Nitrous on 2.5 Drag

[CI STV]

Here’s some more onboard video on the last test hit I did on March 1st, looking at the business end of the boat:


https://youtu.be/Pvqm4dhsG9Q

[CI STV]

BTW: I’ve found that I need to run the motor about 1/4” lower than normal (@ ~1”above the pad) to get the prop to bite decent. The one time I tested it at 1.25” above the pad it blew the prop out pretty bad on the launch and it took about half the run until the slip dropped down to below 25%.

Pretty much the same thing you see with torque converters on a nitrous car, where you have to run a tighter stator and/or thicker oil on nitrous (and as you increase the hit) to keep the torque from “blowing through” the converter.

A very knowledgable fellow on these forums advised me that will need to tweak the prop with a little more cup on the leading edge to get it to bite and hold with all the extra torque from the nitrous. So, I guess that’s will be what I need to do next. Anyone got a nice nitrous-tweaked prop they want to sell, lol?

[CI STV]

I haven’t had a chance to test the boat recently, but I’ve made a few changes to the fuel system that I’m hoping will cure the fuel pressure drop issue.

I’ve now changed the fuel supply line between the pump to 10AN and installed a 10AN to x2 8AN tee:

So, everything up to the Tee is 10AN and the bottom of the tee is connected to a 8AN Speedflow 180 degree high flow fitting which is connected to the rail and the other 8AN leg of the Tee is connected to a 8AN to 6AN reducer which supplies the fuel to the nitrous solenoid:

I also discovered the the 8AN fitting I had on the outlet side of the pump had a very small ID of about the same size of a 6AN fitting, so that might have been acting as a “jet”, which I’m thinking could cause a momentary drop in fuel pressure on the hit when the fuel solenoid opened.

So now everything going to the rail is no smaller than 8AN and are all high flow fittings, so hopefully there should be no drop in fuel pressure now.

Here’s what the Speedflow 180 degree fitting on the bottom of the rail (hidden in pic) looks like:

Im hoping to test it later today, but it would mean running it in with an 17-18mph sidewind based on the weather forecast, so I’ll have to assess that later.

[CI STV]

Did a couple of test hits on Sunday. The larger fuel hose and fittings helped, but the fuel pressure still drops a bit for a split second on the hit. I’m starting to think that may be normal and I’m worrying about something that can’t be fixed.

First pass, I had the trim set at slightly trimmed in and it ran pretty flat but still accelerated pretty good. It hit nearly 94 mph in 440’ on that pass.

EGT on the right bank is still down bad (100-120* lower) at the top end of the run, though. Not sure what’s going on there. Can’t be an injector problem since I swapped those around a couple of weekends ago. Also checked the voltage at the coils and stator and that all checks out, so I’m stumped.

Set the trim at around neutral and did a second hit, but lifted early, since I could feel it was pulling harder and I had almost run out of lake on the first pass, lol.

According to the data log I was at WOT for 360’ and it ran 148kph (92mph) on that pass. Getting there.


Here’s the on board go pro video from the first pass:

https://youtu.be/0FcJy0t0f2Y

Go Pro vid of Second pass:

https://youtu.be/CNbOlfO-8w4

Cell phone video of same pass from the shoreline:

https://youtu.be/-VGgwod5hbE

[CI STV]

This is the datalog from the first pass. The EGT curve for the right bank is highlighted in yellow.

You can see that both EGTs track nicely together but when it reaches around 8,700rpm, the right side EGT starts to drop until I lift. At 10,000rpm it’s around 120 degrees apart:

1076* left, 955* right.

Anyone have any idea what the cause of that might be?

[NICE PAIR]

Dummy question here! Can you change your egt leads to see if the side to side temp reverses? (do the plugs/pistons show the difference?)

[CI STV]

Dummy question here! Can you change your egt leads to see if the side to side temp reverses? (do the plugs/pistons show the difference?)

Not a dummy question at all. That’s the next thing I want to do: swap the probes around. If that doesn’t make a difference, then I’ll probably swap out the stator and see if that makes a difference. Didn’t get a chance to do anything this weekend, but I’m hoping to get back at it next weekend.
I can’t see any difference in the plugs.
They all looked a bit rich to me, but that’s probably from idling in.

[JCSmile]

On motors that are getting dialed in this is less of a problem, but it's pretty common if you are running rich to be reading "flame" on the left bank. #6 sits lower than #5 and this is closer to the egt probe. I run my probes in the exhaust divider instead of the adapter plate and also run very rich tunes for lake cruising and it's pretty common to see 100 degrees different between banks. I'm not saying to go lean it out, but it could be that both banks are happy but one is reading flame. A plug chop or reading piston tops after 4-5 pulls is probably in order, I trust those more than the egt.

[CI STV]

On motors that are getting dialed in this is less of a problem, but it's pretty common if you are running rich to be reading "flame" on the left bank. #6 sits lower than #5 and this is closer to the egt probe. I run my probes in the exhaust divider instead of the adapter plate and also run very rich tunes for lake cruising and it's pretty common to see 100 degrees different between banks. I'm not saying to go lean it out, but it could be that both banks are happy but one is reading flame. A plug chop or reading piston tops after 4-5 pulls is probably in order, I trust those more than the egt.

Thanks. I’ve thought about that, but even the left bank EGT is lower than what I think it would show if it was torching the probe, although I can’t say that for sure.

But, before the nitrous, it was pretty rich when I got it from Diamond and the temps were even then and after I leaned out the mixture a bit, it used to read around 1150 and both banks were closer in temps, until they weren’t. One time, all I did was clean the injectors and that evened the EGTs out nicely.

And here’s the thing, I’m only running 20 degrees of timing. I would’ve thought that would increase the EGTs, but that might not work that way with nitrous, since nitrous enhances the speed at which the A/F mixture burns (hence the need for less ignition advance), so I’m thinking that cancels out the torching effect from late timing which typically happens when it’s off the bottle.

Adding the nitrous sort of changes everything, which is why I started this thread, lol.

And the thing that baffles me is that the EGTs track fairly even through 8000rpm but at about 8500, the right side starts dropping significantly and continues to drop until I let off.

But, I’m sure I’ll figure it out. And when I do I’ll share the results.

Thanks again.

[CI STV]

Just to add some clarity to the post above, I’m running my EGT probes in the two bottom holes in the exhaust divider plate, since I have the 12” F1 mid and that doesn’t use a adaptor plate, so the only place to put the probes is in those two holes:

[108]

Thanks. I’ve thought about that, but even the left bank EGT is lower than what I think it would show if it was torching the probe, although I can’t say that for sure.

But, before the nitrous, it was pretty rich when I got it from Diamond and the temps were even then and after I leaned out the mixture a bit, it used to read around 1150 and both banks were closer in temps, until they weren’t. One time, all I did was clean the injectors and that evened the EGTs out nicely.

And here’s the thing, I’m only running 20 degrees of timing. I would’ve thought that would increase the EGTs, but that might not work that way with nitrous, since nitrous enhances the speed at which the A/F mixture burns (hence the need for less ignition advance), so I’m thinking that cancels out the torching effect from late timing which typically happens when it’s off the bottle.

Adding the nitrous sort of changes everything, which is why I started this thread, lol.

And the thing that baffles me is that the EGTs track fairly even through 8000rpm but at about 8500, the right side starts dropping significantly and continues to drop until I let off.

But, I’m sure I’ll figure it out. And when I do I’ll share the results.

Thanks again.

The stbd side tends to run richer at high rpms. The theory on that is windage from crank rotation.

It was something that was repeatable between my river boat and my champ boat the only difference using the same power head was the tuner plate and the rotation of the engine .
Crown wash and reading plugs is a more better way to gauge happiness. Egts will get you in the ball park.

[CI STV]

The stbd side tends to run richer at high rpms. The theory on that is windage from crank rotation.

It was something that was repeatable between my river boat and my champ boat the only difference using the same power head was the tuner plate and the rotation of the engine .
Crown wash and reading plugs is a more better way to gauge happiness. Egts will get you in the ball park.

Thanks. That’s interesting. So even with the reverse rotation of the champ motor, the right bank runs richer? Or do you mean the EGT is lower? I would’ve thought that if it’s windage, it would reverse when you reverse the rotation of the crank?
I get it that there should be some difference between EGT readings and the right side being slightly lower would be because the lowest exhaust port on that side would be further away from the probe. But 120 degrees difference is a lot.
I have lots of data logs where the EGTs were fairly even and rise consistently as the RPMs increase, all the way through 10,500, which is the highest I’ve turned my motor to date.
The thing that gets me is the rate at which the right bank EGT drops off after 8750rpm and continues to drop until I lift. Almost like the fire is weak on that bank at high rpms.
I’m considering swapping the stator to see what happens.
Worst part is that the weather was perfect for testing the past couple of days, but on weekends the wind is always blowing from the wrong direction!

[Stoker boy]

[QUOTE=CI STV;3445547]Just to add some clarity to the post above, I’m running my EGT probes in the two bottom holes in the exhaust divider plate, since I have the 12” F1 mid and that doesn’t use a adaptor plate, so the only place to put the probes is in those two.

I also run a 12 inch, I’m not using bolt holes 16 and 17 for EGT probe.

[Stoker boy]

[Stoker boy]