> Jensen Healey & Jensen GT Tech > Engine & Transmission > Help ID'ing mystery pistons

 Moderated by: Greg Fletcher  

Joined: 09-17-2007
Location: San Francisco, California USA
Posts: 201
I was surprised to find some fairly clean and tidy piston heads that wiped clean when I pulled the heads off this 73' custom built engine. Heads have had a lot of work and running 104 cams, put out very good power (I was told 190hp when I bought it, dual Weber 45's and custom headers, etc.)

They don't strike me as cast pistons and my first reaction was that they were JE's as they kind of look machined, but as I inspected further with a good light I'm not so sure anymore.

They have the strangest little light (less and 1mm) valve relief cuts. At first I thought- oh no, valve contact! But they are so clean and uniform and the engine was running smoothly with no noise, so that seems implausible that they are indentations from the valves. They seem machined into the surface.

I tried to look for some pictures of JE and some stock Lotus S1 and S2 pistons and could not find anything that looked like these. Did the older Dave Bean style look like this?

Is there any way to precising calculate compression ratios? I could borrow a friends hole gauge and measure the liners exactly and then measure the stroke, but not sure how this would work.


Joined: 09-10-2012
Location: BROOKHAVEN, Georgia USA
Posts: 515
They "look" like J&E for the 9.5:1 compression. We used them as the least expensive way to increase the perfomance(along with excellent reliability) with the Stromberg carbs., using the earlier B1CM slightly richer needle over the B1DK.
The SOP for compression would be the burette with a thick plexiglass bolted to the head, and of course an accurate gage for the piston/crank throw along with the hole diameter. You could "ballpark" the combustion chamber using a sphere" volume with a depth gage, but again this would NOT be as accurate as the burette.
stay safe, bruce

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