Topic: Carb'd 350 runs like shit! Only on certain corners.....?
Hey guys!
Calling out to the smartest gearheads I know, because our engine is making me unhappy. Sometimes. I know as much about old school engines as I do about women; nothing.
Backstory:
Car is a 928 with a Gen 1 Small block. Holley Carb. 300ish-hp. Mechanical fuel pump. 9PSI at idle. 4-6PSI at top speed (per dyno run).
Last week, we were fighting an issue where the car would fall on it's face above 4000RPM. Dyno said off-the-charts lean. We swapped out for our spare carb. Problem solved...
Lead up:
Took the car to HPDE here in Arizona yesterday. It was 95degrees out.
Typically at a Lemons race the car runs at 190 degrees. The track on Sunday was short, so no time to cool the engine. Also it was fking hot.... Engine started out around 210. As the day went on, and the car hot hotter our new issue got worse. Leveled off around 220. Never boiled over.
Issue
On the slowest corner of the track, the RPM would get down to 2500 in 3rd gear. It was a quick switchback (left/right). As soon as I whipped the car back to the right, and floored it, the engine did almost nothing. It made a hell of a racket, but had ZERO power. It wasn't as if it was surging or falling over on it's face, it would just rev at the speed of molasses and the car went nowhere. Eventually as the revs climbed, the issue went away. Normal engine sound resumed, as did power.
I started using second gear on that corner, and the problem was solved. For a little while. Eventually it started happening in second gear also. This was as the car got hotter.
Eventually it started happening in a faster, third gear switchback earlier in the track also. 3000-3200ish RPM.
Note: There are two other places on the track where I was third gear, 3000RPM, that it did not have this issue. The difference? Those were constant corners, and not switchbacks. The issue only seemed to occur on the second part of a switchback corner.
Questions:
Could this be a lack of fuel? Float levels not properly adjusted?
Could this be detonation? 87 octane in a hot engine?
Has anyone experienced this, or something similar? I'd love to hear ideas.
We have a LuckyDog race at Willow Springs in two weeks. The temps will be cooler.
Thanks everyone for reading!
#928 Porsche 928 - West German Pushrodders (Retired)
#3 BMW E36 - The Internet says this is correct