IRONMAN

What is the optimum Compression Ratio for a mild boost Supercharged engine 3-5 psi and 500 - 550 cubic inches. This would be for pleasure use 89 octane and a hyd roller cam at less than 5600 rpm.??

Turbojack

7.5-8. The lower the static compression is the more boost you can add to make more HP. Such as a motor at say 8.5:1 can not stand as much boost before detonation sets in as a 7.5:1 motor.

PROFILE

I would'nt run much more than 8.5:1.Also would use only premium 91 octane fuel.

KNOT-RIGHT

Im with TurboJack. If your building a blower motor I would run 7.5 to 8.0.
Most Blower kits are based on production motors usually 8.5,9.0-1. The majority of the consumers install blowers on production motors. That exsplains why you will see alot of higher compression motors with I.E. Prochargers , Whippiles, etc.
The lower the static compression the more boost one can run.

Check it out.
http://www.kuhlsuperchargers.com/tech%20p05.htm

cobra marty

If you start with too low static compression the motor will be sluggish until up on boost. For 3-5 boost you should be OK and happier with 8.5 with a centrifugal type blower.

Turbojack

Depends on blower. I have had them where at 1500 rpm or less when I went wot I had full or close to it boost & was not sluggish at all. The motor I now have has the hightest compression I have ever had on a blower motor & I am at 8:1

Michael1

Turbojack,

I sounds like a you did not have a centrifugal blower. The boost out of those are highly dependent on rpm.

Michael

ratman

im building 588s with 1071's and in the last three weeks have talked to most of the big blower builders, cobra,tyler crocket, zul, steve burle, the whole combination has to be sized for each other components in that if you have too low a static compression you will need a larger blower or you will have to spin a smaller one too hard to make boost and generate a lot of heat. the better the heads and exhaust flow the more power you can make with less boost as restrictions in the engine increase boost. randy at cobra says exhaust port work alone is worth 75 ponies. i saw the exhaust ports on the brodix heads they run and the exhaust is f**ing huuuge! i was going to go 7 to 1 but they all advised me to run more staic 8.25 to one so my 1071 would work with my 588's and not be lazy at idle from too little compression nor would i have to spin the blower exccessivly hard to make good power under boost. everyone i spoke with also told me to run intercoolers to prevent detonation and make another 75 or so ponies in doing so. so kep in mind heads exhaust, displacement and blower size all must work together. decide waht kinda power you want to make and then pick the components you'll need to make that #. i was down at cobra today and he has a bunch of used blowers that can be bought resonably. i've never seen so many blower motors in one place in my life,they do a ton of em and have blown up enough stuff over the years to know what does and doesn't work. good luck with it ,spend some time talking with these folks they were all kind enough to talk at length about what has worked for them and they have the answers.

ratman

by the way while 3 lbs of boost doesn't sound like a lot, scott at intense marine has a pair of 540" 990 iron head 871 blower motors that dynoed @ 825 hp with 3.5 lbs of boost using 2 850 holley 4150 carbs !

ratman

cobra jack what size motors and blowers do you run? r u over or under driven? what percent? what kinda hp & torque? thx ratman