Chuck---I don't have a PI setup, but your questions regarding info from
the A/F meter got my attention, so I will comment about this below:.
From:
triosan@gmail.com(Chuck Arnold)
Given his times at Pacific Raceway, where I run a car, that sounds
possible. He probably gets close to max rpm at PR also. I am just
shifting from 3rd to 4th when I enter the straight which is as long as a
drag strip and its runout, so lots of time to go as fast as it will go.
Not fast enough in my just getting sorted out TR5. Will go to 7500 in
3rd, but only 5000 in 4th [half way down that straight]. Hope my
adjustments to the PI make a difference when I test and tune next week.
According to my air/fuel meter, at that 5000 rpm I am running a little
rich.
Questions for the group:
1. What conditions should I check to "go faster". My change so far is to
increase the maximum fuel screw on the PI mixture control unit.
2. Since this is PI, does that richness infer too much fuel? Would the
change I mention above get worse?
3. What effect does being just a little too advanced in ignition have on
top speed, versus it being just a little too retarded?
4. If ignition is dead on, what effect on top speed does having the cam
timing retarded versus advanced?
Thanks for all responses, I am sure they will be enlightening.
--
Chuck Arnold
Chuck, Dick here.
On 1.See 2,3,&4.
On 2. It depends on what the meter showed. Most meters don't go beyond
12:1 (with any accuracy) so if all of your LEDs were on, is it possible
that you were even richer than this? We know that going beyond the 12:1
can cause a loss of power on some engines. I'd shoot for 13:1 or a
"blinking" 12:1 to be sure of not going too rich. I'm reasonably sure
that the modern FI engine leaves the closed loop when sensing WOT and
gives the above readings.
On 3. Given the time to distance of pistons and flame fronts at high
rpm, I'd go with the most timing that the octane you're using will
allow, without concerns of detonation.
On 4. The cam grinder should have the card marked for optimum setting of
the cam timing. There are reports of late cam timing (ATDC) giving
slightly better performance at the top end. This would be difficult to
verify without the use of a dyno and experimenting with your particular
cam. Otherwise, if you have a symmetrical cam, I'd shoot for "0" on the
timing.
Dick
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