This was exactly what I was refering to. You have a great NA motor now. Run it. If you run a blower motor and think you will be easy on it think again. Oh by the way build another motor when you do the blower or keep an old 502mag for a spare. Saved me half a summer or more of boating 2 years ago. I just need a spare drive now. I HEAR YOU ON WORRING ALL THE TIME. ;)

allan4
If your scared say your scared
burn it down:D :D

Allan4 - I went through the same thought process on my engines, which are marinized 502/502, 9.5:1 CR, small cam. I wanted to supercharge these engines and at one time I even bought a pair of used B&M 250 blowers. Then I realized that I needed to get the additional air flow with the least amount of temperature and pressure (boost), if I was going to avoid detonation. I decided that an intercooled centrifugal supercharger was the answer, for the following reasons:

1) Very high efficiency - 74%, therefore less heat in the intake charge

2) Compressor selection - with the use of a compressor map you can select the compressor that has its high efficiency "island" right where your engine needs it. You pretty well have to go to Vortech superchargers for this, since Procharger does not publish their compressor maps.

3) Intercooler efficiency - you need a big one, and you are not restricted by the size of the intake manifold as you are on a Roots blower setup.

4) Less mid range torque - torque is the direct result of cylinder pressure. Detonation is the result of too much cylinder pressure. A centrifugal supercharger can be selected to keep mid range torque down compared to a Roots blower.

5) It was this thought process that triggered the whole improved intercooler project that I've been working on for the past year. By reducing the restricition to air flow through the intercooler and carb box, I can spin the compressor slower for a given increase in air flow, therefore even less heat.

When people give you advice about spinning a B&M 250 slower, and ask you if you are using an intercooler, they are steering in the right direction, but the low efficiency of the Roots style blower is still a problem. I think by the time you bought a bigger blower and put a Whipple intercooler under it (the best one for Roots blowers) you would have spent as much money as buying an intercooled centrifugal supercharger setup.

Will this work on your 9.9:1 CR engine? I don't know. I decided that my engines were just fine the way they were, and got my jolllies out of designing and testing the improved intercooler. It's aimed at Mercury engines with stock compression ratios and that is what we will be testing on the dyno.

Good question. Good luck, what ever you decide to do.

tomcat, thanks for taking the time to explain what you experienced. I was super gung-ho about going with a blower, but I have about 10k in the motor as is and it only has 70 flawless hours. I would really hate to hurt the motor, and hate even more worrying about it everywhere I go. I built it to be n/a, shoulod probably keep it as such. My buddies (namely Khadley and merlin 540:D :D ) are going to badger me until I give in, and call me all sorts of crap, but it is looking more and more like if I do anything it will be head work and cam upgrade. Not sure yet, but as of right now it makes more sense than risking a meltdown. If I break it right now, I am screwed, I do not have the $$ for a major rebuild. Then next winter I can either modify this motor or build a true blower motor. Who knows, my have the funds to go with a bigger boat by then anyhow.

This is really a bummer, I was super reved up about going blown. I'll have to give it some more thought. Thanks all for your input, and Tomcat thanks again for all the info.

Oh yeah.....Hadley.........how did your circumsision procedure last week turn out??......:D

This is what I like about OSO. Sometime it makes you spend $ & sometime it saves you $ by not doing stupid things. (been there, done that)

allan
do you want to sell the blower? I have a guy with a 240 sport that might want it
I would hate to see him out run you with it
:D

i still have the blower in question allen didnt pay me for it so yes it is for sale also i have a b&m 250 and a weiand 6/71 all complete :D

I was just going to say that Chaz, I did not give him the dough yet, so it is not mine to sell. Hey Charlie, if anything would it be better to go with the 250?? Hell, I guess I better just call you and see what the heck the deal is here. Thnaks for the input, you too Mr Hadley.....did you guys do any sledding last week??:D :D

allen i will sell you the 250 for the same price;)

My opinion, the 250 is good for a 454. But for a 502/509, you should be looking for a 420, with that compression ratio. Less boost, less heat. I'm not here to sell ya a blower, just telling you what I learned. But, I do have a 420 for sale, complete. Before you spend, do a little more research. Just my .02