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dvkk dvkk is offline
Fuchs w h o r e
Join Date: May 2003
Location: Vancouver, Canada
Posts: 644
Originally posted by RoninLB
Originally posted by dvkk

If your carburated engine makes more power when it is cold out, that proves your mixture is waaaay too rich when it is warm.
Since your engine does make more hp when it is cold out, that proves you are dumping in the necessary extra fuel at all time.
------- Sounds good but that hasn't been my experience
My EGT's are about 25degF hotter at 70degF than at 40degF. If I lean out 70degF operation EGT's will become hotter and will have greater deviation between hotter and colder EGT.. in other words the spread of piston power will become greater. It's as lean as I could make it and be easily streetable for my act.

This means your carbs aren't as rich as Alex's

Since the fuel has considerable mass, what it does is put out the fire, absorbing the heat of combustion, reducing hp. By leaning out the jets, you will regain some of the lost hp you notice when it is warm out.
---------- it does put out the fire but it still feels stronger at night. I have hard numbers on that.

Because you are slightly too rich in warm weather, closer to the optimum A/F ratio at night.

A few of you made the same observations with your FI cars. Those of you that are smart enough to have your O2 sensors hooked up are having your A/F ratio properly adjusted to compensate for the colder air.
-------- FI is another story somewhat because FI doesn't have the atomization critical issue that carbs have. A cool carb and intake allows the mix to be dense as possible.

A hot carb and manifold causes the air to heat up, making it expand, reducing the amount of O2 in a given volume. In other words, a warm intake causes the mixture to go rich. The O2 sensor on FI cars will compensate for the rich A/F ratio, but not for the lack of O2

I don't really have a text answer on what's happening but i think I could get away with 1/4 idle mix leaner at night and make even more power. That 1/4 turn is worth about the 25degF in EGT. Then I'd have to reset for daytime hotter ambiant. I'm figuring the above on 30-40degF ambiant difference.

Idle mixture settings have no effect whatsoever on max hp when you are at WOT. You need to play with the main cct to affect peak hp.

Last edited by dvkk; 10-12-2005 at 12:10 AM..
Old 10-12-2005, 12:07 AM
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