Power loss at high speed on track?

[CptMorgan]

I had the roadster on the track for the first time. The car did really well. It's amazingly rewarding to drive fast.

I'm getting an abrupt power loss at the end of the straightaway.
It's happening at 6000 RPM in 4th gear (~200 KPH / 125 MPH).
It's repeatable, on every lap.
Once the car slows down a hair, the power comes back full on.

The car is momentarily starved for air or fuel. It's not a rev limiter. (limiter is 6800 RPM)

I'm running a 750 carb. No induction. There is a lot of wind pressure at that speed. And the roadster is as aero-dynamic as a (flying) pig. Has anyone else experienced this?

[Kivyee]

What if you shifted to a different gear, e.g. 5th gear at the same speed? Just wondering if its RPM or Speed related.

[Jeff Kleiner]

...Has anyone else experienced this?

Yes, when the fuel filter was clogged.

Jeff

[Jim1855]

You're using a fair amount of gas at that point. Are the fuel lines, pump and full system up to task? Jeff's comment on the fuel filter relates to this.

Are float levels set correctly?

Sounds like when you back off the fueling system has a chance to catch up.

Maybe a chassis dyno session would help to evaluate when the power drops off and what might be happening. It's pretty easy to monitor fuel pressure and floats during the run IF the dyno operators will let you watch. But you may not be at full power long enough to take effect.

I do know that a traditional fueling system can work well. Mine from years ago: 427w, 540hp, 780 4150 carb, 3/8 hard lines, AN-6 flexible lines, Edelbrock mechanical pump, bypass regulator, Canton fuel filter at the rear axle. 6,500 RPM, 140mph in 4th every lap at Grattan or VIR. Could have gone faster on VIR South track but it just wasn't worth it.

Jim

[Al_C]

I'm with Jeff on this one. Swap out the current filter for a new one and I bet the problem disappears. You can end up chasing a whole bunch of potential problems, but I would start here. At least that's my experience. It was also my experience to get a 93 octane shower because we didn't eliminate the pressure in the fuel line when we took the old one out. Learn from my error...

[CptMorgan]

Thanks, guys.

I'm running 3/8" hard lines and a mech fuel pump, but I wasn't too concerned about fuel flow when I did the build.
I think you're right. I'm simply running out of fuel flow at the end of the 1/2 mile straight. It feels like a fuel cutoff.

The fuel filter is only a year old with 1000 miles on it, but it was the filter that came with the kit.

[Jim1855]

Find a good filter that flows more than you could need on your wildest day. The cute little plastic ones are often not up to the task and then load up with particulate way too soon. Yup, you spend money, that's often what it takes to solve problems.

Jim