Have a few blower questions for everyone here, I've searched this and many other forums, just want to make sure I have everything right.

I understand the 71 is the CI of air, first number is the cylinders its meant to support. so a 8-71 is good for a 568ci motor, 10-71 good for a 710ci motor ect....

I understand how sizing would be important but wouldn't a bigger blower be better for a smaller motor (say a 10-71 where only a 8-71 is needed) as long as it was under-driven more or would it be a less efficent because the added mass of the rotors would not equal the gains of the cooler air charge? Is it just a street-ablity issue with this or is there a reason? Would it be worth just keeping the smaller blower and running a intercooler under it?

I know a 10-71 is the proper size for the motor I'm going to be beginning soon, but after doing alot of research there are a few things that are a little cloudy, I understand what people say but trying to understand the logic behind everything.

Thanks for the input,
Eric

Eric,
Based upon your address, I'm assuming that you are in the military. I just want to thank you for your service. It is much appreciated here back home.

Now, on to your blower questions. There are a few different schools of thought regarding blower size vs. engine displacement. I have a BDS 8-71 blower on my 392 Hemi. I could have used a 6-71, but I decided to use the larger capacity blower. My reasoning is that the blower will pass the same amount of air at a lower (blower) rpm, thus imparting less heat into the intake charge. I even went as far as doing some calculations of engine rpm vs. blower rpm vs drive belt speed. I finally decided the larger capacity was the way to go.
Others say that the larger capacity will do nothing in the way of a cooler charge temperature, and all you are doing is spending more money on a blower size you don't need. You didn't say what engine you are using, but if it's not strictly a race motor, a 10-71 may be overkill on the street.
You're doing the right thing by researching before you buy. If you haven't visited their website, try BDS. Their website is http://www.blowerdriveservice.com. Check out the recommendations and tech info links.
If you can get a copy, a good book to read is Street Supercharging by Pat Ganahl. A lot of blower theory is discussed, including the pros and cons of blower size vs. engine displacement.
Hope this helps,
Steve

a smaller blower would offer less parasitic loss over a largert unit i would think. personally, id run a bigger unit then necessary so you dont have to run it to its limits, it will build less heat if you dont have to spin it to its max potential.

steve392; First I'd like to say Thank You for the support, you are correct I'm in the military. I've been home since late Nov. 2009.

Thanks for your input, this was what I was thinking also as far as over sizing the blower. I'm still not sure what to do for my top end but have a few parts ordered already. The truck is mainly going to see track use, but the occasional drive to work, maybe once every other week if the weather is perfect for the day.

The motor I'm building is a 632 BBC; 8:1 CR Forged Pistons, 4340 Crank, H Beam rods, Dart Big M block, Heads AFR 375cc CNC heads. Those are the parts that I have ordered already.

Probably going to be EFI, still not sure what size blower, a 10-71 would be the right size, haven't really seen many 12-71s around, so I'm still undecided.



chevy1500z71; Thanks for the input this is also what I was thinking.



Eric