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CRANKCASE EVACUATION

C

COLD

Well-known member
Here is another one pointed kind-of a Waterthunder! He runs vacuum pumps on most of his stuff from what I see. I remember crankcase evacuation systems, Chrysler airpump one way valves in headers, guys saying they needed to run seals backwards because of so much negative in block pressure. Now would that only be in a 11000RPM drag situation and would there be not near enough evacuation a 3500 RPM? If I buy a good pump, Seals installed normal? Would an old $5.00 wrecker A.I.R. pump set up to suck instead of pump work? Just looking for best band for the buck! :lol:
 
I run dual breathers one in each valve cover the large clamp on variety. I have heard that the vacum pumps the drag racers run are like most things in the drag racing world in that they are meant to run for short duration of time and then need maint. which appears to be a foriegn country to most airboaters. The headers suckers will work but not so well if you place them downstream of the x-pipe, resonators and three chamber mufflers at least not on my boat.

I tried an electric vacum pump and it did build negative crankcase pressure but actually the two big breathers worked just as well and nothing to break on them.

My engine was getting tired and had been run hot several times so the rings were letting too much comp. past them. I rebuilt it well actually replaced the block because of other problems and the problem was solved. We were very careful during assembley to file the ring gap according to a nascar engine builders standards that we know personally. I am very happy with the results I was not happy about all the parts I found when I tore the engine down but it had lasted three years in very harsh use so I guess it worked ok. I am building a new engine and it will have a little better parts in it for sure.

I would say that unless you are turning some very serious rpms your blow by is probably a sign of other problems if it is strong enough to cause seal issues.

and in closing ... just remember.. " the original point and click interface was a smith and wesson"
 
All you need is the $45 MrGasket E-vac and if you run mufflers be sure to install them after the muffler. You can see up to a 18HP gain on iron blocks and over 30HP on aluminum. But that is not the main reason to run a EVAC. They prevent oil leaks and help control oil from entering the combustion chamber which causes detonation.
 
I'm sure everybody knows this but the lower RPM's an engine turns the more crucial ring seal is. The idea of sufficient crank case evacuation isn't to compensate for a problem it's to do other things in your motor.
 
Thunder, I sure didn't know it. I thought that CC pressure built with rpm, and that if you weren't really turning a motor you didn't need to worry about it.
I'm goin to school here ...... please explain.

BF
 
You build more pressure with RPM's but I said ring seal is more crucial at lower RPM's than it is at higher. That is why gap less rings are a huge benefit to airboaters but not to drag racers or circle track guy's. Once again there are several things tied in together here there is more than one cause and effect. I have seen drag race motors with over 25% leak down set national records. Now an airboat motor with 25% leak down would be a terd. I better drop this subject all I can say is G.M. put allot of effort into manipulating these pressures. While designing and testing the LS1 G.M. actually found 12HP gains by manipulating pressures in the crank case. If you look at the bottom of an LS1 block you will see what GM did to equalize crank case pressures. That is one reason they were able to go to the thinner metric ring and reduce parasitic drag. Thin rings are even more critical not to have a positive crank case pressure than the standard 5/64 rings. Nextel cup guy's use their dry sump as a crank case evacuation.
 
So are you saying, generally speaking anyway, that the application (manifold pressure required for the application) determines the need for Evac?

If I'm right about that, then a guy with a 3000 rpm DD motor needs to pay more attention to evacuation than a guy with a 6200 rpm gearbox motor. Or did I miss something?

BF
 
Wow! 8) am I ever glad I asked! Thanks again Waterthunder!! :lol: Negative pressure in crankcase also pulls gas and possible condensation out of the crankcase and oil. Just makes sense tha you would get more HP if there is no pressure in the crankcase and thanks for the gapless ring tip, I hate file fitting anyways and ring gap is a little more crutial with the hyperutectics I am planning to use. Thanks! 8)
 
Thunder,

Now you're givin away your trade secrets! I know how you engine builders are so secretive about this stuff!

Can you please explain why the set-up that Cntry explained with crossover would not work with an "after-muffler" evacuation?

Good topic Cold!

Thanks,

Basketcase/Jeff
 
I'll take a stab a BF's thoughts. He said you need to pay more attention to Ring seal. Lower rpm, more time for cyl to leak. bigger percentage of power lost. I think good crankcase evacuation is important on anything, Thats why I asked about the best way to achive it! 8)
 
I have tried re-installing them at different angles different depths, different brands, different shaped tips on them I believe I have tried most things to make them work but I am always open to new ideas especially if they make sense or are based on someone elses learning curve. SOMEBODY HELP ME LOL

by the way being over the hill ... is better than being under it.
 
For power...Vacuum pumps are used mainly to allow the use of lower tension ring packages, and acheive more stable ring seal as well as oil control at higher RPM. But in the low RPM AKA Airboat community, lower RPM creates more blow-by/cylinder pressure, and the only real effect is to reduce oil leaks. A header evac works great, as long as it keeps up with the blow by. In other words...If you make BIG power, and do it at a lower RPM.....You will probably blow the gaskets out of the engine with header evac, and you would be better off with a good set of breathers. If you turn big RPM, the header evacs will actually create vacuum and a power increase, but realisticly the low exhaust velocity won't create enough volume/low pressure to keep up with the high pressure the rings bleed off, and actually pressurize the crankcase.

Bottom line...Use breathers unless you know enough about engine building to spec and maintain a pump, and honestly from my testing for whatever it's worth..Avoid header evacs in airboat applications unless you have a race boat and an engine that turns big RPM...The blow-by (Even on a "tight" engine) vs exhaust velocity isn't high enough to make them work any where near as well as breathers...

JMO
Felber
 
http://www.mr-gasket.com/e-images04-350//6002.jpg I remember Chrysler used the check valves for an air injection system and not a crankcase evacuation system however they were plumed into the cast iron exhaust manifolds, so before the mufflers and I do remember there being suction even at idle. Will suction be better with them installed after the mufflers?
 
It's all about pressure (Actually a differential of it) as well as volume (CFM). The key to an exhaust evac is a siphon. But a siphon relies on velocity, and the effectiveness of the siphon has to be greater than the VOLUME produced in the crankcase.

SO....A siphon may be able to create great negative static pressure once the exhaust velocity is high enough, but can it overcome the CFM of air built in the crankcase? In a high RPM engine where crankcase pressure drops in relation to the exhaust velocity (negative pressure as well as volume) a exhaust evac is a great tool. But where you have a much higher load over a long period of time with relatively low exhaust velocity, it becomes positive pressure, rather than negative, like you wanted to in the first place.

If you're hardcore, and maintain a high level boat..go for the vacuum pump. If you have a high ratio gearbox, and the exhaust evac actually works...go for it, and enjoy the free extra ponies. But if you're just an average guy who isn't sure what to do.....Put a couple big breathers on it. And also food for thought....Use shielded breathers that the openings face rearward toward the prop, and let her eat.

Felber
 
Thanks FELBER at leastr I know I may be getting old but not totally stupid yet. I couldn't get the evacs to work at all so I just went to what we run on the stock car and have had no problems. I did put one in each valve cover instead of two in one like on the car though becuase I don't turn left all the time at high G applications only some of the time LOL.
 
On a direct drive the ring seal and valve seal is far more crucial than a motor turning 6,000RPM. I believe if you have a motor that isn't turning any RPM's and don't want to fool with an air pump. Just run two hoses off your valve covers one on each side to the cage cut the hose on a 45 deg angle and have the tips end a few inches in front of the prop this will pull a slight vacuum the prop moves allot of air and will siphon the hose. Plus when your prop is not moving fast the hoses will still function as regular breather so you will be covered under all conditions. This is also very cheap and simple to install. I personally hate oil leaks and have strived to prevent them, this simple hose system works great.
 
WHAT ABOUT AIRCRAFT ENGINES? SHOULD THE HOSE GO OUT OF THE TOP OF THE CAGE OR THE BOTTOM? HEARD ONE TIME ABOUT WATER (CONDENSATION) GETTING IN THE CASE IF ITS ON THE TOP OF THE CAGE.
 
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