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type 4 fan peak airflow rpm
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oprn
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PostPosted: Tue Mar 21, 2023 6:44 am    Post subject: type 4 fan peak airflow rpm Reply with quote

I did a search but came up with nothing yet, just talk about removing fan blades.

I am playing with gear changes/tire sizes to optimize fuel economy but do not want to compromise cooling on my type 4 engine. What I want is to lower the RPMs at a 60 mph cruise without running the engine too hot. To that effect I think that peak fan efficiency should be at 70 mph. 70 mph is the highest hour after hour sustained speed I will drive this car, normally we cruise at 60 mph. I am guessing 3000 RPM for peak cooling airflow? Set up the gearing for 3000 at 70 and at 60 mph with the lighter load, I should still be ok?

Is my thinking in line?

Bare in mind this is NOT in a Bus but in a much lighter car. 1432 lb empty weight but I am asking here for the type 4 knowledge base as I am running a Bus fan. I don't know if the 411, 412 or 914 fans are the same or not.

Thanks in advance.
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PostPosted: Tue Mar 21, 2023 10:36 pm    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

The fans are all basically the same. No idea if there is an optimal speed to run the fan or if removing some of the blades has a positive or negative effect.
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PostPosted: Tue Mar 21, 2023 11:16 pm    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

Someone wrote a tome about this including stall speeds and the like. Maybe Robbie?
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PostPosted: Tue Mar 21, 2023 11:36 pm    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

VW engineers already did that work for you.
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PostPosted: Wed Mar 22, 2023 4:45 am    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

SGKent wrote:
VW engineers already did that work for you.

Sweet! And published it... where?
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PostPosted: Wed Mar 22, 2023 6:05 am    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

I still think a venturi ring might be the way to go here.

I had this made by a guy here that makes venturi rings for type 1s. I still havent gotten around to running back to back measurements on this.

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PostPosted: Wed Mar 22, 2023 6:14 am    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

Owners manual tells you the maximum recommended speed (=highest recommended continuous load), its 75 mph and at that speed 2.0 bus will have about 4000 rpm. Top horsepower comes at 4200 rpm. Same fan was used in 914/912E and then top hp rpm was at 5000. Typ 127 industrial engines had only 46hp at 3000 rpm but I´d guess factory built in plenty of cooling reserve since they were used in hot places too.
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PostPosted: Wed Mar 22, 2023 6:27 am    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

Yes that would tell us that the peak is somewhere between 3000 and 5000 RPM. The advantage of the crank mounted fan is that a broken belt will not end in a really bad day. The disadvantage is that unlike the type 1 engine you cannot change pulley sizes to match the fan output to your normal driving habits.

Yes it would be interesting to see what kind of difference that vortex ring makes. Keep us posted please!
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PostPosted: Wed Mar 22, 2023 6:49 am    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

While a venturi ring ...."should"....allow slightly more air to reach the blades "quicker".....but that effect also "might" circumvent one of the biggest producers of VELOCITY in the fan. That would be the central floor of the fan. Centralized low speed inlet air (relative to the velocity around the edges of the fan) in fans of this design....that enter and make first contact in the center of the fan.....are accelerated radially when they make contact with the floor.

This is also why some of the earlier fans with the conical spinner have a series of rqised partial radial grooves cast in that act like "wing fences" on older aircraft. These keep the air in contact at the surface longer and for a few more revolutions to accelerate it.

So the venturi ring should increase volume. But I would say more surface ridges may increase velocity. How all of this affects static pressure within the manifold is what should be watched for.
Interesting!
Ray
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PostPosted: Wed Mar 22, 2023 12:47 pm    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

oprn wrote:
SGKent wrote:
VW engineers already did that work for you.

Sweet! And published it... where?

The point is politely, you are over thinking it. These engines have been used in SCCA Formula Super Vee in years past, and F Production (914-4) racing with the stock arrangement more recently. Some have gone to down the middle shrouds and a big Porsche fan for more cooling. You are many years late to the party.

If you want to keep your engine cooler then the easiest path is to ceramic coat the heads, exhaust ports, and piston tops. You can't control heat on these engines just by playing with the shroud and fan. Besides, you can buy a bigger fan and DTM shroud already if you have the $$.

https://lnengineering.com/type-4-store/dtm-cooling-systems.html?limit=12

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PostPosted: Wed Mar 22, 2023 1:55 pm    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

SGKent wrote:
oprn wrote:
SGKent wrote:
VW engineers already did that work for you.

Sweet! And published it... where?

The point is politely, you are over thinking it. These engines have been used in SCCA Formula Super Vee in years past, and F Production (914-4) racing with the stock arrangement more recently. Some have gone to down the middle shrouds and a big Porsche fan for more cooling. You are many years late to the party.

Ah! So you don't know the answer either then. No harm in just saying so...

Thanks anyway!
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PostPosted: Thu Mar 23, 2023 4:46 pm    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

I was hoping this information was out there but it appears it is not, at least not with any of the 264 who have read this thread. I will just have to figure it out. When I get it back on the road I will thread a fitting into the fan housing somewhere to connect a manometer and take it for a drive. At some RPM the pressure should peak.
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PostPosted: Thu Mar 23, 2023 4:59 pm    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

Flow, pressure, and heat transfer may be non-uniform throughout the air path, so a single measurement may not tell you much. I's an interesting experiment. But I think VW answered it not just with data, but with real-world experience. They probably instrumented cars and made changes, measuring oil/head/exhaust temp, power output, etc. and came up with a reasonable compromise.
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PostPosted: Thu Mar 23, 2023 6:28 pm    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

264 touched this thread, and 259 quickly clicked away
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PostPosted: Thu Mar 23, 2023 6:42 pm    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

the flow is dependent upon how well you clean the individual vanes in the fan. It also depends on the condition of the inside of your shroud, and the type cylinders you have. The Mahle and Kolbenschmidt cylinders are slightly different as to the fins. The flashing and condition of the fins in the heads also help determine what the flow is. Thinking it is "A" single number is an error. Even the speed of the vehicle moving forward thru the air helps determine what the flow is. Like I told you, VW did all the engineering for you. Let us know how all your testing works out. I'd love to have a spread sheet to post on the wall with a note under it that says, "This is what happens when people have too much time on their hands." Laughing
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PostPosted: Thu Mar 23, 2023 7:29 pm    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

Excellent idea!

I will print off this thread, highlight a few choice replies, hang it on the wall and put a sign on it that says "This is what happens when you ask a simple question on the Samba!"
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PostPosted: Thu Mar 23, 2023 7:32 pm    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

oprn wrote:
"This is what happens when you ask a simple question on the Samba!"


Your question is anything but simple. As someone who posts daily in the engine forum, I would think you know this already.
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PostPosted: Fri Mar 24, 2023 6:02 am    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

Maybe I didn't word the question the best. All I wanted to know was what is the peak efficiency range of the stock type 4 fan. Is that complicated?

We know a lot about the type 1 fan. It flows well at 2800 to 3000 engine RPM, peaks around 4000 engine RPM and starts to come apart above 6000 engine RPM. Simple! What do we know about the STOCK type 4 fan?

I did not ask about cutting off blades, cleaning the fan, fixing the tinwork, flow characteristics of various replacement cylinders, cleaning up the casting flash on the heads, the effects of the engine ducting on the car as it goes down the road, who used them in racing and in what class, ceramic coating the heads, exhaust ports, and piston tops, Porsche fans, DTM conversions and on and on... the responders are the ones who complicated it!

I have been told the VW engineers figured it out... ok, fine - where is that data so I can see and apply it? I put it in the Bus section because I thought someone here would know.

I did not start this thread with the purpose getting a pi$$ing contest going but the trolls showed up and here we are!

My apologies for asking the question! Good Lord! Rolling Eyes
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PostPosted: Fri Mar 24, 2023 9:19 am    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

yes, your snarky attitude and remarks started the pissing contest, and you know it so playing it wasn't me gets noticed. If you are really interested in peak fan efficiency, clean the shroud, fan, and fins of the head and cylinders first. The fan blades are air foils. Take a small jewelers' file and touch up any burrs and nicks on the fan vanes. Check for cracks but don't take it apart. If you paint it, try to do so evenly. The best place to ask about fan RPM is the 914-4 forum. They race type 4 engines.

This is Len Hoffman in his 914-4. Do you plan to push your bus this hard? This car races in F-Production. I built racing engines in the 70's and 80's for winning F-Production Fiat 124 spiders that constantly turned 10,000+ RPM. Len has to be pushing this pretty hard against cars like that. There is one video out there somewhere where he had a fan explode at RPM while racing.

Quote:
902 views Jul 27, 2011
Racing with Randy Wagner for F-Prod class win. Video picks up with Len Hoffman slipping by Wagner in lapped traffic. Hoffman won the race, while Wagner set a new F-P track record, beating Hoffman by .013" second!
Viewers can't see in the video, but Randy is tucked right on Hoffman rear bumper for the rest of the race.



Link

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PostPosted: Fri Mar 24, 2023 11:22 am    Post subject: Re: type 4 fan peak airflow rpm Reply with quote

SKGent, it has become blatantly obvious to me that you have not comprehended my first post nor the last one in which I attempted again to express my information request, my fault perhaps for having poor communication skills, so as a result we are singing from two different hymn books. Any further exchange between us on this subject would be of no value.

Thanks for your efforts! Merv
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