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topic 11667

Acid porting cylinder heads and intakes


My question would be related to acid for the purpose of cleaning cast iron and smoothing out the roughness of the cast in the intake manifold and cylinder heads ports and to cover any previous marks left behind from the die grinder after port work has been preform ,as to what type of acid should be used and in what time frame should it be applied. I know there are some companies doing this but they don't disclose enough info. Increasing port diameter is the objective. Could you shine some light on this? I would be grateful.

Thank you,

Richard Lavoie
- Vancouver Island, British Columbia



Acid cleaning/polishing of ports? I don't believe it!

Surely the good old way of using abrasive grinders is the only way to do it... finishing off with superfine grit wheels. Even if you could achieve a mirror finish, would that really add even l/4% to the performance? Nah!

The grinders would work far faster than any acid, too. Then on the cylinder head you'd have to ensure that no acid got into the valve ports, especially the valve lips. What is important is the l00% matching up of the inlet port to the inlet manifold. Any 'steps' in this area would lead to eddy currents. Smoothness is the key.

Sorry to be a doubting Thomas.

Happy Grinding (away).

freeman newton portrait
Freeman Newton
White Rock, British Columbia, Canada

(It is our sad duty to
advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

... where no eagles soar, only seagulls.


I'm certain that the inquirer was asking about the use of etching to return the appearance of the port surfaces to the original "cast" look. Some ruling authorities will be interested in rejecting parts that look like they've been machined. In other words, port grinding is a disallowed modification. Visual inspection will easily reveal die-ground port expansion and matching maneuvers.

I am curious about the technique of etching to remove metal bulk from "over-engineered" parts. Some parts are quite heavy and have a complex shape that would make machining a tedious, often impossible task. The object would be to reduce weight without revealing obvious modification. I'm thinking of H2SO4, isolated somehow to limit the exposure of the iron parts to surfaces not easily seen or measured. Even a few ounces removed from outer reaches of heavy rotating parts such as wheels and rotors would tremendously aid in performance response.

Bill Slawson
- Spencer, Iowa

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