The Shop Truck

[r3dd0g]

Well, in an effort to make sure I check everything at the track I've been working on a post run checklist to go through between rounds. During this process I've been digging into my datalog from the last run at Duct Tape Drags. I noticed the fuel pressure seemed to stay flat through the run rather than raise with boost pressure, I changed the scaling to make it stand out better and I came to the realization that I'm running out of fuel pump.
It was making 9.4psi of boost on the 2 step and fuel pressure was great, but once boost got to 12.5 with the nitrous also coming on it couldn't keep up anymore. CL comp saved my butt, but it was hitting 15% added fuel by the time I let off. I'm not certain I can trust the EGT temps since they seemed to be erratic, but 3 cylinders peaked at just over 1500°F which isn't good.

I have the 3.5gpm Fuel Lab pump, unfortunately I have tried to use their 5gpm pump twice and both times it didn't last more than an hour. The 3.5GPM pump seems to be rock solid.

Amber and I brainstormed about this and I think there is a fairly simple solution. When I built my fuel cell I put a 6an drain on the bottom, I can hook a fuel line to this and run an external pump for a dedicated nitrous fuel system. This will remove the nitrous load from the main fuel pump and I could even add more fuel than needed for the nitrous to help out the main fuel pump at WOT. The main fuel pump has 3 ORB fittings for return lines, I'm currently only using one so I can easily add a second. I already have the fuel solenoid from before, so I just need to get everything plumbed up. This has the added benefit of cooling the intake charge down even more.

I checked my day zero log from Michigan Miles as I ran that one NA. Even there fuel pressure was short by a couple PSI, so I'm on the borderline with the party pulley.

I'm going to try to get something set up so I can test Friday, that way I'll be able to do the 10.50 bracket, otherwise I'll need to drop down to the 11.50 bracket to save the engine.

 

[shady]

Positive it was running out of pump?
Should be able to tell by seeing what your injector duty cycle was during a run.
If it's hitting 95-100% or something I'd say yeah, out of pump, too small of lines, etc..

Could the boost signal to the regulator not be working correctly? Or the reg it's self?

 

[r3dd0g]

It's definitely the pump. You can see in this datalog, blue is boost pressure, red is fuel pressure, teal is CL Comp. Base fuel pressure is 45psi, on the two step, boost is 9.2psi, fuel pressure is 54psi (45+9). When I let off the trans brake boost starts rising quickly to 12.5psi and fuel pressure follows to 58psi (45+13) but at that point it starts dropping and no longer follows boost but just sits around 57psi for the remainder of the run. This indicates that the pressure regulator is fully closed and not returning anything to the tank.

CL Comp is 0% on the 2 step and peaks out at 15% at the end of the run. I still have injector left as it was only at 85% duty cycle. Increasing the pressure of the fuel will lower the duty cycle, but it will also lower the output of the pump making the problem worse. You can see in the CL Comp graph how it's compensating for the lack of fuel pressure. It should be hitting 61ish psi at the end of the run (15.8psi of boost) but it's only at 55psi by that point.

 

[shady]

I've seen setups where it has main fuel line, Y's out, has two pumps, then Y's back to one line.
You could run something like that, with 2 of the 3.5's. and have the second kick on above X amount of boost, or when nitrous is engaged....

I'm sure you have enough line for it.

Think I've even seen like Dual pump headers to parallel pumps. Seem to remember that when I was looking up pumps back when I wanted to turbo my old engine.

 

[shady]

This is the one I seen, but I'm sure there's a higher flow version..

 

[r3dd0g]

I've seen setups where it has main fuel line, Y's out, has two pumps, then Y's back to one line.
You could run something like that, with 2 of the 3.5's. and have the second kick on above X amount of boost, or when nitrous is engaged....

I'm sure you have enough line for it.

Think I've even seen like Dual pump headers to parallel pumps. Seem to remember that when I was looking up pumps back when I wanted to turbo my old engine.

I had thought about that, but it would require pulling the fuel cell and modifying it. I can't get that done by Friday.
Switching to a wet shot should fix my issue, I could even program the nitrous fuel solenoid to work like water/meth injection on the road, but I'd have to change the fuel jet for that. A wet shot is going to give me the additional fuel I need and cool the intake down. It's a win win.

The truck is almost to where I want it, it doesn't really justify putting another 3.5gpm pump in.

 

[r3dd0g]

I'm running an in-tank pump, so I'd have to run 2 identical in tank pumps.

 

[shady]

At that point you could go to dual 2.5 or something..
But yeah, the dedicated smaller pump for nitrous should be enough for drag racing.
Playing on the street or road course you'd never be in it that hard that long.