Lean and heat
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Road Master
Joined: Jun 2007
Posts: 958
Likes: 1
From: Birch Bay, WA
Lean and heat
OK, in my continued edjumukayshion with my first Harley experience I need a question answered.
Does a hot engine always mean a lean condition and vice-verse, or, can a twin cam (regardless of 88 or 96) run too lean and not be too hot for the rider?
Just curious.
Does a hot engine always mean a lean condition and vice-verse, or, can a twin cam (regardless of 88 or 96) run too lean and not be too hot for the rider?
Just curious.
Road Warrior
Joined: Aug 2008
Posts: 1,442
Likes: 8
From: south
It is the ratio of air to fuel.
To much air-not enough fuel=Lean
To much fuel-not enough air=rich
The factory is forced to manufacture the engines lean to meet government emissions standards. They are also forced to use restrictive exhaust to meet noise regulation.
These two things make for a hotter running engine.
Correct these two things and you engine will run cooler and make sitting in traffic more comfortable.
To lean is not good, engine damage will/can occur. To rich can thin the oil and wash the oil off the cylinder walls and cause damage also.
Best thing is to get the Air/fuel ratio correct.
To much air-not enough fuel=Lean
To much fuel-not enough air=rich
The factory is forced to manufacture the engines lean to meet government emissions standards. They are also forced to use restrictive exhaust to meet noise regulation.
These two things make for a hotter running engine.
Correct these two things and you engine will run cooler and make sitting in traffic more comfortable.
To lean is not good, engine damage will/can occur. To rich can thin the oil and wash the oil off the cylinder walls and cause damage also.
Best thing is to get the Air/fuel ratio correct.
Road Warrior
Joined: Dec 2004
Posts: 1,726
Likes: 12
Easiest way to tell the general running condition of the motor is to perform a sparkplug check. Look at the straps on the tip of the sparkplug. An ideal running condition will produce a paperbag color, a lean condition will produce a white deposit, and a rich condition will produce a black deposit.
Elite HDF Member
Joined: Jul 2008
Posts: 4,270
Likes: 1
From: Central Virginia
harley-jones and Sincecrazy are right on target. Also, to answer your question, "can a twin cam (regardless of 88 or 96) run too lean and not be too hot for the rider?", you're going to get heat regardless, so there are other methods to reduce the heat. Many of us put on mid-frame heat deflectors, true-duals (to eliminate the pipe under your right thigh), synthetic oil, oil coolers, fans, etc. and these things do help to some extent. But you're going to get some heat because you're sitting on top of an engine. But like was said, the mixture should be correct.
Last edited by Ultra 08; Sep 16, 2008 at 09:03 AM.
Road Warrior
Joined: Aug 2008
Posts: 1,442
Likes: 8
From: south
Just to add one more thing about the plug reading.
With the ECU controlling the Air/Fuel mixture it is very hard to get an accurate plug reading. The engine can be lean at one rpm and rich some place else. That is why tuners place probes in the exhaust to keep mapping the Air/Fuel ratio at different rpm's.
In the old carburetor days you could do a full throttle run, hit the kill switch, pull the clutch in, stop and check the plugs and get an average idea of a rich/lean condition.
Today, looking at the plugs is a good way for a general idea, but you really can't do a tune by using this method anymore with the ECU constantly changing the Air/Fuel ratio throughout the rpm range.
With the ECU controlling the Air/Fuel mixture it is very hard to get an accurate plug reading. The engine can be lean at one rpm and rich some place else. That is why tuners place probes in the exhaust to keep mapping the Air/Fuel ratio at different rpm's.
In the old carburetor days you could do a full throttle run, hit the kill switch, pull the clutch in, stop and check the plugs and get an average idea of a rich/lean condition.
Today, looking at the plugs is a good way for a general idea, but you really can't do a tune by using this method anymore with the ECU constantly changing the Air/Fuel ratio throughout the rpm range.
Outstanding HDF Member
Joined: May 2008
Posts: 2,009
Likes: 0
From: South Jersey
First 1/2 of the question. The ideal af ratio for an internal combustion engine is 14.6:1 Idle and cruse with something around 13.5 under heavy load and 9.1 to 12.1 at excel (initial crack of throttle)
Now, Let us apply this to a HD V twin. The average motor (Remember I said average)can only run 13.9 to 14.2 at idle and cruse without detonation and over heating. The trade off with even those ratios is heat. All the other #s are somewhat consistent +/- a couple tenths.
second 1/2 of question. If your motor was run at maximum efficiency, it does and will fry your a$$. That is why people richen the af, add heat deflectors, oil coolers, and use true duels to relocate the rear pipe.
IMO HD has successfully continued to keep the air cooled V twin within federal emissions standards. The complaining of heat is just that, complaining. It's a harley, add your personal touches to it and if cooling it off is on your list of TTD, cool'er off. Can't wait to see how hot they will be with the new regs coming?
Now, Let us apply this to a HD V twin. The average motor (Remember I said average)can only run 13.9 to 14.2 at idle and cruse without detonation and over heating. The trade off with even those ratios is heat. All the other #s are somewhat consistent +/- a couple tenths.
second 1/2 of question. If your motor was run at maximum efficiency, it does and will fry your a$$. That is why people richen the af, add heat deflectors, oil coolers, and use true duels to relocate the rear pipe.
IMO HD has successfully continued to keep the air cooled V twin within federal emissions standards. The complaining of heat is just that, complaining. It's a harley, add your personal touches to it and if cooling it off is on your list of TTD, cool'er off. Can't wait to see how hot they will be with the new regs coming?
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