Richer mixture reduces cylinder head temperature

[axl911]

Does a richer mixture reduces cylinder head temperatures? Especially if timing was retarded to reduce ping.

If so, how rich does it need to be?

thanks,
anthony

[aston@ultrasw.c]

A richer mixture will reduce CHT as will eliminating detonation.

Max power is produced at about 13:1

I would say this is the most rich you want to go.

[Por_sha911]

Wouldn't it be more accurate to say that a lean mixture will increase temps. You don't want to fix one problem (cyl head temp) by creating another. If the mix is too rich you will have other issues. Make sure your car is properly tuned including plug wires, cap & rotor, filters... and then adjust it to the proper mix. If its still running hot then find the cause rather than make the mix too rich.

[aston@ultrasw.c]

Originally Posted by Por_sha911

Wouldn't it be more accurate to say that a lean mixture will increase temps.

Yes!

Unless you are starting at 15:1

[axl911]

Originally Posted by Por_sha911

Wouldn't it be more accurate to say that a lean mixture will increase temps. You don't want to fix one problem (cyl head temp) by creating another. If the mix is too rich you will have other issues. Make sure your car is properly tuned including plug wires, cap & rotor, filters... and then adjust it to the proper mix. If its still running hot then find the cause rather than make the mix too rich.

This is for a boosted/supercharged 3.6 engine. I am comptemplating increasing the fuel mixture at part idle/cruise to prevent high cht by the supercharger.

Intake temperature is very well kept in check by. Next up would be to control the cylinder head temp.

Wondering whether it is worthwhile to richen up the mixture at part throttle/cruise to reduce cht and keep detonation in check.

WOT is currently below 12.3.

thanks,
anthony

[Por_sha911]

Fuel mix can be adjusted for non-stock applications. Also consider adjusting to a higher octane. What compression P&C's and octane are you running?

[axl911]

Originally Posted by Por_sha911

Wouldn't it be more accurate to say that a lean mixture will increase temps. You don't want to fix one problem (cyl head temp) by creating another. If the mix is too rich you will have other issues. Make sure your car is properly tuned including plug wires, cap & rotor, filters... and then adjust it to the proper mix. If its still running hot then find the cause rather than make the mix too rich.

Originally Posted by Por_sha911

Fuel mix can be adjusted for non-stock applications. Also consider adjusting to a higher octane. What compression P&C's and octane are you running?

11.5 compression for the stock 3.6 engine with 5psi boost from TPC. I am limited to 91 Octane here but altitude is high.

[Tippy]

Richer mixture should reduce temps.

Retarding timing increases temps.

[axl911]

The car is running great both cruise and WOT. But on long hill climbs at partial throttle (not full/WOT) cylinder head temp can climb. I am thinking of richening the mixture to keep cht in check. Worried that a high cht can lead to detonation and other bad stuff.

[axl911]

Originally Posted by Tippy

Richer mixture should reduce temps.

Retarding timing increases temps.

That is what I am thinking. Richer reduces cht, and reduces detonation. Motronic engine management will see this and increases timing which then further reduces cht. My logic correct here?

[Tippy]

Originally Posted by axl911

That is what I am thinking. Richer reduces cht, and reduces detonation. Motronic engine management will see this and increases timing which then further reduces cht. My logic correct here?

I don't have that answer as I am a newbie to Motronic myself (I only have 3 threads asking questions) but that is what I learned from basic engine theory and firsthand experience (on other cars).

[stlrj]

The fuel / air ratio for best power is around 1:13 and for best specific fuel consumption (SFC) it is 1:17. Peak EGT occurs at the chemically correct ratio of 1:14.7(02 sensor range) and peak CHT at a slightly richer ratio.

Aircraft Engine Leaning, Mixture, EGT, Fuel Air Ratio, Lean of Peak, Best Power, Ground Procedures, Airplanes - EAI

[stlrj]

Originally Posted by aston@ultrasw.c

Yes!

Unless you are starting at 15:1

Which is where all cars with 02 sensors start at. So anything leaner is cooler to the point where it stops running and that's really cool.

[RoninLB]

higher power output = higher CHT
higher oil temps = higher CHT
detonation = higher CHT
high ambient air will increase CHT

Many issues cause a higher or lower CHT. A clearer discussion would be related to mix and resulting EGT imho. You can lower CHT when a cylinder is abnormally lean. The EGT will skyrocket but CHT will fall

increasing mix lowers EGT and power

[brads911sc]

This is not entirely true. I agree that 12-8-13.6 is the sweet spot for most conditions. So perhaps 13.1 is a good number.

What you are after is a lambda value of 1.0 which indicates a full burning of the fuel. The AFR number associated with a Lambda will change based on what type of fuel you are running. Pure Gas, E10, E15, E20 will all translate into a different AFR. Example, AFR for pure gas is
higher than what we mostly buy at the pump which is E10. If you set your fuel for E10 and then run E15, you will be lean because it will have a lower AFR number. If you run gas you will be rich...

I think its good to get it in a close range. Taking into account the fuel you are running... not everyone in every condition will just target 13.1. We should all be targeting a Lambda of 1.0. Many software packages will allow you to see the Lambda as either Lambda or AFR. Many will also allow you to adjust the tables automatically based on fuel type and atmospheric pressure...

Originally Posted by aston@ultrasw.c

Max power is produced at about 13:1

I would say this is the most rich you want to go.