Solex 44

[Alex Goodhart]

Thanks

[Greg Scallon]

Alex,
All I can offer is that I have a 2332cc VW type one engine in my '56 bus and I run a draft tube down through the engine sheet metal and into open air, just below the engine case. It's working fine with no gunk spitting up on the engine or any other negative consequences that I can tell.

Good luck with your conundrum. Your engine sounds awesome by the way. Tons of fun.

-Greg

[Ron LaDow]

The 'carb venting' was a sop to the US emission regs. Yes, it will give you 'oily carbs' for the same reason the vented rocker boxes 'leaked' (they didn't): the vented fumes come out of the case as oil vapor, and that vapor condenses as liquid oil on the nearest 'cool' surface, just like the humidity condenses as water on the side of that beer can.
If you vent directly to the atmosphere, the vapor tends to 'liquefy' on hitting the cool air and lands on the muffler (or the car following you) as oil with predictable results. Pick your poison.
But if you are really testing the limits of CR, you should know that oil vapor has a really crummy octane rating, and might cause 'pinging'. My twin-plug engine vents to the right hand Zenith, since I want it to look stock. All four chambers are all within .1 of 10:1. It does rattle on a rare, hot, sea-level WOT pull.
Probably should take it apart and see if the right hand pistons show any evidence, but instead, I just treat the throttle gently if I hear it. And wipe off the carb from time to time. And then the engine has really good ring-seal, so it's really not 'blow-bying' and venting a lot; YMMV.
Pick your poison; there was a guy/car in the bay area who was quickly noted as an 'oiler'; no one wanted to get stuck behind him on tours.

[Alex Goodhart]

The engine is

[Alex Goodhart]

Thanks

[C J Murray]

My 2133cc has 25,000 miles on it. I originated the use of the 45mm Honda rod bearings that allow the 82mm stroke. Mine has single ignition and basically stock chambers with enlarged intake valves. It works flawlessly even though it took some development to make it run that way. On an engine dyno with one of my racing exhaust systems it made 160 hp. I would never voluntarily vent my crankcase to a carburetor. Porsche would not have done that if "the man" would not have made them. How you vent it is based on what you like and how you want the engine to look like. Larger displacement engines move more crankcase gasses and should have bigger "mufflers", breather cans, to control the amount of oil spittle that makes it's way to the atmosphere as the pulsing occurs. I have attached a picture of mine which shows that the factory breather can is attached to a catch bottle which is then vented to the road. I get essentially zero oil accumulation in the catch bottle but the volume it adds dampens and slows the exit speed of the crankcase gasses so that the oil droplets fall out of suspension before they even reach the catch bottle. If I did get oil accumulation in the catch bottle it would be an indication of bad ring seal or detonation. If you just vent the factory breather can to the road you may have excessive oil drops under the car.

Since you brought it up....$42k for an engine? Yikes!

[Alex Goodhart]

Hi CJ . I have thought about a catch can.

[C J Murray]

sorry, forgot pic before...

The catch bottle is a modified Moroso item.

[Alex Goodhart]

If I use a Road Draft Tube

[Ron LaDow]

images.jpg

If I use a Road Draft Tube to pull fumes out of crankcase from the rectangular oil filler, how does air get into the engine if the heads are sealed and oil cap sealed?

For starters, I am in thorough agreement with Cliff regarding preferences for venting. I do dump it into the right-hand carb for (irrational) appearance desires; if the factory had the C engine bay otherwise, I wouldn't. But it doesn't seem to cause any harm, and then Cliff is welcome to beat on me about that choice.
Anyhow, the air gets into the engine via the intake ports. Not to worry, there's more than enough blow-by to satisfy any case 'exhaust' system you prefer. I don't know the source of your first illustration, but I doubt seriously if that rocker box breather is allowing atmospheric gases into the rocker box. It is most likely allowing exhaust venting of the blow-by.
Consider the March's DFV, when it was really fresh, leaked less than 5%, far better than most any 616 is going to match. This is a 3L engine, spinning at near 10KRPM: 5% of 3L per rev, X 10,000 per minute; 150cc/rev X 10,000 = 15,000L/min.
your 616 engine is likely leaking closer to 10%, so at 5KRPM, you are shoving 15,000L/min out of what ever venting you care to design. Getting air in is not a problem.
(OK, I had never done the total leak numbers before, and I keep looking at those numbers and re-checking them. Neil, our math 'corrector'; did I miss a decimal point?)

[Alex Goodhart]

It seems getting oil into the intake is bad

[C J Murray]

My long time friend who has set many land speed records uses strong vacuum pumps attached to the crankcase to reduce "pumping losses" in his engines. Pumping losses occur when the piston must compress the air that resides UNDER the piston on the downward stroke. The air under the piston at TDC can't get out of the way quick enough because of the various structural elements inside the crankcase restrict its movement. If the area under the cylinders was unrestricted it could balance/reduce the pumping loss by going to the cylinder with opposite movement. Some engines are carefully designed to have almost no barriers between cylinders within the crankcase. Conversely some engines have been carefully designed to seal the area under each piston so that the air under that piston compresses on the down stroke but then pushes the piston back up the bore on the up stroke.

When I raced motorcycles some engine designs wanted to push oil out of the breather and some did not. Oil leaks on a road race motorcycle is a definite no-no. Sometimes I used a labyrinth of sorts to make the breather gasses twist and turn which causes the oil to drop away from the other gasses and run back into the crankcase. All the solutions used a sort of system like my 2133 in that it increase the volume of the breather system. It should be noted that some stock motorcycle engines were designed with a "timed" breather system which only opens the breather when the designer wants it open so as to control crankcase pressure. I'm talking about engines designed in the 1950s. Breathing is has always been a concern.

Street engines that are enlarged or raced at constant high rpm often overtax the breather system.

[Ron LaDow]

Street engines that are enlarged or raced at constant high rpm often overtax the breather system.

Exhausting the sump to negative pressure is pretty much universal in every real race engine I've ever encountered. But then "race engines" are almost always dry-sump engines. Check any reference by Smokey Yunick, Grumpy Jenkins or any of the serious drag-race builders way back when; get that oil OUT of the sump, and do so in a way to pull a negative pressure in the engine case. Some used a vent in the 4-into-1 exhaust collector to find a negative pressure area, but I doubt that was sufficient, given the numbers above.
I'll see if I have photos to post, but the DFV used a "roots" pump (yep, a sort of "2-20 blower" if you will) to evacuate the sump, and it was positioned such as to take advantage of the crank rotation and the sump design (there is, say, 1/8" clearance between the sump surface and the crank extremities), with a knife-edge 'peeler' on the lower right. Which 'peeler' dumped what it 'peeled' into a sort of manifold leading to the "blower" which exhausted from that to a centrifugal 'separator'; the radial exhaust going back to the oil tank, the center exhausting to the puke can (presumed to be "vapor", not liquid).
(Jon, you dealt with the oil 'exhaust', right?)
So:
1) There is ALWAYS more (positive-pressure) blow-by in the case than the alternative.
2) Finding a way to separate the oil liquid from the vapor is more complicated than you imagine and more complicated than most of us want to deal with. And in street engines, probably not worth a lot of effort.
3) As Pre Mat, I have looked at many, many, many possible ways of returning the oil to the sump and venting the vapor in a way which sort of looks 'stock'; I've failed.
If you are serious about a large displacement street engine, or about running a smaller one at high RPMs, Cliff has probably done the homework for you regarding 'breathing' the case; you need VOLUME.

[Alex Goodhart]

CJ Your system looks about the best option so far. The Moroso item is which one exactly they make so many to pick from.
Thanks for the feedback

[C J Murray]

Alex, I think it started out as this but then we welded on various modifications in a way that the hoses were fairly tidy. I eliminated the breather filter so as to have no oil mist in the engine compartment. There is almost no sign of oil at the end of the hose under the car. If you do this and if you collect oil in the can then suspect detonation. Dyno testing is not equal to road testing and you may have to do final tuning based on your actual use.

https://www.summitracing.com/parts/mor-85465/overview/