Who still drives their cobra in the summer heat

[Ace23]

Originally Posted by eschaider

Depending on how and who set up your carb you may or may not get some level of the summertime blues. Carbs tend to be a black art for the average enthusiast but there are good shops that can work wonders with them - for a price.

The other alternative you might want to explore is one of the many EFI systems out on the market today. If you go that route you want to make sure it supports a Mass Air Flow (MAF) fueling model if at all possible. All the EFI providers will attempt to steer you into a speed density fueling model system. If you go that route you will still suffer from some level of the summertime blues, just not as bad but still present.

MAF based systems measure the actual mass of air entering the engine in lbs per unit time and adjust fueling correspondingly to meet the tuner's commanded AFR or lambda. The MAF based systems give the most uniform performance across all altitudes and temperatures anywhere in the world. Speed density — not so much. It is not as bad as a carb but it can't hold a candle to the MAF based systems for fueling control.

BTW the reason the auto manufacturers use MAF based systems is that they are the only systems that will keep the EPA out of the manufacturer's pockets for emission violations. The metrics the EPA requires a manufacturer to adhere to are an order of magnitude or more stringent than our tuning demands. MAF based systems hit the bullseye the first time and every time for the manufacturers that must comply with the EPS emission standards — and they do it anywhere in the world.

If you elect to go the EFI route there are a number of air valves than mimic popular carburetor footprints like 4150 and 4500 Holley carbs. That will allow you to keep a period correct appearance for all but the most critical eye and still benecit from the EFI system. If you elect to go the period correct look route, you will end up needing to use a speed density system because no one offers a MAF sensor that looks like an air cleaner.

If the period correct issue is not an issue the there are a number of other systems that you can go MAF based with.

As a parting thought don't forget, I believe it is Borla that makes a Weber look a like system. The system is actually not Webers but EFI which gives you the look of Webers with the predictable starting, performance and operation of a Detroit assembly line vehicle with EFI.



Ed

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.

[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