Who still drives their cobra in the summer heat

[eschaider]

Originally Posted by Ace23

Thanks Ed. The QF750 with mechanical secondaries was setup on the dyno by Wayne Presley of very cool parts down in Alabama. I have no cranking issues or fuel boiling in the bowls...no sputtering or anything of the matter in the heat.

If I was going to go EFI it would be multi-port injection. FAST is local here due to comp cams. I would probably try to hook up with a local engineer for install and tuning. I would also go with an in tank fuel pump. I have no idea what fuel injection would do for me...I would just want it done right. The carb runs smooth idle through WOT but I’m sure EFI still wins. As I previously mentioned I just don’t like the down on power feel in the summer.

Any time air temp goes up air density goes down and so to does engine power, but proportionally. Here is a graph that visually illustrates the phenomena;



The hard numbers look like this;

Air Density at 70˚F is 0.0749 lbs per cubic foot,
Air Density at 120˚F is 0.0685 lbs per cubic foot.

That is a decrease of air mass equal to 8.5%. An 8.5% loss of air mass will produce an 8.5% loss of power when properly tuned. For many people this is around the threshold or just past the threshold where they become aware. When not properly tuned, the 8.5% loss of air mass will produce a much larger loss of power because you not only have less air available, you now also have a surplus of fuel that makes the engine run rich,

Your Cobra should not loose proportionally more or less power than a daily driver across the same temperature change. If the Cobra is noticeably more lazy across the same temperature change, then your Cobra is not properly tuned and/or you carb is also out of whack.

Both sutuations need to be attended to. EFI will not create power but it will, when properly installed and tuned, optimize the power available for the ambient conditions at hand.

I took a quick look at the FAST website because I was unaware of a MAF based system they offered. There might be one but, the website doesn't seem to indicate they offer one at this time. That of course could change with time.

A speed density system will be better than your carb but you will still have some level of summertime blues form the temp changes that will still require some level of attention to a speed density EFI system to optimize engine power output.


Ed