A 671 Weiand is a roots style blower correct?

They are the least efficent blower and produce less horsepower.

In this combo:

Horsepower: 690 HP
Engine: 383ci - Blown with 671 Weiand
Heads: AFR 195 Competition Package
Compression: 7.8
Carburetor: 2 Holley 650 Double Pumpers
Ignition: MSD Billet Distributor 32° Timing
Cam: Xtreme Energy Hyd Roller Comp Cams
230°/236° .544-.555 lift 114 Lobe Center
Exhaust: 1 3/4 Headers
Fuel: 93 Octane Pump Gas


If it were a super ram or mini ram with a ATI intercooled procharger, would the gains be much higher? Would you be allowed to run compression a little higher? How much boost do you think this combo is running?


Anything else in the above I should know about... I'm curious of it.

 

Yes they are. Just for the record, the "6-71" is a GMC designation that means the blower was designed(sized) for a deisel 6 cylinder with 71 CID per cylinder. A 12-71 flows twice as much at the same RPM.

Roots blowers have less adiabatic efficient (about 50%) meaning they add more heat to the air compaired to more efficient blowers at the same boost level There is also mechanical efficiency, which compaires how much horsepower it takes to turn the supercharger at any given boost level, and volumetric efficiency, which compaires the actual air the supercharger moves to what it "theoretically" should.
Roots supercharges produce more boost at lower RPM than centrifugals. Roots units produce boost in a linear proportional fashion. Double the RPM and you double the boost, triple the RPM you triple the boost. Centrifugals are not so linear. The change in boost is the square of the speed of the impeller. So if you double impeller speed the Boost is not just doubled, it is squared. This means that for any given maximum boost (or impeller/engine RPM) you will have less boost at lower RPM compaired with a roots blower. This means less power at lower RPMs, and near maximum boost only at high RPM.

As far as the amount of power made by centrifugals compaired to roots there are just too many variables to really compaire. An engine designed to work best with a roots style may not work as well with a centrifugal. Keep in mind also that the most powerful cars on earth (NHRA Top Fuel & Nitro Funny Cars) use roots style blowers. They are producing over 6000 HP. The roots blower is only part of the engine package. The entire engine combo is purpose built to work together in harmony, with each part taking maximum advantage of each other part.
The electronic fuel injection would allow for more acurate tuning of the air/fuel ratio and if you add digital spark timing control you can tune for even more power with drivability than a simple mechanical unit. The centrifigal supercharger would make less power at lower RPM but could be set up to make the same or more power at higher RPM. At the same time though, there is probably more power to be had in the roots combo than it is making now. I would definately use the intercooler if I did do the swap. The adiabatic efficiency of the roots supercharger does not take into acount the cooling effect of the fuel being fed into the system before the supercharger. This has a considerable effect on intake cooling. The intercooler will help counter act the loss of this cooling effect the fuel in a wet system has.
Most likely you would, and you would want to. The reason being that it would improve low spead drivability and throttle response as well as power. Since the centifugal will not make as much boost down low, an increase in compression will help make up for that. Also as mentioned earlier, the electronic fuel injection and timing control will also allow for more compression and/or boost.
There is no way to know without viewing the boost gauge. There are just too many variables that determine as to what the engine can take without detonation, not to mention how much of the intake charge the engine can consume from the blower before it begins to back up in the intake as back pressure (boost).
Since the output of the supercharger is directly proportional to It's RPM, the ratio of the drive belt pullies changes the amount of boost considerably. Ultimately the blower drive ratio, and whether it is over, or under driven will determine boost.

 

Thanks, that helped alot. Now I just need more money