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The Rebel Super Charger

23K views 79 replies 19 participants last post by  Ulltron  
#1 ·
The Rebel electric Supercharger

This thread is an off shoot of "The Performance Challenge". There was some good debate, mostly negative, about the difficulty of improving Rebel performance and the limits of the electrical system. Some excellent electrical specifications were also provided. I will be using a separate rechargeable battery system to power this supercharger and figure out the best charging options later

I decided to use a DC electric drill motor and the fan blades from a computer power supply. It was not difficult mating them together. With the fan blades attached, the motor draws 10 amps at 12 volts and blows a good volume of air pretty hard. I will be barrowing an air flow meter to determine its actual output and how well it will match up with the Rebel intake needs.

The first picture shows the motor assembly followed by a view of the stock air intake on my 1985 rebel.

Next picture is a top view on how I intend to position the motor. I will be fabricating a custome housing around it. There are then side views showing the motor extending into the housing. The opening into the air box will have to be expanded but the plastic is easy to work with. The raised spring seat works great with this project.

As I explained the in Performance Challenge thread, I will be racing the engine this weekend recording performance with the Android app "Racing Tester" which I will publish here. I will then be installing the Supercharger and testing again to record performance changes.
 

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#4 ·
These are just preliminary pictures of planned layout. NO work has begun because I have to document the stock system performance first. It will be a couple weeks before I get the super charger running and ready for testing. It will look quite different when the housing is fabricated.
 
#5 ·
I just replaced the stock filter a few months ago. The 1985 rebel uses a reuseable oil soaked foam cover over a metal mesh. I looked into the Iridium plugs and may try them one day but I have new Honda OEM plugs now.
 
#6 ·
I do recommend the NGK Iridium plugs. They made a big difference in how my bike starts and idles especially when it's cold. I'm very impressed with them. The plugs I took out were like new NGK standard plugs.
 
#7 ·
I'd suggest to get good numbers for your test you should run the test in two directions like they do at Bonneville and average the 2 runs. This should help eliminate both wind and terrain effects.
 
#9 ·
racing test



You are correct. And if the times are not close, I will run again to reduce human error. I am also going to run a test racing from 50 to 75 in 5th gear so no shifting is involved. Terrain is not much of a problem here at the coast - very flat.
 
#10 ·
Looks more like an attempt to sorta attempt a turbo..Spooling speeds will be no where close, its more like a glorified heres some air volume, stationary air intake. How much boost ya figure you'll get out of it?

Good luck with it. I dunno if you'll see any performance gains, kinda doubt it. But give it a shot dude. :thumb:
 
#11 ·
It looks like an attempt to copy the concept used on various cars on the website referenced earlier. I think the data on boost and flow offered there was clearly not technically accurate due to the theoretical horsepower needed to compress 1000 cfm of air to 5 psig being about 10-15 times the power of their electric motor. I would expect that the proposed computer fan setup will actually reduce horsepower due to the altering of the airbox and the production of negligible boost pressure.
Atmospheric pressure is 14.7 psi (absolute) . Any increase in engine air flow requires a pressure that is significant compared to that since the flow will be roughly proportional to the the boosted absolute pressure divided by 14.7.
That is if you had an increase of pressure of say 1" of water column inside the airbox (.036 PSI gage pressure), which is doubtful with the computer fan, the increase in theoretical air flow would be about (14.7+.036)/14.7 = 1.000244 x normally aspirated.
I would expect the negative effects on airbox tuning would more than offset this microscopic gain.
 
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#12 ·
A very interesting proyect. I like this idea of a kind of "soft turbo".

I have been thinking about something similar, but using some kind of air collector but without increasing air resistance... well my chances are low against honda's engineers.:D

The only effecive way to improve efficiency on the rebel that I have found is removing the sissy bar, and adding a small a curved windshield. This provides an increase in mileage around 0.1-0.2 L/100KM.
(And I had to reshape my windshield several times, because a big or bad shaped windshield increases fuel consumption :nonono:)
 
#14 ·
#17 ·
This is no computer fan



I simply barrowed the fins from a computer fan, but matched it to a motor with 20 times more power. It generates over a 1000 CFM in free air based on the air speed instrument I loaned from work. A 234cc four stroke motor only draws about 30 CFM at 8500 rpms. Fact is, I may have to reduce the blowers CFM.

I am putting a vacuum gauge on the bike and connecting it between the carburetor and the air box. This will give me good data on the effectiveness of the blower and if it is doing its job, I expect a noticeable drop in vacuum.

I am looking of low pressure boost and not aiming to force air into the engine under pressure. This is not a racing engine and I am only looking to enhance its performance with hopes are achieving a maximum improvement of 20%.
 
#16 ·
If you do get this operational and have a significant increase in air intake you will need to be extra careful with your fuel mixture. If you start running lean it may sound and feel like it's running great and making lots of power for a short period of time right before you burn a hole in a piston.
 
#19 ·
Are they metal fan blades or plastic? I still think the shape of a computer fan blade designed for moving small amounts of air, would differ completely from that of a fan designed for thrust and massive amounts of air. Are you using a brushless motor? How do you plan on triggering it? I installed 2 inline ducted fans into a VW Ghia beforeabout 1500cfm actuated when the pedal was fully depressed. It would bog down the engine anytime it was not at FOT (full open throttle)
 
#24 · (Edited)
:lol2: Ram air huh?

My old Mooney airplane had a little trap door on the airbox just under the prop that could be opened at altitude to bypass the airfilter and ram air directly into the FI induction system.
At 165 mph it bought you about an extra 1" or so of mercury manifold pressure depending on altitude. This is roughly 4% boost. So ramming air into a Rebel at full speed is not going to add much in the way of noticeable performance.

Ram air pressure is proportional to the square of the speed as well , not linear, so half the speed would give 1/4 the ram pressure.
 
#26 ·
super charger installed but issues

I completed the supercharger install and did a little testing this weekend before the rain came in. Unfortunately, I could not get the android racing tester program to lock on GPS so these are just observations for now.

When the fan is turned on with the motor running about 5000 RPM in neutral, it seems to pick up speed slightly but no noticeable change on the vacuum gage.

The bike ran OK but is a little hesitant when first starting out and has to be rev'd higher then normal. I believe opening up the air box inlet has upset the fuel/air mixture at low speed.

When running on the highway in 5th gear at about 50 MPH, turning on the fan causes the engine to immediately loose power and speed to drop. Same thing happens a wide open throttle, looses power. Vacuum appears to drop slightly lower with fan on from the .5 reading when the fan is off. The power drop is so significant that it almost feels like you hit the kill switch.

I am thinking that I may be pushing too much air at the carburetor causing it to malfunction. I will have to install be speed control and reduce the air flow as suggested by Crispy. If these carburetors had a butterfly valve, I would say the burst of air is closing it off. Perhaps these carbs can't operate under pressure, only vacuum. I am interested in hearing other's thoughts. Below are some pictures of the layout.
 

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#27 ·
Is your carb floatbowl still vented to atmosphere? If so, the elevated pressure in the carb throat could be pushing down the fuel level in the mainjet tube resulting in a leaned out mixture.
 
#30 ·
If that is happening, then it is a good sign, isn't it? It would indicate that my fan is creating enough preasure at least to screw things up:)
Well it would not take very much change in pressure to drastically change the amount of fuel induced into the airflow in the carb venturi. pressurizing the throat while leaving the carb vent open to atmosphere is equivalent to changing the float level which will change the mix significantly. To get a real benefit as in more air and more fuel, you still need significant boost pressure..
 
#29 ·
I use to run twin turbo mustang with Felpro EFI.
But I got my start with a blow through carb.
On it I had to run a boost line to the fuel pressure regulator.
So when the boost came up so did the fuel pressure.
If the boost was greater than the fuel pressure it would push the fuel back into the tank.
So your fuel pressure has to be higher than your boost. That way it can over come the back pressure created by the boost.
Hope this helps.
 
#32 ·
Good advice

Good advice guys on this:thumb:

It will be easy to move the carb overflow tube to the air box inlet that was used for the engine ventilation. I already extended the engine vent hose to under the engine for direct vent so air box preasure would not hamper proper crank case ventilation.

I remember reading that super charges often required upgrades to the fuel pump to work against the boost in preasure. Since the Rebel fuel is gravity feed, I image this too could be a problem if the super charger is run too long using up all the gas in the float. Since the boost is low and intended only to increase power for a short time during quick acceleration, I am expecting that this won't be a problem.

I should be able to perform full testing this Friday with temperatures expected to be in the mid 60s. In addition to the carb vent change, I intend to have a motor speed control ready so I can dial in the amount of boost for best results. This will also have the advantage of decreasing current draw on the battery. This will be important later if I hope to run this on the motorcycle battery instead of the seperate battery I am currently using.