horsepower gain from a vacuum pump

[chevy art]

friend of mine said that just adding a vacuum pump to a sbc race engine can add 40 horsepower . is that true? if so, how or why? thanks art

[maxracesoftware]

friend of mine said that just adding a vacuum pump to a sbc race engine can add 40 horsepower . is that true? if so, how or why? thanks art

yes it can add 40 HP on a bad Pan design or with other problems

if the Vacuum Pump adds much more than 25 HP or so on a 700+ HP V8
that can mean your Oil Pan design is not good enough or there are oil control or drain-back issues

[panic]

True, that.
Also relevant: the basic block design has an effect; larger volume has smaller pressure spikes.
The crankcase volume proper consists of:
» the empty space in the oil pan above the oil level
» the empty space surrounding the crankshaft
» the empty space inside the cylinders below the pistons (including the piston interiors)
The engine’s total internal volume also includes the empty space inside the valve cover(s) and inside the pushrod/valley compartment, but these are only remotely connected to the crankcase through the pushrod clearance and drain holes.
Stroked low deck engines (Windsor 347) are more prone to pressure-related problems than stock stroke tall engines (BBM 440).

[andyf]

Lots of dyno tests on that question. A 40 hp gain would require a really bad oil pan design or a bad crankcase design. You might see a gain that big on a really large engine with a small oil pan. Maybe a 572 Chevy BB with a stock pan or something like that. Here is a dyno test that I just did for Car Craft: http://www.hotrod.com/articles/dyno-tes ... ake-power/

[Cougar5.0]

Lots of dyno tests on that question. A 40 hp gain would require a really bad oil pan design or a bad crankcase design. You might see a gain that big on a really large engine with a small oil pan. Maybe a 572 Chevy BB with a stock pan or something like that. Here is a dyno test that I just did for Car Craft: http://www.hotrod.com/articles/dyno-tes ... ake-power/

Excellent info, thanks for sharing.

[ptuomov]

Would a reasonable starting point for this sort of estimate be an approximate formula for crankcase pumping work done? Then reducing the density in that formula based on how much vacuum one plans to pull?

[randy331]

Would a reasonable starting point for this sort of estimate be an approximate formula for crankcase pumping work done? Then reducing the density in that formula based on how much vacuum one plans to pull?

I don't think you can put a simle formula to it.
I have one engine that doesn't show any power gain with vacuum, and I don't know why. It had a big deep dyno oil pan on it the frist time vacuum was tried. Pulled 13" but no gain in a-b-a testing with/without vacuum. I sealed the engine up better and tested again. 15''-16'' vacuum this time, but no power gain. Tried it later with a smaller chassis pan. (just a cheap one from competition products that fits a nova) and a different vacuum pump, still no power gain with vacuum. Still don't know why.

Every other engine I've seen vacuum on, gained something. Even without thin rings they have gained some power.
My son's 355 gained 15 HP with vacuum, 1/16 1/16 3/16 non low tension rings.

Workin on a 468 cube pullin truck engine and a 421 cube pullin truck engine currently, and both will get vacuum tried when dynoed.

Randy

[ptuomov]

Would a reasonable starting point for this sort of estimate be an approximate formula for crankcase pumping work done? Then reducing the density in that formula based on how much vacuum one plans to pull?

I don't think you can put a simle formula to it.
I have one engine that doesn't show any power gain with vacuum, and I don't know why. It had a big deep dyno oil pan on it the frist time vacuum was tried. Pulled 13" but no gain in a-b-a testing with/without vacuum. I sealed the engine up better and tested again. 15''-16'' vacuum this time, but no power gain. Tried it later with a smaller chassis pan. (just a cheap one from competition products that fits a nova) still no power gain with vacuum. Still don't know why.

Every other engine I've seen vacuum on, gained something. Even without thin rings they have gained some power.
My son's 355 gained 15 HP with vacuum, 1/16 1/16 3/16 non low tension rings.

Randy

I said as a starting point. There are a couple of approximate crankcase pumping formulas that people have developed. The key parameters are crankcase gas density, rpm, stroke, bore, engine configuration (e.g., cross-plane V8), and _importantly_ the size of the openings between the crankcase bays. If there are very large breathing areas between bays, the crankcase pumping losses are small. If they are small, then the crankcase breathing losses can be large. Reducing the crankcase gas density will make a small difference in the first case and a large difference in the second case. It could be that the breathing areas between bays in the engine in question are very large to start with, and that's why there's not big power gain. And the vacuum pump consumes some power as well. In my opinion, this is the sort of a situation in which simple formula is better than no formula, but obviously the simple formula isn't going to be the final answer.

Any chance that the vacuum pump had a problem and ended up eating a lot more power than they usually do? Just thinking out loud.

[randy331]

Well, like I said, I tried 2 different vacuum pumps on it and no gain. Both pumps gained power on several other engines, and they pulled just as much vacuum on my engine that didn't gain as they did on other engines.

All the formulas about gas pumping etc don't explain that one.

Randy

[ptuomov]

Well, like I said, I tried 2 different vacuum pumps on it and no gain. Both pumps gained power on several other engines, and they pulled just as much vacuum on my engine that didn't gain as they did on other engines. All the formulas about gas pumping etc don't explain that one. Randy

I missed that you tried two different pumps, just saw two different pans being tried.

I agree that a crankcase pumping loss formula isn't going to explain that result. No formula is ever going to explain everything all the time, the world is too complex and has too many moving parts.

[randy331]

Well, like I said, I tried 2 different vacuum pumps on it and no gain. Both pumps gained power on several other engines, and they pulled just as much vacuum on my engine that didn't gain as they did on other engines. All the formulas about gas pumping etc don't explain that one. Randy

I missed that you tried two different pumps, just saw two different pans being tried.

I agree that a crankcase pumping loss formula isn't going to explain that result. No formula is ever going to explain everything all the time, the world is too complex and has too many moving parts.

I have theories about it. LOL

Randy

[GRTfast]

I agree that a crankcase pumping loss formula isn't going to explain that result. No formula is ever going to explain everything all the time, the world is too complex and has too many moving parts.

There is a saying that we in the engineering group at work use all the time.....

All models are wrong, some are useful.

[bigjoe1]

It is pretty common to not get much if any HP increase when you put a vac pump on a good stock type short block. I have dyno tested many of these pumps over the years, and 15 or 20 horsepower is a very common gain. On a specially built drag race engine, when I removed the pump, it lost over 50 horsepower. This engine only used two rings but was gas ported ( vertical ) BB Chevys are much more likely to see a big gain than most small blocks




JOE SHERMAN RACING

[Star Hg]

Let me try to explain this by pointing out just a couple of simple accepted observations and considerations. Gains from vacuum are like a jigsaw puzzle. There are several reasons for the HP increase, put them all together and you get to see the big picture. The largest piece of this puzzle is low tension rings. With all things being equal, HP gains with respect to vacuum will be proportional to displacement because the bore is typically larger so there is more ring area. As mentioned above, excessive windage due to a poorly designed pan generally responds positively to vacuum. Windage is oil suspended in air. The higher the vacuum, the less air is present resulting in less windage. Reduced windage is just one of the many pieces of the vacuum puzzle.
As with any component driven off the crank, like your pay check, there is a gross and a net gain. Generating the vacuum is not free (unless you are generating the vacuum by something that is NOT driven off the crank). A mechanical vac pump is not a perpetual motion device. If you want to experience the largest net, you will need the most efficient vac pump.
One paragraph doesn't even scratch the surface of the crankcase vacuum topic but I hope this helps.

Steve/Star Machine

[BILL-C]

We had a vac pump equipped sbc 406 on dyno yesterday. After noticing this thread i decided to remove pump on last pull and share results. Engine is simple bracket race engine, 23* heads, 12.6 cr Mahle pistons with 1.5,1.5,3mm ring pack. Moroso box style oil pan with power kickout. At 5000 rpm start of test, hp dropped from 518.2 to 515.6 .At 7000 rpm, the peak hp dropped from 673.1 to 658.6. There was 10" vac at 5000 rpm and went to 12" at 7k. Vac pump also caused oil pressure to drop approx .75 psi per inch of crankcase vac.