Last week some one had a thread about cleaning the casting flashing in the middle of the type VI heads and since I have mine off for a valve job I thought I'd ask if it would help the air circulate any or are they meant to be plugged. Gordon

I've cleaned them on both 914 heads and VW heads. It greatly improves air flow through the heads.

I'd posted this photo in another thread, but the excess flash from casting had blocked off substantial portion of fin thru passages particularly around exhaust ports. this results in poor cooling air flow. I have no history on these heads as just acquired, but cleaning out cooling air flow passages I would consider very helpful.
I noted that my other bus heads were much better in terms of excess flash. It was only the 3 bolt intake heads that has so much excess flash. Photo shows incomplete clean-up accomplished
While you're in there always applies.

Click to view attachment

There's an old story about the ear when Rolls Royce adopted the GM automatic transmission for use in their cars. The enterprising British engineers decided the internal casting was too rough for use in a Rolls, so they did a massive cleaning and smoothing of the passages. The results was a transmission with severely degraded performance due to the loss of turbulence inside. A cautionary tale, but something to think about nevertheless. Maybe that flash should be there? Why wouldn't the Porsche-only 2.0 heads be more carefully prepared than the run-of-the-mill VW heads? Porsche has a boatload of apprentices to do menial stuff like that. Think before you act.

The Cap'n

Krusty;
True rough surfaces have better convective heat transfer coefficients than smooth ones,, however in this case severely reduced flow rates dramatically reduce heat transfer. Remember, convective coefficient goes up with velocity.
Barefoot

Rough surface caused turbulance is one thing. Blocked air passages is another. Air is supposed to flow through those passages to help cool the heads. Porsche may have a bunch of interns but how many did they have over 40 years ago? The 914 was their entry level affordable car. Attentention to detail was much lower than on their 911 & 912 models. Look at a 911 or 912 case compared to a 914 case. The higher end cases were beautifully casted and finished whereas the 914 cases have cast flashing everywhere. I just spent a couple of days cleaning and deburring a 2.0 914/4 case. Almost all exterior surfaces are covered with these flashing imperfections. I don't think they were engineered that way for cooling but for cranking out a bunch of inexpensive cases for their lower end cars. The same goes with their heads.

I am active in the aircraft world where big (360 cubic inch) air cooled flat fours rule and cooling can be problematic. Flash in the casting fins is a known cause of high cylinder head temps and smoothing the fins is a common practice. Everyone in that world is shooting for 400 F max temperatures, the beleif being that aluminum looses about 1/2 of it's strength at 400F and degrades quickly from there.

I've always cleaned up the flashing on heads, never an issue. I don't polish the fins as they should be rough.
IMHO VW/Porsche didn't do it because it wasn't cost effective to do it or needed on a car that was only meant to last 4-6 years and/or 100K miles.

There was an article in Hot VWs a few years ago that talked about removing casting flash from heads, they did see a drop in temps. Just to note they were Mexican T1 heads and were blocked pretty well.

Hand work on head castings, VW not likely, Ferrari for sure.
There was a feature on TV "how it's made" that showed Ferrari hand working the sand mounds for cylinder heads to insure no parting lines remaining.

All hypothesis.

Too bad you didn't have data prior to the valve job.

Clean the flash and report back....it would be interesting.

When parts are die cast, there is usually a lot of flash around the part. Next step is to put the part into a trim die to trim off the flash. The trim dies for the holes in the head would be long pins which would be prone to wear and breakage. I'm betting the trim die trims around the head, trims the larger holes, but not the smaller holes.

Attached is a picture of flash on a diecast part. Mold halves fit together pretty well so the flash is minimized.

spend your time designing an efficient engine combination, then optimizing it's tune. You'll run way cooler than you will spending time whittling on cooling fins.