Are these air/fuel numbers acceptable?
12-02-2001, 10:36 PM
#1
Burning Brakes
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Are these air/fuel numbers acceptable?
Did a test with a gas analyser on my '77 on Sat to see how rich/lean it is running. It showed around 13.2 at idle, 13.5 at cruise (1500-2000rpm), down to about 11.2 at WOT. At gear changes it is around 12.5 (th350).
I've got a Qjet with 75 jets/41 rods, ported heads, 2.02/1.6 valves, stock exhaust, 3.08, and an xe256 cam. It's slow up to 3000rpm :( and starts to boogie after that :) . My off the line leave a lot to be desired, hence the test. I think I may have to go up to a 45 rod as I think maybe its getting too much fuel too quick (?).
Are these A/F numbers reasonable? I have noticed economy is about 5mpg less (highway) since the cam install.
Our club is having a dyno day on the 15th and I'm trying to fine tune it before I get there.
:cheers:
I've got a Qjet with 75 jets/41 rods, ported heads, 2.02/1.6 valves, stock exhaust, 3.08, and an xe256 cam. It's slow up to 3000rpm :( and starts to boogie after that :) . My off the line leave a lot to be desired, hence the test. I think I may have to go up to a 45 rod as I think maybe its getting too much fuel too quick (?).
Are these A/F numbers reasonable? I have noticed economy is about 5mpg less (highway) since the cam install.
Our club is having a dyno day on the 15th and I'm trying to fine tune it before I get there.
:cheers:
12-02-2001, 11:29 PM
#2
Le Mans Master
Re: Are these air/fuel numbers acceptable? (Chris O')
I agree, I think that's a little rich. You want something between 12.5 and 13 at WOT. What's you timing set at? A 256 cam shouldn't be very slow below 3000 rpm.
Of course, you should put together a package of rods with a range of tune-ups and take that to the dyno test. Testing how the engine responds to different A/F ratios is what a dyno is all about. After all, you really don't know what your engine likes until you test it.
Of course, you should put together a package of rods with a range of tune-ups and take that to the dyno test. Testing how the engine responds to different A/F ratios is what a dyno is all about. After all, you really don't know what your engine likes until you test it.
12-02-2001, 11:33 PM
#3
Tech Contributor
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Re: Are these air/fuel numbers acceptable? (Chris O')
Chris -
The primary rods have no effect on WOT performance - only cruise and idle/off-idle. Based on your numbers, you might want to drop your main jet size 2 sizes to see if you pick up a little throttle "crispness" on the low end.
The primary rods have no effect on WOT performance - only cruise and idle/off-idle. Based on your numbers, you might want to drop your main jet size 2 sizes to see if you pick up a little throttle "crispness" on the low end.
12-02-2001, 11:57 PM
#4
Burning Brakes
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Re: Are these air/fuel numbers acceptable? (lars)
Thanks fellas.
I figured a bigger rod might help in the transition to WOT. Sorta like kinking a garden hose then unkinking it, 1st a steady stream then heaps at once.
Jets and rods can't be bought freely over here. The WOT performance above 2500rpm is way cool now. I'm trying to tune the low end acceleration better.
What are the "normal" A/F ratio's? (or the range)
Thanks
I figured a bigger rod might help in the transition to WOT. Sorta like kinking a garden hose then unkinking it, 1st a steady stream then heaps at once.
Jets and rods can't be bought freely over here. The WOT performance above 2500rpm is way cool now. I'm trying to tune the low end acceleration better.
What are the "normal" A/F ratio's? (or the range)
Thanks