posted October 22, 2003 12:16 PM
Edited By: jimp on 22 Oct 2003 13:21
Interesting Item In The 10 motor The sleeve's or bore has holes at the bottom to release the pressure on the down stroke to help push the piston on the upstroke
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posted October 25, 2003 05:10 PM
What if the crankcase was divided with crankshaft rings, and reed valves were used to maintain a slight negative crankcase pressure.
About 18 years ago I had a 17' Baja Boat with a 2.4 liter 2 stroke V6. It had 6 sets of 14 reed valves, and 3 two barrel carbs. Being a "loop-charged" engine its crankcase was divided in such a manner with crankshaft rings.
By isolating each cylinder and its respective crankcase volume the positive pressure that is produced below the piston is used to "inject" the cylinder with the fresh air/fuel charge.
So if these rings were used on a 4 stroke cycle engine, and the reeds were flipped then the crankcase would evacuate itself. The key here is cylinder/crankcase isolation. Without it you would have no differential in total crankcase volume and no pumping action will happen.
I dont know of any form of racing that is doing this and I've never seen it done. I wonder why? We know that maintaining a negitive pressure in the crankcase makes more power than having a positive pressure.
Cost is a factor in a production engine. But in an engine like kawis gp engine that has machined cases from billet, money is no object.
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posted October 25, 2003 05:15 PM
What a lot of drag racers do is put a vacumn pump on the crankcase. It's sposed be worth a couple hp. A semi-homebrewed solution is to plumb one of the fresh air inlets to the positive crankcase vent.
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posted October 25, 2003 05:17 PM
If you want to make real HP on almost any given motorcycle engine you can put a vaccuum pump on the crankcase breather....you can do the same to some car engines......an old trade secret.....or not.
posted October 25, 2003 05:24 PM
Parasitic draw of the vacuum pump negates a percentage of the bennifit.
So i wonder what that percentage is?
I've seen the mod for the crankcase vent to the reeds for the exhaust freshair system. But I really dont think the volume of vacuum from the exhaust is matched very well to the volume of blowby the crankcase produces. You really need to move alot of volume to actually see a negative crankcase pressure. Welding a tube of proper shape dia and angle into the collector on a 4 into 1 header will actually work to evacuate the crankcase. Unfortunatly its rpm sensitive and works best at a particualr rpm band and will do nothing at other parts of the rpm band.
Youve all seen it on the dragsters at the track.
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posted October 25, 2003 05:42 PM
Edited By: jimp on 25 Oct 2003 18:44
quote:If you want to make real HP on almost any given motorcycle engine you can put a vaccuum pump on the crankcase breather....you can do the same to some car engines......an old trade secret.....or not.
Yea, but size vaccum pump would you need to really pull a vaccum on the crankcase. Have you every attached a vaccum gauge to the crankcase of a motor running 12000 rpm's
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posted October 25, 2003 05:53 PM
Pesonally....I have not put a vaccuum gauge on....but I can tell you that several roadrace teams use these pumps to make anywhere from 2 to 5 HP.
quote:What if the crankcase was divided with crankshaft rings, and reed valves were used to maintain a slight negative crankcase pressure.
now THAT is a hulluva idea! i suspect it may be tough to get an ideal result cause the cylinders would have to be so well sealed, and the reed valves woudl have to be near theoretically ideal (allow NO air in, but let air out with even the slightest pressure difference). but i suspect even a real world implementation woudl work reasonably well. some a them "total seal" rings would probably help a whole lot with this setup too. obviosuly not give the same results as a pump since u'd be limited to ambient pressure at BDC (is that a term?) , but u'd be negative everywhere else (which obviously isnt a good thing during upstroke but what can u do?).
posted October 25, 2003 08:04 PM
come to think of it, if u used crankshaft rings to isolate not individual cylinders, but opposing pairs (if thats possible with the cylinder configuration), wouldnt that work just as well, if not better? this way u would have constant pressure in each portion of the crankcase. you would still be moving air, but u couldnt be moving it against anything, just back & forth a little . which i guess is already the case to some extent, but it's not ideal.
nevermind, i'm overthinking this. it should be ballanced already. the whole point is just evacuating the case so there's less air to mvoe, regardless of if it's being moved against anything (i think). only thing i'm thinking is, if u sealed the crakcase pretty well, coudlnt u just use a vacuum pump to suck the air out initially, and then jsut run it real low to keep any small leaks in check? seems to me u could get away with very little parasitic losses on teh pump in that case. maybe those total seal rungs are the answer here?
posted October 26, 2003 05:57 AM
Edited By: Y2KZX12R on 26 Oct 2003 06:08
If there was no blowby then an initial evacuation and then slow the pump to maintain would work. But blowby is real and its more than you would think. Every engine is different but typically the larger the bore the more blowby. Just for the record, my buddy did a test of the childs and albert zero gap rings as well as the total seals and a few others. They look good in theory with the interlocking designs but in fact the ring end gap is not how most of the blowby gets past. And they showed no difference at all. He has used then in 1000+ hp big blocks and even turbo inports and claims they dont work any better. (marketing)
Typically engines with excessive blowby have improper ring side gaps. The rings are to loose in the grooves. This causes flutter at high speeds and has a dramatic effect on cylinder pressure. The catch is you need this gap to make the ring seal if you have no piston ports. The pressure has to go above the ring between the ring and top ringland to get behind the ring to push out and expand the ring. Without this expansion the natural static tension of the ring is nowhere near enough to seal the pressures of combustion. So its a catch 22, you want tight rings but you need the side gap to be enough to move pressure. This is where piston ports come in.
Freek, i guess if you had an additional set of reeds on the crank counterweight it self or the back side of the case with "balance" tubes then you might be able to pair up cylinders. I'd have to really think about that one. It might need a high speed ecu controlled gate valve setup to open ports at exactly the right time.
On another note, I designed a 2 stroke 350 chevy engine about 10 years ago using a GMC roots blower much like a detroit diesel using the lifter valley as the plenum and only using the exhaust valves in the head. Ports would be cut into the cylinder from the lifter valley. A second design used a flat head and had exhaust ports on the outside of the block. The engine wasnt loop charged and relied on the blower for scavenging much like a two stroke disel like a detroit diesel (city busses are two stroke diesels).
It never got past the paper but I had the aluminum block, blower and related drives all lined up but didnt have the time and money to develop it.
There also wasnt any racing application for it. The projected HP figures (900+ hp) were staggering even when the blower was run just slightly above scavenging pressures. Anyway that was then.
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posted October 26, 2003 06:21 PM
veyr interesting about the rings! i always thought they made perfect sense & must work very well. guess i wont be wastin my time on any such rings in the future. thanks! i remember u talkin about ring ports a few months ago. now im dying to see it done!
and that 2stroke 350... let me jsut clean off my monitor k? man that woudl be beautiful. surprised there was no market for it.
re pairing up cylinders, i realised it woudl be useless cause the volume of air in teh case shoudl be constant on a 4cyl as is, since there are 2 pairs of pistons at 180deg. so splitting the case would be useles.s the only thing u could do to help the airflow inside the case woudl be to remove air (the point of the thread to begin with) or remove turbulence by directing the air better, but i'd say that would be hard to do & likely produce truly negligible results.
posted October 27, 2003 03:33 PM
Have you ever seen the french design from the 1920's where the cylinder moves and the piston is stationairy? Theres some wierd stuff out there.
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posted October 27, 2003 04:48 PM
Yah. Did you know that in the wayback days, 2 stroke dirt bikes would be modified so that the cylinder could be moved, thereby moving the port up and down?
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posted October 27, 2003 04:55 PM
how about the rhone rotary engine where the crankshaft is bolted to the airplane and the propeller is bolted to the crankcase and the whole case spins and not the crank.
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posted October 28, 2003 09:55 AM
i remember seeing some news piece long ago abotu this "incredible, revolutionairy" engine that was supposed to have insane power to weight ratios & be real fuel efficient (jsut liek every new design right? ). was 12 tiny cylinders arranged in a circle (all pointing the same direction, not like those engines u see on old planes), but instead of turning a crank, they turned a ring with a wavy surface on the piston side. the ring was always sitting on top of all 12 cylinders, spinning around the long axis of the cylinder arangment. looked very trick, but dont see where the claims of superiod design came in.
posted November 05, 2003 12:32 PM
Here in CT. theres an avation museum now called the New England Air Museum and they have several prototype aircraft engines etc. One that they have on display is an inverted liquid cooled V-16 made by chrysler.
Its amaizing what had to be done to run the engine like that.
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quote:... Have you ever attached a vaccum gauge to the crankcase of a motor running 12000 rpm's
Yes, almost. did it up to 11500
A couple yrs ago I did multiple dyno tests with a FBG vac pump (w/vac guage attached) on my 1361.
The pump could generate about 15"+/- vac (i forget the exact #) at idle, but the blowby would overcome the pump's ability to pull vac when rpm got high.
At the end of the dyno pull the vacuum in the crankcase had about gone, even tho the pump was purring furiously.
Got 2-3 hp midrange, but at WOT that advange goes away in several seconds.
I took the pump off & sold it.
Besides, using the pump would make my oil lite flicker at idle... BAD ju-ju!!!
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posted October 22, 2003 12:16 PM
Edited By: 
man that woudl be beautiful. surprised there was no market for it.
). was 12 tiny cylinders arranged in a circle (all pointing the same direction, not like those engines u see on old planes), but instead of turning a crank, they turned a ring with a wavy surface on the piston side. the ring was always sitting on top of all 12 cylinders, spinning around the long axis of the cylinder arangment. looked very trick, but dont see where the claims of superiod design came in.
