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many408 Samba Member
Joined: September 28, 2009 Posts: 38
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Posted: Thu Jul 24, 2014 1:18 am Post subject: Air pressure in engine compartment |
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I'm wondering how much the carbs are affected by the engine fan sucking air out of the engine compartment. |
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kielbasa Samba Member
Joined: November 28, 2007 Posts: 1443 Location: Garbage Grove, CA
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Posted: Thu Jul 24, 2014 1:24 am Post subject: |
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I will go out on a limb here and say ZERO _________________ Gotta give my props to:
Wolfsburg Motorsports
Dubbers Toy Box
Jeff's VW Speed and Fab
4inbore.com
Kielbasa Industries |
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Brian Samba Moderator
Joined: May 28, 2012 Posts: 8340 Location: Oceanside
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Posted: Thu Jul 24, 2014 1:44 am Post subject: |
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Biggest restriction for input air flow is probably the air filter. _________________ Wash your hands
'69 Bug
'68 Baja Truck
'71 Bug
'68 Camper
Only losers litter |
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Eaallred Samba Member
Joined: May 18, 2003 Posts: 5756 Location: West Valley City, Utah
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Posted: Thu Jul 24, 2014 5:51 am Post subject: |
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Engine bay vacuum is a major issue that most people overlook. It affects engine cooling by a very significant amount. _________________ Eric Allred
You have to remember something: Everybody pities the weak; Jealousy you have to earn. |
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wcfvw69 Samba Purist
Joined: June 10, 2004 Posts: 13385 Location: Arizona
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Posted: Thu Jul 24, 2014 6:28 am Post subject: |
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Eaallred wrote: |
Engine bay vacuum is a major issue that most people overlook. It affects engine cooling by a very significant amount. |
Totally agree. There's a reason so many folks run convertible engine lids on non-convertible bodies when running larger engines. This is really true of the BIG engines w/air thirsty dual carbs. Even folks running 1600's in early 60's bugs found out they needed more air.
The German's figured this out, that's why they started punching in the vents in the engine lids on sedans. The 1500 single port engines were known to run a bit hotter and if I remember correctly, the 1970 bugs with the pre-doghouse shrouds had the vented lids first to try and help cool them off a bit. This allowed enough air for the fan to work correctly and made an impact on the cooling of the engine. When they went to the doghouse fan shroud to help further with engine cooling, the vents were really needed to allow enough air into the engine compartment. The Germans put even more rows of vents (from two to four) I think in 73 to further help keep engine temps at bay with the increase to the 1600CC engine.
I stuck a OE convertible engine lid on my 67 sedan and noticed a drop in engine oil temperatures. I also noticed the extra air circulating in the engine compartment cooled off the ancillary items bolted to the engine. It no long vapor locked in 100 degree plus heat. I'm sure letting the cooler air in helped the engine and ancillary parts not sit in a closed, heat sink environment. _________________ Contact me at [email protected]
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Decades of VW and VW parts restoration experience.
The Samba member since 2004.
**Now rebuilding throttle bodies for VW's and Porsche's**
**Restored German Bosch distributors for sale or I can restore yours**
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**Restored Porsche fuel pumps or I can restore yours**
**Restored Porsche distributors or I can restore yours** |
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VWCOOL Samba Member
Joined: June 02, 2006 Posts: 1821 Location: Down under
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Posted: Thu Jul 24, 2014 6:34 am Post subject: |
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The relatively tiny amount of air - at high vacuum - consumed by the carbs is not affected by the relatively huge amount of air - at low vacuum - consumed by the fan
Yes, the later engine lids have more holes for more air but the real benefits are for the cooling
But every little bit helps |
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74 Thing Samba Member
Joined: September 02, 2004 Posts: 7374
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Posted: Thu Jul 24, 2014 7:05 am Post subject: |
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If you are running dual carbs on an early VW that does not already have modifications to the engine lid to allow for more air then most likely you will have to make some changes to allow more air into the engine compartment (this is especially important on convertibles with the top down). If you don't drive a lot of miles you will not notice it, but if you drive 30, 40, 50+ miles on the highway in hot temp you will notice it right away.
You should look up Eric Allreds post years ago on "engine bay vacuum" and his water bottle and hose test. |
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Hotrodvw Samba Member
Joined: July 06, 2004 Posts: 6327 Location: Orygun
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Posted: Thu Jul 24, 2014 1:19 pm Post subject: |
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People forget that the stock air intake grill on a VW is designed to provide enough air for a stock carb and the cooling fan to cool the engine. You go adding dual carbs (4x the CFM over stock) and all of a sudden that stock intake grill under the window is too small. _________________ '67 Sunroof
Eric
78x94 with IDA's....oober fun
Horsepower is an addiction........Addictions cost
lots of money!
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chrisflstf Samba Member
Joined: February 10, 2004 Posts: 3413 Location: San Diego
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Posted: Thu Jul 24, 2014 1:25 pm Post subject: |
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Quote: |
The relatively tiny amount of air - at high vacuum - consumed by the carbs is not affected by the relatively huge amount of air - at low vacuum - consumed by the fan |
Thats a bunch of BS |
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Glenn Mr. 010
Joined: December 25, 2001 Posts: 76760 Location: Sneaking up behind you
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Posted: Thu Jul 24, 2014 1:29 pm Post subject: |
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I've seen cars with non vented decklids get sucked down when you goose the gas on a stroker engine with dual IDAs.
They certainly can rob the fan and decrease engine cooling. _________________ Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
Member #1009
#BlueSquare |
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Anvil Samba Member
Joined: September 28, 2009 Posts: 248 Location: Golden, Colorado
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Posted: Thu Jul 24, 2014 3:53 pm Post subject: |
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An engine is just a glorified air pump so it makes sense that the bigger and faster the pump, the more air it's going to need. A 2332 @ 6500-rpm would consume over 200-cfm of air through the carbs whereas a 1600 @ 4500-rpm would only require about 100-cfm. I don't know how much extra capacity the VW engineers built into the system, but it doesn't take a math genius to see that a bigger, more powerful engine has the potential to stress the supply system. _________________ A man with any character at all must have enemies and places he is not welcome—in the end we are not only defined by our friends, but those aligned against us. |
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Hotrodvw Samba Member
Joined: July 06, 2004 Posts: 6327 Location: Orygun
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Posted: Thu Jul 24, 2014 3:56 pm Post subject: |
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My IDAs are rated for up to 1100+ cfm.... _________________ '67 Sunroof
Eric
78x94 with IDA's....oober fun
Horsepower is an addiction........Addictions cost
lots of money!
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Eaallred Samba Member
Joined: May 18, 2003 Posts: 5756 Location: West Valley City, Utah
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Posted: Thu Jul 24, 2014 4:23 pm Post subject: |
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By the time VW finished the aircooled Beetle, it had the louvers under the window, four sets in the decklid, and another behind the license plate.
That was all for a bone stock 48HP 1600 with a doghouse.
Put a big motor in an earlier sedan with no provisions to get more air into the engine bay and you're asking for trouble. _________________ Eric Allred
You have to remember something: Everybody pities the weak; Jealousy you have to earn. |
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Hotrodvw Samba Member
Joined: July 06, 2004 Posts: 6327 Location: Orygun
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Posted: Thu Jul 24, 2014 4:25 pm Post subject: |
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Yup..If you read the updates as the new models were released, it states that air louvers in the deck lid were installed to accommodate for the larger engine needs. _________________ '67 Sunroof
Eric
78x94 with IDA's....oober fun
Horsepower is an addiction........Addictions cost
lots of money!
Hose & Fittings |
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modok Samba Member
Joined: October 30, 2009 Posts: 26743 Location: Colorado Springs
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Posted: Thu Jul 24, 2014 6:10 pm Post subject: |
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To answer the question........air pressure? negligible. Even several inches of water vac is not enough to feel.
However temperature?? temperature is critical. If there is not enough flow of fresh air into/through the engine compartment then it will tend to get very hot in there. A few inches water of vac will cause it to re-circulate quite a bit even with all stock baloney on place. When the carbs get over 100 degrees you will feel the loss of power and it tends to go rich. Two carbs are twice as sensitive to being too hot then one.
PITA today when it's 95 degrees
I hear a lot of berg coming through here. Now you know the real reasons for what he describes as the fan stealing the air. He wasn't a scientist but he was honest about what he observed. |
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Joel Samba Member
Joined: September 04, 2006 Posts: 11099 Location: NSW Australia
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Posted: Thu Jul 24, 2014 11:20 pm Post subject: |
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Eaallred wrote: |
Put a big motor in an earlier sedan with no provisions to get more air into the engine bay and you're asking for trouble. |
Trouble is too many people listen to these keyboard mechanics with their oh i've run like that for years with no probems crap.
Most of them it takes the car bursting into flames before they realise anything is even wrong. _________________ Quick little bug, you got a Porsche motor in that?
1974 Germanlook 1303 2.5 Suba-Beetle |
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Brian Samba Moderator
Joined: May 28, 2012 Posts: 8340 Location: Oceanside
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itHaKa Samba Member
Joined: February 20, 2008 Posts: 254 Location: Argentina
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Posted: Fri Jul 25, 2014 8:53 pm Post subject: |
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Eaallred wrote: |
By the time VW finished the aircooled Beetle, it had the louvers under the window, four sets in the decklid, and another behind the license plate.
That was all for a bone stock 48HP 1600 with a doghouse.
Put a big motor in an earlier sedan with no provisions to get more air into the engine bay and you're asking for trouble. |
x2
pics of the late itamar fusca, 1600 dual carbed had a thermostat controlled louver behind the license plate
_________________ 76x88 , 1849cc engine build :
http://mundoescarabajo.com.ar/me/viewtopic.php?t=635 |
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gt1953 Samba Member
Joined: May 08, 2002 Posts: 13843 Location: White Mountains Arizona
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theDrew Samba Member
Joined: May 17, 2011 Posts: 1155 Location: Camas, WA
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Posted: Sun Jul 27, 2014 9:16 am Post subject: |
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My experience with the doghouse fan is that it can really suck! On the 3rd test drive of my 2276, I hit 6500rpm and BANG! it managed to suck a loose wire in and then pulled the wiring harness into the fan and destroy it all. Now I have a lot more respect for it and use 2x the number of zip ties! _________________ Turbo 2276 MS3X build http://www.thesamba.com/vw/forum/viewtopic.php?t=673125
1985 Vanagon Campmobile w/ 2005 EJ25 |
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