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Re: Header evac tubes- how do they compare to vac pumps?
[Re: tjmarcus1]
#624314
02/25/10 09:39 PM
02/25/10 09:39 PM
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Joined: Dec 2008
Posts: 603
Central Oregon
Rodney
mopar
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mopar
Joined: Dec 2008
Posts: 603
Central Oregon
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3-5" is about all I've been able to get out of our Areospace vacuum pump we are running on the 572. While running a vacuum pump the engine has to be meticulously sealed. I was talking with tech @ areospace last week about the pump he said the larger engines may not get much more than 5" which is ok with me the main reason we are running it is to control the engine from oil leaks due to the larger stroke. It's doing that  no serious leaks last year... well almost no leaks. plugging the hole where the dip stick went, a Charlies custom oil pan and a new set of Indy valve covers with NO holes except the port for the vacuum made the difference in the pump working or not for us.  we also run the evac tubes on the 500 in the GTX they work great for that application. 
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Re: Header evac tubes- how do they compare to vac pumps?
[Re: tjmarcus1]
#624315
02/25/10 10:32 PM
02/25/10 10:32 PM
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Joined: Jun 2004
Posts: 1,496
Sask, Can.
72demon416
OP
pro stock
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OP
pro stock
Joined: Jun 2004
Posts: 1,496
Sask, Can.
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Quote:
they don't work well with exhaust pipes and mufflers.
Really? I would have thought that a well designed exhaust system with x/h pipe would actually help due to a greater vacuum created by the extra exhaust pulses compared to open headers that only see one bank of cylinders.
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Re: Header evac tubes- how do they compare to vac pumps?
[Re: 72demon416]
#624316
02/25/10 10:51 PM
02/25/10 10:51 PM
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Joined: Nov 2004
Posts: 2,119
sc
tjmarcus1
top fuel
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top fuel
Joined: Nov 2004
Posts: 2,119
sc
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Quote:
Quote:
they don't work well with exhaust pipes and mufflers.
Really? I would have thought that a well designed exhaust system with x/h pipe would actually help due to a greater vacuum created by the extra exhaust pulses compared to open headers that only see one bank of cylinders.
it's been my experience that mufflers and exh. systems create back pressure.
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Re: Header evac tubes- how do they compare to vac pumps
[Re: tjmarcus1]
#624317
02/25/10 11:25 PM
02/25/10 11:25 PM
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Joined: Jun 2004
Posts: 1,496
Sask, Can.
72demon416
OP
pro stock
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OP
pro stock
Joined: Jun 2004
Posts: 1,496
Sask, Can.
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Did you notice any mph difference?
Last edited by 72DEMON416; 02/25/10 11:26 PM.
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Re: Header evac tubes- how do they compare to vac pumps?
[Re: 72demon416]
#624318
02/26/10 12:23 AM
02/26/10 12:23 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:
Quote:
they don't work well with exhaust pipes and mufflers.
Really? I would have thought that a well designed exhaust system with x/h pipe would actually help due to a greater vacuum created by the extra exhaust pulses compared to open headers that only see one bank of cylinders.
In all my testing of the evac systems, the most I could
produce was 5"hg and if you run a exhaust system
that has ANY back pressure it will reduce the effect
of the evac by the same number as the back pressure,
in other words, if your exhaust has 2" hg back pressure
it will reduce the evac by that amount 5"- 2" = 3"
and if the exhaust system is greater than 5" hg it
will back up and burn out the check valve at the
collector and start to pressurize the crank case
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Re: Header evac tubes- how do they compare to vac pumps?
[Re: 72demon416]
#624320
02/26/10 09:42 AM
02/26/10 09:42 AM
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Joined: Oct 2004
Posts: 8,165
Left Coast
BobR
master
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master
Joined: Oct 2004
Posts: 8,165
Left Coast
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Quote:
Quote:
they don't work well with exhaust pipes and mufflers.
Really? I would have thought that a well designed exhaust system with x/h pipe would actually help due to a greater vacuum created by the extra exhaust pulses compared to open headers that only see one bank of cylinders.
It doesn't help. In fact, like stated, it will render your evac system completely useless. IMO they are basically useless anyway. Our vacuum pump pulls 19" of vacuum. All VP's are not created equal.
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Re: Header evac tubes- how do they compare to vac pumps?
[Re: Crizila]
#624322
02/26/10 10:37 AM
02/26/10 10:37 AM
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Joined: Oct 2004
Posts: 8,165
Left Coast
BobR
master
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master
Joined: Oct 2004
Posts: 8,165
Left Coast
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Quote:
Quote:
thanks Raff, It looks like it's almost pointless to run a header evac system when running a exhaust system.
the good part is you just saved me some time and money
I'm sure a pump is the way to go for the serious racer with an engine making big HP, but I'm not sure you can't have your cake and eat it too with an exhaust evac system. I will have my own answers to that question when I'm able to run my car instead of my snow blower - hopefully in a month or two. For now, I know I can pull 10" of H20 at idle with my exhaust system in place. Assume I can pull more vacuum than that with open headers at all engine speeds. Don't have any numbers yet though. Also no info on what will happen at speed with the exhaust system in place - crankcase pressure will likely go positive. I understand the benifits of running a vacuum in the crankcase, but not sure if there is a measureable HP gain between running 5"HG and 15"HG. The only thing sucking around my garage right now is the weather
First, in order to realize any significant power gain the ring pack hass to be optimized for the vacuum-usually a real low tension oil ring. Second, at wot, even on a mechanically sound motor, there will be some blow-by that will quickly overcome the evacs initial vacuum. This even happens with a good pump but the pump has much more capacity than the evac and can handle more blowby before the crankcase gets pressurized. Look at the pro stockers and comp cars. They all use vacuum pumps even though there is a small amount of parasitic loss. For maximum HP there just isn't any comparison.
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Re: Header evac tubes- how do they compare to vac pumps?
[Re: 68LAR]
#624325
02/26/10 10:59 AM
02/26/10 10:59 AM
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Joined: Dec 2008
Posts: 603
Central Oregon
Rodney
mopar
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mopar
Joined: Dec 2008
Posts: 603
Central Oregon
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Quote:
Quote:
As far as how much vacuum is created... It really doesn't matter. Any vacuum is better than pressure. With that, a vacuum pump will use up some horsepower. A tube type evac system doesn't.
Again, my 
you got that right.
even tho my vacuum pump only creates 4-5 " I scraped the oil pan and ground a pretty good hole in it after a pass. didn't realize I did this until I shut the engine off in the pit. The vacuum pump was holding the oil in the pan I guess since the leak didn't start until the engine was shut down once I parked the car.
After I discovered I was pouring oil out of my pan and got a drain pan under it I retraced where I may have hit something. I found the spot in the return lane over 100 yards away 
my only guess was the vacuum was holding the oil in the engine 
What ever caused the oil to not leak until then I was sure glad 
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Re: Header evac tubes- how do they compare to vac pumps?
[Re: Crizila]
#624327
02/26/10 02:45 PM
02/26/10 02:45 PM
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Joined: Jan 2003
Posts: 2,915
A shed in England
Tig
master
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master
Joined: Jan 2003
Posts: 2,915
A shed in England
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We developed a leak at the last race of the season last year. We couldn't get anywhere near our -12in/hg. Car dropped off 1.5mph and 1 tenth, It was all we could put it down to 
'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
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Re: Header evac tubes- how do they compare to vac pumps?
[Re: Tig]
#624328
02/26/10 03:01 PM
02/26/10 03:01 PM
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Joined: Jun 2009
Posts: 644
Minnesota
Barnstorm
mopar
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mopar
Joined: Jun 2009
Posts: 644
Minnesota
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Diff on the dyno[my 2in Hooker super comps] was 11 hp...500in 440-1 motor. No vac readings. Will pull a little oil thru, but I want plenty of oil uptop. I think headder evacs work well. Cheap 11hp.
The little old lady from Pasadena is back!
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Re: Header evac tubes- how do they compare to vac pumps?
[Re: 68LAR]
#624330
02/26/10 05:07 PM
02/26/10 05:07 PM
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Joined: Oct 2004
Posts: 8,165
Left Coast
BobR
master
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master
Joined: Oct 2004
Posts: 8,165
Left Coast
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Quote:
Just curious... Why would any evac system create horsepower? Would it be because the rings seal better? Or the intake? Or is it something else that I'm not seeing or understanding? Help me understand. Thanks,
Crankcase vacuum stabilizes the ringpack and allows a better seal. You should also use a low friction oil control ring and that frees up some more. If the crankcase is pressurized there will be some resistance against the piston bottom as well.
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