CLASS RACER FORUM - View Single Post - 1957 283/270hp dual quads drag testing on a 350

wheezer · 09-07-2009, 09:32 PM

This is a testing update.
Tested the setup Sunday afternoon (6Sep09, 14:00-16:00) at the new Dallas Raceway on the 1/4 mile. Air temps were warm 94-97F or better described as hot from my perspective. The front power pistons with their weak springs were tied open on both carbs (the up position). Then the secondary air valves were tied open. This netted 2 runs in the 12.6 sec range at 106 mph (3700 lb). The engine really ran rough in the pits but gave .3-.4 second improvemnt in the quarter mile.
The bad news is the slight hesitation is still present till high gear. I'm begining to suspect the secondary jets are too small. The jet area vs. the venturi diameter comparison from the front to rear carb throats is vastly different. The rear venturies seem to have a 36:1 lessor and different ratio of jet area to venturi area compared to the front venturies. What I'm trying to say is the bigger secondary venturies don't compare in jet area to the primary venturies. Looks like I need to change the rear jets to a larger size to kill this hesitation. Comments?

09-07-2009, 09:32 PM	#12
wheezer Junior Member Join Date: Sep 2009 Location: Dallas/FtWorth Posts: 13 Likes: 0 Liked 0 Times in 0 Posts	Re: 1957 283/270hp dual quads drag testing on a 350 This is a testing update. Tested the setup Sunday afternoon (6Sep09, 14:00-16:00) at the new Dallas Raceway on the 1/4 mile. Air temps were warm 94-97F or better described as hot from my perspective. The front power pistons with their weak springs were tied open on both carbs (the up position). Then the secondary air valves were tied open. This netted 2 runs in the 12.6 sec range at 106 mph (3700 lb). The engine really ran rough in the pits but gave .3-.4 second improvemnt in the quarter mile. The bad news is the slight hesitation is still present till high gear. I'm begining to suspect the secondary jets are too small. The jet area vs. the venturi diameter comparison from the front to rear carb throats is vastly different. The rear venturies seem to have a 36:1 lessor and different ratio of jet area to venturi area compared to the front venturies. What I'm trying to say is the bigger secondary venturies don't compare in jet area to the primary venturies. Looks like I need to change the rear jets to a larger size to kill this hesitation. Comments?