Blower Carb CFM?

I took this off the BDS site:

http://blowerdriveservice.com/faq.php

It says :" To measure CFM on a blown engine:
{(CID x RPM) ÷ 3456} x {Boost ÷ 14.7 + 1)} = CFM required.

So on a 292 I6 spinning 6000RPM w/ 10#'s it'd be:
(292x 6000)÷ 3456x (10÷ 14.7)+ 1= 851CFM Right?


P.S: where the #?*! is the #?*!ing divide key on the key board? I just copied and pasted the one from the link...

 

I also found this to find the final compression ratio:

Final Compression Ratio (FCR) = [ (Boost÷14.7) + 1 ] x CR

That would mean I'm running around 14:1 compression with 8.5:1 base and 10 lbs boost...
Maybe I'd better go with 8:1 to bring it down to around 13:1...

 

If you're seriously going to run that kind of boost, I'd really think about reverse cooling the engine (water goes IN the head and out the block). That's a long engine, and your mixture is likely to be off from one cylinder to another. Feeding water to the head at both ends wouldn't be a bad idea, either.

At 13:1 it's still a race gas engine, so that extra 1/2 pt. of static compression isn't gonna matter all that much. You'll just need 116 instead of 110 octane...

 

Using that formula My calculator says 346 cfm. That can't be right. By that formula my 540 @ 6500 and 14# of boost only needs about 950 cfm. and I am running 1500 cfm. What am I missing here? jim

 

The divide key is /

Jim

 

I'm going to be running a water/methanol/alcohol injection kit from Snow performance...

 

Haven't checked your math but its not likely that you will find an 851 CFM carb and altough you can probably get by loosing 1 cfm you will be better off to go the next size bigger off the shelf. The added CFM won't hurt you at all.

 

Division key is ALT-0247 (hold alt and then type 0247 then let go)

In terms of the blower, 10lbs of boost is a fair bit for a roots style blower. Do you have O-Ringed heads, 4340 bottom end? Is this a street or track motor?

It is possible to run over CFM w/a blower. So you might be able to get away with 1500 cfm, when you have a blower motor it's going to draw in what it needs. Overcarbing a blower motor is a tough thing to do, on my ole setup I was running 2 775 carbs on an 871 littlefield w/a 391 sbc, I'm guessing that calculator is meant to show you the least amount you can get away with. Personally I'd call littlefield, BDS/Wieland both make loose blowers for street cars, found that out the hard way.

(on a side note) that also seems like alot of RPM for an inline 6? What's this going in? What's the motor? Sounds cool!

 

Holley makes Carbeurators designed for draw thru setups in 600Cfm, 750Cfm, 800Cfm, and 950Cfm.
Do you think I should go with the 800 or the 950 version? or should I use something like 2 500Cfm 2bbl's?

 

What's the blower? What manifold do you have for it?

 

It's a 292 Chevy, search on here, or look through the pages, My set up is on here... The blower is a 6-71, and I was going to rig up a
dual quad intake to mount the blower on.
All this is going into a 1949 Chevy Pickup on a 1993 S-10 frame.

 

☻ there's lots of stuff you can do when you hold alt! ☻ôσT~╦╖⌠~-═{☼☼♫♫p¬1¼j¡♦4ôq│ô▼πb

 

You can't use a vacuum secondaries carb for a draw thru setup, can you? If it's possible that would REALLY widen up my choices!

 

I am running a single 750 Vac secondary carb on a 327 @ 7 PSI and it works very well.

 

okay, that's the answer I was looking for! thanks!