Hello! Log in or Register   |  Help  |  Donate  |  Buy Shirts See all banner ads | Advertise on TheSamba.com  
TheSamba.com
 
Air pressure in engine compartment
Page: 1, 2  Next
Forum Index -> Performance/Engines/Transmissions Share: Facebook Twitter
Reply to topic
Print View
Quick sort: Show newest posts on top | Show oldest posts on top View previous topic :: View next topic  
Author Message
many408
Samba Member


Joined: September 28, 2009
Posts: 38

many408 is offline 

PostPosted: Thu Jul 24, 2014 1:18 am    Post subject: Air pressure in engine compartment Reply with quote

I'm wondering how much the carbs are affected by the engine fan sucking air out of the engine compartment.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
kielbasa
Samba Member


Joined: November 28, 2007
Posts: 1443
Location: Garbage Grove, CA
kielbasa is offline 

PostPosted: Thu Jul 24, 2014 1:24 am    Post subject: Reply with quote

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
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Brian
Samba Moderator


Joined: May 28, 2012
Posts: 8340
Location: Oceanside
Brian is offline 

PostPosted: Thu Jul 24, 2014 1:44 am    Post subject: Reply with quote

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
Back to top
View user's profile Send private message Send e-mail Visit poster's website Gallery Classifieds Feedback
Eaallred
Samba Member


Joined: May 18, 2003
Posts: 5756
Location: West Valley City, Utah
Eaallred is offline 

PostPosted: Thu Jul 24, 2014 5:51 am    Post subject: Reply with quote

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.
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
wcfvw69 Premium Member
Samba Purist


Joined: June 10, 2004
Posts: 13385
Location: Arizona
wcfvw69 is offline 

PostPosted: Thu Jul 24, 2014 6:28 am    Post subject: Reply with quote

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]
Follow me on instagram @sparxwerksllc

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**
**Restored German Pierburg fuel pumps for sale or I can restore yours**
**Restored Porsche fuel pumps or I can restore yours**
**Restored Porsche distributors or I can restore yours**
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
VWCOOL
Samba Member


Joined: June 02, 2006
Posts: 1821
Location: Down under
VWCOOL is offline 

PostPosted: Thu Jul 24, 2014 6:34 am    Post subject: Reply with 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

Yes, the later engine lids have more holes for more air but the real benefits are for the cooling

But every little bit helps Wink
Back to top
View user's profile Send private message Gallery Classifieds Feedback
74 Thing
Samba Member


Joined: September 02, 2004
Posts: 7374

74 Thing is online now 

PostPosted: Thu Jul 24, 2014 7:05 am    Post subject: Reply with quote

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.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Hotrodvw
Samba Member


Joined: July 06, 2004
Posts: 6327
Location: Orygun
Hotrodvw is offline 

PostPosted: Thu Jul 24, 2014 1:19 pm    Post subject: Reply with quote

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!

Hose & Fittings
Back to top
View user's profile Send private message AIM Address Gallery Classifieds Feedback
chrisflstf
Samba Member


Joined: February 10, 2004
Posts: 3413
Location: San Diego
chrisflstf is offline 

PostPosted: Thu Jul 24, 2014 1:25 pm    Post subject: Reply with quote

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
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Glenn Premium Member
Mr. 010


Joined: December 25, 2001
Posts: 76760
Location: Sneaking up behind you
Glenn is offline 

PostPosted: Thu Jul 24, 2014 1:29 pm    Post subject: Reply with quote

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
Back to top
View user's profile Send private message Send e-mail Visit poster's website Gallery Classifieds Feedback
Anvil
Samba Member


Joined: September 28, 2009
Posts: 248
Location: Golden, Colorado
Anvil is offline 

PostPosted: Thu Jul 24, 2014 3:53 pm    Post subject: Reply with quote

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.
Back to top
View user's profile Send private message Visit poster's website Facebook Gallery Classifieds Feedback
Hotrodvw
Samba Member


Joined: July 06, 2004
Posts: 6327
Location: Orygun
Hotrodvw is offline 

PostPosted: Thu Jul 24, 2014 3:56 pm    Post subject: Reply with quote

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!

Hose & Fittings
Back to top
View user's profile Send private message AIM Address Gallery Classifieds Feedback
Eaallred
Samba Member


Joined: May 18, 2003
Posts: 5756
Location: West Valley City, Utah
Eaallred is offline 

PostPosted: Thu Jul 24, 2014 4:23 pm    Post subject: Reply with quote

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.
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
Hotrodvw
Samba Member


Joined: July 06, 2004
Posts: 6327
Location: Orygun
Hotrodvw is offline 

PostPosted: Thu Jul 24, 2014 4:25 pm    Post subject: Reply with quote

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
Back to top
View user's profile Send private message AIM Address Gallery Classifieds Feedback
modok
Samba Member


Joined: October 30, 2009
Posts: 26743
Location: Colorado Springs
modok is offline 

PostPosted: Thu Jul 24, 2014 6:10 pm    Post subject: Reply with quote

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 Shocked

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.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Joel
Samba Member


Joined: September 04, 2006
Posts: 11099
Location: NSW Australia
Joel is offline 

PostPosted: Thu Jul 24, 2014 11:20 pm    Post subject: Reply with quote

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. Rolling Eyes
_________________
Quick little bug, you got a Porsche motor in that?
1974 Germanlook 1303 2.5 Suba-Beetle
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Brian
Samba Moderator


Joined: May 28, 2012
Posts: 8340
Location: Oceanside
Brian is offline 

PostPosted: Fri Jul 25, 2014 12:54 am    Post subject: Reply with quote

Speaking of problems:
Image may have been reduced in size. Click image to view fullscreen.


(All about that open air)
_________________
Wash your hands

'69 Bug
'68 Baja Truck
'71 Bug
'68 Camper

Only losers litter
Back to top
View user's profile Send private message Send e-mail Visit poster's website Gallery Classifieds Feedback
itHaKa
Samba Member


Joined: February 20, 2008
Posts: 254
Location: Argentina
itHaKa is offline 

PostPosted: Fri Jul 25, 2014 8:53 pm    Post subject: Reply with quote

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


Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.

_________________
76x88 , 1849cc engine build :
http://mundoescarabajo.com.ar/me/viewtopic.php?t=635
Back to top
View user's profile Send private message Visit poster's website Gallery Classifieds Feedback
gt1953
Samba Member


Joined: May 08, 2002
Posts: 13843
Location: White Mountains Arizona
gt1953 is offline 

PostPosted: Sun Jul 27, 2014 8:12 am    Post subject: Reply with quote

What I have done with the dual carbed engines is open the engine lid at the bottom. The result is oil temps lower which to me means more air to the compartment. So the carbs probably are not getting starved.

http://www.thesamba.com/vw/forum/album_page.php?pic_id=1236483
http://www.thesamba.com/vw/forum/album_page.php?pic_id=1236484
http://www.thesamba.com/vw/forum/album_page.php?pic_id=1236481
http://www.thesamba.com/vw/forum/album_page.php?pic_id=1236482

http://www.thesamba.com/vw/forum/album_page.php?pic_id=1236480
_________________
Volkswagen: We tune what we drive.
Numbers Matching VW's are getting harder to find. Source out the most Stock vehicle and keep that way. You will be glad you did.

72 type 1
72 Squareback
({59 Euro bug, 62, 63, 67, 68, 69, 73 type ones 68 & 69 type two, 68 Ghia all sold})


Last edited by gt1953 on Sun Jul 27, 2014 9:33 am; edited 1 time in total
Back to top
View user's profile Send private message Gallery Classifieds Feedback
theDrew
Samba Member


Joined: May 17, 2011
Posts: 1155
Location: Camas, WA
theDrew is offline 

PostPosted: Sun Jul 27, 2014 9:16 am    Post subject: Reply with quote

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
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Display posts from previous:   
Reply to topic    Forum Index -> Performance/Engines/Transmissions All times are Mountain Standard Time/Pacific Daylight Savings Time
Page: 1, 2  Next
Page 1 of 2

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum

About | Help! | Advertise | Donate | Premium Membership | Privacy/Terms of Use | Contact Us | Site Map
Copyright © 1996-2023, Everett Barnes. All Rights Reserved.
Not affiliated with or sponsored by Volkswagen of America | Forum powered by phpBB
Links to eBay or other vendor sites may be affiliate links where the site receives compensation.