Fan shroud venturi/ velocity rings - Expensive gimmick or worthwhile addition?

[Deanodynosaurs]

Just interested about what everybody thinks about the aftermarket venturi/ velocity rings? (for example see http://www.awesomepowdercoat.com/Venturi_Ring.html)

I understand the principle that as your narrowing the entrance into the fan your increasing the speed of the air going into the fan, but is it really that effective/ worthwhile? Or is it just a expensive add on?

I'd be very interested to hear your thoughts/ experiences.

Dude 

[DWL_Puavo]

Narrowing / speed increase isn't the main thing with this. The most important is the air that is "sucked in" from the _outside_ of that ring. I remember reading about 5% better cooling but I haven't the reference available, sorry. Was it Torben that recommended this in some thread?

...I just saw some british document where this princible was demonstrated - they had long flat plastic hose laid in the field, and then filled first with a normal fan. Then this kind of ring was added and the speed of fill was greatly improved. The ring however was added in between the fan and the hose, not in the front of the fan but the principle is the same. Supposedly the effect is weaker then there's some back pressure and radial fan.

[Deanodynosaurs]

Narrowing / speed increase isn't the main thing with this. The most important is the air that is "sucked in" from the _outside_ of that ring. I remember reading about 5% better cooling but I haven't the reference available, sorry. Was it Torben that recommended this in some thread?

...I just saw some british document where this princible was demonstrated - they had long flat plastic hose laid in the field, and then filled first with a normal fan. Then this kind of ring was added and the speed of fill was greatly improved. The ring however was added in between the fan and the hose, not in the front of the fan but the principle is the same. Supposedly the effect is weaker then there's some back pressure and radial fan.

Thanks for this Puavo,

Ah, so it increases the speed of the air into the fan. Whilst i can see this is a good thing, to have improved cooling does the fan also not need to turn faster? Or is it that there is a bigger volume of air available at the fan tips thats important.

I seem to also remember i read somewhere that people saw a 5% improvement in cooling. I've fitted a external cooler and fan anyway but as they say, every little helps.

Cheers,

Dude 

[Shane Noone]

Hey Neil, sent you a message on FB but here is the customer feedback lifted straight from Awesomes Website 

CUSTOMER'S FEEDBACK:

Of course, "your actual results may vary."

1 - Customers have seen an average oil temperature reduction of 33F, with a max reported of 60F.

2 - Customers have seen an average cylinder head temperature reduction of 68F, with a max of 100F.

Quotes from customers:
"The motor definately runs cooler."

"I can touch dip stick after a hard run when I could not before."

"The engine has a more stable idle due to cooler running."

"It has made a huge difference in temperature reduction.  I have to race the vehicle, (in the 5000 rpm range sustained) to generate high
temps at all."

"The car runs at 180 to 190 max now."

"Its a great product, all my VW's will have a ring."

I believe an oil temperature reduction of 33 degrees represents way more than 5% ............ sales pitch / customer feedback sure makes it a tempting product 

[Deanodynosaurs]

Hay Shane,

Message received on FB.

Yeah i saw customers feedback on the website, but i'm always a bit skeptical of feedback published by the vendor on their own site. I'm sure it all 100% above board, but what about the other feedback such as, 'it didn't do shit!', or my 'engine cooked with it on!'. They tend not to get published!

I thought asking on a forum such as this were there a good wealth of experience on here, and that i'd probably get me a more leveled opinion on the benefits/ issues etc.

By the way, i'm not slagging the company or product off in any way, i'm just interested in real experience of/ and opinions of use.

Yours feedback FB is noted mate. :-)

Dude 

[Zach Gomulka]

VW did it, I trust their engineers' research over others.
I just pick up a cheap FI shroud at a swap meet and remove the ring.

[Torben Alstrup]

I have never seen that kind of temp reductions. But 5-7 C. degrees at a constant 75 mph is pretty normal (oil temps)

T

[Deanodynosaurs]

Hi Zach, good point. Sadly we dont have 'cheap' parts in the UK anymore, as many selers nowadays seemly think there old parts are made of gold!!
In all seriousness though FI stuff is difficult to find in the UK, as as far as I know it was never a option.

Ah, thanks for that Torben, nice to hear from some who is running one.

Dude 

[Shane Noone]

I have never seen that kind of temp reductions. But 5-7 C. degrees at a constant 75 mph is pretty normal (oil temps)

T

Hi Torben, as Neil says good to have some real world feedback on this product. Out of interest, what constant RPM's would you equate to a constant 75 mph for us guys running a close ratio 4th gear on the street ?

For example my maximum constant RPM in 4th would be typically between 3-3500 however as I steer clear of long stretches of constant driving such as freeways / motorways / autobahn etc my rpm's tend to fluctuate.

What I'm getting at is would you expect to see a 5-7 degree typical oil temperature reduction even with varied rpm's, in other words  would you expect it to take " X " amount of minutes at a constant RPM / road speed to actually see this reduction in oil temps and lower cylinder head temps ...........

Thanks, Shane.

[glenn]

CUSTOMER'S FEEDBACK:

1 - Customers have seen an average oil temperature reduction of 33F, with a max reported of 60F.

Oil needs to be 190-210F so it boils off the water from condensation. My engine runs 215*F on the hottest days after long high speed runs.  215-33=182*F. That's a bit too low and the thermostat will barely open.

On cooler summer days temps are a good 10 degrees cooler and 172* is too cool for the oil.

[neil68]

I have never seen that kind of temp reductions. But 5-7 C. degrees at a constant 75 mph is pretty normal (oil temps)

T

I switched from a '74 OEM doghouse set-up (sold that engine) and then built a new higher displacement Type 1 with a '75 OEM FI doghouse with venturi (I believe it is a '75 shroud...maybe someone can confirm from my photo below).

Anyway, I also bumped up the CR to 9.3:1 and then 10.7:1 and have obtained similar oil temperature decreases - i.e. 10-12 degrees Fahrenheit, which if my math is correct, would be 5.5-6.6 degrees Celcius.

What I like about the venturi setup is that I can run 10:1 CR with 91/94 octane (95-98 octane for Europe) and the oil temps stay in the stock range 180-210 F.  I can only push the temps slightly above 210 F after hot lapping at the drag strip

[Zach Gomulka]

I've noticed there are three different doghouse shrouds. One has a long slot with a scoop that gathers air for the oil cooler. The other has a long slot, but no scoop. The fuel injected shrouds only have a short, oval opening to direct air for the oil cooler. Now, I'm not a aerodynamics engineer, nor have I done the research/testing to back it up, but looking at the three designs side by side by side make me think that the long slot with a scoop directs more air to the oil cooler. My explanation for this is that the fuel injected Beetles ran hotter head temps (fact) so they increased air to the heads by taking some away from the oil cooler and adding the venturi ring to the back of the shroud. On anything I build, I choose the doghouse shroud with the scoop, and ad the venturi ring to it (along with a type 4 cooler and 356/912 pulley). Seems to work very well in the sweltering Arizona desert.

[Torben Alstrup]

Shane, we have to remember that oil temperature is almost directly related to rpms, so your question is spot on. I mainly build street and bus engines, so in my world 75 mph should be iin the 3650 - 3800 rpms. (larger engines can handle higher ratio´s.)

I like my engines to hover in the 85 - 95 degrees C. when they are working hard. Periodic spikes to 110, 120 even 130 degrees no problem, as long as you use a decent oil.  I usually tell my customers never to run a constant temperature above 105 degr. C. both because the engine will loose power and also begin to burn oil

Glenn is right with the oil having to reach a certain level of heat to get rid of condense etc. But it does not have to reach boiling temps. Condense will vaporize above 85 degrees C.
That is also the reason why I almost always reconfigure the thermostats nowadays when external coolers are installed. I have found that an opening temp at about 85 degr. C. is more suitable for most engines than the regular 75 degr. C. which IRL typically gives an operating temp of about 70 degr. C.

T

[modnrod]

I've noticed there are three different doghouse shrouds.

 On anything I build, I choose the doghouse shroud with the scoop, and ad the venturi ring to it (along with a type 4 cooler and 356/912 pulley). Seems to work very well in the sweltering Arizona desert.

Gday Zach.
I never knew there were different doghouses.   We never got the FI versions here, but I haven't played with the late stuff much either.
Do you have a photo of the doghouse with the "long slot and scoop" at all? I'm wondering if my '73 Super has that style.
Our temps are similar, so it should work here too OK.

PS Oh, and with the venturi rings.
Are they sealed up against the doghouse on the outer edge, or is there an air gap between the outer lip of the venturi and the doghouse fan inlet (sorta like a "laminar lip" for the fan intake) ?

[Shane Noone]

Hi Neil,

Have you got a pic of your Venturi Ring install from a side view and or birds eye view to see how close you have it sitting into the fanshroud itself ? When I offered one I have up to my aftermarket 36HP style with doghouse shape without bending any of the legs, so as it comes, there was quite a gap between the lip of the ring and the outer edge of the fan intake section on the shroud. And this gap varied due to the shape of the shroud so was larger at the top and less at the bottom. So kind of same question ModnRod is asking. I too wondered if you were meant to bend the legs to allow the ring to sit inside the opening as a snug fit but Awesome's website say to expect a gap pretty much the same as what I have found........anyone's comments and or pictures on fitment that have yielded the temperature reductions observed ?

[Peter Shattock]

Thanks to all who have contributed their real life experience here.

I agree with Torben about the oil temps keep them as low as you can whilst accepting that the oil needs to get up to operating temp for optimum protection / performance.

I have found adjusting driving speed to a given oil temp temperature / pressure is a reasonable way to pass the time on the long journeys as sad as that may seam!

I like the idea of extra cooling to the heads as a general principal. As the heads are where the vast majority of the engine heat comes from and they see the highest temperatures for the engine as a whole. to me it seams logical not to use any of the head cooling capacity to cool oil, basically try and take away as much of the heat at the source. Consequently I've run a non dog house fan shroud for many years now and cooled the oil remotely which I've found very effective.

Like the "hot head" EFI motors we create the equivalent heat and more by raising the CR to improve performance so the heads do need as much help as they can get in my book as obviously cool heads also make more power.

The other major issue is expansion based on oil / engine block temperature. I have it on good authority that the case alone expands 0.5mm from ambient temp to 75 degrees in a parts washer (just the case). Think of the consequences of this relative to clearances for the lifter bores and mains etc. You can see the effect by comparing engine oil temp and oil pressure on a drive. Clearly you only need so much oil pressure and too much is not as bad as not enough, but there are unnecessary pumping losses and frictional losses to consider if you are trying to maximise what you have (keep oil temps under control and reduce the pump size).

Take this a step further to the expansion beyond the case where things get really hot out towards the heads and you can see why the engines get noisy when they get hot. We spend for ever setting static clearances but when the motor gets hot there is the potential for them to go out the window if not controlled and the cam duration and lift figures from the card shrink quite considerably and the baggy old lifter bores get a beating! 

As with all things its a balance based on your own application and external environment (Arizona / Norway / UK), but I think the basic principals are the same for all of us its just about degrees (excuse the pun) to which they apply to allow you to optimise your set up.

As suggested above I think it best to try and control the issue (heat) at source and if you can do this successfully all the resulting consequences down the line are reduced and more efficient.

Having said all that I've not got a ring on my fan shroud, but I will have next year based on what I've read here. I would be happy to have those few extra degrees in temp control as they would mean a few extra mph on the long drives to the track with the same oil temps and tolerances in the motor. Something I'm sure all the close ratio box guys on here long for!

Peter   

[Eddie DVK]

^^^^^  

Plus, have a look at the back of a 356 fan schroud  , and everybody knows those porsche people weren t crasy.

For examples: http://www.thesamba.com/vw/classifieds/detail.php?id=976647
                     http://www.thesamba.com/vw/classifieds/detail.php?id=1469722

Regards Edgar

[Donny B.]

Engine speed is critical when it comes to temperature.  Real world experience here.  When I was running my 1776 engine in my '66 I would drive at about 3200 RPM with stock final gear ratio.  Then I would accelerate to about 3600-3700 RPM and the oil temp would drop about 10 degrees F.  Most people I talked with did not believe it so I had to get them in the car and prove it.  Try it for yourself and see...

[Jim Ratto]

part of the reason Porsche used the air horn on 356 shroud was due to what was done on the Carrera fan and shrouds When the Carrera dual fan and shroud were designed it was found that rounding and contouring the air entry to fan, it lessened HP to drive fan. The Carrera 4 cam and the VW T1 are totally different animals, and I highly doubt VW added the air horn to lessen HP pull on our fans. The "cone" on the forward facing Carrera fan (in 356) was designed for same thing, to smooth entry into the fan. Wonder what a cone would do on the VW fan?

[neil68]

Hi Neil,

Have you got a pic of your Venturi Ring install from a side view and or birds eye view to see how close you have it sitting into the fanshroud itself ? When I offered one I have up to my aftermarket 36HP style with doghouse shape without bending any of the legs, so as it comes, there was quite a gap between the lip of the ring and the outer edge of the fan intake section on the shroud. And this gap varied due to the shape of the shroud so was larger at the top and less at the bottom. So kind of same question ModnRod is asking. I too wondered if you were meant to bend the legs to allow the ring to sit inside the opening as a snug fit but Awesome's website say to expect a gap pretty much the same as what I have found........anyone's comments and or pictures on fitment that have yielded the temperature reductions observed ?

Since the engine is currently installed and the breather box & IDA stacks are partly in the way, I can't get any new photos with a side/top view. I'll try with my wife's camera later.  However, here's another photo that shows a partial side angle.  As you can see, the venturi ring is not evenly spaced inside the opening.  I don't know if this is correct, but I assumed a slight upward tilt was part of the design.  On the other hand, it could have been damaged by the previous owner:

[Zach Gomulka]

Neil, every one I've removed (a dozen or so) have been placed evenly around the opening. I suggest you adjust yours.

[neil68]

Neil, every one I've removed (a dozen or so) have been placed evenly around the opening. I suggest you adjust yours.

Thanks for the reply...I'll adjust it this winter.

[autohausdolby]

I'd never realised that they are a F.I. shroud when they have the venturi ring - I've seen a couple over the years but not put the 2 together.

[Eddie DVK]

Ok getting this old topic back up

Tried it this the whole summer



I have to say I think it works, have done a lot of driving this summer, we had a 'hot' summer for the Netherlands a lot of days with 25+ dgr Celsius temps.
In city driving the oil temps just stay at around 80 dgr celc. even on some really hot days..
Did a few long trips in warm temps with 3 hours plus of highway driving (120km/h with long gearbox) and the oil temp never exceeds 100 dgr celc.

So my guess it gives you a 5 - 10 dgr celc. reduction in oil temps. (ok the 10 is maybe a little te high but it is between 5 and 10 somewhere)

The fun part is I don t have any sound deafening in my car and you can really hear it sucking in air, which I didn t hear before  .

Regards Edgar

Oh Ps I don t have a extra oil cooler just a type 4 in the shroud

[andy198712]

interesting stuff!
the theory of feeding the fan via a venturi is used on jet engines too, helps to guide the air in, in a turbulent free efficient state...

[karl h]

i once made an airhorn out of the trumper shaped part of the stock fanwheel. just tacked it to the rear of the shroud.

[DKK Ted]

Talked to Gary Berg on this some time back, bottom line, THEY WORK.  I have one and putting it on.

Ted