MG Sports Cars

engine swaps and other performance upgrades, plus "factory" and Costello V8s

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BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
MGV8 PCV plumbing
Posted by: BlownMGB-V8
Date: January 08, 2008 04:25PM

Hey Carl! Did you see the photo of Ken Smith's engine in the 3rd press release article of the new newsletter? I noticed right away that the engine has twin PCV suction lines coming from the inside center of the MG valve covers and going to the dual carbs. That means there has to be a vent somewhere else on the engine to let fresh air into the engine. I couldn't see where that is but it might be worth trying to find out. It would give us more insight into how MG plumbed the system

Jim


Moderator
Curtis Jacobson
Portland Oregon
(4576 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

authors avatar
Re: MGV8 PCV plumbing
Posted by: Moderator
Date: January 08, 2008 05:04PM

I think the info you're looking for is in the photos/captions of the Dave Wellings article: [www.britishv8.org]


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: MGV8 PCV plumbing
Posted by: BlownMGB-V8
Date: January 08, 2008 08:39PM

Close, but no info on how the breather tube is connected to the engine. With both rocker covers plumbed to the carbs logic would seem to dictate a tube connected to the crankcase, such as through the pan, or perhaps more sensibly, a breather on the fuel pump block-off plate. This plumbed into a filter base would do the trick.

Carl has the MG rocker covers and was having trouble with the plumbing for them, as they are a bit different than either domestic or Rover. I'd think a 5/8" hose from the above location would do the trick.

However there's one more detail. Since it's common for British systems to use a flame trap on the line(s) to the carb and no PCV valve, they use a restrictor orifice on the inlet side. That's fine but done that way it won't handle the same volume of blowby as a 5/8" inlet vent line and PCV valve on the suction line, even with both 3/8" suction lines plumbed directly to the intake manifold. A twofold increase in diameter yeilds a fourfold increase in flow.

On the other hand, my Rover covers had I think a 3/4" hose coming off the flame trap and a small orifice on the other cover, presumably the fresh air inlet. In this case, plumbing the large hose into the intake manifold would work just fine, and the resulting crankcase vacuum under cruise conditions could improve fuel economy if incrementally. Perhaps Carl should run a large line with a flame trap from the block off plate to a large fitting in the intake manifold, and put a restricted filter element on one or both of the valve covers. Both approaches seem equally valid and equally effective. Hope that analysis is helpful to you Carl.

Jim


Kerbut
Nigel Ricardo
, Weymouth, Dorset ,South of England
(22 posts)

Registered:
12/26/2007 06:14AM

Main British Car:
1931 Austin 7 ,1973 MGB Roadster , 1996 MG RV8 (1 )747 cc, (2) 1800 cc (3) 3900cc

Re: MGV8 PCV plumbing
Posted by: Kerbut
Date: January 09, 2008 07:15AM

If I can help,let me know what you want and I will photograph the bit you want and post it,I am not sure what a PCV valve is. There is a breather on the back of the block ,which is clipped to the carbs,I will photograph it and send it to Curtis to post, Rover used a fuel filter in the breather.


MGBV8
Carl Floyd
Kingsport, TN
(4511 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB Buick 215

authors avatar
Re: MGV8 PCV plumbing
Posted by: MGBV8
Date: January 09, 2008 07:48AM

"There is a breather on the back of the block ,which is clipped to the carbs,I will photograph it and send it to Curtis to post,"

Yeah, I was going to mention that the early Rover blocks had a breather behind the intake.


Moderator
Curtis Jacobson
Portland Oregon
(4576 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

authors avatar
Re: MGV8 PCV plumbing
Posted by: Moderator
Date: January 09, 2008 09:01PM

Here are Nigel's photos...

NigelRicardo-H.jpg

NigelRicardo-I.jpg

NigelRicardo-J.jpg

NigelRicardo-K.jpg


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: MGV8 PCV plumbing
Posted by: BlownMGB-V8
Date: January 10, 2008 01:58PM

Quite helpful, now I wonder where the hose goes to connect to the crankcase? Back of the lifter valley pan? (would need a special pan) Hole drilled and tapped in the block? (would need an extra hole somewhere that didn't already exist) Other?

After some rather meticulous measuring I've learned that the orifice diameter for the Rover valve covers is .038", which is matched by a Yamaha carb jet # 97.5 but unfortunately I do not have the 5mm tap needed to use it. That's also smaller than a # 60 drill, I think it comes out to about a #62. Fortunately though if you happen to have a set of tip drills for your torch (Everybody has a torch right? Well at least HF carries a cheap tip drill set with a pin vise that stores them. Very handy.) there is one drill in the set which is an exact fit in the Rover orifice.

I find this new information very handy. Due to my air inlet design I cannot run the fresh air inlet of a conventional American PCV system to an opening behind the air filter element because the entire filter is under vacuum and the system would not work with vacuum on both sides. And if this line is not located at the inlet any excess blowby that can't be handled by the pcv valve will be vented to the air. That's the current system and under heavy boost it exhausts smoke and minute quantities of oil mist. The British system otoh will work just fine. Like they say, more than one way to feed the dog... or was that water the cat? Any way I'm making up a large diameter tube to connect from the blower inlet to the pcv grommet, placing the crankcase under vacuum, and have nearly finished a plug for the opposite valve cover's oil filler tube with 0-ring seal, and only need to drill an orifice and fit a filter element of some type. At this point I'm leaning towards a sintered bronze element screw in filter but may find something better.

Jim



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