Breathing

beth · Post by **beth** » Wed Jul 09, 2008 10:05 pm

By not paying enough attention at the right time I have managed to get an SD1 engine with P6 rocker covers. Which I have connected up in the usual way with flame traps to the carb breather ports. It didn't dawn on me until reading various posts on this forum that therefore there is no fresh air input to the crankcase or rocker area, and there really ought to be. D'oh!
I don't have the original SD1 rocker covers.

So, where to go from here? I'm contemplating drilling and tapping a suitable fitting into one cover and putting a breather filter on it. Will that be 'good enough'? or should I really be trying to get hold of some SD1 covers, somehow.

Beth

ppyvabw · Post by **ppyvabw** » Wed Jul 09, 2008 10:12 pm

I never bother with the crankcase breather to the carbs, just have open breathers either into thin air, or into a catch tank.

Are you not supposed to have one of the rocker cover breathers to the carbs with a flame trap, and the other is open air with a small seperate filter, or into the carb air filters?

beth · Post by **beth** » Wed Jul 09, 2008 10:34 pm

The P6 has breather pipes on both covers which are plumbed into the carb breather ports individually, via flame traps. Additionally there's a hole at the back of the block which should be connected to the air filter box, and which the SD1 block doesn't have.

Breather filters would suit me fine. What do you do about the carb ports, just blank them?

ppyvabw · Post by **ppyvabw** » Wed Jul 09, 2008 10:45 pm

hole in the back of the block? :S

News to me. I'm confused.

Yeah just plugged them up.

RoverP6B · Post by **RoverP6B** » Thu Jul 10, 2008 2:34 am

On the P6 engine, at the top rear of the block venting the lifter gallery, just to the side of the off side (R/H) rocker cover is the engine breather filter. Air enters the filter at this point and travels via the crankcase before leaving the engine at each rocker cover, through each flame trap and into the SU carburettor on that side of the engine.

If the ports on the carburettors that accept the flame trap hoses are blanked off, and a catch tank etc used instead, then would not that influence the air fuel ratio in such a way as to richen the mixture?

If so, then either different needles would be required or modifications to the existing needles would be necessary.

Ron.

bodger · Post by **bodger** » Thu Jul 10, 2008 10:20 am

just connect an inline fuel filter of some sort to that pipe on the back of the block ad leave it hanging , this is the air inlet for the crankcase ventilation as roverp6b says , having the filter will stop any rubbish being drawn in
DON'T CONNECT THIS PIPE TO THE AIRBOX or you will end up with a vacuum in both directions
the rover v8 block really does like to have some sort of posative crankcase venting , so leave the carb pipe conected
you could end up with a bulging valley gasket , the EFI engien are more prone to ti but i have seen it happen on the carb engine too

kiwicar · Post by **kiwicar** » Thu Jul 10, 2008 12:47 pm

spot on, you want the crank case depression, it reduces oil leaks, gives you a couple of very cheep BHP and stops the car smelling of hot oil. (that is unless you like the smell of hot 20/50 while you drive in which case it is a bad thing)
Mike

ppyvabw · Post by **ppyvabw** » Thu Jul 10, 2008 1:20 pm

Agreed about the oil smell, but I don't mind that

Other than emision control I see no advantage of positive crankcase ventilation. It's invention was to reduce unburned hydrocarbons entering the atmosphere which was the biggest cause of smog in the 50/60s. Have not encountered the problem of bulging valley gaskets myself but might have to on my new efi engine if that is the case.

beth · Post by **beth** » Thu Jul 10, 2008 5:21 pm

I've re-plumbed the breathers. One rocker cover breather goes through a flame trap and then into both carb ports. The other cover breather has a 'breather filter' sat on it. As expected I had to adjust the mixture settings, but it's no big deal - I need to look at fuel/air mix as well as I have individual K&N filters and currently running BCF needles. Was running BBW but they were too weak.

Paul B · Post by **Paul B** » Fri Jul 11, 2008 5:54 pm

beth wrote:I've re-plumbed the breathers. One rocker cover breather goes through a flame trap and then into both carb ports. The other cover breather has a 'breather filter' sat on it. As expected I had to adjust the mixture settings, but it's no big deal - I need to look at fuel/air mix as well as I have individual K&N filters and currently running BCF needles. Was running BBW but they were too weak.

Had to adjust the mixture settings???

How much does your motor breathe?

I fitted the same system to my '84 sd1 motor, using a small restrictor instead of a proper PCV, and into the carb base port, and I expected the idle to come up a bit due to a little more air sucking in, but it made no difference. i then drilled a larger hole in the restrictor to make it breathe better and the idle still never moved. It did cure the occasional oil drip from the K&N I had fitted to one rocker cover though, so it must have been sucking a bit.

beth · Post by **beth** » Fri Jul 11, 2008 6:40 pm

Hmm, I haven't put any form of restriction in the breather filter. Yet. The adjustment was relatively small, about 1/16th of a turn, but I haven't had the chance to take it round the road to see if I've upset it too much. Just started it and checked it idled okay.

kiwicar · Post by **kiwicar** » Fri Jul 11, 2008 6:43 pm

Paul has a good point, I cant see fitting a breather set up needing more ajustment to mixturethan can be got from the mixture screw at idle, may be at worst you may need to move the needle up one position on in the piston. To change the needle would make me think you have a pretty big air leak in the inlet manifoldit would be worth a check around the inlet manifold. have yo checked for missing bolts in the inlet that could be letting alot of air? are all the ports on the carbes accounted for?
Mike

mgbv8 · Post by **mgbv8** » Fri Jul 11, 2008 6:53 pm

Have you connected the flame trap pipe into the air filter?
If you have connected it to the manifold side of the carb it will run lean as it is effectively a vacuum leak.

Paul B · Post by **Paul B** » Sat Jul 12, 2008 2:55 pm

beth wrote:Hmm, I haven't put any form of restriction in the breather filter. Yet. The adjustment was relatively small, about 1/16th of a turn, but I haven't had the chance to take it round the road to see if I've upset it too much. Just started it and checked it idled okay.

Why did you adjust the mixture? Did the idle increase? A lot simpler just to tweak the idle down a fraction I'd have thought.

mgbv8 wrote:Have you connected the flame trap pipe into the air filter?
If you have connected it to the manifold side of the carb it will run lean as it is effectively a vacuum leak.

That is what I did, put it into the manifold vacuum port, but even with a 1/16" hole in the restrictor made no difference to the idle, so I don't see how the mixture would need tweaking.

mgbv8 · Post by **mgbv8** » Sat Jul 12, 2008 6:50 pm

Ahh!
With you now Beth. You would be surprised how many folk stick the breather straight into the mani at full bore.
The whole Rover V8 breathing thing has many different opinions. My main concern for what I do with my car is to make sure I get rid of all crankcase pressure during a run. And make sure when the breathers pull back in when coasting after a race that the air going back in gets filtered.

I have seen many folk fit K&N's to their MGB's and wonder why they have to richen things up a bit.