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Drilling holes in your heads - will it make them run cooler???

5229 Views 8 Replies 9 Participants Last post by  so67vw

if you go into one of the old VW service books from the 60's, there is a bulletin in there for 1200cc engines, if they experience "pinking" (pinging) under load, VW said to drill holes through fins. I don't have book at hand, it's buried at home, so i don't know size, how many, etc. And no I have never tried it.

I looked this up in the old VW service book....for 40HP motors with old round boss 1200 heads....VW suggested drilling 10mm holes (6) in the ribs that extended from above rocker cover rail (upper) to outward most fin. It was done to lower head temperature and reduce pinging on heavily loaded motors.

In the seventies it was very popular to do this modification on moto-cross bikes, they were all aircooled at that time.
the ratio is:D should be less than 2s, =thickness of fin, D=diameter of drilled hole.

Ex:if you drill a hole that is four times the thickness of the fin you have the same cooling area, but if you drill a hole that is two times the thickness of the fin you have 50% more cooling(exposed) area.

The thickness of a cooling fin on an original type one head is aprox 2.5mm, with the ratio D=4s, shows us going bigger than 10mm hole decreases the cooling area, I think that 5mm hole could be a good starting point.

Other thing to consider is the effect of the reduced conductive area trough the aluminum for the heath to quickly migrate from the hot areas around the chamber further trough the fins. It will be maybe better to increase the number of holes towards the end of the fins. In theory the concept seems valid. Now we need some real word testing.

Just food for thought?
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Hey Throttle, that looks like a good idea. I just wonder if it had been tried and does it work.
Looks like a good Saturday project when the wife leaves you alone in the garage and your have a drill press and your bored LOL

How would you drill those holes shown in the manual photos? looks way down in there?
I think that drilling the RIBS help circulate "stale" air and drilling the fins would reduce the heat emissivity???
I did the math on this a few years ago and when I 'share' my info with anyone they tell me "bad idea" but have nothing to back that up with.

The pattern and holse size I was looking at doing would increase the total cylinder fin surface area a full 74% when all was said and done. Which in theory would mean you could use 74% more power with the same cooling as long as you had enough airflow to shed it.

Nice to see I wasn't so far up in the night after all. Maybe i'll have to do it one of these days to 'see' what it actually does.

I have it all written down and drawn up around here somewhere.........
There's a few heads on nitro RC cars that have the fins drilled. Not sure how much that would transfer over. In that example, though, there's generally not a fan blowing/forcing air across the fins. The holes could disrupt air flow. That's a guess on my part.
i think your misunderestimating the purpose of those holes,, they aren't for increasing the surface area,, they are to allow cooling air to go from the area by the intake port to flow through those holes and down in between the intake and exh guide,, in other words, they increase air flow at the exh port,, i dont think this would apply to a dual port head,,
Boy that is one to be tested....

I increase surface area as much as I can for pond filter systems but also need to consider holding time and flow together..... If you drill out material it doesn't increase surface area because you are actual removing material from the cooling fin... Though it does seem that you could devert air to where you would like it to go....

I'm sure that someone has some Data on this....
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