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roadkill2 02-12-2014 06:01 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 01:39 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 03:10 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 04:46 AM

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

roadkill2 02-14-2014 06:52 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 07:01 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 07:27 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 10:32 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 11:09 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 02:50 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.

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