Cylinder Fin Style

[veeracer98]

Anyone have any experience with the thick fin cylinders vs the thin fin cylinders. JC Whitney used to call the thin fin ones "super cool cylinders" or something similar.

[Steve Davis]

David,
I'm not POSITIVE, but I THINK the 'fat ones' are the OLD original 1200CC VW cylinders. All of the newer versions (mostly AA) were built with thinner 'plates'. IIRC, the FIRST vee I ever raced used the original back in the 70's. I haven't seen any of them since that time, but if you are junk yard shopping, you might find some. I recommend the newer, thinner ones - pretty sure you won't find any of the fat ones from any current supplier. Not only are the fat ones.. fatter, there are FEWER plates and therefore less efficient in cooling. Be sure to use the lower 'splitter' tins unless you have some serious air input to that area, or, are feeding air FROM THE BOTTOM of the cylinders.
Steve, FV80

[Hardingfv32]

My take on this subject of thick 12 fin per cylinder vs thin 18 fin cylinders:

The early cylinders, thick fin, were later upgraded to thin fin with more fins per inch. Not sure this was VW's idea or Kolbinschmidt.

The thin fin units have been out of production for maybe a couple decades. FV competitors made a special purchase of the Kolbinschmidt units many years ago. At the time there were no Chinese units, so this was necessary to keep the class supplied. At this time most of those Kolbinschmidts, in the hands of engine builders, are mostly gone and the AA Chinese cylinders are all that is available. The AA Chinese units are thick finned.

The science: Thin fin do have more surface area for heat transfer, BUT the space between the fins is much tighter with the thick fins. The stock engines use a blower type cooling system. While you might think that think that our 100 mph air flow from our cooling ducts equal to the task, this is not the case. The small clearance between the thin fins cylinders can cause flow stagnation at lower flow pressures. The extra fins can provide extra cooling ONLY if you can keep the flow moving.

So it is my opinion that the AA Chinese thick fin cylinders are possibly better at cooling a duct cooled FV. This is very hard to demonstrate on the dyno. It would take a cooling system that matched perfectly the duct system on a FV. I do have measurements from a car's duct system that show a very small pressure increase, just above atmospheric, at the fin surface. This is a well designed expanding duct cooling system not typical of most FV's. Nowhere near the high pressure that you might see with the stock blower.

Now all that said, this is purely academic as the AA Chinese thick fin cylinders are all that is available.

Brian

[veeracer98]

David,
I'm not POSITIVE, but I THINK the 'fat ones' are the OLD original 1200CC VW cylinders. All of the newer versions (mostly AA) were built with thinner 'plates'. IIRC, the FIRST vee I ever raced used the original back in the 70's. I haven't seen any of them since that time, but if you are junk yard shopping, you might find some. I recommend the newer, thinner ones - pretty sure you won't find any of the fat ones from any current supplier. Not only are the fat ones.. fatter, there are FEWER plates and therefore less efficient in cooling. Be sure to use the lower 'splitter' tins unless you have some serious air input to that area, or, are feeding air FROM THE BOTTOM of the cylinders.
Steve, FV80

Thanks Steve

[veeracer98]

Thanks Brian.

[Jon Adams]

David & Brian,
FYI, AA Performance also has thin fin cylinders available and in stock. They are listed on the website as European 40hp Cylinders p/n VW7700T40EL, the cylinders have a large base diameter that require no machining or O-rings when using a new 1600cc case.

Jon

[Hardingfv32]

Jon

Have you actually seen these? The product photo is showing thick fin.

Brian

[FVRacer21]

Jon

Have you actually seen these? The product photo is showing thick fin.

Brian

Brian

I found this

https://mooreparts.com/products/empi...-40hp-set-of-4

AA Brand Cast 77mm X 64mm Aircooled Vw Pistons And Cylinders.
77mm X 64mm = 1200cc/40HP

But pictures are not updated sometimes - I have found that with many vendors - the manufacturer does not always provide the correct picture.....or consistent in making the same part...

Same part number - larger fins https://thevdubfactory.com/products/...-european-40hp

All above caveats apply.....

ChrisZ

[Jon Adams]

Yes, I've purchased several sets.

Jon

[Steve Davis]

Brian

I found this

https://mooreparts.com/products/empi...-40hp-set-of-4

AA Brand Cast 77mm X 64mm Aircooled Vw Pistons And Cylinders.
77mm X 64mm = 1200cc/40HP

But pictures are not updated sometimes - I have found that with many vendors - the manufacturer does not always provide the correct picture.....or consistent in making the same part...

Same part number - larger fins https://thevdubfactory.com/products/...-european-40hp

All above caveats apply.....

ChrisZ

Yes.. but the first listing is for Pistons/Cylinders/wrist pins and Rings. The second is for CYLINDERS ONLY. I didn't see any actual part numbers. At least they ARE available though.
Steve

[DLRacing]

Anyone have any experience with the thick fin cylinders vs the thin fin cylinders. JC Whitney used to call the thin fin ones "super cool cylinders" or something similar.

Hey Dave it's Crosby,

AA jugs are 12 fin. Koby and Cofap are 17. Think a minutes about surface area heat displacement. What gives up more heat when air passes across it? Thick metal or thin? Think metal retains heat and thin metal dissipates. I've 13 original 1200 engines on the trailer and every one has 17 rib jugs. Also I've found the AA 12 fin jug cylinder bore warps at the center. Unless one can keep CHT below 300 degrees F the AA jugs are a one season deal. I use AA but pitch better half of them at rebuild. Gotta run what is available I guess.

If your running a hot engine then #3 has to be honed out and additional .002" and ring gap has to be set accordingly.

Cheers,
Dave

[Hardingfv32]

Hey Dave it's Crosby,

AA jugs are 12 fin. Koby and Cofap are 17. Think a minutes about surface area heat displacement. What gives up more heat when air passes across it? Thick metal or thin? Think metal retains heat and thin metal dissipates.

The theory is correct but in our application, SCCA FV, this does not meaning better cooling. Our ducted cooling air flow does not have enough pressure to make efficiently flow through the fins of the 17 fin barrels. These cylinders are designed for blower fed cooling system.

Assuming or stating that cylinder head temps are measured at or near the spark plug seat, you will never see temps below 350 degrees with a ducted cooling layout.

Brian