jimclark - 19 April 2009 06:15 PM

What's a vacuum pump? What's it for? Or, I should say, what does it create vacuum for?

I still await an answer...

Well Jim, a vacuum pump is a small belt driven and in some instances electrically driven pump; it’s about the size of an alternator. It normally uses either a three or four vane type construction. It has two lines coming off of it; one an outflow line that normally goes to your breather or oil overflow tank. The other line is the suction line which will be plumed into your crankcase. The purpose of the pump is to create a vacuum inside the crankcase/oil pan region. High horsepower, high compression engines create a lot of blow-by inside the crankcase; in many cases that blow-by actually creates a positive pressure situation inside the crankcase. Blow-by steals horsepower, causes your engine to leak oil, and contributes to a lot of the contaminates that get in your oil. If you can create a negative pressure inside the crankcase the piston rings seal much better and blow-by is drastically reduced. The increased ring sealing capability increases horsepower by about 4 and in some cases probably as much as 7%. A normal 500hp engine with a low tension ring setup could probably see a 12 to 15 horsepower gain by running a vacuum pump. Vacuum pumps really got their jump start many years ago in the NHRA sportsman divisions; since that time they have become a mainstay in the Pro Stock division and as they have become cheaper to buy a lot of bracket cars run them.

Like I said in my earlier post they are not allowed in NASCAR and with a dry sump oil system you really don’t need one; most of the NASCAR engine builders will tell you that they like to see at least 8 and no more than about 10 inches of negative pressure in the crankcase, and they can get that with the scavenge side of the dry sump pumps that they run. If you get the negative pressure higher than that you really don’t see any gains on the dyno, and you can run the risk of creating oiling problems. Like all things in life too much of anything can be bad and a lot of weekend bracket races probably run more vacuum than they need. I hope that helps to answer your question.

Understood, thank you kindly, sir. (I am being a bit presumptuous, aren't I?)

I'm not mechanically illiterate, but I never heard of this before. Thanks again.

In all reality a internal combustion engine is nothing more than a fancy vaccumn pump. It has to create a vacuum for complete combustion even though 100 percent combustion is never reached. Vacuum , spark,air and fuel are as important, without vacuum the engine will not run period !!!

Hey Clark in the old days a car engine needed to make vacuum to draw the air fuel ratio from the carburator through the intake manifold and into the combustion chamber when the intake valve is open and the exhaust valve is closed. If you elimanate the carb and intake manifold gaskets the process of combustion will very limited.

All piston engines, past and present, that I can think of anyway, rely on a relative vacuum, or more accurately, a pressure differential, to charge the cylinders with the necessary air or air/fuel mixture. The easiest way to move air is by pressure differential. Often referred to as a partial vacuum. This applies to not only naturally aspirated but also pressure-charged (turbocharged, supercharged, or scavenged blower) engines.

Hey CatManDo; To me I'm thinking we are on the same path. Let me ask you if you or anyone else that reads this has ever set the ignition timing with a vacuum gauge and a tachometer??

Later

^If I didn't have a timing light I used to simply time by ear. Advance it till you heard the idle drop a bit then back it off slightly. That was often a better solution then a timing light anyway, since back in the '60's the factory timing marks were often inaccurate.

yes a timing light will get the job done and so will my ear as you say . I have found oil soaked harmonic dampners , sloppy timing chains or gilmore belts or better yet just a plain old tired out engine. or a hand built racing engine with different camshafts a vacuum gauge with a tackometer will get you the best performance anyway you want to measure it. Maybe you would be so kind as to clue me in on this Fast Reply vs. Post Reply. Thanks (what is it ?)

Gasman28 - 27 August 2009 07:07 PM

yes a timing light will get the job done and so will my ear as you say . I have found oil soaked harmonic dampners , sloppy timing chains or gilmore belts or better yet just a plain old tired out engine. or a hand built racing engine with different camshafts a vacuum gauge with a tackometer will get you the best performance anyway you want to measure it. Maybe you would be so kind as to clue me in on this Fast Reply vs. Post Reply. Thanks (what is it ?)[/quote]

Not a clue!