Racing engines and PCV valves

#1
What's your thought on this, I think they would take power away from your engine. My thought is to just run your crankcase vent to a breathing catch can.
I may be wrong on this, What do you guys think? The stock engines have a PCV built into the Valve cover.
 

delray

Well-Known Member
#6
rob, I run a return line from my canister back into the block on my flathead Tecumseh. it's always puking oil at 7000+ rpm's . on my clone I do the same,but that one never pukes oil. even at 8000 rpm's not sure why some people set up there can's without a return. kind of like having a death wish by trapping most of your oil so it can not return as your engine is spinning 7-8000+ rpm's. I also try to keep the canister higher then the engine. this way to gravity keeps thing down(oil). just make my canister out of pvc material and purchase a small breather that mounts on top.
no expect at this....just a gear head.
 
#7
I always keep either the cover reed or if running roller rockers where I have to remove reed baffle plate I use one or two power brake booster check valves. If your breather is large enough I doubt you would build up much pressure unless you had excessive blowby but the reed valves keep a vacuum in the crankcase which helps stop leaks, blowing out seals and gaskets and helps with ring seal. I'm sure the gain by better ring seal on these little engines is to tiny to measure but on drag cars it is significant.

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#8
About 35 years ago I had a Triumph Bonneville 750 and the crank breather was an open to the atmosphere tube running along the rear fender. When it was idling I remember you could put your hand by the end of that tube and feel the air breathing in and out.
 
#9
The earlier BSA and Tri 650's had timed breathers driven on the triumph by the inlet cam and the bsa on the cam. It opened on the downstroke as both pistons went up and down together. Later engines of both makes and Norton as well took off the drive side engine seal and vented the crankcase thru the primary cover which yours had. On mine I added breathers to the valve covers but also modded PCV valves to act as check valves.
 

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#10
rob, I run a return line from my canister back into the block on my flathead Tecumseh. it's always puking oil at 7000+ rpm's . on my clone I do the same,but that one never pukes oil. even at 8000 rpm's not sure why some people set up there can's without a return. kind of like having a death wish by trapping most of your oil so it can not return as your engine is spinning 7-8000+ rpm's. I also try to keep the canister higher then the engine. this way to gravity keeps thing down(oil). just make my canister out of pvc material and purchase a small breather that mounts on top.
no expect at this....just a gear head.
Well my dragbike runs on methanol. So every single time i start the engine, i change the oil and drain the carb flush it out with gas and 2 sroke oil.
Every
Single
Time
Whether it’s just idling or not. Every time I start it, I know that I have drop the oil and flush out the carb.
I use Lucas Jr Drag oil, 12oz is just about right.
The motor is going to puke what it’s going to puke, the engine will have a sweet spot where it pukes out only a tiny bit.
That’s where I’m at, and I just drain the tiny bit from the puke tank and dispose of it with the rest of the waste oil.
I can’t use the oil again anyways lol
 
#12
Hey Ole, I see your a fan of the PC valve but don't you think in a racing configuration where the engine sees just a few seconds of WOT and then gets shut down it would be better to not have one.
 
#13
They are drag race mini’s. But stock clones and other engines also c
use them. Go look at the new billet sidecover from EC carbs it comes with a billet check valve and a explanation of why it is used vs open breather.
 
#14
https://www.eccarburetors.com/ecsc2...qXJJThIODBOeYua8i0tRl2SMEw0cZ7E5prlYEnt_ZtJCo

Description

281 EC Billet PCV Valve 3/4"-16 fits the Burris side cover.
The 281 Pressure Control Valve is used primarily to help control crankcase pressure. Unlike many vents, you’ll find crankcases our PCV Valve uses a check valve that only allows crankcase pressure air and gases to flow one direction. A common mistake is using a simple brass or aluminum fitting without a check valve. This means air is pushed out but also air can be sucked back in and in a sense defeats the purpose of a vent. In built engines its not enough to vent crankcase pressure but control crankcase pressure. Check out technical page for more diagrams and info.
This new style is all aluminum eliminating the plastic check valve. This improved model will be more durable for using methanol.
 
#16
I say both, Run your breather to a catch can with a PCV valve on it. Here is why. As your piston comes down it pressurizes the crank case. if you can vent that pressure you will not slow the piston as much. now when the piston is traveling upward, it wants to create a vacuum behind it because the PCV valve is a one way valve. This will in turn suck the piston(to a point) back downward, thus boosting efficiency on that stroke. I have run motors without a PCV in the past, and I know for a fact a properly vented crankcase makes more power. I run 25-50 laps at a time on the motors I build at 7,000+ Rpms
 
#17
According to new technology, nowadays There are new technology of solar engine which is using in vehicles. I may be wrong on this, What do you guys think? If you have any suggestion please give me because I want to know more about this.
 

DaddyJohn

Well-Known Member
#18
The earlier BSA and Tri 650's had timed breathers driven on the triumph by the inlet cam and the bsa on the cam. It opened on the downstroke as both pistons went up and down together. Later engines of both makes and Norton as well took off the drive side engine seal and vented the crankcase thru the primary cover...
I believe 1970 was the first year for that, so other than that one year, It's mostly an OIF feature.
 
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