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Adding modern scoop for split bus engine bay cooling / pres.
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Sambafraser
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PostPosted: Wed Mar 27, 2013 11:08 am    Post subject: Reply with quote

chrisflstf wrote:
I've always wondered when you add a big motor/big dual carbs to a bus, where does the air come from that the carbs now need?. Does it compete with the fan or is it now negative air in the engine bay? It would seem logical that you now need more air coming in.


The 2 large A4 size louvres on the side of the bus. Unless you are changing the fan size or rpm considerably then you will have a neglidgable change compared to stock. I can see what you are getting at - You can turbocharge your car from the air going past. But in reality you would be better to run an airbox that allows the air to flow smoother rather than lean out your air/fuel ratio with road speed.
Easiest way to look at an old motorbike from the 60's and they just have a set of trumpets sitting into open air - the thinking is it allows it to breath.
But this isn't true. The best example of this is a modern sportsbike.
The fueltank above the engine is an airbox and the volume/size/shape of this has a huge effect on the power allowing the trumpets to do their job effectively. Just like the size and shape of the exhaust is the length it has changed since the hotrod days of the 60's of thinking that a short pipe = power.


First you need to know what is inside the box before you think outside of it.
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Sniperx
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PostPosted: Wed Mar 27, 2013 1:35 pm    Post subject: Reply with quote

I just thought of something.

Barring upgraded motors why did Vw do what they did?

Let me clarify. If more air equals better cooling (which it does) why did Vw but ALL of their motors in the rear and build an active cooling system instead of mounting the motor at the front of the car to allow some passive cooling to occur?

Think about that one...
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mandraks
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PostPosted: Wed Mar 27, 2013 2:04 pm    Post subject: Reply with quote

Sniperx wrote:
I just thought of something.

Barring upgraded motors why did Vw do what they did?

Let me clarify. If more air equals better cooling (which it does) why did Vw but ALL of their motors in the rear and build an active cooling system instead of mounting the motor at the front of the car to allow some passive cooling to occur?

Think about that one...



hmm, weight could be a consideration?

engine up front, rear drive requires a looong driveshaft,

engine up front and front drive already existed (next logical option)

engines up front get in the way of your feet if you build a small vehicle

tires need room to turn, making engine room smaller requiring an upright layout....

engine in the rear, less noise, better traction

front cooler requires plumbing, and potentially a fan (so it can cool when the vehicle is stopped in traffic on a hot day)

forced air makes sense then...

overall it is all about simplicity (no water plumbing and gauges)
compact size
low weight allows for lower horsepower and better fuel economy
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Derek Cobb
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PostPosted: Wed Mar 27, 2013 2:21 pm    Post subject: Reply with quote

I think the reasons for putting the engine out back had very little to do with cooling. It was all about minimalizing the parts to produce a very inexpensive vehicle. No water pump, no radiator, no driveshaft. When you review the evolution of the Beetle (and the Bus) you see the progression of technology and cooling systems seemed to be modified and updated most often.
A passive system could be a real problem say, moving slowly up a long, steep hill with a tail wind. Active system draws what it needs as it needs it.

The bus must have had thoroughly adequate air vents as they changed very little from the 25hp through the 1500, then only one change in 1968 through the end of the aircooled production, unlike the Beetle that was constantly getting added louvers each time the engine was upgraded.

I think the margin for the Bus was extremely wide, to the point that I seriously doubt any Bus has ever overheated from a lack of airflow to the engine compartment. There are dozens of other culprits that'll burn them up, but inadequate access to cooling air is very, very low on my list of things that need tweaking.
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Sniperx
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PostPosted: Wed Mar 27, 2013 2:53 pm    Post subject: Reply with quote

Theres a problem here...

You're both assuming all front engine cars are water based or all water cars are front engined. Both are far from true.

I also wasn't saying SOLELY passive cooling...anymore than a water cooled car is SOLELY passive cooling.
------------------------------
engine up front, rear drive requires a looong driveshaft,
--Correct, so thats out

engine up front and front drive already existed (next logical option)
--Right, but is this a bad thing? FF cars are fine and prevelent today.

engines up front get in the way of your feet if you build a small vehicle
--Ghias aren't small, bugs have a giant underhood space...Busses have no leg room. Its contradictory throughout VWs line...so this wasn't the reason for VWs only engine layout and placement all the way to present (porsche, vw, audi....all diffierent layouts in similar cars...of course theres some differences)

tires need room to turn, making engine room smaller requiring an upright layout....
--THIS may have more value. By having front wheel drive they need more complex steering parts and other problems like suspension.

engine in the rear, less noise, better traction
--Less noise? Debateable. Better traction, yes....but the under powered vehicle has little problem hooking up as is.

front cooler requires plumbing, and potentially a fan (so it can cool when the vehicle is stopped in traffic on a hot day)
--EXCEPT...we're not talking liquid here...ducting to take air from the front of the engine across the motor at speed allowing for a smaller fan and less HP used to turn it.

We're not adding weight here....just engine location to take advantage of naturally occuring forced air in addition to a VW inspired fan system.


Derek: You're right about the margins as I showed by my blocking of the cooling vents.
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BRANDEN HOY
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PostPosted: Wed Mar 27, 2013 3:49 pm    Post subject: Reply with quote

I awlays thought it was common knowledge that Porsche's rear engine location was to improve handling and weight transfer under hard breaking conditions and keeping the weight over/behind the rear drive tires helped traction. I could be wrong.
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Sniperx
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PostPosted: Wed Mar 27, 2013 4:10 pm    Post subject: Reply with quote

Its entirely probably that that is why PORSCHE did it...but why did VW do it for so many vehicles, for so long....and none of them being offered from a "high performance" angle.

Not saying its good, bad, right or wrong....but AM saying that if the VW system as a whole across the market had cooling problems...they should have exploited the natural airflow produced by the car moving forward in addition to the active cooling system.


BUT...they didn't need it. 1968 saw scoops installed on the upper corners, you say? Thats correct. However...they kept those same scoops from the 1600 all the way to the 2.0. Meaning the addition of 400cc did not warrant a redesing of the airflow system.

NOW. What I DO think and have heard similar confirmations of, with increased highway speeds came increased wind speeds. This increase across the vents possibly acts as a vacuum, lessening the airflow into the engine compartment...thus in 68 they added the "ram air" system to the equation.

but this is all moot...everyone knows the internet knows better than any engineer..............


I guess I'll do my OWN impromptu water gauge to prove to myself my thinking is wrong. I will stick a hose in a glass of water and the other end stuck into my air vents. I will then free-rev the motor in neutral and observe any changes. That will take wind induced vacuum out of the equation.
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cru62
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PostPosted: Wed Mar 27, 2013 4:41 pm    Post subject: Reply with quote

Sniperx wrote:

I guess I'll do my OWN impromptu water gauge to prove to myself my thinking is wrong. I will stick a hose in a glass of water and the other end stuck into my air vents. I will then free-rev the motor in neutral and observe any changes. That will take wind induced vacuum out of the equation.


I, for one, look forward to those results.
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mandraks
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PostPosted: Wed Mar 27, 2013 5:34 pm    Post subject: Reply with quote

just to be clear, i am quite intrigued by this, and am not in any way suggesting that your are wrong! I only provided some thoughts prompted by your question above Smile

and, no i am not assuming that front engine cars are all watercooled, i am quite familiar with DKWs, similar vintage and shape, same country, too no tto mention the awesome NSU Prinz, and Spider.

I only suggested that Porsche needed to show something the other guys did not, otherwise they could have similar picked a different manufacturer's design.

you come up with something clever, and i will be more than happy to look at the pictures and review your results.
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CoastalAirCooledVW
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PostPosted: Wed Mar 27, 2013 8:15 pm    Post subject: Reply with quote

Derek Cobb wrote:

The bus must have had thoroughly adequate air vents as they changed very little from the 25hp through the 1500, then only one change in 1968 through the end of the aircooled production, unlike the Beetle that was constantly getting added louvers each time the engine was upgraded.
.


Sniperx wrote:

BUT...they didn't need it. 1968 saw scoops installed on the upper corners, you say? Thats correct. However...they kept those same scoops from the 1600 all the way to the 2.0. Meaning the addition of 400cc did not warrant a redesing of the airflow system.



I guess I'll do my OWN impromptu water gauge to prove to myself my thinking is wrong. I will stick a hose in a glass of water and the other end stuck into my air vents. I will then free-rev the motor in neutral and observe any changes. That will take wind induced vacuum out of the equation.


I just wanted to point out that bay windows did change scoops after 1968. When VW made the switch to the pancake engine the scoops gained a considerable increase in size. What is interesting is that a 1700 and 1600 are a similar size but the 1700 has much bigger vents. A 1700 and a 2.0 are quite different in size but have the same vents. What does this all mean? Beats me Laughing . This is a very interesting subject and I look forward to your results. You would think that at least one person who works for a modern car company and has access to a wind tunnel would own a split bus too Confused
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flemcadiddlehopper
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PostPosted: Wed Mar 27, 2013 10:18 pm    Post subject: Reply with quote

Wow, this got people talking.

Couple of points made back there somewhere that are wrong. (i would do the thing with all the quotes from who said what but that looks like too much trouble). First of all, the motorbike thing...yes trumpets in the wind did not work for carbs, no, superbikes do not have large air boxes because they don't use ram air. They do use ram air, the ram air charges the air box, the air box is of a certain size to accommodate sudden full open throttle and to smooth the pulses between the cylinders pulling at the air in different directions. Second porsche did rear engine because VW did.

I like the Sniperx test with the blocking off of the vents, that would have been interesting to see what the water metre said on that one.

My one question that no one seems to be able to answer (and what I want to test for) What is the pressure in the engine bay during various driving conditions? And would adding more air to the engine bay change the variances of those pressures? And would having those variances evened out make changes to the engine performance and/or cooling?

I do realize that no one has or has ever had a problem with running out of air, (volume) especially in Canada , in their VWs.

Just think for a moment, what if they were to design a bus, today, and had to use our existing drive assembly? Without any knowledge of what was done by VW or Porsche in the past. What would the air intake for the engine bay look like?

gordo.
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PostPosted: Wed Mar 27, 2013 10:26 pm    Post subject: Reply with quote

cru62 wrote:
Sniperx wrote:

I guess I'll do my OWN impromptu water gauge to prove to myself my thinking is wrong. I will stick a hose in a glass of water and the other end stuck into my air vents. I will then free-rev the motor in neutral and observe any changes. That will take wind induced vacuum out of the equation.


I, for one, look forward to those results.


If you do....remember the non test end of the water meter needs to be in a non pressure effected area, so as not to skew your results. Remember pressure changes in the cabin area at speed too, unless it is completely sealed.

Gordo.
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Sniperx
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PostPosted: Thu Mar 28, 2013 9:22 am    Post subject: Reply with quote

I'm going to put a glass on the ground, put a hose in the vent, and rev the engine. Driving the car will not affect how the engine uses air in this case.

Do you think air scoops were something that just dawned on engineers in the 90s?

This is what your modification will do. It will put cooler air into the engine bay under pressure when driving at speed. Congratulations. What will this do for your car? Cool the motor by air rushing over over it and out the side vents. It will not give you "boost" in the intake. It will not provide significantly cooler air temperature to the intake as the air entering the intake is not heated that much to begin with.

Fixing problems that don't exist.....
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PostPosted: Thu Mar 28, 2013 12:28 pm    Post subject: Reply with quote

flemcadiddlehopper wrote:
Wow, this got people talking.

... Second porsche did rear engine because VW did...



I was referring to Dr. Porsche, not Porsche the company. I guess I could have been more clear. I would also guess that Porsche, the company, did not do it because VW did, bt instead they did it because Dr. Porsche, the MIC, believed it to be an efficient design and that's how he wanted it.

But I could be wrong...


Weren't there changes to the cooling tins and the oil coolers made along the way also? I can think of the switch from the 36hp style shroud to the 40hp style, then to the doghouse cooler and i believe there are diferent sized fans along the way also. it seems to me that there were always improvements being made to the cooling system.
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Sniperx
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PostPosted: Thu Mar 28, 2013 12:51 pm    Post subject: Reply with quote

However...all of those changes did NOT change how air actually came into the engine bay. This leads me to believe...they didnt see a need to change this.
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PostPosted: Thu Mar 28, 2013 7:40 pm    Post subject: Reply with quote

Sniperx wrote:
However...all of those changes did NOT change how air actually came into the engine bay. This leads me to believe...they didnt see a need to change this.


What the designers intended has been thrown out the window once a high revving,porsche fanned, 4x51 mm throttled, large displacement engine is installed.
Compare this to what was intended. Engine compartment volume is roughly 36 cubic feet. Stock doghouse fan moves 25 cubic feet/sec or 1500 cubic feet/min @3900 rpm. stock carb sucks 200 cubic feet/min. The air exchange rate of the engine compartment is 47 times a minute.
A Porsche fan moves 3000 cubic feet/min. dual 51mm webers flow test at around 1500 cubic feet/minute. The exchange rate is now 125 times/minute.

That is a 266% increase in air flow. Still inside the design parameters from the '50s ?
I would think that adding the 1558cfm from my 3" forced air pipe would be welcomed.


Gordo.
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zombievws
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PostPosted: Thu Mar 28, 2013 8:40 pm    Post subject: Reply with quote

what happens if you don't run a engine lid? my ratty 67 singlecab seems fine around here. what about freeway driving?
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PostPosted: Thu Mar 28, 2013 9:23 pm    Post subject: Reply with quote

zombievws wrote:
what happens if you don't run a engine lid? my ratty 67 singlecab seems fine around here. what about freeway driving?

Just Don't. It is bad.
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PostPosted: Thu Mar 28, 2013 9:57 pm    Post subject: Reply with quote

Quote:
A Porsche fan moves 3000 cubic feet/min. dual 51mm webers flow test at around 1500 cubic feet/minute. The exchange rate is now 125 times/minute. That is a 266% increase in air flow.


Yes, thats true, but can you pull that much air through the stock vents?
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PostPosted: Thu Mar 28, 2013 11:40 pm    Post subject: Reply with quote

chrisflstf wrote:
Quote:
A Porsche fan moves 3000 cubic feet/min. dual 51mm webers flow test at around 1500 cubic feet/minute. The exchange rate is now 125 times/minute. That is a 266% increase in air flow.


Yes, thats true, but can you pull that much air through the stock vents?


That is the point being made here. The designers,I feel, had no view of what future customizers would do to their creation, and that increase in air flow is most likely beyond their spillage factor.

Yet we know the engine is not going to run our of air, but a pressure drop must be occurring. The stock VW fan has an increase in pressure of 5 psi (@ 3900rpm) above atmospheric pressure, so a pressure drop in the engine compartment is a pressure drop in the cooling air. Albeit marginal.

Gordo.
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