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 Post subject: vacuum pump
 Post Posted: Sun Oct 02, 2011 8:34 am 
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when is a vacuum pump needed? will i gain any power from useing one?

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BEST TIME TO DATE 9.99 1/4 MILE @132MPH.


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 Post subject: Re: vacuum pump
 Post Posted: Sun Oct 02, 2011 10:52 am 
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JEFF69Z28 wrote:
when is a vacuum pump needed? will i gain any power from useing one?


"Needed" is a relative term, ie, obviously you don't have to have one but in most cases you can make more power with one than without. A lot of guys that run methanol use them to pull the condensate from the crankcase to keep from milking up the oil.

Evac systems like the ones you see from Moroso, Mr Gasket, etc do the same thing only not as efficient. Evac systems are probably the most cost effective since you can make those up yourself from parts bought locally. The backfire valves I use are made for a 1980s year model Chevy Chevette p/n AV7 in a Standard brand name. The pieces that get welded in the collector are made from a 6 or 8 inch long 1/2" pipe nipple that you can get from your local hardware store then I cut it in half in the center on a 45* angle. Use a drill and die grinder to finish the hole so that that nipple sits in there on a 45* angle. You can go to the Moroso Website and see their assembly instructions to see how to install them.

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 Post subject: Re: vacuum pump
 Post Posted: Mon Oct 03, 2011 5:03 am 
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I use the header evac system I got from moroso.is there any signficant gains by useing a vac pump.

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JEFF WINTERS
1986 SS MONTE CARLO
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BEST TIME TO DATE 9.99 1/4 MILE @132MPH.


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 Post subject: Re: vacuum pump
 Post Posted: Mon Oct 03, 2011 8:59 am 
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JEFF69Z28 wrote:
I use the header evac system I got from moroso.is there any signficant gains by useing a vac pump.


From what I've read there is much more vacuum pulled on the system with a pump. So much so that a relief valve is usually installed in the opposite valve cover and different crankshaft seals are made for this application. I've also heard that there is a HP gain but I don't have specific dyno numbers to back that up.

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 Post subject: Re: vacuum pump
 Post Posted: Tue Oct 11, 2011 9:26 pm 
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You should realize HP gains from for two reasons.
The higher the vacuum you pull on the crankcase allows your rings to seal better.
Secondly with a negative pressure on the crankcase you can run a lighter tension and a narrower ring pack which results in much less friction which frees up horsepower.
One of the draw backs of lots of vacuum is it removes enough of the oil mist from the crankcase that moving parts that depend on this mist for lubrication can suffer from lack of lubrication.
Specifically rod bushings and the pins in pistons if not fed oil from the oil ring land.
Due to this lack of oil mist it is a good idea to open up the rod pin bushing clearance.
I run my vacuum at 8-9" and run my rod bushings at .0015 I have ran higher vacuum and have pulled the bushings out of the rod.
Depending on the size of engine and ring package you should be able to gain 12 or more HP.

With standard rings generally the exhaust vacuum system is quite sufficient.

Hope this is of some help.

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 Post subject: Re: vacuum pump
 Post Posted: Thu Oct 13, 2011 1:32 pm 
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To add to others comments ...
One of the biggest gains IMO from a vacuum pump is the reduced pumping losses inside the crankcase. When the pistons are going up and down they are not just pumping air into and out of the engine thru the heads, they are pumping air from the bottom side of the pistons between cylinders on the crankcase side. Moving that air around takes power and is nothing but a HP loss. With vacuum the air density is much less resulting in reduced HP pumping losses. The crankshaft spins in the vacuum easier also. That pumped crankcase air also causes a lot of extra oil to be carried with it making the windage problem worse.

My 414sbc (normal tension rings) gained ~15-20HP with the vacuum pump around 7000rpm. Higher rpm engines gain more, if you have lighter tension rings you will gain more.

Rick


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 Post subject: Re: vacuum pump
 Post Posted: Sun Oct 16, 2011 8:09 am 
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We saw a 13 HP increase on the dyno connecting the V-pump belt and pulling 11 Hg on an 800 HP engine.

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 Post subject: Re: vacuum pump
 Post Posted: Sun Oct 23, 2011 11:53 am 
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Should you have your relief valve and pulley setup so your against the relief valve from the point you get on the transbrake? So that it maintains the same level of vacuum the whole run, every run? Just thinking would eliminate any potential repeatability issues due to varying vacuum levels if it is allowed to ramp up during the run.

Tanner

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 Post subject: Re: vacuum pump
 Post Posted: Wed Nov 23, 2011 12:09 pm 
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I did some testing on a chassis dyno years ago and on several engines I saw over 25 rwhp. The lowest gain I ever saw was 15 rwhp. Testing done on a DynoJet 248.


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