Experimental supercharger
 

Hi Guys,
There is this pumped Super charging idea I am playing with these days, and wanted to get your opinions on this rather crude idea.
It revolves around using a small cox attached to the rear PTO of a piston ported weedwhacker (about 24 cc) on a rubber coupling (direct drive), drilling the glow head to accept a check valve and feeding it into the manifold downflow to the carb. The cox could have its own glow fuel supply for lubrication and exhaust ports could be sealed off.
As a direct drive it will give me 3.5% boost in pressure at any given RPM, and which obviosly need to be geared up bit.

Would it work? Has anyone tried it before? What does 3.5% (15~ 20 % is really what I am after ) pressure boost means to a small engine in real world (I can crunch numbers myself, but here I need practical info on small gas engines)
Your opinions please.

Sid

RE: Experimental supercharger
 

You'd be better off to find an engine with a complete through crankshaft and put a pulley/gear on that rear shaft where it comes out the back of the case. Use that to drive your supercharger.

RE: Experimental supercharger
 

Supercharging two-strokes doesn't work very well. There is no way to trap the extra charge, it goes right out the exhaust. It has been tried on jetskis, offering very little power increase with double the fuel consumption.

RE: Experimental supercharger
 

Rear PTO engines are through shaft - rear end of crank accepts a starter clutch in a weedwhacker configuration

KWeasel, any more details on these jetskis???

RE: Experimental supercharger
 

Oh no here we go again,, no matter what the nay sayers say blowers/turbo's do work on 2/s, they just need to be setup right, after all what is a 2/s motor but an air pump,, they put turbos on snowmobiles for a boost in HP as much as 150%, do a net search ,,

""What does 3.5% (15~ 20 % is really what I am after )"" do you know how much air your weedeater motor uses naturally ??

I don't think the Cox motor will produce the numbers your going to need,, I don't know what the numbers are but your blower is going to need to produce the X amount of air your motor uses naturally, plus another X amount for the power boost you want,,

another thing, that Cox will only work as a pump, it will NOT produce an constant amount of air, while a real blower/turbo WILL produce a constant amount of air,,

but if you had the right blower you may find that you need to mount the carb on the intake side of the blower, this way your blower sucks the fuel from the carb,, if you just blow air into the carb you may restricted fuel flow,,

plus you may need a reed valve too..

Jim

RE: Experimental supercharger
 

from the link,,

Two stroke and turbo
Almost any engine can be turbocharged. The two-stroke engine can also be turbocharged but is more sensitive to backpressure in the exhaust system and due to reliability problems and rather cold exhaust gases not as suitable to turbo charge as a four-stroke engine.

http://www.princegeorgeyamaha.com/turbonews.htm

Jim

RE: Experimental supercharger
 

Good points,
First, I am thinking about introducing the pumped air down draft to the throttle, in the manifold area - so that i dont restrict the normally aspirated engine's orignal airflow, as well as increase reliability. With this setup I can not go high (say 50%) boost, as I am not throttling the compressed air. Because it is direct drive engine, any changes in throttle would change the volume of compressed air, which would become self regulating.
As it is a normally aspirated engine, I am looking that the volumetric differntial between my pump and engine. It is 0.8 cc against 24 cc one is to one. Because coxes are designed to run as high as 24k, I can safely have 4:1 gearing, which will give me a 13.33% differential at 1 atm. I could use cox's induction system to enrich the compressed airflow as well as lubricate the little critter. At 4 to 1 gearing, I assume it will have more or less constant volume flow comparative to the engine. The benefit I see is at lower RPMs where the gains in volumetric efficiency shall be more pronounced. I am also considering the fact that the whole contraption is going to add less than 5 ounces to the total weight and could be made maintenance free.
Am I assming too much - where are the cracks?

RE: Experimental supercharger
 

We are talking about super charging and not turbocharging

RE: Experimental supercharger
 

Don't let anyone here discourage you from trying it. It has already been done many times and the results are always dismal. If you need 20% more power just burn methanol and nitro, or better yet get an OS160 and enjoy a 50%+ increase in power.

RE: Experimental supercharger
 

Thanks, I have all sorts of engines - both model and full size, gas glow - this is supposed to be fun.
do you know who has done that before? I am looking at a drawerfull of cox engines that I am never going to use - they are cheap as chips and if together we find a use for them.....
I have seen small chainsaw motors attached to coverted VW as starters on experimentals. I have attached all sorts of hydraulic and electric motors on various engines when I used to experiment with UAVs, but I have never heard of a pumped supercharger. I can imagine that a piston pump is much more expensive to manufacture than a airscrew or fan, and that perhaps explains why this approach has not been applied by others before. But a piston pump is also more efficient -
I am just snow balling here, get a critical mass of opinions before cutting and drilling - it is dismally bad weather here, and my workshop is not heated[&o]

RE: Experimental supercharger
 

Many years ago this was done by DKW motorcycles for their racing motorcycles. They were world champions. But modern motorcycle make way more HP using tuned pipes and EFI.
Due to loses in the system the pump needs to move about 2x the displancement of the "engine". So to supercharge a 25cc engine you would need a 40-50cc pump, or run a 25cc pump at 2x crank speed

RE: Experimental supercharger
 

What tkg is telling you is the volume of the air pumped creates the increased pressure that results in increased power output. Whats the size of the little Cox? 1cc? You would need 26 of them just to supply the air for the engine normally.
A tuned pipe is a supercharger and it does it with no moving parts

RE: Experimental supercharger
 

I think it's a neat idea, but the Cox engine may not have enough displacement for a 24cc unless you overdrive the heck out of it. There are superchargers out there:

http://www.rbinnovations.com/catalog...d8bd32099776aa

"Typical power gains range from 15.6% to 27.3%..."

Maybe you could try a drive setup like that, and substitute the impeller system with the Cox piston pump setup you're wanting to use. If you're the type that likes to tinker and experiment, I say go for it.

RE: Experimental supercharger
 

Here's a supercharger for a car glow engine.

http://www.rbinnovations.com/newsite...percharger.htm



And here is a turbocharged MDS .68 that a guy did. He was kind enough to post it on RCU:

http://www.rcuniverse.com/forum/m_3628976/tm.htm

RE: Experimental supercharger
 

I agree whole heartedly, experiment,, I just feel your going-na need a different blower..

Jim

RE: Experimental supercharger
 

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How many turbos/blowers work on a glow two-stroke? Name one.

There's no replacement for displacement. Need more power? Get a bigger engine.


Ed Cregger

RE: Experimental supercharger
 

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By all means try it. I'm not saying not to try.

Let's do some thinking here for a minute first.

How much air does your intended to be boosted engine flow through its crankcase and cylinder per revolution?

How many times will the little Cox engine have to turn for every single revolution of your primary engine just to flow the same amount of air? Then figure out how much boost you need and factor in the extra revolutions of the Cox engine that will be required. So, let's see. If it takes 10 times the revolutions for the Cox engine to flow as much air as a pump, than the primary engine flows in one revolution and the primary engine is projected to run at say, um, 9,000 rpm, that means that a single Cox .049 operating as an air pump is going to have to be turning at 90,000 rpm just to equal the stock carburetion system. Am I right?


Ed Cregger

RE: Experimental supercharger
 

Wow - I used to run a blower on my street sleeper Olds -a GMC type - they work
On a two stroke , the power gain from a proper exhaust extractor is a far more effective approach
If you turbo and use a proper pipe - better yet - but for NET power gain (something has to power the supercharger) the good exhaust system is the best --even if you go to a dual path setup (short n long head pipes ) -o r a slider setup etc..
tinkering is fun - I once re did the induction setup on YS1.4 engine - -I made a long resonant tube which accumulated and fed an AVERAGE higher pressure to the intake valve - it was clumsy tho and YS trumped it with their really clever valve cover accumulator and drilled intake paths around the valves.

RE: Experimental supercharger
 

RB innovations.

RE: Experimental supercharger
 

Or shave the cylinder base down to increase the compression. Raise the exhaust port up to increase duration. Add a tuned pipe. Get a set of higher compression rings from Frank Bowman. Send it to RCIGN1 and have him knock a pound of weight off the engine. Or, you could do all those things and take a fresh change of underwear with you the first time you start it. [sm=lol.gif]

Guess what I'm planning to do in the near future? ;) My wife is at Target right now getting the new underwear. ;)

RE: Experimental supercharger
 

""There's no replacement for displacement. Need more power? Get a bigger engine. "",, want to bet,, as Rcpilet pointed out, money is a big replacement !!

I have 2 brothers, 1 has (still has) an 86 944 turbo (bought is in 86), it's a 4 cylinder, in 89 my other brother bought a new 89 Mustang GT V8,, both cars were rated with the same HP, what car do you think was faster ?

the 4 cylinder..

Jim

RE: Experimental supercharger
 

I bet if both the cars weighed the same and had the same gearing and the hp and torque was the same then it would make no dif what the displacement of the motor was. I had a mustang with 300 rwhp and 410 rw ft/lbs of torque and raced a guy with same car and same gearing and he had 350 rwhp and 300 ft/lbs of torque with a motor that had 45 more cubic inches of displacement and i still pulled away from him from a 3rd gear rolling start even though he had more displacement and more horsepower and was still slower. So peak hp, peak torque and displacement are all misleading. Its the average of the curve and where it is in the curve that matter more.

RE: Experimental supercharger
 

oh yea i forgot to add my car had a turbo...so there is a replacement for displacement. Its called any way to raise the cylinder pressure.

RE: Experimental supercharger
 

The only substitue for cubic inches is cubic money

RE: Experimental supercharger
 

Why not use a little Nitrous Oxide? The simplest way to go. There are kits for snowmobiles, motorcycles, etc....Hit the switch on the transmitter and BLAST out of a hover! You'd have two solenoids, one for the nitrous and one for the fuel. Your main settings on the carb would not need to be changed. Might want to back off the timing a little bit too prevent detonation, but that depends on how much nitrous you're spraying. Man this would be fun to play with if I had the extra cash laying around.:D