GermanLook Forums  

Go Back   GermanLook Forums > Articles > Technical Articles

Thread Tools Display Modes
Old April 29th 2010, 21:35
zen's Avatar
zen zen is offline
Registered User
Join Date: Jul 2002
Location: atlanta, ga
Posts: 2,946
Post Porsche 911 Cooling Kits

by Alexander Niederfahrenhorst
Jun 24, 2003


There have been alot of statements and rumors about 911 cooling kits on the net. The reason for this tech article is to give you some additional information on this subject so that you can make up your own opinion.

First of all I want to thank Gerd Weiser, Gerd Kummetat and Rolf Klaus for providing me with the information needed for this article. I was overwhelmed by the material that Rolf Klaus showed me on this subject. The information in this article is based on a Technical University engineer assay, original VW and Porsche efficiency diagrams and several dyno diagrams and dyno reports from the forum.

You also have to understand that the kits were developed in a country that has no speed limits. The cooling system needs to provide adequate cooling at high speeds for a period of time. In most other countries a tuned engine is used for the drag strip or for some sort of illegal street racing.

How do the different systems compare?

Efficiency ratings for several cooling systems:
  • Porsche 911 -> 70-73%
  • VW 411 -> 43% (much better than T1)
  • VW T1 -> 30% (without oil cooler, 20% with oil cooler)
  • VW GOL (VW T1, only in Brazil) -> 80% (Has extra piece in front of the Axial fan to get optimal airflow into the fan)
  • KHD (for industrial AC engines) -> 70%

These numbers are based on original VW and Porsche diagrams. They are related to cooling fin spacing / surface area and airflow resistance on the engines they belong to. A very primitive example for the efficiency rating of 70% would be for example an engine producing 10hp would produce 7hp in cooling. Again, this is a very simple and primitive example. You need to take into account as well the Air Pressure, Air Velocity and the Air Density.

How does this relate to Porsche cooling kits on AC VW engines?

Well, it does not. Looking at original Porsche efficiency diagrams you can actually say that the Porsche cooling kit will not work very well on AC VW engines using Porsche pulley ratios. The reason for this is the bad relation of cooling fin spacing / surface area and airflow resistance. From the Porsche diagram you can tell that the fan will lose substantial amount of its cooling effectiveness. This is the reason why the fan RPM needs to be increased to get better cooling for i.e. a T4 engine with higher pulley ratios. The ratio that should be used is about 1.6-1. To give you an example for this effect would be an airplane ascending too steep and lift is lost.

So the amount of cooling can be regulated by the pulley ratio and which Porsche fan blade is used. Looking at original Porsche material the best fan is actually the rare 911 Turbo 11 blade fan. It has a diameter of 225mm.

Measurement showed that turning down a C2 (12 blade curved) fan will give you a 40% loss in airflow. This 225mm C2 setup is still good on smaller engines up to 140hp where not that much cooling is needed. The diameter of the fan blade is given anyways by the Porsche cooling kit you will use or buy. There are quite a few choices when it comes to Porsche kits.

There are many different ring diameters:
  • 270mm -> Used for most original Porsche rings
  • 260mm -> Made to offer low cost systems with their own rings
  • 240mm -> Made to make the kit more compact so it will fit under W decklids and to make use of central airfilters.
  • There are also other manufactures that offer other kits with other ring diameters.

Who are manufactures of Porsche cooling kits?

As of my knowledge these are the companies that make Porsche cooling kits for T1 and T4 engines:
Ahnendorp, FAT, Sharpbuilt, MSS, Remmele, CIP1, Willibald, Riechert, Klaus, PowerTuningParts, and Bergmann

I probably forgot to list quite a few that I do not know of. Some of those kits will use the Golf alternator. You can buy rings or adaptors so that original Porsche alternators can be used.

How much power does a Porsche fan use on a VW AC engine?

Recent dyno pulls showed that the Porsche fan does not use that much power. One example is a 2316cc T4 engine were the fan used 6hp. It is said that the Porsche fan will use between 5-10hp. Other information shows that the hp loss is less at higher engine RPMs which is one reason Porsche cooling kits are used on engines. One of the big losers is the Riechert vertical fan which used 17hp due to is long belt and forcing all the air directly onto the engine block. This is one reason why upright kits were developed.

Why should you use a Porsche cooling kit?

Hmmm...this is good question.

  • It looks good and gives the engine bay a clean look. Working on carbs is a lot easier too.
  • Slightly less HP loss compared to a T1 fan at high RPMs
  • Produces more air compared to a T1 fan (10-15%)
  • Better suited for high reving engines (T1 fans could fall apart at higher RPMs as reported)

  • It costs a lot more than an original cooling setup on a T1 engine.
  • On most kits #2 will get more air than other cylinders because of the lack of vanes in the shroud.
  • Fitment on older beetles with W decklids (240-254mm systems should be used to clear the decklid. Check this with the vendor when you want to buy a kit.)

One thing needs to be said before I am misunderstood: The T1 cooling system is an effective cooling system. It was also said that the T1 radial fan would not produce anymore airflow above 5000-6000 RPMs. I read this on the net and I have to say that this is not true. You will start seeing problems at about 8000-9000RPMs when the fan spins so fast that the air can not get into the fan for distribution. The other thing is that there are many reports about failed T1 fans.....even welded ones.

The T1 cooling system is also a lot cheaper. This is only true though on a T1 enigne. You need to get a cooling system for T4 anyways if you want to fit it into a beetle. You can either buy the Cali kit, DTM or a Porsche kit. Porsche kits start at about 600$ complete with used 911 fan/ring and alternator with a FAT shroud (requires cutting of the decklid) and will go up to about 1000$ for carbon kits.

There is also a problem with air distribution in most 911 kits because of the lack of vanes. Rolf Klaus actually molded a new Porsche shroud that provides equal air to all cylinders and is considered to be the best T4 Porsche cooling kit by many tuners in Germany. In the pictures below the internal vane supplied with the kit is not shown. Rolf Klaus also invented the cylinder backside cooling with 911 kits.

There is a lot more documented information based on tests that were done by VW and Porsche for their cooling systems. I think that I covered the more important information that relates to the T1 and T4 engine enthusiast. One last thing needs to be said: The Porsche cooling kit will NOT overcool your engine if it is properly setup. If not it will not actually cool very well which I hopefully explained well enough in this article. With some of the kits that do not have a good fitment you should also seal the shroud to the engine and to the fan ring to achieve the best cooling for this setup.
'73 2316 TIV GL Standard Bug (quasi)

Company Branding, Graphic Design, and Web Services at DigiVinci Design
Reply With Quote

cooling, cooling system, fan, porsche, shroud

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT -4. The time now is 13:32.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
© 2002-2017. All Rights Reserved