TUNING FOR ALCOHOL SMALL BLOCK CHEVY

[escott427]

I haven't been here in a while,need some basic help. Running a 355" SBC on alky, Mechanical injection.When runing in the Texas heat 95+ degrees, started leaning out the engine ,kept going faster every time. This weekend , temps dropped into mid 50's, car slowed down. Should I lean it some more, or start the other way because of the cold?
Long question, but this is my first injection experience , thanks

 

[patprimmer]

Hot air tends to be light. Cold air tends to be heavy.

To be right on the money with mechanical injection, you need to measure air density and adjust tune accordingly. If the temperature went down significantly I would expect to need to add a little fuel.

A site called HRE.com specialises in tuning MFI, but it is not free. The owner of the site also publishes an MFI manual that has a truckload of useful data.

When tuning alcohol fuel engines you read the cadmium plating burning of the ring on the bottom of the threaded area and the threads, not the porcelain. Once the cadmium plating is burnt off you need new plugs to get another reading.

Regards
Pat
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[escott427]

Thanks for the help. I've noticed the plating burn you mention, but only across the ground electrode. SHould the color change extend to the thread portion as well? and if so, when?

 

[patprimmer]

Start rich and sneak up.

The burning of the cadmium on the centre electrode is moe effected by ignition advance.

The base ring and threads are more effected by a:f ratio.

Near on maximum power will develop with a safe tune that pretty much burns all the cadmium off the base ring and up to one thread at the extreme point. It will be uneven with more burning on the exhaust valve side.

If it burns any point to three threads you are at the maximum without risk of burning a hole in a piston. Past three threads you risk doing serious damage.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules