Don Terrill’s Speed-Talk

Just curious what benefits do you gain by running a vacuum pump? Why does it actually make better power? How does it help the ring seat?

Also I am curious to here hp/et gains that people have gained. I have one coming and I am hoping that it will help seal up a worn motor. Also any tips to using one will greatly be appreciated. I am new to running one.

Thanks

This thread should answer some of your questions:

https://www.speed-talk.com/forum/viewtopic.p ... acuum+pump

On a nice ,well broken in 406 Chevy that was making 650 HP, The pump was only good for 3 or 4 HP. This was stock rings, no gas ports. On two differant race engines, 043,043 and 3 mm, with gas ports, I saw a 50 plus HP increase. If you dont have any blowby, it almost doed nothing, if you have a real light tension ring package, with gas ports, it can rally make a big differance. I dont know what it will do for your engine.

JOE SHERMAN RACING ENGINES

I have a theory on why it builds hp in loose motors and nothing in tight motors. Could it be introducing vacuum into the crank case helps the engine in the intake stroke by increasing the vacuum in the cylinder. This in turn increases the amount of air/fuel mixture that gets into the cylinder. Maybe even sucks out a little residual exhaust. This would result in a cleaner charge in the cylinder and results in more cylinder pressure. In a sealed up motor nothing is getting by the rings so it doesn't help. What do you guys think, Is this reasonable?

Does nascar or prostock run vacuum pumps?

Also has anybody measured engine vacuum before and after the addition of a vacuum pump?

Are you suggesting the rings would be leaking enough that the vacuum pump creates a higher depression on the intake port?

If the rings are leaking that bad, wouldn't they also be leaking on the compression stroke, and the vacuum pump would increase this leakage, causing most/all of the increased intake charge to be leaked into the pan?
Also if the rings are leaking that much, oil contamination would be a problem.

Randy

Just an idea,

I was thinking that if the crank case has positive pressure,and when the piston comes down on the intake stroke, it could potentially suck in some of the crank case gases thus reducing the vacuum created by the piston coming down, With a vacuum in the crankcase this lose is substantial reduced. You are probably right that it would have to be pretty extreme.

I am not sure what effects a vacuum has on ring seal, but on the compression stroke, positive combustion chamber pressure should assist in ring seal, I would think vacuum would have negative effects on it. Just thinking out load here.

My overly simple mind thinks of the pressure differential (albeit relatively small) created by the vacuum pump. It reduces the pressure on the bottom of the rings, increasing bore seal. Right or wrong, this is my mental model

Steve

Steve, I agree with you. If the pressure below the rings, in the pan, is greater than the pressure above the rings, blow by is increased. I've never run a pump, but do run a gauge. I can only build about 7 inches on the finish line with the manifold vacuum and headers.

I believe the vacuum pump maintains a constant pressure polarity across the ring package thereby preventing ring flutter. Without a vacuum pump, the pressure polarity cycles between more pressure on the chamber side (combustion and exhaust) to more pressure on the crankcase side (intake). As the ring "flutters" from one side of its ring groove to the other to follow the
pressure polarity, its leaks. Of course the inertia of the ring also plays a role in "flutter".

vwbased wrote:I believe the vacuum pump maintains a constant pressure polarity across the ring package thereby preventing ring flutter. Without a vacuum pump, the pressure polarity cycles between more pressure on the chamber side (combustion and exhaust) to more pressure on the crankcase side (intake). As the ring "flutters" from one side of its ring groove to the other to follow the
pressure polarity, its leaks. Of course the inertia of the ring also plays a role in "flutter".

Thats the way I understand it too, it allows you to run a lighter ring tension without getting flutter, and the lighter ring tension gains you power.

Mike

A significant portion of the horsepower your engine makes is lost due to friction and a significant portion of that frictional horsepower loss is attributed to the rings. IMO, the easiest/best way to recover some of that loss is by using low tension rings, gas ports and increased pan vacuum.

With the top ring, the gas ports push the rings out to provide good ring seal on the power stroke and the top ring gets a free ride on the other 3 strokes. The low tension second and oil ring reduce frictional loss and the pan vacuum helps the rings seal to keep oil out of the combustion chamber.

Has anyone tried using a small vbelt driven roots as an evac pump?

Seems like a Eaton M45 used as a vac pump could keep up with ~anything, and is non contact, might even like oil mist...

Should also be ~bulletproof,

Admittedly half baked idea.

banjo wrote:I have a theory on why it builds hp in loose motors and nothing in tight motors. Could it be introducing vacuum into the crank case helps the engine in the intake stroke by increasing the vacuum in the cylinder. This in turn increases the amount of air/fuel mixture that gets into the cylinder. Maybe even sucks out a little residual exhaust. This would result in a cleaner charge in the cylinder and results in more cylinder pressure. In a sealed up motor nothing is getting by the rings so it doesn't help. What do you guys think, Is this reasonable?

Does nascar or prostock run vacuum pumps?

Also has anybody measured engine vacuum before and after the addition of a vacuum pump?

This would actually be easy to verify. All that's needed is to compare air consumption with and without the pan vacuum. In fact, I have such a pair of dyno sheets right here. Sealing the vents on a 4 stage dry sump ~500 HP 6,500 RPM 357 SBC added 30 HP with less than 7" of pan vac. But... Damn! We didn't have the air turbine hooked up!

Edit: Just found another set of sheets: This engine had a conventional ring package and only gained an average of 7 HP from 6,500 to 7,500 (peak gain of 14) but airflow increased an average of 5.75 CFM. That's only ~ 0.8%, so more data is called for, but your theory looks promising banjo. After all, this engine peaked at 598 HP so the power gain was only ~ 1.2%... (Didn't have a gauge hooked up to the pan for this one.)

OK, here's another data point, this time a 15:1 604 c.i. aluminum hemi. It had carburation issues and was not fully sorted at the time but went from 1044 to 1084 HP @ 6,600 RPM when a 3 vane Moroso pump was added, giving ~ 9" Hg. pan vac. The V.E. went up 2.2% on average, with an increase of ~4% from 6,400 to 7,100.

Not only does this support the theory that improved ring seal on the intake stroke is a factor, one could argue it is the entire source of the gain, as a 4% V.E. increase from a previous peak of 113% would equate to 1081 HP, only 3 less than the observed result!

Another thing to consider is the amount of air being moved around by the pistons/rods/crank. The total power consumed by air movement can be significant. The greater the vacuum, the less air being moved....the more power available. Does this make sense?

Ron