MILD THUNDER

iTrader: (3)

I consider this, the bare minimum. For example, if this equation tells you 1200CFM, a pair of 750's in the real world, will work better than a pair of 600's. This is one of the few areas of engine stuff, where bigger is better. Within reason of course.

The size of carb(s) or CFM required for a given application can be calculated by the following formula A: {(CID x RPM) ÷ 3456} x {Boost ÷ 14.7) + 1} = CFM required. The amount of CFM required will determine carburetor size and quantity. If you try to use a carb with less CFM than required, performance and economy may be greatly reduced. Bigger is not always better when selecting carbs that are 30% over what is required, you may encounter problems in fuel distribution.

That calculator tells me for my engine, 1200cfm. I am currently running a pair of 850's. They work great. Fuel curve is very good, response, economy, its all there.

Baja Rooster

iTrader: (1)

I'm pretty sure that you just keep going bigger until you run out of money.

MILD THUNDER

iTrader: (3)

Right on Matt. Look at the 525sc engine. Had a baby blower, with a single 1050 Dominator. Fukin thing had 98 jets squared on a engine that made under 500 propshaft HP. I can see a single dominator, on top of a 6-71, thats sitting on top of an engine that might have some better heads, or better cam, needing alcohol jets to fuel the engine. If its economy what you seek, it isnt there.

SB

iTrader: (1)

I disagree. I say Jets don't really play much roll on atomization.

That's the boosters responsibility along with the amount of air that flows thru it.

Again, IMHO.

Old Navy

Don't you think that blower is just a big blender making the A/F mix pretty good? Thanks guys, I like the responses so far.

MILD THUNDER

iTrader: (3)

You would think so. But when running a single 1050 carb, on my 250 blower, the rear cylinders were rich as heck, fronts lean as heck. Later they came out with a carb adapter that moved the carb a little closer to the snout, not sure if that helped much.

Those most HP Ive seen made, with a single dominator on a pump gas roots blower, was right around 700hp range. Roots blowers arent really compressors, they are more or less "air movers". If theres any restriction on the top side, it hurts their efficiency. For example, lets say you got that 671. You want to make say 7psi on a 454. You may bolt the 1050 carb on, and have to drive the blower at say 10% over, to make 7psi in the manifold. Now, you take the single carb off, and bolt on a pair of 750s. All of a sudden, now you are making 8psi, or 9psi at 10% over. To get back to 7psi, you can slow the blower down, and see some cooler intake temps as well. Of course thats just throwing numbers out there to give an example. Although, I know of several roots blown combos, that have went from smaller carbs, to larger carbs, and picked up a bit of boost, with no other changes.

Now a Blow thru setup, heck, a single dominator will support tons of power, being blown thru.

MILD THUNDER

iTrader: (3)

Heres a test they did many years ago, in my old B&M book from 1990. While its old info, and some today look at the B&M blowers as "cheaper" alternatives to whats out there, they sure sold alot of superchargers back in the day. At the time this particular book was published in 1990, they had already sold 14,000 supercharger kits. Thats alot of blowers. lots of great info in this book, with testing data. I found it on ebay, had to have it. Paid 100 bucks for the friggin book lol but a great read.

Crude Intentions

iTrader: (1)

Good info joe.

buck35

A roots blower is just an air pump, first rule, don't restrict the intake they don't like it.

donzi matt

iTrader: (1)

Your right, I was completely talking out my a$$, I don't even really know why I was thinking that.

Might have something to do with the Jaguar rear wheel bearing job a good buddy sent me today....