Nitrous on 2.5 Drag

[CI STV]

This is from the datalog from Sunday. Check out the huge dip in fuel pressure right after the hit, it dropped all the way down to 28psi!

[CI STV]

Here’s the video. You can hear how it’s struggling.

https://www.youtube.com/watch?v=jUxk_dIH3Nk

[Stoker boy]

What are your Pyro temperatures doing during the bog? What is your voltage meter telling you?
When you look at the spark plugs, what are they telling you? Are you sure your nitrous solenoid is in injecting. When you don’t hit the nitrous button, does everything work fine? Balance between fuel and nitrous injection is kinda important. I’m not familiar with your system, I imagine your nozzles have orifice sizes. I suppose those are what regulate the amount of fuel. On my old antiquated system I have pressure regulators. I flow test to make sure the balance between fuel and nitrous is correct. Enrichment fuel is injected at the rate of about 5 to 6 Psi.

I think you’re on the right track, use a Y or a T for the injection system, just don’t use the extra port on the regulator. It’s possible you’re injecting at too high of a pressure for the fuel.

[CI STV]

What are your Pyro temperatures doing during the bog? What is your voltage meter telling you?
When you look at the spark plugs, what are they telling you? Are you sure your nitrous solenoid is in injecting. When you don’t hit the nitrous button, does everything work fine? Balance between fuel and nitrous injection is kinda important. I’m not familiar with your system, I imagine your nozzles have orifice sizes. I suppose those are what regulate the amount of fuel. On my old antiquated system I have pressure regulators. I flow test to make sure the balance between fuel and nitrous is correct. Enrichment fuel is injected at the rate of about 5 to 6 Psi.

I think you’re on the right track, use a Y or a T for the injection system, just don’t use the extra port on the regulator. It’s possible you’re injecting at too high of a pressure for the fuel.

EGTs are stable during the bog, and I have the resolution on those at 20Hz, so they should read accurately any significant fluctuation in the air/fuel mixture. The fuel pressure drop happens quickly and only lasts for a fraction of a second, as you can see from the datalog.
I need to check voltage but I’m sure that’s not the problem.
Plugs looked fine when I checked them and both the plugs and pistons are clean, wet and shiny, and I don’t see any sign of detonation, thankfully.
I’m certain the nitrous solenoid is working.
I don’t use a push button. I use the throttle activated WOT switch on my trim timer to trigger the window switch, which turns the nitrous on at 3,000rpm and off again at 10,500. Then I have a simple progressive system pulsing the solenoids to ramp in the nitrous from 40% to 100% in 1.5 seconds.
I know that the nitrous/fuel mixture is very critical, which is the primary reason I started this thread.
My system uses 6 individual nozzles with jets in each one, as can be seen in the photos early on in this thread.
I’m using the recommended jetting stagger for 56 psi, and my system comes as a flowed kit from Nitrous Outlet, and they certainly know what they’re doing.
I’m certain it’s dropping because I’m pulling fuel off the second port on the regulator, which is downstream of the fuel rail, and I can imagine that when the fuel solenoid opens, the regulator sees a sudden drop in pressure and simply can’t keep up.
I’ll know soon enough anyhow.

[Stoker boy]

My activation is at the bottom of my foot throttle so I only get the nitrous system engaging at wide open throttle.

[CI STV]

My activation is at the bottom of my foot throttle so I only get the nitrous system engaging at wide open throttle.

That’s really the only way anyone should do it. A part throttle cough back is ugly. Don’t ask how I know.
I use the window switch as an extra precaution to make sure it can’t activate the nitrous rpm before 3,000rpm. Not that it makes any difference since it only takes like 2 nanoseconds to get there when I nail the throttle anyhow.

This is how I have it set up so I can see and reach everything from the seat. I even have a 0-2,000psi sensor that I’m going to install and connect to the nitrous solenoid so I can monitor and log bottle pressure from the dash.

[Stoker boy]

I have a pressure gauge upfront for the nitrous bottle as well.

[CI STV]

Reconfigured the fuel supply to the nitrous today. Hoping this will solve the fuel pressure problem. Will see if the weather permits me to at least get a quick hit tomorrow to see whether it works.

[Stoker boy]

Hopefully that electronic timer can withstand any vibration. Interesting plumbing job.

[CI STV]

Hopefully that electronic timer can withstand any vibration. Interesting plumbing job.

That little Maximizer box was on my Vette for about 5 years and has already seen plenty of vibration already, lol. In any event, I have it mounted with HD Velcro on the ACU lid, and the ACU is mounted with rubber washers to the fiberglass lower pan, so I don’t think it sees much vibration.

I’m going to tidy up the plumbing a bit once I see that it works configured like this. I put this all together in an hour using fittings I already had, so it looks a little cobbled together, because it is.
If this works, I’ll use a 180 degree Speedflow fitting on the bottom and I may also put a fuel pressure sensor on the nitrous fuel supply side to make sure that the fuel pressure is stable going to the fuel solenoid.

[CI STV]

Finally got to test the boat this afternoon. In short, the fuel pressure is still dropping on the initial hit , albeit not as bad, and then it recovers after a split second but the pressure is a bit choppy after that.
Starting to think the regulator might be the problem. It’s the “compact” Aeromotive version and the diaphragm is pretty small and I’m thinking maybe it can’t respond quickly enough to the sudden demand for extra fuel when the fuel solenoid opens.
I have a new larger regulator that I’m going to try, just to see if that cures it. If not, then it’s going to get a separate, dedicated pump for the nitrous.
Something also went wrong with the trim and it shows that it only trimmed out to to 27mm on the Datalogger, when it should’ve been 31mm, which equates to right around 1 degree of positive trim.
So it ran flat the whole pass. It still ran 89.8 mph in ~395 feet, so I figure when I get it sorted it will run.
You can still hear it surging a bit in the video:

https://youtu.be/qIBDOGBJDDE

[BUZZIN' DOZEN]

Does your regulator have a vacuum reference?

[CI STV]

Does your regulator have a vacuum reference?

No, I disconnected it and installed a breather fitting because it didn’t want the high vacuum pulling down the fuel pressure when I let off after a WOT pass.

[CI STV]

Tested the boat again this weekend with a new regulator, but the fuel pressure is still dropping on the hit although it recovers quickly, but is still a bit wavy, as can be seen on the datalog below:

I’m going to reconfigure the whole system and check filters etc to see if there’s a restriction somewhere.

Here’s a video a friend made of the run with his phone from the shoreline:

https://youtu.be/omklVqmfNZA

Here’s the onboard one from the GoPro:

https://youtu.be/kIlBInsHtUE

However, as you can hear if you listen closely, it’s still burbling a bit on the run, and the datalog is showing (highlighted yellow line) significantly and increasingly lower EGTs on the right bank as the RPMs increase.

You can see where it tracks the left bank EGT (orange line which peaks higher than everything else on the chart), but it reaches a point around 8,000 rpm where all of a sudden it starts to drop and by the end of the run, it’s 200 degrees less than the left bank (906 * vs 1105*). There’s something definitively wrong there.

It still went from 8.2 mph to 90.8 mph in ~400’, so it still moved out decent, but I could feel that the motor wasn’t running right.

I was thinking that the difference in EGTs was from a bad/dirty injector that was hanging open causing a rich mixture on that bank.

But I’ve now pressure tested and flowed all of the injectors and they each held pressure and didn’t show any signs of dribbling, sticking etc. and when I flowed them they each flowed almost exactly what I had recorded from the last time I cleaned and flowed them a few months ago. I’ve switched each pair around, just so I can see if the problem switches to the left bank.

But now I’m starting to think it’s ignition related, so I’ll test that next.

BTW: the main nitrous supply hose from the bottle vibrated loose at some point in that run and by the time I got back to the trailer the bottle was completely empty. When I looked back and saw the fog, I thought it was smoke and assumed I had finally fubared the motor. Nearly had a heart attack then, lol.

Once I’ve reconfigured the fuel system and checked the ignition system, I’ll test it again report back on here.

I figure once I can get it to scream, it will fly.

[CI STV]

Just to update the thread, I checked for spark at the coils and that appears good, checked voltage at the coils and that was all good, with all of them reading the same at 150 volts. Then checked stator and high speed and low speed coils voltage is consistent on both switch boxes, although it appears high speed voltage goes up well above 160 volts at above 2,000rpm. Can’t see that being a problem though?

So, I’m now at a loss as to what is causing the 200 degree difference in EGTs at high (8,000+) rpm.
Starting to wonder if it’s something as simple as the probe going bad? I’ll try swapping them around next to see what that does.

I’ve also changed out pumps again and put back in the Weldon 1100 and I’m installing -10AN hose all the way to the rail, although I’ll have to reduce it to -8AN at the Tee next to the rail, since the -10/-8/-8 Tee I ordered hasn’t arrived as yet.

I’m hoping this now cures the fuel pressure dip on the hit.

Hoping to test it today if I get a chance.