Planet Minis

lowbike1

Haha thats why I bought one, it looks cool... I cant tell the difference @ all

Xr50s4life

it actully relieves pressure and revs quicker IMO you can put your hand over the tube and it has pressure that is released depending on the rpms. you can do this mod with lifan covers. just where you drill the hole has to be on the side otherwise the rocker arm will hit it... having less pressure in your motor makes it more effective and its better to have somethin g release it rather then it blowing up... heres pics of mine. http://i128.photobucket.com/albums/p...fe/bike011.jpg

melloyello

Here's the deal. You put your kit on and run it WOT for a long period of time and see if it spits some oil out the crankcase tube. If not, then great. If it does, contact me and I'll send you a vent for cheap and see if it doesn't fix your problem.
That's how my gpx was from day 1 in stock form and 131cc. Put the vent on and no more problems. I sold that motor to a friend who rides the roads all the time and WOT for as long as it takes. He came to me a couple of days later saying it was blowing oil out the crankcase vent. He wasn't running a vent kit so I hooked him up w/ one and no more oil blowing out.

Korbenw7p3c

Mello, I'll take you up on that. I might as well try one out so pm me and let's get a price worked out. On the track that I run, I usually run 3rd pinned and it revs out 'til it won't rev anymore. I can hit 4th, but it's pointless because I have to downshift as soon as I hit 4th. It does slow the reving process at high RPM's when she is up there singing. Thanks, Tim.

minichopperfan

It is well known that a negative crankcase pressure will help a engine gain power and revs. Just venting to atomosphere does little to relieve crank case pressure. Sure it helps some but not as well as can be done. All the modern 4 cylinder performance bikes have windows cut into ajoining main webs or a cylinder skirt that is short between 1-2 and 3and 4. Why is this? To stop crank case pumping and parasitic hp loss. In the old days of Triumphs we used to vent the case to the primary case as well as run a vent from there to the back of the bike where it hung off the rear fender only to oil the rear tire. Om the Z1 we used to add additional vents to get rid of crankcase pressure. But with a single as well as old bikes and even cars one thing that has worked thru all kinds of tests is a use of the exhuast system to vent the crankcase. While every one speaks of exhaust pressure it actually will show a vacum if a small pipe is inserted into the pipe set at a 90 degree angle facing the towards the muffler. Just as a poor valve seal on the exhaust will allow oil to be sucked out of the guide because it causes a low pressure area near the guide { Yes I know the exhaust has pressure but it creates a low pressure are all along the wall length of its flow} So if you have a breather installed on the head or crankcase with a holding tank for oil if a on- off throttle is used with a return to case or a breather run from the head to the exhaust pipe with a small diameter pipe inserrted into the exhaust with a rearward facing flow close to the wall of the pipe then the crankcase will show a negative pressure. Install the pipe before the muffler and also add a pcv in line with the crankcase this will stop reverse flow of exhaust when backing off the throttle. The pipe should have about 2 inches facing towards the muffler. Keep an eye on oil levels and run the piss out of it. The Honda and it`s clone do not have ebough volume or venting for above the design rating of 49cc.

This will not help a engine that has poor ring or valve sealing. It wil also not help a engine that has poor valve guide to valve stem sizing or lack of seals. A wobbly valve in the guide is worn out on these engines and not the same as the feel of valves and guides on a old Ford or Cheyt which have larger stems abd longer guides.

Brent878

I always put one on a built engine as not to blow out seals due to crank case pressue. I have had such problems with bigger engines which a extra breather tube fixed. I haven't blown out any seals on any of my 50 engines but I have always ran breather tubes so I never gave it a chance. I don't know if it helps out perforance wise but I do it for peace of mind for me so one less thing to worry about.

Kurlon

Hrmm... never considered using exhaust to draw a vacuum. Nice idea minichopper! My exhaust is going to smell wonderful real soon I think... : )

MikeeeP

A couple questions - do you have any data that supports negative crankcase pressure causing power gains and higher revs? I'd like to see it, never seen anything like that before - no doubting you, just want to see it so I can read up on it. Basic theory would say negative pressure would slow the revs as the piston would have to fight harder to go UP to top dead center, but then would return to bottom dead center quicker because the negative pressure would suck/pull it down a bit quicker so it should be a wash - the extra strain to go up, and less strain to go down should just about cancel each other out. I'd love to read up on it though if you can find anything for me. I know that some of the older brit engine builders talk about it - but they can't offer any proof - possibly on a horizontal verticle twin it might help somehow? But no proof just "do it" comments.

Venting to atmosphere does help quite a bit. Check with any drag racer and his engine is well vented. Even street cars put the vent filters on the valve cover so the engine can spin up faster (we're talking cars here). We had a big block that made so much bottom end compression that it would literally blow the oil fill cap off the engine - unless we vented it and put one of the vented/filters on it - and it really needed it on both sides. =BUT= you are 100% correct in stating that the webs are used now for greater performance (thank you Suzuki for putting this in production bikes!). The new Gixxers have this so they run much better and it helps to make a great deal more performance and HP (along with other mods to make hp).

My concern on this is I just want to make sure on these little horizontal engines that the bottom end compression is not used for anything such as camchain or bearing oiling (I know it has a pump)... I just need to break out a schematic and check it over really well.

I'd really love to see that negative pressure info you're talking about. That's very interesting!

Mikeee P

yamaha

i dont think soi had one got used to it and took it off. my bike seemed to have less ppower

mattmoto441

I am sure there is plenty of info out there if you look. Negative crankcase pressure is not new or just theory, it is fact. Your drag racer friends can and should have already pointed this out to you. Almost every drag car has it's engine vented to the exhaust at the back of the headers through a PCV system. The piston already has pressure or force against it while going up, The improvement with a vacum in the crankcae is that it helps the piston go down quicker, not only after the compression stroke but also on the exhaust stroke. .The oiling system on these engines is dependant on oil pressure and splash, not crankcase pressure. Another advantage to a evacuation system is that it draws fresh cooler air (filtered hopefully) into the engine as it draws the overheated air out through the exhaust, thus aiding in cooling and efficeintcy, and improved engine life, and oil stays thicker longer. I will get some pics of a system that is on our 138 engine. Also if multiple cylinders can "cancel" out each other, there would be no need for any type of venting system?

orracle

Also to note, Alot of high performance motors will also use a vacuum pump for crankcase ventilation. Not that it would be use on our motors. The main performance gain in using a system like this is to aid in ring sealing and reducing blow by.

MikeeeP

Negative crankcase pressure is not new or just theory, it is fact.
Negative crankcase pressure on larger engines I can see. I want to see the theory work on tiny little engines making anywhere from 2.5 to 10hp.

Almost every drag car has it's engine vented to the exhaust at the back of the headers through a PCV system.
I know numerous drag racers and none of them have their engine vented out to the back of their header. Not that what you're saying wouldn't work on a multi-cylinder engine making a lot of power. As stated I'd just like to read up on negative engine pressure and it's affects/effects on a small cc' single cylinder engine.

The piston already has pressure or force against it while going up
That's right. So a vacuum from below would cause it to go into the upstroke even slower...

Also if multiple cylinders can "cancel" out each other, there would be no need for any type of venting system
I've never seen a multi-cylindered Honda CRF50 or CRF70 - we're talking about a small displacement single cylinder engine here. So the vacuum on the upstroke would cause parasitic loss, and the vacuum on the downstroke would add performance as I stated - but I have to wonder if one wouldn't cancel the other out by being harder on the upstroke and easier on the downstroke.

I'm not saying vacuum isn't a good thing. I'd just like to see it on a dyno on a small bore motor like we're talking about here. I'd almost bet that the less drag or parasitic loss we can cause on both up and down stroke - the quicker the engine would rev and thus be quicker around the track.

Mike

TripleKingCrew

^^^^^^
ponage.

mattmoto441

This was taken from an old Cycle magazine from May 1990, So it is not "New" .
"Performance
It is well known that performance gains can be had if the crankcase is under a slight source of vacumm which helps reduce crankcase windage losses. Many engine builders have seen decent gains by using either an electric or mechanical pump to help evacuate the pressure generated in the crankcase and even generate a vacuum present. Regaining lost power through the introduction of vacuum pressure evacuating the crankcase will not be as noticable on a small displacement engines as compared to a larger displacement engines. Despite this, it should still be of importance to explore the various configurations and attempt to "free-up" any power hidden in our engines which can easily be tested on a dyno."

mattmoto441

Also IF your drag racers friends do not have a positive crankcase evacuation system through the exhaust, They really are not serious drag racers and must just have street cars.


These Mr. Gasket crankcase evacuation systems are primarily drag race
systems designed to reduce pressure buildup in the engine crankcase. They provide better piston ring seal, less intake charge contamination, and a reduced chance of oil leaks, while increasing your engine performance

FASTFREAK693

I HAVE THOSE ON MY RACE CAR!

MikeeeP

Whoa Matt - I think you took this personal for some reason. I simply asked if you had any legit info out here on the net I could look at. You see, we're talking about a very low hp single cylinder engine not a multi-cylinder engine.

The data/info quote you made above is a quote that it appears YOU MADE on the Honda-Tech forums for Honda Civics etc... (or at least someone named Matt from Florida made) and you/he were talking about 8 cylinder and 4 cylinder motors, did it come from Cycle World ? It doesn't appear so since it's talking about 8 cylinder motors... it appears it's from the 1995 post on the Honda-Tech car forum. (see link below)
Honda-Tech.com: Forced Induction: The Official Crankcase Evacuation thread for Turbo Hondas / PCV / Catchcan /

I noticed in the post you made above some of the wording was changed so it would apply to this (not mentioning 4 and 8 cylinder engines etc...).

My concern is that on low hp and low torque single cylinder engines such as this - that the vacuum might not provide anything at all as the negative pressure as the stroke/piston goes up (slowing it down) might outweigh the downstroke where it indeed would return quicker under a vacuum.

I'd love to see how it works in this single cylinder "HORIZONTAL" engines. Also windage on a single cylinder engine isn't nearly as improvable as on a multi because the multi of course has multiple pistons coming down so that it has to get rid of that bottom end compression somewhere - and having larger webs allows that air/pressure to escape elsewhere... these engines really aren't designed that way being single cylinder. Downstroke can be improved (windage) but not nearly as radically as on multi-cylinder engines.

I'm thinking that freeing them up in any manner such as having a freeier breathing bottom end, is going to offer the largest boost in performance by allowing them to rev quicker ie: greater crankcase breathing would allow quicker rev up... Any thoughts?

Remember this is a discussion on performance not an attack as I'm afraid you might have taken it for some reason. I'd just like to see what can be done with these motors...

Mike

hooptytank

Back from the dead. What everyone fails to mention here is the atmospheric vent.

Regardless of cylinders in an engine, when the cases are vented by a vacuum source, be it intake manifold, exhaust or vacuum pump, there has to be a breather to outside air to replace the air drawn from the crankcase. The goal is to keep the case at atmospheric pressure or slightly negative. The exhaust vacuum is used to aid in the evacuation of positive pressure in the crankcase, but not actually put it in a Hoover style vacuum. Too much negative or positive pressure in the crankcase will not only affect the piston travel, but will have an impact on ring sealing. Piston rings are usually designed to seal best with pressure in the combustion chamber.

On the downstroke, the vacuum helps remove pressure so the piston does not have to do it.

On the upstroke the atmospheric vent allows air to easily re-enter the crankcase so the piston wouldn't be working against a vacuum. This is why the piston would NOT be working against a vacuum.

If this helps one gain 1/2 HP on a 10 HP motor, it equals to 5% power increase. not bad for some fittings and hoses.

When running a setup like this especially on a street machine, a oil vapor separator should be used, along with a PCV valve, otherwise a straight hose to the exhaust will suck a quart of oil out in a hurry.

TheCRKid

50/70 and china motors run hot ,the vents helps cool it off some so its good = 2 cents

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DBAKER

I have one on e on my 143 and it works nice it comes from the cam cover and getting ready to put a small one on the tap it cover. a local engine builder told me this would be a good idea