Information About Boost and Various Blower Designs Behavior
All blowers are a compressor. So all blowers will make positive pressure in the manifold.
Weak blowers have dual rec. openings, they are 60 degree twist (Standard Helix), so they have a lot of drag, and are generally set up with loose clearances for Gas. Can you use E-85 or Methanol? Yes. The level of boost will be minimum unless the blower is designed with tight clearances, and has high helix (120 degree twist).
The greater the twist, the less friction they have and a high helix rotor will continue to make boost well up in the 10,000 rpm Blower Speed, where a std. helix will flatten out at around 7000 rpm blower speed.
Blower speed is a product of the drive ratio – so 25% overdrive = 8750 rpm blower speed on an engine turning 7000 rpm.
This is why you are wasting your time and energy spinning a 60 degree rotor blower at anything over 20-30% overdrive usually.
Methanol likes lots of air, and lots of boost since it uses twice as much fuel as gasoline. So high helix, high boost, big butterflies works well in general with methanol.
Blowers designed more for methanol have V Shaped discharges called “Delta” openings – The air is further compressed by forcing it through a smaller opening, thus adding speed and boost.
E-85 is an alcohol based fuel – it also likes boost, and it runs cool, has much higher detonation limits than Gas – Drum E-85 is usually 117 octane.
Gasoline – Burns fast, and HOT. The octane is limited to 93 for pump gas, and some have octane up to as high as 116 – However gas is difficult to tune in mechanical injection, expensive to buy in high octane form, and runs very hot. Gas blowers are set up to not make much boost since gasoline is intolerant of high compression in most forms, so not much effort is put forth to create boost.
Boost + Static compression = Effective compression which puts pump gas out of the picture when effective compression hits around 11:1.
This is why you will hear from many who have some knowledge, but don’t understand the whole picture; they will say that you have to have 8:1 compression with a blower. They don’t know why necessarily, but if their advice is taken without research and they build a 8:1 Alcohol engine, it will be a slug. Methanol and Drum E-85 can easily tolerate 11:1 12:1 static compression so when coupled with the blower boost they often have compression ratios of 20:1 which is fine with alcohol based fuels, but not with Gasoline.
Call Alkydigger 615-457-3192 for more insight into the design of a good supercharger system.