Acid porting

[MR. 327]

There's a whole book you can buy on this subject called Hidden Head Porting by Don Terrill from racing secrets.com! check this out http://acidporting.com/acid_porting.shtml

[jeff klei]

I used to do all the acid porting at Batten heads in the late 80's. It was done out side with a 2 part acid solution. Nasty stuff, but it did the job. Block the intake and exhaust ports and valve guides up, level the valve seat, pour just up to the seat, let sit for a day, then do it again the next day. Two times was all you need. Looked like stock ports when done the right way. Those were the days!!

[motormonkey]

Lets say if done, dont waste time wating for the acid. Port lightly first and then acid. When that is done iron oxide blasting helps. Practic first and dont get greedy. You really need access to a flow bench. I never worried about the entrances on sbc heads, more on the floor,pushrod pinch and the guide. It hides easier in the port. Oh, sometimes sinking the valve for pocket porting helped.

[TheEngineWorks.com]

I used to do all the acid porting at Batten heads in the late 80's. It was done out side with a 2 part acid solution. Nasty stuff, but it did the job. Block the intake and exhaust ports and valve guides up, level the valve seat, pour just up to the seat, let sit for a day, then do it again the next day. Two times was all you need. Looked like stock ports when done the right way. Those were the days!!

[3V Performance]

I used to do all the acid porting at Batten heads in the late 80's. It was done out side with a 2 part acid solution. Nasty stuff, but it did the job. Block the intake and exhaust ports and valve guides up, level the valve seat, pour just up to the seat, let sit for a day, then do it again the next day. Two times was all you need. Looked like stock ports when done the right way. Those were the days!!

Still are shhhhh

[Metrobilly]

Not many specific "how to's" in response to the original question. Is readily available Muratic acid (30% HCl) a suitable, What do you use to protect places that you don't want treated such as valve guides and seats? Silicone? How about using acid to restore the texture where iron was altered with a carbide bur?

A fellow racer once said "It takes some time to grow a good head casting." Then winked at me. I think he knew the answers to these questions.

[automotive breath]

From what I hear, duplicating "as cast" texture is now done by blasting with
weld slag or coal slag. Air pressure is adjusted to achieve desired texture.

[David Redszus]

In the world of two stroke racing, transfer port cores were often subject to shifting during the casting process. As a result, the transfer ports were not symmetrical producing uneven port timing and a mixing of exhaust gas with inlet charge.

But some cylinders did not suffer from core shifts and were much more uniform and produced better performance. To compensate, racers would grind the transfer ports for timing and flow balance. When the area to be modified was too small to reach with a cutting bit, acid (nitric, sulfuric or hydrochloric) was applied with a small brush and flushed with mild ammonia water.

The sand cast texture was then reapplied using aluminum oxide which has sharp edges and simulates a new sand casting. Abrasive particle size and pressure could be used to obtain the proper texture. It was important to blast all surfaces so the appearance was uniform.

This process is still used today. It is used merely to get back to the performance level of a good stock casting and never used to obtain a competitive advantage.

[jfholm]

Not many specific "how to's" in response to the original question. Is readily available Muratic acid (30% HCl) a suitable, What do you use to protect places that you don't want treated such as valve guides and seats? Silicone? How about using acid to restore the texture where iron was altered with a carbide bur?

A fellow racer once said "It takes some time to grow a good head casting." Then winked at me. I think he knew the answers to these questions.

If you go back to my post on this I thought I pretty much detailed the answers to these very qustions. Look for post by me, jfholm.

John

[hopperpwr]

to aid in getting the "as cast" look try dusting a florescent spray paint over the ports... where the overspray lands and drys the acid will not etch, thus leaving small dimples in the port after 2 washes with the acid solution... takes a little practice but definately gets the job done ... the media blasting looks too perfect and not as a casting..... a cotton swab and some bluing also works for putting the dots in the floor of the runners