Volume IX, Issue 3, Page 37

FUELforTHOUGHT

by Dave Koehler
03/08/07

Hi Dave,

Is there an optimum temperature to burn fuel, under normally aspirated carbs and also with N20? Also, does this vary with octane ie C16,C12 etc.? Thanks.

Rob Smallworth, England

Hi Rob,

I am not sure if you are asking about water, oil, cylinder, or exhaust temperature. I will go with water just for kicks.

Optimum? Perfection? Nah. It has to vary from car to car and how you have to race. IE, round robin or towed back. I will admit I am still a little old school on warming the car up to 180 degrees and then letting it sit to heat saturate the whole engine. However, all the dynos and dataloggers that have come down the road in the last 2 decades have proven me incorrect and indicate that a cooler gas engine makes more HP. I have always liked stone cold automatic transmissions and slightly warm rear gears and I am slowly coming around to the cold engine scenario.

It could be assumed that this HP increase might be due to the fact that the internal clearances are closer to where they were machined at room temperature. Maybe,...but more likely, on a normally aspirated engine this is due to the cooler intake charge air along with the fuel not getting any hotter than necessary. Using nitrous will obviously help the intake cooling but your nozzles are probably low on the intake runner. This results in the incoming air ahead of the nozzle to still be subjected to residual heat from the rest of the engine.

 A caveat to this would be that if you are running heavy straight weight oil you still need your oil warmed up so don't skip the intial warmup completely. If the inside of the trailer was 120 degrees on the way to the track and it's a 80 degree or higher day you might be able to skip the warm up altogether.

Some racers use the electric pan warmers to get the oil warmed up and never fire the car until they are at the head of the staging lanes. Therefore, it might be worth your consideration to do some testing. After you have done your initial check out for the day, cool the engine down as far as you can. Go to the line as cold as you can and go. Try it for a couple of weekends to see if it is of any help to your combination. Naturally, monitor your spark plugs.

Have a safe race,

Dave Koehler
www.koehlerinjection.com

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