Fan Speed & engine RPM

jakriz · 2003-08-14T21:43:10+00:00

I've been thinking about the pro's & cons regarding using a full size pulley on a high revving engine. If a stock motor & fan is designed not to be really revved over say 4500rpm, then once u start revving the engine to 6000rpm up to 7500rpm, does the stock fan become useless, like it is spinning so fast that it creates some type of void of air that doesn't actually get pushed over the heads & cooler? So if I was to use a power pulley on the track it would actually cool better since the revolutions of the fan would be a little closer to what the stock fan does at 4500rpm , to the power pulley spinning at 6000rpm & higher? Am I just thinking too hard? regards Jak

Peter Leonard Moderator Volatile

1,456 posts · joined Apr 2003 · 18 Aug 2003, 11:11 pm

#75608

my old, base 1916 Pobjoy motor never runs that hot, but I have a heap more ventilation in my engine lid than CT. I do run hoodjacks on really hot days, or on freeway missions, but only because i like to stay below 110 degrees. sans hoodjacks I get 120 degrees blasting up long hills, but air is free... I like to feed mine as much as it's blessed little aircooled heart can take. interesting to find that the fan belt starts to slip at high revs due to increased power demands on the pulley/belt with respect to the fan smashing at the air, mebbe it's possible to get some kind of belt drive system? air can be quite solid when you push it hard; check out the friction generated when you're coming back from the moon one day. re-entry is a bitch. 😀
OR stick your hand out the window at 110k's, it's way cheaper as an experiment, and you can do cool wavy flappy motions :thumb
interesting to find out what airspeed/pressure it takes to start pushing the limits of the fanbelt's grip. or maybe thats just me. love to have a squiz at wes's thesis.
one more thing: the oil cooler isn't the only thing that cools the engine, the better your tinware is sealed, the better the stock cooling system can direct the air around the rest of the motor. another possibility is the addition of fins/heatsinks wherever you can make them fit in the airflow. i guess.
good topic. 😀
keep on ramblin....

let sleeping dubs lie

lugnuts Custom Title Time!

1,070 posts · joined Aug 2002 · 19 Aug 2003, 3:54 am

#75703

Hey CT why no stock oilcooler,shouldnt you run both ( i know buggerall thats why im askin).😉

fullnoise Fahrvergnugen

964 posts · joined Sep 2002 · 19 Aug 2003, 7:47 pm

#75957

I used to have a Berg pressure relief oil pump cover pumping the oil to a filter and then to a thermostat and then to an oil cooler and back to the engine where it went to the standard oil pressure reliefs and stock oil cooler.

Stan Pobjoy said that was all too complicated and may cause oil surge. Stan suggested to run some short oil lines from where the stock cooler mounts and to keep it simple. So that's what i"ve done.

I modified my fan housing so no air goes to where the dog house cooler used to be and no air goes to the heater ducts. With all the air dedicated to cooling the heads and barrels this may help too.

I might try an original 36 horse shroud with a 1500 fan to see if there is any temperature difference. I think the smaller fan housing would help the carbs breathe. I think my air cleaners seem quite boxed in between the fan housing and the cars body work. The extra room may also give me the opportunity to build some cold air boxes. That way I can feed the carbs with cold air from under the car and stop the carbs robbing the fan of cooling air.

If it works I'll tell you.

CYA, CT

esratrams

Craig Torrens 6 times Australian, 7 times State Hillclimb Class Champion

8,040 posts · joined Jan 2003 · 19 Aug 2003, 9:12 pm

#75982

Jak, have you changed something with your setup, I thought your temps on the track rarely went over 120deg ?

CT, have you thought about running the stock cooler, with the external cooler oil lines running off an adapter plate mounted between the case and cooler ?

I have seen them at Vintage VW, not too sure if they work, just an idea :thumb

I run a 36HP (aftermarket) "doghouse" shroud, you will love the extra room in the engine bay !
I think Wes has studied/researched the internal fins of the various fanhousings,will the standard 36HP shroud have enough fins to direct the air flow?

lugnuts Custom Title Time!

1,070 posts · joined Aug 2002 · 20 Aug 2003, 4:54 am

#76060

Thanks :thumb

Baja Wes V6 Baja Pioneer

3,119 posts · joined Aug 2002 · 20 Aug 2003, 9:38 am

#76150

actually Brad did the fan shroud destruction 😀

http://offroadvw.net/tech/brad/fanshroudtech.htm

Just get the last dog house shroud, and cut the sides off. That will make it thin. Cutting the sides off will not effect the air flow. As you can see in the pics, the sides are just dead ends anyway. On one of my old engines I cut the sides off, and also cut another little section near the top that didn't do anything. It made a cool funky shaped shroud.

Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... 🙂
www.taylorcycles.com.au - My DH MTB racing brothers shop.

modulus Veteran Volks Folk

2,009 posts · joined Jul 2003 · 20 Aug 2003, 12:01 pm

#76220

Jak,
Autospeed had a very interesting article about water cooling spray on an air-air turbo intercooler, viz:
http://www.autospeed.com.sg/cms/article.html?&A=0527

This is IMHO, one of the better thought through and tested performance cooling articles and much of it is directly applicable to oil cooling.

HTH

Peter Hill
1975 Type 2 Double Cab
modulus.com.au

Brad Wolfsburg Elder

3,764 posts · joined Aug 2002 · 20 Aug 2003, 12:52 pm

#76233

Craig Torrens wrote:I run a 36HP (aftermarket) "doghouse" shroud, you will love the extra room in the engine bay !
I think Wes has studied/researched the internal fins of the various fanhousings,will the standard 36HP shroud have enough fins to direct the air flow?

In short NO, teh stock 36HP shroud need the stock oil cooler to invert the air and remove the void that is created by the removal of fins to allow the fitment of the cooler in the first place. Follow the link Wes posted for more details.

I think you need to get your mixture correct before you worry about the other stuff. You can cool your oil all you want if she is lean you will stuff it anyway.

Brad
Why copy when you can own an original ?
Meyers Manx Australia

jakriz Wolfsburg Wizard

560 posts · joined Sep 2002 · 20 Aug 2003, 6:26 pm

#76320

Thanks for that Link Peter, most appreciated, & thanks Wes for the pic of the fan housing, I'm sure that many like myself have never seen that before.
I found a link on the Shop Talk forums regarding the air flow from the porsche fan on VW motors,basically the motor can't use all the air & runs too hot, the solution was to make 2 holes in the back of the fan housing to let some of the air out.
I've included the link.
regards
Jak

http://www.shoptalkforums.com/viewtopic.php?t=53582

Congratulations to Ben Durie for breaking the hillclimb record at Ringwood in his stroker beetle!

fullnoise Fahrvergnugen

964 posts · joined Sep 2002 · 20 Aug 2003, 6:31 pm

#76323

Hmmmm, it was interesting to see the cut-away of the dog house fan shroud. After seeing that I'll just modify another dog house shroud instead of going for the 36 hp option. I've already modified my housing in a similar fashion. However it's copped a few two many modifications over the years.

What are the aftermarket shrouds like. I've heard they're crap but has anyone ever done a cut-away as per above?

CYA, CT

esratrams

Craig Torrens 6 times Australian, 7 times State Hillclimb Class Champion

8,040 posts · joined Jan 2003 · 20 Aug 2003, 9:07 pm

#76411

my aftermarket shroud is of good quality, there seems to be the same number of fins as a standard doghouse, and the temp runs the same as the original. I bought it years ago at a swap meet. I have seen some crap ones where the fins have only 1 spot weld per fin !

Looks easier and cheaper to customise a stock 1600 shroud.

VWCOOL 23 Windows of Awesome

5,158 posts · joined Jun 2003 · 20 Aug 2003, 11:34 pm

#76520

Buggy Brad wrote:
Craig Torrens wrote:I run a 36HP (aftermarket) "doghouse" shroud, you will love the extra room in the engine bay !
I think Wes has studied/researched the internal fins of the various fanhousings,will the standard 36HP shroud have enough fins to direct the air flow?
In short NO, teh stock 36HP shroud need the stock oil cooler to invert the air and remove the void that is created by the removal of fins to allow the fitment of the cooler in the first place. Follow the link Wes posted for more details.

I think you need to get your mixture correct before you worry about the other stuff. You can cool your oil all you want if she is lean you will stuff it anyway.

What I think he meant was, his fan housing is a 36hp 'shaped' narrow unit, with no heater ducts, to provide extra space for the carbies, but all the internals of a 1600 including the fitment of a doghouse (external breathing) oil cooler

Pay your debts, CxxT

Brad Wolfsburg Elder

3,764 posts · joined Aug 2002 · 21 Aug 2003, 11:50 am

#76652

What are the aftermarket shrouds like. I've heard they're crap but has anyone ever done a cut-away as per above?

Ok there are several aftermarket shrouds availible. Most of the ones which come fitted with a dog house cooler have internal ducting which is similiar to the one I cut up above.

The aftermarket shrouds which are not fitted with a dog house generally suck in terms of internal ducting.

You best option is to cut down a factory dog house shroud and use its fan as well. If you cut them down as seen in the above picture you can take quite a bit off them.
I have a shroud I cut open and then removed evry mm I could get out of it. I am now going to put a perspex front on it after paint the internals with fluro paint and a inserting one of those ricer glow sticks. This way I can easily explain how it works to people and dispell a lot of the miss information people have gained in relation to it being a good idea to pull out the internal oil coolers to assist air flow in the pre dog house shrouds.

Brad
Why copy when you can own an original ?
Meyers Manx Australia

vw59 Turbo Boy

79 posts · joined Jan 2003 · 21 Aug 2003, 1:06 pm

#76675

Hi,

I very rarely post a reply but I thought I'd ad a bit about what I've learned.

I found that when modifying a motor, ie: stroking the motor it changes the width of the motor as we use shorter barrels etc, so the tinware doesn't always fit as well as it did standard. It may look unsightly but I use black silastic to fill all small gaps in the tinware between the shroud and head tinware, any small gap is allowing cold air to escape which is not being pushed over the cyclinder heads & cooler.

Gas can indeed cavitate, I am a Hydrographer by trade so see it happen. When a gas say for instance enters a valve which has not been sized correctly (ideally a valve should operate at about 70% of it's total rangeability which is maximum flow/mimium flow. If a valve is incorrectly sized the gas cools to a liquid (large pressure drop across the valve which ideally should operate with 1psi but often doesn't due to flow characteristic problems) it cools, then on the exit of the valve it speeds up again turning back into a gas. This is called flashpoint! Its what makes a gas pipe very noisy around a restrictive valve. Ideally a valve should not cause gas to cavitate as it should be ranged using the turndown equation which is maximum normal operating range/ minimum operating range.

I have heard of several fan exploding but only because the person had solid mounted the gearbox so unfortunately the road car when driven on the street has to absorb every bump and vibration which is transfered to the fan from the solid mounts. Rubber is installed to absorb vibrations on a road car from our not so great roads!

When changing the compression of a motor the fan is designed to supply a certain CFM per minute. When we up the compression, I think we also need to change the 4th gear as the motor is running hotter in theory but the fan is still turning at the same rate if ideally cruised in 4th down the highway. A lower 4th will make the rpm increase so the fan will operate faster but the motor will also be working just that little bit harder.

Cheers Leigh

🙂🙂🙂:bounce

A 12 sec street car that is street driven!

Baja Wes V6 Baja Pioneer

3,119 posts · joined Aug 2002 · 21 Aug 2003, 5:19 pm

#76742

Hi Leigh, it was good to meet and chat with your at Valla.

vw59 wrote:Gas can indeed cavitate, .... ....gas cools to a liquid....

Gas does not cavitate. Read any good encyclopedia or dictionary definition of the word and you will see it doesn't apply to gas. What you are describing is the gas condensing, and then the liquid form cavitating or more correctly flashing off. And we don't need to worry about this problem on the VW engine cos the air sure won't cool to liquid oxygen as it goes through the fan.

But the main reason I posted is the theory of changing the engine speed on the highway up or down to change the cooling. I've seen US vw mags publish that the VW engine is at it's most thermally efficient at 3100-3300rpm, so that's what rev's it should do on the highway.

My practical experience was my baja. When I had an L bug gearbox;
3rd gear at 100kph was doing 3200rpm
4th gear at 100kph was doing 2400rpm.

I can tell you if I used 4th at 100kph it ran a lot cooler and used less fuel than 3rd. You don't have to spin the vw fan that hard to make it work. The extra fuel you use spinning everything that much faster counter-acts the extra cooling from the fan. Or at least it did on my 1915cc Baja. 🙂

Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... 🙂
www.taylorcycles.com.au - My DH MTB racing brothers shop.

vw59 Turbo Boy

79 posts · joined Jan 2003 · 21 Aug 2003, 6:19 pm

#76764

Hi Wes,

Thanks, I too enjoyed meeting you. It was great to see such a greatly engineered and well thoughtout project with all the documentation to prove it theory and design principals. No your right, sorry I meant to type water not gas. It cavitates as it turns from water back to a gas, my mistake. Thanks for correcting me on this one! But your correct in saying also that air cannot cavitate.

Looking forward to seeing you Queenslanders at the next Valla.

Cheers Leigh

🙂:bounce

A 12 sec street car that is street driven!