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Old 02-12-2007, 01:08 PM   #1
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VW Rabbit Diesel Engine flow work

After removing the cylinder head due to a blown head gasket in my 84 vw rabbit 1.6L diesel, I decided to do more work since everything was torn down anyway. I smoothed the rough casting edges in the bowl area of the head, back cut and lapped the valves, smoothed the intake air flow, and increased the diameter of the exhaust downpipe.
Here is the rough edge of the casting of an intake bowl.

It is hard to see but the bowl has been smoothed

The valve seat was pitted and there were sharp edges around the valves in the combustion chamber, I smoothed the sharp edges and lapped the valves. The cracks between the valves are common and apparently are not anything to be concerned with so I left them all as they were.

The valves were very dirty and there was a sharp transition between the valve seat and the rest of the valve so I back cut the valves so that the air would flow past the valve better.

I removed a restrictor plate that was in the intake from the factory. It was vertical and in front of the port openings. It came down to where the red lines are in the picture. It is easy to see how this will smooth flow through the intake.

This is the stock "toilet bowl" downpipe flange where the exhaust manifold meets the exhaust. It steps down quickly from the manifold to the ultra tiny exhaust. Its easy to see this is less than optimum. I welded up a larger pipe to the stock flange to make the step less drastic. I could have spent more time here to make it a completely smooth transition but I have too many other things going so I didnt bother flaring the pipe to transition more smoothly to the flange.

I have not figured out the gas mileage yet but it was ~41 mpg overall combined city/highway driving. I have not changed my driving habits so I will drive a ways to see how Im doing now. There is more engine noise and definitely more power so I imagine the engine is operating more efficiently. We will see though

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Old 02-12-2007, 01:51 PM   #2
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Very impressive, I wish I had such skills!

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Old 02-12-2007, 03:41 PM   #3
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Is that a crack in the head between the valve seats?

edit: oops, I just re-read that.
Reality is merely an illusion, albeit a very persistent one. - Albert Einstein
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Old 02-12-2007, 03:53 PM   #4
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Yes, and noted by the poster.
I'm more concerned about the gap between the valve seat inserts and the head in the vicinity of those cracks. It looks like there are at least two separate cracks and two separations of seat from the head. Images 2 and 3 look to me like two different valve seats.
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Old 02-12-2007, 05:52 PM   #5
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Yes those are all different valve seats/ports. The crack between the intake and exhaust valves is apparently very common judging by all the reports of it in vw forums. Where they are cracked is a thin portion but it beefs up significantly up in the head before it gets to a water jacket. I dont know if the gap around the outside of the valve inserts is anything to be concerned about or not, none of them were loose and there was no sign of shifting in the ports so I didnt worry about them. I am tired of fixing things and spending money on this car so I decided not to take it to a machine shop or buy a new head, hopefully this one lasts a while. The wife's patience has run out for repairs on this thing even though I have proven that I can afford a whole lot of repairs with the money I save in gas and insurance.

Hopefully it will run strong for a while so instead of fixing it I can start modifying it one thing at a time for aerodynamic and mechanical efficiency.
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Old 02-14-2007, 06:34 AM   #6
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Very, very good improvements to your "air pump" ! I'm sure you'll see improvements! But I hope you won't see more of the stress(es) which caused those two cracks! Temperature probably had a lot to do with making these stress risers.... Will it run cooler now that it is "opened up"? It should.

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