospheric.

You can see the blue line take huge, violent dip in MAP (=increase in vacuum) when I chop the throttle at the end of a run (yes, I can do that, it’s an STV, so the thing rides like it’s on rails). Then it recovers to about the level of MPA/vacuum that it had at idle as I was coming up to the start.

I don’t know yet how the MAP reading corresponds exactly to the cells in the fuel graph, but I’m pretty sure that at high vacuum, it references the cells closer to the bottom of the graph, which might include those cells located in that “hole” I referred to in the preceding post. So I’m not going to take the chance that after a nitrous run, when the rpm is decreasing from 10,000+ and there’s no fresh air charge coming into the cylinders to cool the motor, the fuel mixture goes lean.

I realize that’s probably why many use a “wash down” system with nitrous on two stroke motors. Who knows, perhaps that’s actually only needed because the fuel mixture goes way lean when the throttle closes at the end of a run? So, maybe there might be no need for an external wash down, you can use the ECU to add more fuel through the injectors as the RPM is coming down at the end of a run? Bear in mind this is a race boat, so I couldn’t care less about how rich it will be at part throttle high RPM. I’m not going to be doing any river cruises with this boat.

BTW: there’s a bunch of other issues a trained eye will see from that log, including that it “bogged” a bit as it rolled over onto plane, so the RPM spiked a bit and then dipped. There’s two reasons for that: not the right prop and not using my trim timer. I’m going to address that too.

[CI STV]

Sounds good to me.

On oil content, when I ran the ‘50’s era Mercs in kneel down, I ran 8:1 oil.

As in, 1 qt oil to 2 gls gas!

In 9 yrs, never fouled a plug!

Had no access to dyno testing for power loss as RBT spec’d but know it has to happen somewhere.

I always looked at oil like insurance.

W/them it was hard to find parts.

W/your stuff, it’d be, hard to pay for parts!

Im a carb guy but your theory on going lean at shut down is real and we have fought it forever and has burned down many motors.

Yep, Marty recommended that I run this motor on the Mercury red oil at 32:1, which I’ve done religiously. But he had my limiter set at 10K
Brendan did a nice Tech Tuesday video on this a little while back, where he swears by that Merc oil as well, for anything run under 10K, but recommends it mixed at 40:1.
And the only other oil he recommends, for race engines turning over 10K, is the Redline 2-Stroke Race Oil (now rebranded as “Racing Kart” oil, since “two-stroke” is now passé, I guess?) mixed at 25:1.

BTW: my first two motors where Johnson 3.0L loopers with carbs. The first was an ‘88 I think, and the second was one of the later Venoms with the factory finger ports. I was diehard OMC back then.
I seized two pistons in the first motor tight one evening, at part throttle, after running it WOT for about 3 miles, I had to slow down to drive over a wake from a sailboat and when I eased off and went back on the throttle, it just shut out.
I ended up sending that block to Gordon back in the late 90s, after I fubared the second motor, and he made a beast out of it. That Monty built powerhead never let me down, but the evolution big bore carbs sure did. Or I let them down, by unknowingly running too much fuel pressure.
Then I eventually called Chuck Goodman and got an 85hp nitrous kit from him to put on that Monty motor. That was the largest system Nitrox sold that would run on gasoline augmentation. He said anything higher than that needed methanol and a washdown. That would’ve been sometime around 1998. He was the man back then. And Gordon was the madman, although he looks he’s still going strong at that, lol!

[RBT]

With the brucato/849/ppe box I always wrote a wash down into the map

[CI STV]

With the brucato/849/ppe box I always wrote a wash down into the map

Thanks for sharing that. I knew someone must’ve done it before!
Would you by chance be willing share how or give me any pointers on where to start?
If not, I completely understand.

[RBT]

Thanks for sharing that. I knew someone must’ve done it before!
Would you by chance be willing share how or give me any pointers on where to start?
If not, I completely understand.

Sure, don’t have my computer with me or I’d show a screen shot of an older pro gas map that I wrote, basically 9500 and up once you introduce vacuum (3-4 load cells
down) you add a bunch of fuel.
The ecu operates on vacuum and rpm, when you lift you add vacuum you move down in the load cells with the motor still spinning it can have a good bit of fuel coolant flushed through. Not too much or you will snuff it out.

[CI STV]

Sure, don’t have my computer with me or I’d show a screen shot of an older pro gas map that I wrote, basically 9500 and up once you introduce vacuum (3-4 load cells
down) you add a bunch of fuel.
The ecu operates on vacuum and rpm, when you lift you add vacuum you move down in the load cells with the motor still spinning it can have a good bit of fuel coolant flushed through. Not too much or you will snuff it out.

Thanks man. That’s exactly what I was thinking, hence me bumping up the numbers in that “hole” in the 8000 and 8250 columns.

[CI STV]

Finished up installing the bottle and other bits and pieces today and she’s ready to test.
Had already removed and cleaned and flowed the injectors last Sunday.
I have reduced the timing to 20 degrees, and will try adding a degree back at a time and watch the plugs and piston tops.
Only thing else to do is install the bottle heater and foam in the fuel tank, since I sometimes get fuel slosh on decelerating if the tank is less than half full.
Should be able to do a small test hit in the pond tomorrow, just to see if everything is working. Hopefully I won’t blow it up.

[CI STV]

Did a quick test hit on the nitrous with the 22N/12F jetting ~(100hp) yesterday afternoon, just to get some data.
EDIT: Data from the AIM datalogger shows that I was WOT for 3.765 seconds and 291 ft and that it went 9101 rpm and hit 132kph (82 mph). When the dash lit up because the fuel pressure dropped, I lifted immediately.
Looking at the data and the plugs/pistons, it’s running pig rich, especially on the right bank. The data log shows max EGTs at ~1052* on the left and ~980* on the right. Starting to wonder if I have an injector that’s hanging open or something. Based on what I saw when I flowed them (on my cheap Chinese machine) the other day, there’s a significant variation in flow, but I didn’t see anything weird in the flow pattern and they all held fuel pressure etc.
As I wasn’t sure what it was going to do, I ran it with no trim and with the motor height about 1/4-1/2” lower than normal, so it was floundering around on the run, but it felt strong, so I think when I get it dialed in it’s going to be mean.
The biggest issue was that the fuel pressure dropped on the run from 56psi to 52psi, which lit up the dash, since I have it set to alarm if the pressure drops below 53 (or the EGTs go above 1175).
I pondered this all last night and I’m pretty sure it’s just that I’m running at the edge of what the pump can deliver (~55GPH @55psi) and especially with it being rich, it just ran out of volume.
Here’s what Weldon publishes for it:

I’m going to figure that out and, if necessary, I’ll put a stand-alone fuel system in it.
And if I do that, maybe I’ll even swap the fuel solenoid out so I can run methanol.
I think the easy fix for now is changing the pump, though.
I’m going to also change out a couple of 90* fittings on each end of the fuel rail to high flow fittings, because they could also be causing a restriction.
I’ll post a screenshot of the datalog up later.
Tried to get a decent video of the spray pattern from the nozzles, but it was overcast bad, so that didn’t turn out too good.
When I get the pump changed out, then I can do some more testing.

[CI STV]

After a bit of research, I think I found a suitable replacement pump for the Weldon A-600, which only delivers around 55 GPH @ 56psi.

https://www.racetronix.biz/p/fuel-pu...t-e85/rxp525le

I’ve been sourcing fuel system products from Racetronix for the last 10+ years and they’ve never let me down, and their service and prices are as good as anywhere else.

This pump is actually a Walbro that’s rated for 470lph @ 43.5psi (124+ GPH), and the great thing is that it’s the same diameter (2.75”) as the Weldon in my boat now, so it should be an easy install, without changing brackets, hopefully.

I ordered it a little while ago, but I’m sure I won’t get it until next week (next year!), so I guess any further testing is going to have to wait.

[CI STV]

HAPPY NEW YEAR to all of the S&F community.

Here’s some screenshots of the data log from the 291’ test hit on Monday:

The thick black line is RPM (read from ECU). It hit 9101 max (I had a 22P on it with 2:1 gearing). You can see from the erratic slope how the rpm was jumping around as the boat was flouncing around from being trimmed in too much. It’s typically much smoother than this. The water pressure (blue lime) was all over the place as well, which I’ve also never seen before (bottom picture). The boat was plowing around plenty on the run, but man that motor was screaming. It hit 132kph or 82mph in 291 ft and in 3.76 seconds (starting at 11kph or 6.5mph), so although that run wasn’t optimal at all, it’s making decent power.

But look at the EGTs: Max on left bank was 1052 and 980 on the right. Both sides are low, which is weird, since just the reduction in timing from 25 degrees to 20 degrees should raise the EGT. But something funky is going on with the right bank. You can see that when you highlight the right bank EGT curve (thick yellow line), it rises up sort of linear but still below the left bank, then halfway through the run it takes a dip and basically plateaus from there.

Would love to hear everyone’s thoughts on this. I have an idea that its the injectors, since when I flowed them the other day, the flow numbers were all over the place (137, 138, 144, 151, 153 and 154ml at 60 seconds and ~40psi). So, I was able to match the top and bottom pairs fairly closely, but the two injectors in the middle are fairly far apart (144ml vs 151ml), so I’m wondering if that’s part of the problem? I should’ve noted exactly which injector went where, but I was more focused on pairing them and putting the higher flowing ones in the bottom.


Want to see how bad it was wallowing around on the run? Check out the sawtooth pattern on water pressure curve (highlighted blue line). Never seen it do that before:

[CI STV]

Here’s a video I made of the test hit on Monday. Update: YouTube link below.
I mounted the camera like that because I was trying to see the spray pattern into the intake slots, but it was too overcast to see much.
But from what I can see, there’s no blow back or fuel splatter even inside the slots after the run, so I think the nozzle angle is good.
You can also see from the video that the motor is tilting in significantly on the run, which altered the reading on the datalog by 3mm, hence the boat was running really flat and wallowing around. I need to figure that out too.
https://www.youtube.com/watch?v=cdVg1dfmGEg

[skialot2]

Here’s a video I made of the test hit on Monday. Hopefully the FB video link works.
I mounted the camera like that because I was trying to see the spray pattern into the intake slots, but it was too overcast to see much.
But from what I can see, there’s no blow back or fuel splatter even inside the slots after the run, so I think the nozzle angle is good.
You can also see from the video that the motor is tilting in significantly on the run, which altered the reading on the datalog by 3mm, hence the boat was running really flat and wallowing around. I need to figure that out too.

https://www.facebook.com/10006316014...4572367817614/

Link does not work

[CI STV]

Link does not work

Great. Gotta love this FB crap.
I’m going to load it up on YouTube in a bit and will post a link.

EDIT: YouTube link added. Hopefully you can view it now.

[Scream And Fly]

I just want to say that motor looks like a scary beast! And also that this is a very interesting topic and I hope it continues to expand on this subject.