Club 80-90 Forums

These always seem to have a degree of misalignment between the casting and the machining, most evident when looking up the ports from the combustion chamber side. Some are worse than others!
An couple of hours careful die-grinder work with a carbide burr on a flexi extension blending out the steps and smoothing off the casting snots is time well spent, improving gas flow and giving better cylinder filling especially at lower engine rpm.
Before and after:

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Blimey that looks like a fair bit of metal removed.

Less than an eggcup full when I swept up, from both heads

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Do you put these on a flow bench to compare ports and see the difference before and after porting?

No, I dont flow test them, but they can be so bad that any amount of smoothing and reshaping must be beneficial. The torque delivery of my engines suggests that I'm doing the right thing

Checked the exhaust valve guides and surprise surprise, the 9.0mm reamer wont go down the bore as per usual...

(If the guide isnt reamed out, this will cause a hanging valve when the engine warms up and then a bent pushrod, at best)

AMC/KS really do need to get their act together imho

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Old fashioned empirical engineering

silverbullet wrote:No, I dont flow test them, but they can be so bad that any amount of smoothing and reshaping must be beneficial. The torque delivery of my engines suggests that I'm doing the right thing

Checked the exhaust valve guides and surprise surprise, the 9.0mm reamer wont go down the bore as per usual...

(If the guide isnt reamed out, this will cause a hanging valve when the engine warms up and then a bent pushrod, at best)

AMC/KS really do need to get their act together imho

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Ah fair enough, I was just curious. It's amazing the improved performance that can be had from properly ported and matched ports/manifolds.

937carrera wrote:

Old fashioned empirical engineering

Fitting
When I was a lad apprentice toolmaker, Stan the Man the cylindirical grinder would allow for bush internal diameters closing up when pressed into a bore.

tobydog wrote:

937carrera wrote:

Old fashioned empirical engineering

Fitting
When I was a lad apprentice toolmaker, Stan the Man the cylindirical grinder would allow for bush internal diameters closing up when pressed into a bore.

Yep, that's one of Dad's tricks too

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Funny that golf balls do not have a smooth suface as it lessens drag.
Shark/ dolphin skins are rough, so they can swim fast.

I would think some roughness would be benificial to flow?

kevtherev wrote:Funny that golf balls do not have a smooth suface as it lessens drag.
Shark/ dolphin skins are rough, so they can swim fast.

I would think some roughness would be benificial to flow?

"Dimples on a golf ball create a thin turbulent boundary layer of air that clings to the ball's surface. This allows the smoothly flowing air to follow the ball's surface a little farther around the back side of the ball, thereby decreasing the size of the wake."
https://www.scientificamerican.com/arti ... n-golf-ba/" onclick="window.open(this.href);return false;

Overall port shape/profile is far more important than surface finish for that very reason. I leave them with the finish that results from the carbide burrs used to reshape the port walls.

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