Timing

[ZGjethro]

Here is my take. When I read in the manual that the timing should be 2 after tdc, I disagreed, and I am not very versed in engine tuning. I mostly fiddle with my two stroke dirt bikes and snowmobiles. Ignition after tdc makes no sense. I set my timing at 5 degrees before tdc, but I run my truck from 7000 to 12,000 feet in elevation. I am thinking of trying a earlier timing. I have had several very knowledgeable people tell me to try 10 degrees before tdc for this elevation. Are there any high elevation drivers out there with opinions?

[MSeriesRebuild]

Here is my take. When I read in the manual that the timing should be 2 after tdc, I disagreed, and I am not very versed in engine tuning. I mostly fiddle with my two stroke dirt bikes and snowmobiles. Ignition after tdc makes no sense. I set my timing at 5 degrees before tdc, but I run my truck from 7000 to 12,000 feet in elevation. I am thinking of trying a earlier timing. I have had several very knowledgeable people tell me to try 10 degrees before tdc for this elevation. Are there any high elevation drivers out there with opinions?

That much elevation can certainly make a difference, so will the quality of your fuel; you can bump it up as long as you don't get spark knocking during acceleration. When you start to get pinging, it's too far advanced.

[hbb]

ZGjethro wrote:
Here is my take. When I read in the manual that the timing should be 2 after tdc, I disagreed, and I am not very versed in engine tuning. I mostly fiddle with my two stroke dirt bikes and snowmobiles. Ignition after tdc makes no sense. I set my timing at 5 degrees before tdc, but I run my truck from 7000 to 12,000 feet in elevation. I am thinking of trying a earlier timing. I have had several very knowledgeable people tell me to try 10 degrees before tdc for this elevation. Are there any high elevation drivers out there with opinions?

A good rule of thumb for altitude timing is to add 1 deg of advance for every thousand feet of elevation MSL. The ultimate end result is to get you engine to run at its best with out pinging or over heating and will not take a month of cranking to start with good power.Many out side variables can and will effect the drivability of different engines,some like different fuels,condition of the engine,ambient temps,altitude,driving habits,the guy whom refuses to use all of the gears in his transmission for fear of wearing it out,The condition of the distributer,but the best approach is to start with a good base line of a published timing setting @sea level and work from there.If the engine is fresh and and all of the supporting components are up to speed the only compensation should be your elevation corrections with your 7000-12000 feet a 8-10 deg advance ( 6-8 deg TDC)would apply. Give it a try!
I do think the value of this form is to help when you can and learn when you can,I have picked up information from a lot of the different posts! There is no one in the world that doesn't have something to offer and there is no one in the world that can not learn something.
hb

[topellis]

Charles, Thanks for all you do. Most would have gone by the way side than take the things folks aim your way. Good information based on sound experience.

Mark