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SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Crankcase vent/vacuum/PCV? /cgi-bin/YaBB.pl?num=1470705659 Message started by Armen on 08/08/16 at 18:20:59 |
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Title: Crankcase vent/vacuum/PCV? Post by Armen on 08/08/16 at 18:20:59 Having owned and worked on lots of flat twins and big singles, I'm surprised how primitive the crank vent set-up is on the Savage. At the very least, I usually put some sort of one way crankcase vent so that the motor isn't breathing in and out every time the piston goes up. On the race bike we went so far as to run the crank vent into a can to trap oil mist, then ran a hose from the can to the exhaust to create negative pressure in the lower end. The NASCAR guys live by this. Evacuating the bottom end of air pressure makes the rings work better, and frees up some horsepower that is lost when the piston goes down into a pressurized area. Anyone play with this stuff on theirs? thanks, -Armen |
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Title: Re: Crankcase vent/vacuum/PCV? Post by justin_o_guy2 on 08/08/16 at 19:18:33 Evacuating the bottom end of air pressure makes the rings work better, and frees up some horsepower that is lost when the piston goes down into a pressurized area. There's a No duuh... and I never thought about it.. That might be worth messing with. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Kris01 on 08/08/16 at 19:34:37 Could be one of the reasons why it burns a little oil at interstate speeds. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Dave on 08/09/16 at 04:55:24 In the stock setup, the breather hose is connected to the air box and if it huffs/puffs in and out....so at least it is getting filtered air. The hose is connected to the air filter box just before the carb inlet...so it is not subject to a lot of vacuum - but does get a bit and it does pull the vapors into the engine where they can be burned (oil and water droplets fall into the bottom of the air box and are drained out). The vacuum is going to increase as the throttle is opened and the rpm increases - but it will only be as strong as the vacuum through the air filter. I am not sure what kind of weird things would happen if you tried to connect the fitting to the engine side of the carb....downstream from the carb. There are really large pulses going on....and being a single....the volume change inside the engine is equal to the volume change at the inlet port to the head - so given enough time to equalize the flow would be exactly the same.....the engine wouldn't try to pull anything through the carb! This would most likely have the biggest effect at low throttle settings when the air flow through the carb is low. The vent system is restrictive however, and the path from the bottom end, metal scrubby screen in the head, and flow through the vent nipple and hose does dampen out the pulses. I would guess that as the engine is running, there is a positive pressure in the crankcase as the piston is near the bottom of the stroke, at a negative pressure as the piston is at the top of the stroke.....and the pressure varies with the rpm and throttle settings (as more throttle/rpm will create more blow by past the piston and rings). I don't know if you will ever be able to create a vacuum in the engine - you might be able to increase the scavenging a bit. When they have a PCV system on cars/trucks - does the PCV port somehow get incorporated into the position of the throttle plates in the carb....so that at idle the engine is not pulling too much air out of the engine and affecting the idle air/fuel flow? |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/09/16 at 05:19:18 Dave, This is all old news in racing. The reason you don't connect the breather can to the intake is because the most vacuum is created when the throttle is shut at high revs. Early NASCAR guys tell stories of shrink wrapping steel oil pans around the bottom end of the motor from the vacuum created by shutting the throttle at full chat. When Udo Gietl and company were building the BMW Superbikes that won the first AMA championship, the guys came up with a system to run negative crankcase vacuum by angling a pipe from the breather into the exhaust header pointing toward the muffler. The air passing over the tube created vacuum in the breather can, and into the crankcase. Read a few issues of Circle Track magazine. Running crankcase vacuum is the norm for the big V-8s. The gag is to use a small line at the bottom of the breather can piped ack into the crankcase. This way, when there is crankcase vacuum, the oil gets pulled pack into the motor. Look at the later crank breathers on Airhead BMWs and Ducatis and you'll see a small hole for oil to get pulled back into the cases. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Dave on 08/09/16 at 06:53:19 Armen: I have seen the drag race cars with the breather pipes running into the headers, with a valve to prevent the backflow of exhaust - I thought they were just getting rid of the crankcase vapors.....I didn't know that the were actually trying to create a negative pressure in the engine interior. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Serowbot on 08/09/16 at 07:00:00 Don't fix it, if it ain't broke... :-X |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/09/16 at 07:15:05 Dave, Exactly. The gag with not using intake vacuum is that the most vacuum in the intake occurs when you need it the least for crankcase pressure. Closed throttle-more vacuum/WOT and very little vacuum. The most ring blowby happens at full chat. Rings don't seal because of spring tension, they seal because the pressure above the piston forces the ring out against the cylinder wall. Most of an engine's internal friction comes from ring drag. In the race motors that use crankcase evacuation systems, they also use low tension rings. By creating vacuum in the bottom end, there is a pressure differential above and below the rings, so even a low tension ring seals well. Less drag=more HP. Serowbot-translation of your comment is "Why move forward?" There have been threads about oil consumption when the bikes are ridden hard. A more sophisticated crankcase breather system might be a way to reduce that problem. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by batman on 08/09/16 at 12:17:45 I'm with Serowbot on this one. I don't think we have low tension rings available so with this setup we have an increase in ring to wall friction=less hp, more wear, so what have we gained? If the design of the can is not very sophisticated,we might have increased oil usage ! You may be taking two steps backward to move one step forward. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by verslagen1 on 08/09/16 at 12:30:11 The advantage multi-cylinders have is only blow by is being huffed out the vents. Whereas the thumper has to breathe and oil loss at high speed maybe from going from vac to pressure because of the 'small' diameter breather line. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/09/16 at 15:20:22 Batman, Really? I used to use a cheapo automotive PCV valve, but then figured out they don't work as well when they aren't vertical. Someone suggested using the one way valve from an auto power brake vacuum tank. Cost is a few bucks. Use one without the whole oil capture gag and you'll still make the bottom end happier. Or not. The ten bucks and ten minutes might ruin your life ;D Verslagen, Take a look at the bottom end of a modern ultra high perf inline 4. LOTS of engineering involved in getting the air under the piston to be able to move back and forth between the pairs of cylinders. They don't get 200 HP from 1 liter by just thinking happy thoughts :) |
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Title: Re: Crankcase vent/vacuum/PCV? Post by verslagen1 on 08/09/16 at 15:28:22 546778707B150 wrote:
still the point is, Ø1/2" breather line vs Ø94mm piston = major restriction. Driving a piston against vacuum is no better than pressure. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/09/16 at 15:35:12 'Driving a piston against vacuum is no better than pressure.' Huh? On what planet? Quick call all the leading NASCAR teams and tell them to remove the vacuum pumps they run off the bottom end of their motors. And you know that real slouch motor, the 1199 Panigale? Yup, fitted with a vacuum pump on the bottom end. Better call Ducati as well. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Ruttly on 08/09/16 at 19:33:33 This the same as ram induction theory , might have a h/p boost on a thousand h/p nascar engine , but on a 33 h/p single cylinder it not going to do squat-crap-zero-nada but maybe blow a gasket & cause a leak!!! There is plenty of H/P to be extracted from these engines without chasing your tails for 1/10 of one h/p ! The Topic Terminator has spoken ! |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Ruttly on 08/09/16 at 20:18:52 Listen to Bot , he's honest & wise |
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Title: Re: Crankcase vent/vacuum/PCV? Post by verslagen1 on 08/09/16 at 20:31:45 6C5F4048432D0 wrote:
what's the diff, push a piston up against 15psi with 0 underneath, or pull a piston down against 15psi with 0 above? and I'm talking about 1 piston, not 2, 4, 6 or 8. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by batman on 08/09/16 at 21:50:59 52617E767D130 wrote:
YES LOTS ,of engineering ,but we don't have another piston to move the air under! Versy already made the point that it can be done with a four cylinder ,that's because two of pistons are moving up while the other two move down ,BUT we only have one! |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/10/16 at 04:25:05 Huh? Less crankcase vacuum means less leaks. More pressure= more leaks. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/10/16 at 04:26:34 Batman, Reread the comments. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by batman on 08/10/16 at 12:33:12 Armen ,someone on this site once told me the proof is in the puddin',so why don't you do this on your bike and come back and tell us how much hp you gained and the cost and the process you used . |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/12/16 at 02:29:36 Batman, I will when the bike is done. In the meantime, if someone wants some test guidelines, here goes: Take the bike out (stock) on a long section of flat road. Run it up as high as it will rev to in each gear. Take a note of the MPH (or KPH). Come back and remove the crank breather hose from the airbox. Plug the hole in the box, and put a K+N crank vent filter on the end of the hose. Repeat the run. Cut the hose and insert a one-way valve such as a automobile power brake vacuum valve in the hose and reinsert the hose into the airbox. Repeat the run. Remove the hose from the airbox, and reinstall the K+N crank vent filter. Run again. The folks from the Triumph Rat list saw consistent improvements by not routing the hot, oily crankcase vent air into the airbox. The last thing the engine wants (in other than freezing weather) is hot air. And the oil mist generated at full chat lowers the octane of the gas when it all meets up in the combustion chamber. As Verslagen pointed out, the breather hose is pretty small for a big single. By only allowing air out (one way valve) of the bottom end, the only air pressure building up in there wold be from heat and ring blowby. By the way, I did test all this stuff. Early 90's when I built an SR500 (punched out to 560) that won the AHRMA Sound of Singles Senior Class national championship. If you go to the vintage races, take a look at what the front runners are doing with the crankcase breathers. Cheap, easy, proven, and it works. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by KennyG on 08/12/16 at 06:26:55 Armen, Obviously you know more about tuning engines than most of us. If you could point us to a specific one way valve that would get some of us started in the right direction. Kenny G |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/12/16 at 07:14:13 Hey Kenny, Will do. I'll take some pics this weekend. I was actually thinking of running two breathers. Keep the stock hose and attach a brake booster valve to that. And since I'm not using a mechanical speedo drive, I was going to use the hole in the crankcase to run either a BMW Airhead or Ducati reed valve. take care, -Armen |
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Title: Re: Crankcase vent/vacuum/PCV? Post by ohiomoto on 08/12/16 at 08:08:02 Armen, I hope you do a build thread to document your project. You've posted enough bits here and there to pique my interest. Tim |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/12/16 at 09:00:40 Thanks Tim, I've been taking some pics and some notes. Just ordered the RYCA rear set brackets. Yes, I can make them, but I just don't have time ::) Next step is bracing up and chopping up the swingarm to allow the wheel to move forward. 18" wheel and larger front pulley makes things too cozy. Then the forks get twiddled. And, and, and.... |
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Title: Re: Crankcase vent/vacuum/PCV? Post by ohiomoto on 08/12/16 at 09:15:05 Hurry up. I'll probably start my project this winter (if I can wait that long) and I'm sure all want to steel some of your ideas! ;) Tim Oh, and for the rearset bracket, I took the battery tray mounts and flipped them upsidedown on my spare frame. Needed just a tad bit of grinding and we have the beginnings of the bracket. (My build will be relatively simple and inexpensive compared to some of the nicer builds.) |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Dave on 08/12/16 at 09:20:32 1E2D323A315F0 wrote:
When I did my swingarm.....I cut it up, made the new pieces, welded them in.....and the the rear wheel axle and spacers wouldn't fit between them anymore. Seems the welding caused the swing "arms" to pull in as the welds cooled. I had to put a bottle jack in to spread them out.....and I am not sure they spread equally on both sides as I am having trouble getting my belt centered in the pulley (I will get it fixed when I pull some things apart this winter). Make a spacer to put between the arms to maintain the spacing before you weld.....and/or make a jig or template so you can make sure things stay in alignment. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by springman on 08/12/16 at 09:29:12 Ruttly, you are so assertive. 8-) I think I'll follow along on a different thread where English is spoken. ;D ;D ;D |
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Title: Re: Crankcase vent/vacuum/PCV? Post by springman on 08/12/16 at 09:35:38 Actually now that I have re-read some of this it sounds interesting. I just wish I knew enough to understand the explanation you are giving Armen. I'm willing to try to learn. :-? |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/12/16 at 10:00:59 Dave, Thanks for the thoughts. I was planning on adding the bracing, then cutting away. And I was going to jig up both ends so that they stay in line. Always a chance that things will twist. Springman-sorry if I wasn't clear. Tell me what doesn't make sense and I'll try to clarify. Have to admit, I was looking at the rear pulley this morning and thinking about how many holes I could put and where :o -Armen |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Ruttly on 08/12/16 at 10:15:02 I am in full agreement with Armin , I just don't believe the gain is worth the hassle for a 33 h/p engine,better off cutting weight & doing engine mods ! |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/12/16 at 11:47:52 It's really not much hassle. And precisely because the bike is so gutless that you have to look for ways to make it better. And I think 33HP was measured at the ad brochure, not at the rear wheel ;) No one says you have to do anything. I'm just trying to share what little I know. In the old days, when someone would come to the shop and complain that their bike wasn't fast enough, I'd put them on the back seat, take it out and redline it in all gears. Then I'd ask "At what point was the bike to slow?" Usually the person was scared half to death by that point and never mentioned how slow the bike was ever again. With these bikes, it's a different story. They are legitimately slow. All the bikes with the over-stretched cam chains are running cam timing so retarded the valves should be traveling in a little yellow school bus. Nice to be figuring out how to make the bikes a bit snappier. Preferably without major work and bucks. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Ruttly on 08/12/16 at 12:09:55 I'll buy that , I threw some cash at mine it is no longer slow. Far from slow almost a little scary when held wot and going thru the gears. No math just saw what it needed & built it ! If you were in CA might let you take it for a blast , even handles pretty damm nice ! I'm still impressed of what I built ! |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/12/16 at 13:22:38 Thanks Ruttly! |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Ruttly on 08/12/16 at 15:08:07 Ya know the oil fill plug would be ideal to modify to draw that vaccuum on crankcase and still have a breather off the top of the engine. I bought a aftermarket plug on eBay it would be easier to modify than stock plug ! |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Ruttly on 08/12/16 at 15:14:55 Aren't you the one who lightened the flywheel? |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/12/16 at 17:17:52 'Aren't you the one who lightened the flywheel?' Yup. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Ruttly on 08/12/16 at 18:55:52 Got it running yet ? |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Ruttly on 08/12/16 at 19:31:38 Wish I could have that done. You definitely have the skills & knowledge , me I'm just a hobbiest , learn from past mistakes and from picking the brains of people like yourself. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Ruttly on 08/12/16 at 20:30:04 So now you got me curious. Exactly how are you going to do it on your bike,details please ! |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/13/16 at 04:28:51 The plan is to run a power brake one way valve off the cylinder head vent hose into a K+N crank filter. Then use either the Ducati crankcase vent valve or make a housing for a BMW Airhead crankcase reed valve and mount that onto the hole from the speedo drive. Also with a K+N crank filter on the end. If the filters are consistently getting wet with engine oil, I'll plug the lines into a catch can full of brass wool, then run a K+N crank filter on the outlet side of that. The goal is to have it work and not look like a plumber's nightmare ;) |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Ruttly on 08/13/16 at 06:56:41 If your running a chain conversion you could skip the catch can and run a hose just above counter sprocket as a chain oiler ! Was looking at electric vacuum pumps but their noisy and not sure they have that volume to keep up with such a big piston(97mm) |
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Title: Re: Crankcase vent/vacuum/PCV? Post by cheapnewb24 on 08/13/16 at 07:10:18 Wow... That's interesting. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/13/16 at 08:32:39 Ruttly, Not running a chain. Want to keep the belt. Never liked the automatic oilers. Had one (stock) on my '75 Norton. FWIW, If you dump the oil on the top of the chain, you are oiling the outside of the chain, which means it just flies off. I'll draw a diagram of the vacuum system we had on the racer. For me, an electric pump would be too much 'stuff'. -Armen |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Ruttly on 08/13/16 at 20:38:24 Looking forward to seeing the diagram , see if it's close to what I came up with. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/14/16 at 15:06:13 Simple version. If the hose from the motor to the vent valve tries to collapse, find a spring that fits inside of it to support the hose. Mount the valve as close to the motor as possible. |
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Title: Re: Crankcase vent/vacuum/PCV? Post by Armen on 08/14/16 at 15:12:52 Moe elaborate version. Still a one way valve in the breather hose after the motor, but it goes to a catch can. Fill the can with brass wool like Chore Boy to slow down the oil droplets/mist coming out of the metal tube. One metal tube goes into the can. End of the pipe is closed. Holes drilled into the sides of the pipe in the can. Another tube comes out of the can to a hose. Hose to another metal pipe welded or brazed to the exhaust or header pipe. The metal pipe in the exhaust is installed at an angle pointing in the direction of exhaust flow. The vacuum created by the pipe angled toward the exhaust flow makes for negative pressure in the motor when the one way valve is open. End result is that the piston has less work to do on the downstroke Less power wasted. Rings work better. Less leaks. Less oil consumption. |
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