Supercharger

[2seater]

I have access to a large Roots type blower from a Detroit Diesel, an 8V92. I read through some of the previous posts about power requirements to run one at decent pressures and flows, although not one quite this large. Three phase isn't an option at this time but the power I am using now is between 30-40 amps @ 240 volts single phase. That looks to be in the 7.5 hp range for a 230 volt single phase motor. Will this be enough to make a usable blower for a bench?

[gofaster]

If you have a 7.5 h.p. electric motor available, maybe you could bolt it and the blower to something solid (like a sturdy work bench) and see what happens next. You'd need to decide whether you want to make a belt system or a nose to nose drive coupling arrangement.

Those blowers are gear driven, about 2:1 on a diesel engine @ approx. 1500 to 2000 engine rpm, if memory serves me. Haven't touched one in almost 20 years now. An 8V92 blower is literally feeding a V-8, 2-stroke, diesel engine, that displaces 92 cubic inches per cylinder, a 736 cubic inch total displacement 2 stroke. They only have exhaust valves in the heads, no intake valves. Intake air enters through ports in the cylinders when the pistons uncover them. The engine needs the blower to supply cylinder air fill and aid in blow down. Just replacing the base displacement of 736 cu.in. on every revolution (2-stroke) and not allowing for the extra volume needed to assist blow down, @ 1700 rpm, your looking at over 700 cfm. That's a lot of air!

If you decide to play with this baby, please be careful not to get near the inlet when you run it, and don't fully block the openings with anything. Putting something over the inlet is dangerous and crazy, please don't fool around there. The outlet can be throttled by something sturdy, but again, don't block it tight. Probably safer to waste gate it, less heat anyway. Be aware of rotation. When looking into the inlet, the rotors should appear to emerge from the center of the blower and separate towards the outer walls. When they meet at the bottom the air is discharged. The bearings will need some sort of lubrication provision, too.
If you proceed, please keep us posted. It'll be quite an air mover!

[laser3kw]

2seater;
I also am building a bench using a 671 blower as the prime air mover. All the sources I have found suggest that 5hp sould be suitable, but 7.5hp will be ok too. Remember the motor will only pull the amperage it needs to drive the load -i.e. 7.5hp is at max load, anything other than max load will draw less amperage and develop less hp. Another point in our favor is we need only produce 1 or so psi. That basiclly allows us to spin the blower almost freewheel, requiring little more hp than needed just to spin the rotors!

Right now, I am hung up on how to build the orifice network. I am tring to decide wether to use the rotoating disc design (anyone out there have a drawing they could send me?) or a orifice inside a tube or an orifice inside a large chamber.

[2seater]

It would be nice to be able to run the blower with 5hp if possible. There is a substantial difference in cost for a 5 or 7.5 hp motor. If this works out it should prove interesting. I still have to remove the blower from the engine. I have the turbo removed and maybe that will be a jet engine someday:D Thanks for the input.

[Tony]

This sounds like a really interesting project, and I will be watching the results with great fascination.

Gofaster's figures sound just about right. I have displacement per rev figures here for many of the early GM blowers, but not the larger 92 series unfortunately. I think I would direct couple the motor to the blower with a rubber coupling rather than attempt to use belt drive. My blower uses a 10Hp motor driving a large centrifugal, and the belt drive has been a constant source of problems.

7.5 Hp should be entirely adequate, and 700 CFM will be ideal. I am guessing that you might be able to load the blower up to about forty inches of pressure difference before the motor reaches full load current. A nice big easy to read amp meter may be a good thing to have, to know where you are with drive power, so as not to be plunging yourself into darkness every time the power trips.

Just throttling the air at either blower intake or blower exhaust is not going to work. If you close off flow completely, the pressure is going to rise hugely, and it will just overload the motor and blow a fuse.

It will almost certainly require air to be circulated back around the blower as a means of flow control. It may also need some sort of safety pressure blow off valve around the supercharger. This is to prevent motor overload in the event of a unexpected sudden total flow blockage. Without this, you may burst, or implode your bench, as there would be nothing to limit a pressure spike.

The only other slight concern might be noise and air pulsing. I am assuming that the 92 series blowers use the usual GM twisted rotors, so this may never be a problem, particularly at the relatively low Rpm and pressure required. But I think there may still be a slight low frequency 170Hz drone to be heard, but it should not overly effect airflow. This will all be really interesting.

[2seater]

My bench is sort of unusual in that there is no cabinet to worry about sealing or blowing/imploding. It really is just a bench top, actually a piece of countertop (double thick), with a test hole and small settling chamber below, all bolted to the wall. The present motor box is just that. A small box on wheels with up to eight (only six installed) Surplus Center motors inside and it is double sided. I just flip it around to get suck or blow through the selection of pitot flow tubes. It works pretty well. Bruce made a calibrated 2.68" orifice plate for me that I measured at 515 cfm @ 28" and max flow of 528 @ 29.75" of water. I plan to do essentially the same with the supercharger. I appreciate the suggestion of a bypass valve to moderate flow. That should be relativley simple to incorporate. Even with a low pitched hum, it has to be better than the vacuum motors running full tilt, plus the heat buildup. I am guessing a limited wet flow capability would be also be a bonus, but that is not my goal.

[gofaster]

Tony,
you are correct about the rotors, they have a slight twist to them. You mentioned pop offs or some other protection. That is an important consideration.

I think that it would be a good idea to control test pressure with a variable speed control on the motor.

As far as blocking it off, as I said in my earlier post, you never want to completely block this unit on either end. (The e-stop on a Detroit Diesel does exactly that, it allows a steel plate to flop across the inlet of the blower. It stops a running Detroit instantly.) Running the blower with an electric motor and blocking the inlet would certainly cause either the motor to stop, the breaker to blow, the drive to break, or ...? Not good. You may want to consider adding an auxilliary vac port with a vacmotor or two, for the purpose of leak testing or low lift flow tests.

I'd like to add that you would probably want to have a screen or low restriction filter located between the test opening of your bench and the 8V-92 blower inlet so no foreign object could go into the blower.

[Tony]

A variable frequency drive would definitely be by far the best way to control flow in any high horsepower bench, but that cannot be done with a single phase induction motor.

Adjustable motor speed will always give the lowest noise, heat, and power consumption for any flow bench. Very rarely will a bench be run absolutely flat out while actually making flow measurements.

A single phase induction motor, and an air bypass system will work fine. But a three phase induction motor and VFD may be something to think about as a future upgrade.

[2seater]

Thanks for all of the input, I do appreciate it. The screen on the inlet side is a good idea. Motor speed control would be nice and no doubt the most elegant control. Possibly a variable belt drive or just stepped pulleys? Frankly I just don't know at this point until I actually can play with it to see what the performance looks like. I will still have my original motor box and since it is not actually wedded to the bench, they could be interchanged.

[gofaster]

For a single phase motor speed control, you could use something as simple as a heavy duty rheostat and an SCR to vary motor speed to suit your test pressure. Cheap, too.

If you would like to go to 3-phase, a Phase-a matic (single ~ to 3~ converter, static type) would run about $150.00 for a 7.5 hp motor, and used 3~ motors are usually cheap. If you go that route, I would strongly recommend adding an idler motor to the phase shifter, (3400 rpm) to smooth out the power and help with starting torque. Then you could use a freq. drive for speed control.

[DaveMcLain]

I think it could work ok and with a blower that size you won't need to spin it very fast to pump a lot of air. I just wonder how bad it's going to pulsate without a good sized cabinet to settle things down. You should experiment with different size pulleys for different drive speeds, to get you in the ball park but I'll bet the blower won't have to work very hard depending of course on the condition of the case. Be sure to screen the opening so that stuff that gets sucked into the flow bench(this will happen) from getting pulled into the blower rotors.

I think Smokey Yunick's bench was powered by an electric motor driven 671 GMC blower.

[Tony]

[2seater]

I think it will be a while before I get to the drive speed control problem, I will need to figure out a drive mechanism first. This isn't a conventional blower drive system, it was driven from an internal gear as part of the entire engine package. As stated earlier, it is actually a required part of the engine and was designed as an integral part. I finally got it removed from the engine tonight and I will have to clean it up and see what it will take. It is a very large and heavy unit and should prove an interesting project. This blower is from a good running engine, so I am pretty sure it is in decent shape. The pulsing flow may be an issue, but I won't know that for a while. The motor box may need a substantial plenum and I do appreciate the caution about that. Thanks to all for the input.

[hollywood63]

2seater it just so happens that I work for a company that is a distributor for DD. PM me a address and I will send you a screen for the inlet side of the blower. I will also look for cfm numbers if you want. The 8V-92T (turbochargered) made between 38-43 of boost pressure (inches mercury) under full load. The drive ratio for your blower is 2.05:1. 2100 rpm (eng)= 4305rpm (blower).
Art

[gofaster]