Flame Traps/PCV Valve

hunkojunk · Post by **hunkojunk** » Tue Oct 06, 2009 2:50 pm

Hi all,

I have got a 3.5 SD1 engine with rocker covers from P5 engine. The rocker breathers go through a flame trap and to the base of the SU carb on each side of the engine. At the back there is another breather just above the bellhousing which goes through an inline filter to the bottom side of the air cleaner.

My question is should I have Pcv valves instead of flame traps when using HIF6 SU carbs and should one rocker cover be an inlet for air and the other to be feed to the base of the carbs.

Cheers

Quagmire · Post by **Quagmire** » Tue Oct 06, 2009 5:16 pm

On my SD1 block motor I have a normal flame trap on each rocker. They feed into each carb. On my block however, the breather at the rear by the bell housing is actually blanked off, so i have no idea where that goes!

I am using HIF6's.

No problems so far

mgbv8 · Post by **mgbv8** » Tue Oct 06, 2009 7:05 pm

The reason there is a filter on the older engines at the rear is to filter air being drawn into the crankcase on decelleration. Most folk just blank them anyway as they tend to leak oil past the insert tube. And the rocker covers communicate with the crakcase as a space anyway.

The old PCV debate is a long one. Lots of folk for, lots of folk against.

If you run a PCV valve, then it should connect to the inlet manifold in some way so it opens at max manifold vacuum. So you should realy have a flame trap fitted. This setup will eventually see the pcv line getting full of oil. So if you can run it upwards for a way before it connects to the manifold it will aid drain back.

The other rocker breather would normally connect to the air filter.

One blows vapours out under load into the air filter for re breathing. The other sucks excess vapours out when the manifold is at low pressure.

The main thing is that a fully plumbed breather system tends to do away with oily smells in the cabin.

I have 3 large breathers on my engine just open to atmosphere. But I'm not worried about smells.

hunkojunk · Post by **hunkojunk** » Tue Oct 06, 2009 8:37 pm

Thanks for the replies

My engine is not breathing oil, so in that way the system is working well

The tick over is a bit choppy on my motor so I wondered if it was something to do with the breathing system not being right for the carbs and mixtures.

My mate has a 3.5 V8 in his land rover with SU's and it has a valve that the breathers go through and its standard.

RoverP6B · Post by **RoverP6B** » Tue Oct 06, 2009 10:14 pm

The arrangement that you have with the flame traps and the breather filter at the rear of the engine is the correct system when using HIF6 carburettors.

Given that your engine is not blowing oil, that would suggest that the flame traps, hoses and connection points are all clear. Should any become blocked though, it will pump oil from everywhere.

If the idle is a bit rough it could be a range of possibilities.

Are the carbs balanced for airflow?
Is the mixture setting identical for each carburettor?
Is the distributor fitted with points or an electronic system? If the latter, which type?

How much ignition timing is the engine running at idle and at what rpm?
Is the vacuum line from the carburettor to the advance module free of any damage?

A vacuum leak between the inlet manifold and the heads can also result in a rough idle.

Ron.