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Upgrading to Dog House air flow question
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Mr.Duncan
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PostPosted: Wed Sep 30, 2015 8:03 am    Post subject: Upgrading to Dog House air flow question Reply with quote

While my Ghia body is getting blasted, I am going to replace the dead 1300cc SP engine with a 1600SP engine (all new) with Dog House cooling system, with the larger fan.

I know these draw in MUCH more air, and the restricted flow from the stock decklid may be an issue.

Should I cut out the "rain tray" that's in my stock 1966' Decklid to match the later 71+ Ghia deck lids?

I don't mind cutting it, and smoothing the edges out, you wont really "see it" and while its at the body shop they can make it look better.


I'd rather not have decklid standoffs.

Also down here in Texas its hard to find a 71+ Decklid.
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jpjohns
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PostPosted: Wed Sep 30, 2015 9:23 am    Post subject: Reply with quote

I doubt you need to cut anything, the engine area isn't completely sealed off anyway. The fan will move the air.
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c21darrel
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PostPosted: Wed Sep 30, 2015 10:40 am    Post subject: Reply with quote

Im running a stroker, 2017, dual dellorto 40's, Thing doghouse shroud with the earlier decklid. Concur, you shouldnt need to cut your decklid up.
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Mr.Duncan
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PostPosted: Wed Sep 30, 2015 11:23 am    Post subject: Reply with quote

c21darrel wrote:
Im running a stroker, 2017, dual dellorto 40's, Thing doghouse shroud with the earlier decklid. Concur, you shouldnt need to cut your decklid up.


Hmm.. Ill try it out and see how temps are.

I just find it Odd VW opened the lid up more in 71' when they made the bigger fan.
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rcooled
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PostPosted: Wed Sep 30, 2015 1:03 pm    Post subject: Reply with quote

Lots of differing opinions on this issue. Many say that swapping out a 1200/1300/1500 for a 1600 (or larger) motor with a doghouse shroud will require more air flow into the engine bay. This seems to be a more widely-debated question in the Beetle world, where propping open the engine lid is a popular option.

I doubt that the clever engineers at VW who calculated the air flow needs for the 1200/1300/1500 motors designed the system to operate on the ragged edge and provide just barely enough air for these motors to cool properly. Nowadays at least, air flow systems like this are typically designed to provide 2X or 3X the minimum requirement as a safety factor. I would like to think that VW thought along the same lines.

Just as a point of reference, my '67 with a 1600 dp w/doghouse cooler and dual carbs never runs hot, and I've done nothing to increase air flow into the engine bay. My oil temp tops out at 188° after a 45min. run at freeway speeds in 72° ambient air. The highest oil temp I've ever seen was 207° after a 7 mile run up a hill from sea level to 2000' in 90° ambient air. The temps were taken using a digital temperature probe placed right into the sump thru the dipstick tube immediately after the car was stopped.

Don't cut anything, but make sure all your tin is properly installed (Hoover Bit included), the engine compartment seals are in good shape, and the flaps & thermostat are in good working order.
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Last edited by rcooled on Wed Sep 30, 2015 1:11 pm; edited 1 time in total
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Mr.Duncan
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PostPosted: Wed Sep 30, 2015 1:08 pm    Post subject: Reply with quote

rcooled wrote:

Don't cut anything, but make sure all your tin is properly installed (Hoover Bit included), the engine compartment seals are in good shape, and the flaps & thermostat are in good working order.



Thank you for your response, I really appreciate it.

I am a big believer in thermostat flaps & hoover bits. (along with OEM tin)

I use them in all my engines.
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olspeed
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PostPosted: Wed Sep 30, 2015 1:43 pm    Post subject: Reply with quote

I've run a dog house dual port since about 85 when the stock 1300 gave out it's never had any problems. It now has a 1904 with dual 44 webers that was installed in 2001 and I have run it with the deck lid in the stock position and with stand offs with no difference in performance or cooling... where I live cooling is not an issue, as stated before just make sure that all the seals and tin ware is there and you should be fine.
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didget69
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PostPosted: Wed Sep 30, 2015 8:25 pm    Post subject: Reply with quote

The air volume in the KG engine bay remained the same through the years. You shouldn't have any problems.

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PostPosted: Thu Oct 01, 2015 12:00 am    Post subject: Reply with quote

Somebody did some testing with a homebuilt apparatus (plastic tubing and a jar of liquid) and found that at high engine rpm the air pressure in the engine compartment dropped significantly enough that they suspected the stock air inlet on the early decklid wasn't supplying as much air as their non-stock engine really needed to feed twin carbs and a later cooling fan.

When they opened up the top of the decklid, their engine compartment air pressure readings increased seeming to validate their suspicions.
I unfortunately can't tell you where I read it. It was late and I had done a lot of searching and reading. I KNOW I didn't imagine it though! The former science teacher in me thinks it would be an interesting experiment to duplicate!

I lifted the top edge of my decklid about 3/4" because I was setting off my "Save a Bug" temp meter going up long mountain passes in hot summer weather and I have twin dual throat carbs, larger engine and the later fan. After lifting the decklid, I never saw the light flicker again. I also suspect I was running too heavy an oil.

You might also consider adding a velocity ring to your fan shroud. During the last 5 years of US Beetle production, VW added a velocity ring to the intake of the fan shroud to lower cylinder head temps. Either find a late model fan shroud, or purchase the ring itself from an aftermarket parts vendor and install it on your shroud. It functions in a similar fashion to the velocity stacks on twin carb set ups. The ring "organizes" the incoming air and speeds it up by reducing turbulence. More air volume moving faster cools things down more (as long is there is a way for the air to get into the engine compartment). ; )
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PostPosted: Thu Oct 01, 2015 6:20 am    Post subject: Reply with quote

I believe (just my opinion) that propping engine lids or using standoffs are for those that want to show off. If you put a huge engine in your VW, by propping the lid everyone looks and it gives you the attention you are craving. Very Happy
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PostPosted: Thu Oct 01, 2015 11:06 am    Post subject: Reply with quote

mfitzsimor wrote:
Somebody did some testing with a homebuilt apparatus (plastic tubing and a jar of liquid) and found that at high engine rpm the air pressure in the engine compartment dropped significantly enough that they suspected the stock air inlet on the early decklid wasn't supplying as much air as their non-stock engine really needed to feed twin carbs and a later cooling fan.

When they opened up the top of the decklid, their engine compartment air pressure readings increased seeming to validate their suspicions.
I unfortunately can't tell you where I read it. It was late and I had done a lot of searching and reading. I KNOW I didn't imagine it though! The former science teacher in me thinks it would be an interesting experiment to duplicate!

I lifted the top edge of my decklid about 3/4" because I was setting off my "Save a Bug" temp meter going up long mountain passes in hot summer weather and I have twin dual throat carbs, larger engine and the later fan. After lifting the decklid, I never saw the light flicker again. I also suspect I was running too heavy an oil.

You might also consider adding a velocity ring to your fan shroud. During the last 5 years of US Beetle production, VW added a velocity ring to the intake of the fan shroud to lower cylinder head temps. Either find a late model fan shroud, or purchase the ring itself from an aftermarket parts vendor and install it on your shroud. It functions in a similar fashion to the velocity stacks on twin carb set ups. The ring "organizes" the incoming air and speeds it up by reducing turbulence. More air volume moving faster cools things down more (as long is there is a way for the air to get into the engine compartment). ; )



I know of that test. Basiclly making a vacuum meter. 3/8'' vinyl hose running from engine compartment to cabin inserted into glass jar half full of water with line marking its level. If max capacity of air is surpassed it will scavenge for air and create a vacuum and draw water from jar.

Really only a deal on early bugs with small vent openings and with large engines. Later bugs do have vented deck lids as well.
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mfitzsimor
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PostPosted: Thu Oct 01, 2015 3:49 pm    Post subject: Reply with quote

<<If you put a huge engine in your VW, by propping the lid everyone looks and it gives you the attention you are craving.>>

LOL, Good one! If only that were the case....... Unfortunately, given the age of our vehicles and the fact that they were uncommon to begin with, the only attention a bigger crack at the top of the decklid seems to get here is people worry that the trunk of your weird looking old car didn't shut properly and they want to let you know so you don't lose anything.
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motorhead364
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PostPosted: Thu Oct 01, 2015 6:42 pm    Post subject: Reply with quote

It can also be to clear big carb stacks and act as a scoop for air intake.
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Mr.Duncan
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PostPosted: Fri Oct 02, 2015 7:07 am    Post subject: Reply with quote

Thanks Guys,

I purchased a a OEM dog house shroud with the large positive slot for the oil cooler (not the later 75'-79' negative "peanut" oil cooler slot.)

Cleaned it up, gave it a new coat of paint.
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Red 1971 Squareback Thread
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