jet size program

I have used Jetsize by Les Davenport for years but have now switched to Alky Pro which is a more robust program. Jetsize bases its selection of main jet only on what the Density Altitude is regardless of what effect humidity and temperature have in cooling the air coming into the hat above the blower which Alky Pro does. Also Alky Pro computes the change of the Specific Gravity of methanol based on changes of temperature. Sorry to say but Jetsize is a thing of the past. Check out Alkypro.com

 

That is correct but for that price you get great support from Greg Gower plus all updates. I think Jetsize is up to around $600 now and is not updated and is not as good. I have used both and have compared them side by side.

 

I wish it would give you a baseline tuneup. That would be great but don't know one that can do that successfully. If you know enough about tuning fuel systems you could build a baseline setup with it. Normally you would enter your flowed system jets and poppet settings into the program then enter the current weather conditions and get a new recommended main jet size based on humidity, temperature and barometric pressure. Then if needed you can adjust it richer or leaner at the same time having it tell you what main jet change is required for entered weather data change. Without doing that you can chase your tail. Alky Pro gives you a constant readout in a window of the GPM at 1500 ft DA so you have an easy reference as to what fuel changes you are actually making. Also you can use it to change the system to raise or lower the measured fuel pressure by changing all the jet sizes up or down in sizes by a percent so you keep the fuel distribution the same and have it compute the new fuel pressure while keeping the GPM into the motor the same so the tuneup is the same. If you change your blower overdrive and need to change the GPM into the motor then it is simplified by using Alky Pro. If you have a fuel flow sensor then EVERY run is the same as a $800-$1200 flow bench run and you can readily see if you have a fuel pump wearing out or have a fuel problem.

 

Alky Pro uses all of Patrick Hales formulas. I think that maybe Patrick's is ahead of Alky Pro on that. The reason I chose Alky Pro was that fact that it connected with my trailer weather station and could send out the weather and main jet on the internet so I could receive the data via an apps on my cell phone in the staging lanes. I did a comparison test using Jetsize, Alky Pro and Patrick Hale's. Both Alky Pro and Patrick were very close in agreement but both way different to Jetsize.

 

You can use it without a flow meter and use the GPM estimate that the program gives you which will be pretty close. Treat that estimate as what is in your motor and you can increase or decrease the GPM flow from it and it will still give you the main jet required by the inputted weather.

 

Alky Pro (AP) has pump loop with poppet pressures, fuel leanouts and everything else that is required. Another thing AP has is a correction to the specific gravity of methanol due to either ambient temp change or by reading it with a temp gun if you are cooling your fuel. Two major modes in AP; one is called Conventional and the other is Methanol there is a difference in the algorithms between these two modes and can be ten main jet sizes difference between these them. I only use the Methanol mode because it takes into account the cooling properties of the incoming air being cooled by the alcohol. This is especially important if you are using a spray bar in the hat. If you do not take this cooling effect into account then you are not going to have enough fuel in the motor and will overheat your valves and also not make the power that is available by having the spray bar. What the other programs don’t take into the computations is the temperature and humidity. If the temperature is high and the humidity is low like in Las Vegas there is a tremendous cooling that lowers the Density Altitude of the air going into the motor and demands more fuel. If it is high temperature and high humidity then you will not experience the same cooling effect and need less fuel. In high temp and low humidity areas swamp coolers work and misters work but not so in Florida with high temps and high humidity same thing in our injector hats. So the same fuel requirement computation based only on Density Altitude as used in Les Davenports Jetsize is going to get you into trouble.