J1720

:-)

I say it does :-)

Jerry Feather

How do you actually know which way the air might be flowing through the stub, if at all?

jcorenman

xgfhsth, you are a spambot-- that is an echo of what Mike Schmidt said 12 years ago. Go away.

Jerry, the missing page from the Porsche '81 service info (post #25) says that "air is drawn from housing (2) through opening (1) for cooling of the toothed belt (3)". That's how you know

Jerry Feather

Thanks for that explanation. However I am puzzled about just what it means. First, air does not suck it can only blow, so I am not sure what "air is drawn" might mean. Second, if "housing" means the housing around the timing belt and pullys, how is air from inside there and into the intake tubes going to do any cooling. The timing belt is not in the intake tube. Third, I don't believe everything I read, even from the Porsche Factory.

On the other hand, I do think that air enters the belt "housing" from somewhere besides the stub openings and gets pumped up into higher pressure probably around its outer areas and then is blown into the intake tubes through the stub openings. I don't know that because I don't have any other knowledge about the pressure differentials in respect to the three or four areas that might be involved.

Mrmerlin

Jerry the air that passes through the the timing cover starts at the bottom center of the timing cover note the little opening next to the crank damper,
the air is drawn upwards, and is assisted by the heat of the engine as it rises inside the housing towards the top of each cover,
also assisted by the lower pressure air as its moved through the intake tubes.

This system was also made to capture any combustion fumes that might escape the seals at the front of the engine.

NOTE air movement process can be confirmed by observing the small pieces of rubber that accumulate in the air filter .
Take a fresh timing belt job and a fresh air filter run for a few hundred miles,
then tap the air filter onto a white piece of paper,
the particulates will contain rubber shards from the belt as it wears into the belt run.

Alan

Back to sleep....

GlenL

It's always puzzled me that they would duct hot air into the tubes designed to bring cool air into the engine.

I use 3" brake duct with no connection to the belt covers. No venturi. No sound deadening. Worth a pony or three, I figure. Setting the way-back machine... I once ran a dyno test with an open air filter and lost 5 hp! The cool air works.

And... Curse you, Steve, for trolling us all!

mark kibort

not exactly.... the tubes..(at least my tubes that are sealed) have a .035 positive pressure of them, which is higher than the face of the engine or inside the timing cover, however, air moving over the timing belt cover tube opening, creates a low pressure there, where that can pull air out of the timing cover housings.

I don't think you can say that there is 5hp for your brake duct vs stock ducts. temp is a small factor but air flow characteristics are not. ive done that test too. 5hp loss for a perfectly designed air inlet that stuck straight out of the MAF. bell mouthed inlet and a free flow filter. the stock stuff, is more about better flow, rather than venturis, etc.
while there is still a venture with the stock tubes, which is mainly for sound, the fact is, the air speeds up and then slows down again, at a cost of mass flow, if you didn't have the venture. its a pressure drop, plain and simple. getting rid of the tubes, smoothing them out, is a good thing for subtle power gains. most of the air filter and intake tube comparisons are so in accurate, due to the loose fitting tubes and leaky airboxs on most systems.

Im still very anxious to do the air filter test. I was there at the dyno and couldn't find the stock air filter to test at the dyno vs the KN. next time, ill get a good paper filter and do the test.

OTR18WHEELER

to the OP...
go ahead, remove all of that intake tubing, and move to canada with the other guy, after you trash your car, we dont even want your parts.

OTR18WHEELER

these cars werent built for groceries, the vents on the cam covers are there to draw the heat out of the front of the engine trapped behind the covers, to vent. If driven like designed, it works. Dont believe me, pull the cam covers and drive along a gravel road for a day, if you dont catch a rock in the TB, turn around and test you luck again.

danglerb

Does any other car vent the timing belt?

SteveG

Holy airpressure, Batman. I often wondered about which way the air was moving in the covers, but I do know the opening at the top is essentially a venturi, a la Bernouli (and his principle). And Stan just cleared up the question about how air is allowed in. Otherwise Bernouli would be diminished. And I would have not understood the rest of it if you guys hadn't explained it all for me.

RKD in OKC

On my GTS at some point there is enough PRESSURE in the intake tubes to blow an end off.

Alan

I'd say that's pretty much an impossibility... more likely the hose has shrunk and engine movement is causing it to wiggle free - one end of this pipe is about a 3+" open section and the other end sucks.

Alan

mark kibort

I get (measured with sensitive sensor) .18psi at 120mph..... in the tubes................ thats the max you can harness from the oncoming air. hardly enough to blow anything apart or off.