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What is the latest thinking on crankacse venting for a supercharged MGB?

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pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
I currently have a filter sitting atop the pipe from the front tappet chest breather. It seems to stink up my garage with oil smell pretty quickly even with the door open and the exhaust blasting out said door. I used to use the port on my SU to connect the tappet chest tube to but now with the Mikuni carburetor that port is gone. It pulled too much oil anyway...

Since I have basically no crankcase breathing system I'm starting with a clean sheet of paper... and I'd like to only do this one time. What are your thoughts/suggestions?

Adrian



Home built Eaton M62 Supercharger with 7.6psi boost, 8:1 compression, custom "supercharger" cam from Schneider Cams, Mikuni HSR48 Carburetor, Chevy Cavalier 1.6 rocker arms, Maxspeeding rods with Teflon wrist pin buttons, custom aluminum cold air intake, CB Performance computerized ignition, Fidanza 9 pound flywheel, 1.44 exhaust valves in 48cc chamber head, matched manifolds, 2 1/4" exhaust system.

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Gerald O Avatar
Gerald O Gerald O'Docharty
Wake Forest, North Carolina, USA   USA
1972 MG MGB GT
1978 MG MGB
I would just find a way to vent it into the intake under its own crankcase pressure so that the fumes are burnt. Maybe via a catch can.

Unless you want to get fancy and do crankcase vacuum for reduction of windage/pumping losses. Then you'll need to go to a crankcase scavenging pump and seal everything up tight.

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fast-MG.com Gold Member Dave Headley
Cortez, 4 corners, Colorado, USA   USA
If possible, vent to the clean air side of the air cleaner.smoking smiley


Member Services:
Dave Headley, dba FAB-TEK offers full service race car parts and preparation for MGB & MGA race cars, SCCA and Vintage. Dave is a mechanical engineer and has raced MGBs since 1963.
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Jim Blackwood Avatar
Jim Blackwood * BlownMGB-V8
Gunpowder Rd, Florence, KY, USA   USA
Adrian, here's what I did and it works very well. Bear in mind this is a V8 so you will have to adapt it to your I-4 but you can use the rocker cover and tappet cover instead of two rocker covers. So, on one rocker cover I put a metered orifice, in keeping with the British methodology. On the other I put a flame arrestor (metal mesh, pot scrubbers work), in this case a stock Rover screw-in canister. Atop that I attached a vacuum operated 5/8" heater valve and plumbed the diaphraghm to manifold vacuum. Vacuum pulls it closed. There is a small bit of leakage when closed I believe but it's been awhile so I can't say for sure. Should be some details in my 340 thread on BritishV8. I ran the outlet to my blower intake, behind the throttle body and filter.

So, at idle full vacuum is applied to the heater valve but also pulls it closed. (If there is no leakage at all a small bypass with an orifice might be a good idea.) At WOT it opens and allows blowby to enter the blower inlet. So it still allows idle speed to be brought down to a reasonable level and unburned gasses are limited by the orifice, while blowby has a free path. It's the best setup I've seen so far.

Jim

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pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
In reply to # 3908051 by Gerald O I would just find a way to vent it into the intake under its own crankcase pressure so that the fumes are burnt. Maybe via a catch can.

Unless you want to get fancy and do crankcase vacuum for reduction of windage/pumping losses. Then you'll need to go to a crankcase scavenging pump and seal everything up tight.

I just stuck a length of hose on the tappet chest outlet and stuffed the other end down the cold air intake's throat as a test. It seems to take care of the oil smell in the shop but I'm not sure it's the very best setup possible. I expect the tappet chest acts as a catch can in this setup. I'm not interested in setting up vacuum pumps. Perhaps a catch can along with the tappet chest oil separator would suffice? I still have the metered orifice on my stock 73 valve cover. Is that sufficient air intake?

Adrian



Home built Eaton M62 Supercharger with 7.6psi boost, 8:1 compression, custom "supercharger" cam from Schneider Cams, Mikuni HSR48 Carburetor, Chevy Cavalier 1.6 rocker arms, Maxspeeding rods with Teflon wrist pin buttons, custom aluminum cold air intake, CB Performance computerized ignition, Fidanza 9 pound flywheel, 1.44 exhaust valves in 48cc chamber head, matched manifolds, 2 1/4" exhaust system.

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pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
In reply to # 3908082 by Jim Blackwood Adrian, here's what I did and it works very well. Bear in mind this is a V8 so you will have to adapt it to your I-4 but you can use the rocker cover and tappet cover instead of two rocker covers. So, on one rocker cover I put a metered orifice, in keeping with the British methodology. On the other I put a flame arrestor (metal mesh, pot scrubbers work), in this case a stock Rover screw-in canister. Atop that I attached a vacuum operated 5/8" heater valve and plumbed the diaphraghm to manifold vacuum. Vacuum pulls it closed. There is a small bit of leakage when closed I believe but it's been awhile so I can't say for sure. Should be some details in my 340 thread on BritishV8. I ran the outlet to my blower intake, behind the throttle body and filter.

So, at idle full vacuum is applied to the heater valve but also pulls it closed. (If there is no leakage at all a small bypass with an orifice might be a good idea.) At WOT it opens and allows blowby to enter the blower inlet. So it still allows idle speed to be brought down to a reasonable level and unburned gasses are limited by the orifice, while blowby has a free path. It's the best setup I've seen so far.

Jim

That's an interesting setup Jim. I'm going to think on it for while. Thanks for posting.

Adrian



Home built Eaton M62 Supercharger with 7.6psi boost, 8:1 compression, custom "supercharger" cam from Schneider Cams, Mikuni HSR48 Carburetor, Chevy Cavalier 1.6 rocker arms, Maxspeeding rods with Teflon wrist pin buttons, custom aluminum cold air intake, CB Performance computerized ignition, Fidanza 9 pound flywheel, 1.44 exhaust valves in 48cc chamber head, matched manifolds, 2 1/4" exhaust system.

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fast-MG.com Avatar
fast-MG.com Gold Member Dave Headley
Cortez, 4 corners, Colorado, USA   USA
Best to not vent through the rocker cover as blowby gases are tending to push oil up that should be draining down.


Member Services:
Dave Headley, dba FAB-TEK offers full service race car parts and preparation for MGB & MGA race cars, SCCA and Vintage. Dave is a mechanical engineer and has raced MGBs since 1963.
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Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
Adrian I have never had a problem with crankcase venting, I just run the side plate vent to the cold air intake a couple inches pre carb. No sign of oil in the pipe. I feel if a supercharged engine makes excess blowby its an engine problem. Denis



68 B roadster, Daffodil yellow, supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine "3.9L Rover" early in 2016 with high comp pistons and a few other nice bits, plus a T5 ford trans. Started on the body late 2016 and complete late 2017, Did all the work myself, mechanical, body. paint etc.
Finished and going well, great to drive and quick. Now has a nice 3.23 LSD.

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Jim Blackwood Avatar
Jim Blackwood * BlownMGB-V8
Gunpowder Rd, Florence, KY, USA   USA
I agree with Dave, and the stock setup had the orifice on the rocker cover with the tappet cover going to the carbs. With the blower you should expect to have a little more blowby just because of the higher pressures. I tried several different arrangements. Doesn't the rocker cover have a metal-mesh element inside a box that is on the inside? That would take care of the need for a flame arrestor. Be sure you have one, otherwise a backfire can create a crankcase explosion. I've had that happen.

The 1800 has a 1/2" tube on the tappet cover which is not overly large. I like having a positive draw through the crankcase but you have to limit the flow somewhere. VERY IMPORTANT: I just remembered, I did NOT use an orifice on the opposite rocker cover, just a small filter mounted on a small pipe nipple. The reason being that in this system the flow limiter is the water valve. At all costs you want to avoid having the system choked down at both ends. If you accidentally do that, (like my first description) you can force blowby past your seals and gaskets and you don't want that.

A passive system can work I think, but I believe you would then have to use a pcv valve as the metering device. It has a shuttle inside which blocks the main flow at idle, and allows a metered flow instead. The problem is that a typical pcv isn't quite large enough to handle the full amount of blowby produced at full load so the rest is blown out the vent line. Which is OK if they both go to the intake, with the PCV line to the blower inlet and the vent line behind the air filter. Plumbing a pcv to the intake doesn't work because under boost the shuttle would be open.

HTH,
Jim

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tvrgeek Avatar
tvrgeek Scott S
Hillsborough, North Carolinia, USA   USA
1965 MG MGB
How is it done on production cars?

Remember the words of Tom Leher
" When in doubt plagiarize,
Let no ones work evade your eyes
That's why God gave you eyes
Plagiarize, plagiarize, plagiarize"

Or as is done in academia, to copy one is to plagiarize, to copy many is research.


BTW, You can get adjustable PCV valves. Big enough I can't say, I just know they make them.



Cogito ergo sum periculoso

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pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
In reply to # 3908214 by Denis Adrian I have never had a problem with crankcase venting, I just run the side plate vent to the cold air intake a couple inches pre carb. No sign of oil in the pipe. I feel if a supercharged engine makes excess blowby its an engine problem. Denis

This seems to work. I had been using the MG rocker cover orifice system with the SU but it wasn't working at high loads... a lot of oil was getting into the intake. I just disconnected the pipe from the tappet chest and the problem went away. I just had the rubber hose off the tappet chest pointing straight up at the underside of the bonnet; No oily spot developed but it sure stunk up my shop running the car inside. (I had a little K&N looking filter on the end of the pipe.by now)

Anyway... sticking the tappet chest pipe into the cold air intake inlet seems to be doing the trick. I'll fashion a fitting to connect it properly. Thanks for input gents!

Adrian



Home built Eaton M62 Supercharger with 7.6psi boost, 8:1 compression, custom "supercharger" cam from Schneider Cams, Mikuni HSR48 Carburetor, Chevy Cavalier 1.6 rocker arms, Maxspeeding rods with Teflon wrist pin buttons, custom aluminum cold air intake, CB Performance computerized ignition, Fidanza 9 pound flywheel, 1.44 exhaust valves in 48cc chamber head, matched manifolds, 2 1/4" exhaust system.



Edited 2 time(s). Last edit at 2019-03-15 06:33 AM by pinkyponk.

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Jim Blackwood Avatar
Jim Blackwood * BlownMGB-V8
Gunpowder Rd, Florence, KY, USA   USA
Sure thing. Whatever you are happy with. In the '60s they all had road tubes. The move to pcv was partly to clean up the oil streaks on the roads, mostly to make oil change intervals longer, and partly to make cars smell better. The way you are doing it is similar to the old road tube except burning whatever comes out. Pcv forced fresh air through the crankcase for better scavenging of blowby gasses. It greatly reduced internal deposits in the engine. That's the major difference. With unleaded gas it's less important than it once was.

Jim

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pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
Without a diagram I'm afraid I'm lost. Don't vent from the valve cover? Does "vent" mean the stock MG valve cover orifice or does it mean a fat tube to vent the gasses to the intake? Where would the pipe from the tappet cover go? I'm venting the crankcase tappet cover to the engines air intake... with a tiny "vent" in my valve cover. Where does the PCV valve go in this setup?

I don't know enough about PCV valves to know how to choose one. Adjustable would be good I suppose but what would I adjust it to?

Time to go read up on all this stuff I guess...

Adrian



Home built Eaton M62 Supercharger with 7.6psi boost, 8:1 compression, custom "supercharger" cam from Schneider Cams, Mikuni HSR48 Carburetor, Chevy Cavalier 1.6 rocker arms, Maxspeeding rods with Teflon wrist pin buttons, custom aluminum cold air intake, CB Performance computerized ignition, Fidanza 9 pound flywheel, 1.44 exhaust valves in 48cc chamber head, matched manifolds, 2 1/4" exhaust system.

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Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
If you run a PCV valve you vent into engine vacuum (between carb and blower) As you say the vent in the cap controls the flow when venting to the CAI and PCV not necessary. On my V8 I run a pipe from one rocker cover to vacuum with a .125" restrictor and a filter on the other. The carb is then jetted with this allowed for. The SC car is a lot easier and works well. Denis



68 B roadster, Daffodil yellow, supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine "3.9L Rover" early in 2016 with high comp pistons and a few other nice bits, plus a T5 ford trans. Started on the body late 2016 and complete late 2017, Did all the work myself, mechanical, body. paint etc.
Finished and going well, great to drive and quick. Now has a nice 3.23 LSD.

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Jim Blackwood Avatar
Jim Blackwood * BlownMGB-V8
Gunpowder Rd, Florence, KY, USA   USA
The later MGB had a 90° tube about 1/2" diameter on the rocker cover which had a very small hole in the end, right? I think this was commonly connected to the purge line of the charcoal canister maybe? So that's your source for fresh air. Airflow was down through the engine and out the tappet cover to the carbs. But it didn't see full manifold vacuum IIRC, just venturi vacuum. Otherwise it would have let too much air in at idle and upset the mixture and idle speed. Nevermind the small inlet orifice, with that much vacuum air gets pulled in past the seals, presumably the ones on the crankshaft. I tried setting my Olds 215 up this way and couldn't get the idle down.

What you have to understand is that the pcv is a very dynamic system. The operating conditions change a great deal depending on throttle opening and engine load, with blowby, which is likewise dynamic, interacting in interesting ways, and the whole business then goes on to influence the way the engine runs, particularly at idle and low speed.

We're tricked into thinking it's simple because it looks simple. It's anything but.

So, The Brits limit the fresh air inducted to the crankcase, and then limit the suction via their carb design. But if you don't use SU carbs it makes it really hard to use that system because you have to limit the flow somehow, still provide some sort of suction, and provide for the much higher flow from blowby under load. Hard to satisfy all those requirements.

American practice limits suction with the shuttle in the pcv valve at idle, reduced vacuum at cruise lets the shuttle drop and allows more flow through the valve, and under full load the blowby just spews out the other hose into the air cleaner. Unless your carb is set up for venturi vacuum pcv like an SU that leaves the American design as the simplest option. Get a pcv valve from a similar engine, mount it vertically and plumb it to the blower inlet. If you run that from the tappet cover, then cut the end off the tube on the rocker cover, plumb it through the wall of the tube between your air filter and carb and put a miniature filter on the end of it inside the tube. Job done. The miniature filter acts as a flame arrester, that's the only reason for it to be there, and you can't leave it off. But you can use one of a different sort in a different place in that line.

Jim

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