ribs

Damn...this cheap forced induction stuff has been hot both at pelican parts BBS and here. Anyways, sitting down at work with absolutely nothing to do, thinking about the quest for cheap horsepower at hand (for all you n/a guys), there are a few points that should be considered when setting out to perform such a task.

1. Use technology that is tried and proven.
2. The efficiency of supercharging electrically will never reach that of straight belt driven, and turbos will always be the most efficent because they use otherwise wasted energy to drive the compressor. The best one could expect would be 70-80% of the efficiency of belt driven superchargers.
3. You are going to want to do this cheaply.

The main advantages of doing an electric supercharger would be ease of mounting (no brackets for mounting relative to the motor would be necessary, just piping to/from the unit, and holding the unit in one piece), and cost if you do it right.

Here is what I see wrong with what has been discussed so far:

Leaf blowers are not going to build static air pressure. At best, they will create no intake manifold vaccuum, which may be worth 3 HP at most. The E-RAM electric supercharger will not either, because it is not a compressor, it is a fan.

The only solution I see to this problem is to use a real air compressor (like the compressor side of a turbo) and a high RPM electric motor to drive the compressor shaft.

How would one go about accomplishing this? Well, you could go to a junk yard and find a crappy turbocharger off of an older car...volvo or 80's chrysler will work just fine. I am sure one could be picked up for a hundred dollars or less. Take the turbine (exhaust side) apart and disconnect it, leaving just the compressor side and shaft.

Next, you would need to find a suitable electric motor that would be capable of spinning this thing at least 20 or 30 thousand RPM's (just pulled those numbers off the top of my head...something like that though...enough to build serious boost). What I have found that may be affordable and work just for this purpose are hobby motors for small RC electric airplanes. A 15000 RPM (under load) motor can be had for $50. You may need to take two of these motors and assemble them on a bracket (made of wood perhaps?) to get enough go to spin the compressor fast enough. There are probably better suited electric motors for this purpose, but that just happened to be the first one hotbot found. Anyways, attach pulleys to all three pieces (two motors and compressor shaft), arrange them on your bracket/mount, and find a small enough drive belt and the proper sizes for the pulleys to make the compressor compress enough. Wire it all up, run an oil line for the compressor, run a PVC pipe (or what ever type of tubing you see fit) from the AFM to this wooden contraption that is resting somewhere under your hood, and from this contraption to your throttle body, and then and let her rip.

Looking over the small airplane motor specs, just the power rating of most of them (~150 watts, 25 amps, 12 volts) says to me these may not have the umph to spin the compressor fast enough, but there are other electric motors that could satisfy the needs at hand (maybe a 3 HP drill motor with a large pulley?).

A few problems I see: well, the motors will spin the compressor the same speed all the way through the car's engine's REV range, so you would have to put a pressure release valve (kind of like a wastegate, but on the intake...I have seen these for superchargers) so as to not overboost your engine at low revvs, or come up with an electric controller of sorts that spins the compressor's speed relative to the engine speed (probably too much money). If you have an electric motor that will be capable of spinning this turbine at said 10's of thousands of RPM's, it will create quite an electric draw, so you may want to run the power right off the battery, and make sure your altinator will be able to provide the amount of power it needs. It will only be 70% or 80% as efficient as a real supercharger, and you will be using a compressor from an 80's turbo, so it will not be the most up to date design, but done properly, this could be quite effective. I think it could really work and work for less than $200. What do you think?

David J. Harrington

Ribs, our turbos spin closer to 100,000 RPM to create boost. It might be easier to find an old turbo, remove the exhaust housing as you suggest, and turn it directly from the engine. You would need to rake a belt reduction or something. You could have the crank pulley spinning a pulley that was 4 times smaller in diameter. This smaller pulley would be on a shaft where another pulley was mounted. This other pulley would be four times larger in diameter than the pulley on the turbo shaft. This would give you a 4^2, or 16 speed multiplier. This way, when the car was at 6000 RPM, the turbo shaft would be spinning at 96000 RPM. You would definately need to use high speed bearings on all of the pulley mounts. Also, you should mount the pulley on the turbo between two high speed supporting bearings so the turbo shaft doesn't have an unneccisary lateral load on it.

A problems this setup would have might be the following:

-A turbo's compressor wheel builds boost exponentially. You might not have much boost until the thing is spinning close to 80000RPM, but once you start going faster, the boost increases very quickly. It is for this reason I would gear the tubro like my example. Also, you wouldn't want to boost too much since the NA engine has higher compression and no intercooler.

Kindof makes me want to try it on my old Tercel

You know, Einstein went through his life solving thought problems such as we are now


Dave

ribs

So, dave, you basically created a supercharger from the compressor side of a turbo, a bracket, a couple of pulleys, tubing, and a belt. Why do superchargers cost so damn much then? They're like $2-$4 thousand for most, while most turbos can be had for $800-$1600 new (for some reason all the aftermarket turbos for my old RX-7 turbo II were more than $3000...strange). I may pay a visit to a junkyard this weekend, ****** a turbo up, take of the turbine side, break out the old electric drill, attach a pulley to one of the bits, duct tape the whole damn thing to a block of wood, put it in my moms buick with PVC piping and have some fun! I want to supercharge my little sister's neon! Once I figure out how to do this, I am going to play a mean trick on my great aunt and give her toyota camry double the horsepower! I don't know...the ideas of the hundreds of strangers on this board may amount to something better than the handful of engineers they have working at eaton or whipple. Keep it coming guys.

Thaddeus

Take a look at my post below with some pics."Electric supercharger pictures (beta release)" The problem is to find a 12v motor with enough RPMs. I haven't been successful yet.

You needn't use a salvage turbo for the thing, a centrifugal or squirrel-cage fan can build static pressure. In part, you can compensate for the lower RPMs by using a larger diameter blower.

I used a 12v motor from an aftermarket radiator fan. It's plenty torquey but much too slow. If anybody finds a likely motor candidate ( I'm looking for 10,000 RPM), let me know.

Thaddeus

[ 07-11-2001: Message edited by: Thaddeus ]

ribs

That is why you shouldn't drive the fan/compressor directly...set up a set of pulleys to change the ratio so if your radiator fan motor has enough torque but not enough revvs, you can change the gearing of it through pulleys to drive the fan with plenty of speed. It would require fabbing a bracket, but if this is on a volvo, this could be done with wood . I don't know...give it a try if you like. BTW, electric drills often spin several thousand RPMs and have plenty of torque, so I think using pulleys with one could create enough rotational speed, not to mention they are usually variable rate...but they are power hoggs. Have you considered pulleys and brackets thaddeus?

Thaddeus

Yes, but the additional fabrication time as well as the loss of power a belt entails discouraged me.. but that motor is certainly torquey enough! Hm...

I suppose a belt (or chain! Hey, cool...) might be the way to go... hm....I think maybe I will give it a try...

T

Thaddeus

Yes, but the additional fabrication time as well as the loss of power a belt entails discouraged me.. but that motor is certainly torquey enough! Hm...

I suppose a belt (or chain! Hey, cool...) might be the way to go... hm....I think maybe I will give it a try...

T

David J. Harrington

I was just catching up after lunch and noticed something sortof odd. The three of us have 951's. Shouldn't the 944NA guys be having this conversation?!?!?

Anyways, I think you'd be hard pressed to find an electric motor strong enough to turn the turbo close to 100000RPM. Remember that since you are using pulley multiplier, you are losing that same multiplying factor of torque. So if you had a 10000RPM motor and spun the turbo at 100,000RPM, you'd only be getting 1/10th of the motor's torque to the turbo. I think most SCs pull about 5-10 HP from the engine. Also, I don't think that fabing the mounts for the entire assembly would be that hard. Then again, I have a mill, lathe, and pretty much anything else I need.

Dave

Dave

OK, .02 from an N/A guy;

Wouldn't gears of some sort be more efficient than belts or chains. IIRC isn't a centrifugal SC basically the intake turbine of a turbo and a transmission of sorts to get the rpms where they need to be.

I thought I had read somewhere that a belt driven supercharger is more efficient than an exhaust driven supercharger, as the direct drive of a belt has less loss than the indirect drive of a gas driven turbine. (don't forget the backpressure caused by the SC also has to be negated by the boost).

The proposed receipients of where ever this leads, will most likely have a compression ratio that will require less boost than a 951 so the 100000 rpm number may not be needed at all.

A rheostat of some sort could be hooked to the throttle to control speed/boost

How bout a motor from some sort of hydraulic pump, anyone got a spare trim pump from a mercruiser outdrive handy. Something along those lines would have high torque.

David J. Harrington

Dave-

Good that a NA guy is chiming in. Gears probably would be better, but I think you would have to supply oil to the gears to prevent overheating and lube. Also, it might be hard to find the right gears for the desired setup(read: hard to do it inexpensively).

Let's see, a supercharger's driving belt should be more efficient than a turbo's exhaust wheel, however, in terms of overall efficiency the turbo is better. It supplys all of the needed backpressure to the engine, while taking wasted energy(stored in exhaust heat and pressure) and putting it to good use. The SC directly steals power from the engine for it to run.

You're probably right on about the required RPMs. I saw some compressor maps somewhere online that had CFM and boost numbers for a given RPM. Those would come in handy once you knew exactly what compressor you would be using.

Maybe a good solution would be to gear the SC so that it would spin around 100,000RPM when the engine is at 6,000RPM. We know that 100,000RPM is a safe operating speed for the turbo. Then, you could incorporate a bleed off valve into the system so that even though the wheel is spinning at 100,000RPM, you are able to limit the boost to whatever you want(6psi or so). This way, you would first make the 6psi at a lower enging speed, and it would remain at 6psi up to redline. This makes me want to go get a 944NA and try all of this for fun.

Dave

ribs

Well...I have been thinking about this topic the whole way home from work (1 hour) and have thought of a few things on the way. The use of gears instead of pulleys and belts came to mind (all though dave wrote it first), and today I saw which kind of gears/transmission may be suitable for this application: gears for electric remote control airplane props. They are made to increase the prop speed relative to the motor speed a certain amount, depending on the gears used, and they could be used in parallel to increase speed exponentially, and cost $15 or so. I don't know if they will be able to handle the torque necessary to spin a compressor...who knows?

Anyways, as far as controlling the level of boost (if you are doing this using an electric motor of sorts with variable speed, like a drill motor), you would have to either devise a way to spin the motor relative to either RPM or manifold pressure, using some kind of electric boost sensor and a controller that would spin the motor faster if it was under desired boost and slower if it was over desired boost, or you could use a bleed valve like dave harrington said. You could have full boost at idle, meaning V8 like torque, if you were using an electrically driven compressor, but you may want to put a capacitor between the power source and the motor so at idle you will have a little juice saved up and be able to keep the boost up while the altinator is spinning slowly (if electrical drain would be a problem). The only problem I see with a bleed valve is that on cars equipped with a vein AFM, you would be bleeding metered air to the atmosphere and be running richer than necessary, and you would be running the electric motor at full blast all the time.

What else...hmmmm...it is true that to get 951 like power out of our collectively hypothetical supercharger, you would only need to run 5 or 6 psi, and intercooling would bring even bigger gains. I imagine the fuel injectors would be able to flow enough fuel for 200-220 hp, but a higher rated fuel pressure regulator may be necessary. Would the DME be able to compensate for the additional fuel required being that it would be far out of the normal range if this thing actually worked? Chips may be necessary, or at least some sort of FCON, like the apexi unit.

So...if you were to make this work, you would need the following:

old turbo out of a chrysler/volvo/saab/anything you could get for less than $100 from a junk yard

disassemby of the unit and only keeping the compressor side and shaft

electric motor capable, preferably variable rate, with enough torque/hp to spin the compressor several 10's of thousands of RPM's through:

gearing or pulleys and belt. I gave my idea for gearing out of a hobby shop...any other cheap gearing ideas are welcome.

A way to mount this all together. L brackets and a thick sheet of plywood are my best guess, but others out there are handier.

Piping...you would definitely want to set this up between the AFM and throttle body, not outside the AFM because it would blow it open and screw up mixtures and the like. Maybe...if you set it up before the AFM, bleeding boost would no longer be an issue if you use this type of boost control. Piping could be made from 2.5" PVC pipes since we are ghettoizing it. You wouldn't want to use something colapsable. Other ideas for piping?

Extra fuel. Maybe. Don't know on this one.

A lot of ***** to start your car up with a drill attached to 1/2 of a chrysler turbocharger stuck in your intake track. Keep em' coming...come on n/a people...you have to represent better than this (but thanks dave for poking your head in here).

rtyx

After hearing you talk about electric R/C airplane engines, I was thinking, why not try a 2 stroke, gas powered R/C airplane engine? Sure you would have to port the exhaust out somehow and you have the added unreliability of actually running it and additional hazards from fuel, spark, etc (not to mention the rackeet that would come from under your hood!!) but hey since we're talking about some crazy stuff anyway, you can't beat the rpm range/hp output of the small 2 stroke R/C engines.
Just a thought...