3.5 to 3.9 swap..... what is this?

[Mustlust]

Hi All,
Just about finished preparing the engine for re-install tomorrow morning when I noticed that the old 3.5 had a tube in the rear of the block that doesn't exist in the 3.9 block. It looks like a vacuum, and it's too dark now to check the pipes in the engine bay. The pictures below show the pipe on the old dirt block and the absence of any such hole to accommodate the pipe in the 3.9 block.
Is this a vacuum line??? and if so, what can I connect the old line to on the 3.9 engine? Keeping the twin carbies so may be a vac port there??
Thanks,
P

[Marshall8hp]

It goes up, via a filter, to the air filter body. Essentially it is how clean air is introduced into your engine for the pcv system. Air goes in that pipe and out through the rocker covers to the carbs.

[bee utey]

It has nothing to do with vacuum, it is part of the breather system for blowby gases. 3.9 engines didn't come with carbies so you'll have to hang the hose off somewhere else, eg a rocker cover, drill and tap a new fitting into the block, or just ignore it. The engine will still run just fine without it IMHO.

[Mustlust]

Well I wonder if I should drill a hole into the block and refit the breather elbow to replicate the 3.5 set-up? I guess the air needs to enter the block somehow. If I don't have air running into the engine, what are the likely consequences?
Bee utey reckons it won't be a prob.... So maybe it will be ok.

[Homestar]

No issue leaving it off as Bee Utey says. :). If you want to keep the original look, run the hose somewhere and zip tie it to something convenient.

[slug_burner]

You will not be putting air in, I think the crankcase gets pressurised by blow-by gases. To get rid of the gases the various ports are connected back into the induction system, either in the air flow at the filter or at the carb or anywhere in between.

One less port to allow the gases to be sucked into the engine and be burnt will not be critical.

[Mustlust]

Well all is cruisey with the new donk except that I have a sticky tappet that seems to come good once ive driven about 100m. I guess it takes a few revs to get the oil into the head????
I hope to have the next size up needle fitted into the carbie in a week and hope that may free up the motor a little.
Other than that, I am chasing an exhaust leak in the manifold, which makes a distinctive 'chuff' under load. The old 3.5 didnt have exhaust gaskets, but I wonder if the 3.9 engine usually has them?. Ive checked all the bolts and they seem tight enough...... that also includes the 2 that have stripped threads (thanks to previous owner - not me!). I have tried my best to feed bolts that have some bite into the thread holes.... not ideal I know, but a bugger when you find these things after the install.