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jreiley 02-10-2014 10:54 AM

Crank Case Vacumm
Do I need to care what the vacumm is in the crankcase on a bbc race engine? Just curious.

fast2251 02-10-2014 03:51 PM

Are you running a vacuum pump? If yes pulling vacuum will depend on how well the engine is sealed up. Rings and gaskets. If not just make sure the crankcase can breath upward. Valve cover or valley plate.

curtisreed 02-11-2014 03:11 AM

Of more concern is, does the crankcase go positive? Pressure pushes out gaskets, then oil and nothing good comes from that.

Remember also the pistons move as much air below them, if it is there, as they do above them. Parasitic loss is not your friend.


roadkill2 02-11-2014 05:06 AM

20 inches of Vacuum is worth somewhere between 35 to 80 Hp depending on the engine and the oiling system.

But you need to seal it up pretty good . .

We're using an Aviad dry sump system and a Vacuum pump . . Seems to be the hot tip . .

jreiley 02-11-2014 05:50 AM

The way the prior owner of this car got his crankcase vacuum was putting a bung in the valvecover and plumbing to the vacuumm gauge. Is this a good way to get the vac reading. There is no vac pump on this engine and its a normal oiling system.

roadkill2 02-11-2014 06:31 AM

What's he using to create or pump Vacuum? A "Vac-u-Pan system, installed right will pull maybe 4-5 inches on a good day, if he's got his cylinders sealed really good (Good rings, seated, etc) and all his gaskets are working . . If that's all he's using, a really good oil pan is necessary to keep crankshaft windage at a minimum . .

But that's all old technology and if he wants to make the next step, a vacuum pump is pretty necessary . . With a good pump you can pull 7-14 inches and that will work pretty good . . But you still need a good oil pan/scraper to keep the windage down . .

The Engineers claim (and I believe them) that windage in an Engine will require (or use) 35 to 125 HP of parasitic loss. Deeper oil pans with efficient scrapers and directed oil returns lessen the drag of windage around the crank, and you get HP in return. They don't "Make" HP, they just "Free" it up . .

We finally went to the Dry Sump for several reasons . . one, it eliminates 95% of the windage in the engine. Two, it bulletproofs the Oiling system. Three, if, for some reason, you window the block/pan, the diaper doesn't have the large amount of oil to keep off the race track in front of your rear tires that an 8 qt sump would . . And four, it makes a lot of people who race with us look in the engine compartment and say; "WTF?"

Granted, it's kind of 'spensive, but what's your head worth? (Old Crash Helmet question)

curtisreed 02-11-2014 09:39 AM

Originally Posted by jreiley
The way the prior owner of this car got his crankcase vacuum was putting a bung in the valvecover and plumbing to the vacuumm gauge. Is this a good way to get the vac reading. There is no vac pump on this engine and its a normal oiling system.

Yes, that is a good way to get a reading. Pan evac systems may be old school, but not everyone can afford to put a vacuum pump on. There is nothing wrong with doing it that way and if it has 4-5" of vacuum that is much better than positive pressure. Are you running gas, E-85 or alcohol? Gas is much more forgiving of a pan evac system. The expansion of the water in E-85 and Methanol can create a positive pressure in a crankcase if it doesn't have some relief, I.E. vacuum pump, pan evac or just the blowdown tubes you see on blown cars.


jreiley 02-11-2014 12:19 PM

Its sounds that if I want to optimize the engine hp, I should go to a dry sump oil system. Having said that the cost is high but so is the return.. The next question is whose to use? If that just becomes too expensive, would a vac pump do any good? This is on a gas engine.

roadkill2 02-11-2014 12:49 PM

Originally Posted by jreiley
Its sounds that if I want to optimize the engine hp, I should go to a dry sump oil system. Having said that the cost is high but so is the return.. The next question is whose to use? If that just becomes too expensive, would a vac pump do any good? This is on a gas engine.

There's a bunch of 'em out there . . I'm only familiar with three, but I'm sure most of them are quality systems . .

Years back we had an Armstrong on the Alky Dragster, then a few years ago we had a Peterson on both the Super Comp car and then the Blown alky altered . . now, the Camaro S/Pro car has an Aviaid and it's a jewel . .

The three mentioned all will cost somewhere in the area of $2400-$3000 depending on the number of stages, the finish and how much hardware you get with it . .

But . . with a good pump, you can pull 18-22 inches of vacuum and pick up 80 to 125 HP . . as well as pretty much bullet proof your oiling system . . Think about that . . what does a complete set of Dart 355's cost? And how much HP do you expect out of those heads?

Just an old guy ramblin' . . .

TheYellaBrick 02-11-2014 03:48 PM

A coupla years back we had this discussion on Vac pumps. Any new and recommended units out there ?

80 -125hp gain would be worth the investment ! :D :D But then I'd find more weak links and need to spend MORE money ! :shock: :shock:

roadkill2 02-12-2014 05:01 AM

By itself, a vacuum pump is only good for about 14 inches (Max) if they're cranked up . . And there's a lotta wear n tear on em when you're asking that much from one . . Prices on them are around $850 new and while they do pretty good, I'd always choose the dry sump even though it's a hell of a lot more expensive . . By itself, a good 3 stage pump will give you 18-20 inches of Vacuum, which should be the equivalent of a new set of heads with shaft rockers in the HP department . .

Over the years, though, I never thought of a dry Sump system as a HP advantage, but in drag racing, more of a engine safety program . . The system takes inertia out of the ballgame, so to speak, because when you do a hard burnout, you stand the back tires up, pitch the front end down, and then brake hard at the end . . where's the oil in the pan? The front, mostly, away from the pickup, if you have a conventional system. And when you leave, anything quicker than a 1.40 60 ft time, and all the oil is piled up in the back of the pan and up around the rear main. At the other end, when you are getting stopped, where's the oil, again?

With a Dry Sump, your oil pressure never wobbles . . Because it's less subject to movement and inertia . .

But, there's budget, and there's what each individual may see as a solution for his own particular situation . . Whatever works for you ain't bad even if other guys scratch their heads . . . And if they ask, I always say, "Becuz, I didn't know no better!"

Never apologize for what works for you . . .

curtisreed 02-12-2014 12:39 PM

Roadkill, I mean no disrespect to you by this. It's just my experience.

The amount of vacuum depends on different factors. Engine size, fuel, ring type, how well your gaskets are sealed, pump speed, etc... I have pulled 16"-18" with ease on my 383 small block on alcohol spinning half engine speed. I saw no e.t. difference backing it down to 10". This is with a std. Star pump. What I do see is less condensation in the valve covers and a little cleaner oil (the main reason I put it on). On the next build I am going to go with a lighter tension ring set and I do believe I will see a H.P. gain.

I agree with you that a dry sump system is the way to go if a guy can do it. I have zero room for one, but would love to have it. I could dump my accumulator if I had room for one. Major benefits there.


roadkill2 02-12-2014 02:10 PM

Well, yeah . . Normally, we speak in generalities here unless someone puts up specific dimensions . . and of course, most of us understand you can't pull vacuum if you have a screen door for a pan gasket . . (Tongue in cheek here) . . Or no cylinder pressure . . Got leak down? Then you are gonna have a hellova time pulling a lot of Vacuum . .

No, all your other ducks gotta be lined up for either a Vacuum Pump or an external Oil Pump to pull high vacuum . . That is, or should be an "Understood" . .

On the HP gains, Hedrick Racing says high vacuum lowers the pressure on the bottoms of Pistons on the downstroke, and if your scavenge is functioning correctly, it eliminates the HP robbing Windage almost completely . .

curtisreed 02-14-2014 03:46 AM

Here ya go. Dyno back to back without and with vacuum.

roadkill2 02-14-2014 05:52 AM

Good post . . Thank you . . from everybody up here, I think . . .

I have a connection with the Hedrick Engine Program (No secrets divulged, trust me on that!) and they spend hundreds of thousands of dollars looking for a quarter of a horsepower, and more hundreds of thousands making an engine just a little more bulletproof to run 550 miles at 8500 rpm . . So when my buddy tells me something I usually take it for what it's worth.

He has claimed (and I have no reason to doubt him) that with proper oil control devices (Windage control) and just a superior Dry Sump System they pull about 22-24 inches of vacuum and they "free up" about 125-30 HP in their engines . . Plus they get better life out of their piston/rod combinations . .

Rehyer/Morrison claims the same thing . .

You do have to note that actually, neither pump "MAKES" HP, it just "Frees Up" what you're already capable of making . .

curtisreed 02-14-2014 06:01 AM

There is no doubt about oil control freeing up HP. I accidentally had too much oil in my car last year. Couldn't figure out why my E.T. was varying so much. What was happening was, depending on how much I was spotting, (how long I was on the converter at high rpm), I was pumping more oil to the top end and there was less hitting the crank. I was getting .05-.07 variance in E.T. I went from 10 qts in the whole system to 7 1/2. Problem solved.

Anyone who doesn't think windage doesn't cause a problem should try to move their hand in water as fast as in air.


P.S. not asking for tech. but what is your connection to Hendrick?

roadkill2 02-14-2014 06:27 AM

My first exposure to the education on Windage was an engineering article written by Zora Arkus Duntov in about 1957, I think . . He stated that with an adequate Oil Pump, and no windage control, a SBC sould run out of oil in the pan in less than a mile at 7000 RPM . .

And then went on to explain the various ways windage saps Horsepower from the rotating assembly. To a novice Car Nut it was almost frightening. But it certainly started me off right . .

jreiley 02-19-2014 09:32 AM

If I got with a good vac pump, do I want valve covers that don't have breathers or fillers in them? If so, how do put oil in the sucker.

roadkill2 02-19-2014 10:09 AM

Take off the Valve cover . . or, just put a sealed cap in the breather provision if the valve covers come with one . .

Racing engines generally don't have an "Oil Filler Cap" . . If you really race the car, you've got the valve covers off after every race weekend to run the valves and look for shavings, sparkles and other non oil particulate in the lower parts of the head . . As well as inspecting the oil in the pan and filter . .

Happy engine, happy wife . . .

jreiley 02-19-2014 01:50 PM

I do reallly race the car but not to the extent I would like. I'm retired, money is, at times, scarce. I sold another car to set this one up correctly. Thanks for your help.

DRTRCR22 02-20-2014 10:53 PM


roadkill2 02-21-2014 07:15 AM

OK, this is my nickel's worth . .

You have a system called most of the time, a "Vac-U-Pan" (commercial name) which was first seen about 1970 or so on engine installations by Roy McClintock in Albuquerque and Rehyer-Morrison . . If you have the check valves in the lines to the headers, and a good baffle at the valve covers, you shouldn't suck oil. And if the installation is done correctly, it should pull up to about 5" of vacuum . . again depending on how tight your engine is and how well it's sealed up in the gasket/seal department . .

On the competition, at roundy round races, most of the high buck guys have far more HP than they can get to the right rear tire and use . . make your car handle right up on the cushion, learn to pass where nobody else can, and make more torque than HP out of the corners . . You'll win a lot of races!

jreiley 02-24-2014 03:31 PM

Are you running NASCAR late nodel? We have a 1/2 mile dirt track here running with NASCAR sanctions. Even though I am strictly doing drags, the guys I hang with are all modified or late model racers. They all will tell you that the handling of your car is of paramount importance. The rules for engine builders are about as convoluted as they get. Concentrate on chassis setup and you will do welll. Good luck. BTW onr of my cars is a 406 Dart. We dyno'd, on the dyno not in the car, at 560hp.

DRTRCR22 02-25-2014 06:45 PM


roadkill2 02-27-2014 06:50 AM

If you're a good driver, and know how to set up your ride, then you're wasting your (and our) time asking about "Free" Horsepower . . There ain't no such thing . . You've got the old "budget conundrum" and want to race with a bunch of guys with a lot more money than you have . .

Might as well buy a pair of skates and go play hockey with the Blackhawks . .

On the other hand, even a blind Hog finds an acorn once inna while, if you're of that mind . . Good luck . . .

TheYellaBrick 02-27-2014 03:08 PM

I think the term should be 'freed up' horsepower. Excellent thread with good info from a couple a different views. We can all learn during these discussions. I know I did.

The heart of our passion is getting more with the dollars we each have available. More than a few times the 'little' guy has slain the dragon !

Now LET'S GO RACIN' ! :D :D :D :D

roadkill2 02-28-2014 05:28 AM

Two weeks . . First Test n Tune . . . Go out and see if we can run some 8.80's

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