Thursday, 25 September 2014

Port flow improvements

More examples of previous engine work.  This post is concerned with modifications to improve port flow.  Starting from a head off the street models which had an updraft inlet port of about 10deg. in comparison to the similar factory race heads with a small down draft angle.  I wanted to create a better inlet port shape without any welding on the head.  Any significant head welding requires the removal of valve guides and seats, re-heat-treating and re-machining the seat and guide holes.  That is if you want to do the job properly.

Cross section of a stock road head showing updraft inlet port.

The red area shows where I bore a circular recess to allow the fitting of a solid block from which to fashion a new port.

Making the insert block.

Machining the new port with the block fitted to the head.

Final block shape after machining the new port.

Comparison of flow between the standard port and that modified with the block.  This was achieved without any other detailed port work.  Further improvements were achieved by the removal of small amounts of material around the valve guide area.

There are more pix. in the Aermacchi engine folder on my picasa page and there is a PDF report with a lot more detail available for download from

I managed to get a race head casting from Dick Linton which was cast without ports or combustion chamber recesses.  I intend to machine this to use a narrower valve angle to allow for a more compact combustion chamber and steeper inlet port. It will also have significant squish areas which are absent from the original 1950/60s design.

Showing the basic casting.
More details are available for download in a report at


  1. That's some serious work, very nice.

    1. You do some pretty good stuff too. I like the BMW heads that you did.
      Did you look at the 2 pdfs referenced in the above?

  2. Thanks Tony. Have you made any further progress with the raw casting?
    I downloaded both PDFs, fascinating stuff. I really like how the re-angled intake port is a bolt-on (ish)
    affair (no welding), very clever!

  3. I did do some machining on the raw casting, but then I had second thoughts about what bore size I was going to use and that has not been resolved yet so work on this head has temporarily been halted.