100 cfm more with anular and downleg boosters can't beat AFR
A little follow up here.
In posts #1 and 9 the dyno runs reveal the downleg 750's secondaries were drifting lean from mid to top rpm.
So a question was whether I was able to correct that?
Focusing on just high rpms from the dyno that day and the one 1/4 mile run from last year we can see the answer is yes.
Dyno run #32 (same carb config as in first post)
Drag strip run focusing 2nd and 3rd gear.
Secondary high speed airbleeds reduced from .033 to equivalent of .029" dia.
In 2nd gear from 5000 to 6000 rpm, and in 3rd from 4700 to to the 1/4 mile stripe the AFR is now pretty flat.
Because the AFR was staying flat at the top the secondary jets could be further restricted without fear of going too lean.
In addition to jetting the secondary jets 2 sizes smaller, the secondary idle restrictions were moved to the low location and the secondary IABs reduced.
What is going on below 4700 rpm is harder to figure out.
The challenge with only one 1/4 mile run is twofold.
A. Although I got the car off the line pretty well I was rusty and unprepared for how quick the car was pulling. Result was I lifted a little and didn't keep the car truly straight down the track. Additional runs would have been good.
B.While the dyno run had the vacuum secondary opening controlled with a yellow spring, in the quarter mile run a plain spring with slower opening was used. Why? Because my intention that night was to change springs between runs. That never happened.
Looking at the vacuum (blue line) it seems reasonable to conclude that the secondaries late and slow opening may have contributed to richer conditions after the shift. We can see that at the 2-3 shift as well as the 1-2 shift. There may be more to it - maybe the secondary idle circuit is a bit rich.
A little follow up here.
In posts #1 and 9 the dyno runs reveal the downleg 750's secondaries were drifting lean from mid to top rpm.
So a question was whether I was able to correct that?
Focusing on just high rpms from the dyno that day and the one 1/4 mile run from last year we can see the answer is yes.
Dyno run #32 (same carb config as in first post)
Drag strip run focusing 2nd and 3rd gear.
Secondary high speed airbleeds reduced from .033 to equivalent of .029" dia.
In 2nd gear from 5000 to 6000 rpm, and in 3rd from 4700 to to the 1/4 mile stripe the AFR is now pretty flat.
Because the AFR was staying flat at the top the secondary jets could be further restricted without fear of going too lean.
In addition to jetting the secondary jets 2 sizes smaller, the secondary idle restrictions were moved to the low location and the secondary IABs reduced.
What is going on below 4700 rpm is harder to figure out.
The challenge with only one 1/4 mile run is twofold.
A. Although I got the car off the line pretty well I was rusty and unprepared for how quick the car was pulling. Result was I lifted a little and didn't keep the car truly straight down the track. Additional runs would have been good.
B.While the dyno run had the vacuum secondary opening controlled with a yellow spring, in the quarter mile run a plain spring with slower opening was used. Why? Because my intention that night was to change springs between runs. That never happened.
Looking at the vacuum (blue line) it seems reasonable to conclude that the secondaries late and slow opening may have contributed to richer conditions after the shift. We can see that at the 2-3 shift as well as the 1-2 shift. There may be more to it - maybe the secondary idle circuit is a bit rich.