I'm refreshing a 3.1.stroker engine that I bought from a fellow who was swapping in a V8. The engine ran just fine before he pulled it from his car and, in fact, took it to a dyno shop at my request to get data (making about 280 peak HP). He was using dual SU carbs but I plan to use triple Weber 40 or 45 DCOE carbs.

Now, after I pulled the front engine cover, I'm seeing what I think are two head gaskets and my micrometer measures each of them at 1.16 mm thick.

Like I said, the engine ran strong when pulled so this arrangement, while unorthodox, appears to be viable.

Has anyone ever seen a setup like this before?

Here's the photo of the gaskets that I didn't include on the initial posting.

And here's the dyno curve. My error, it's not making 280 HP. The chart title was, as you can see, 280Z HP TQ, and I overzealously misinterpreted it.

The PO said that the SUs could not flow enough air to get more power but the triples would allow that to come up to well over 200 HP.

Has the head been shaved? Maybe the guy overdid it. You can get an idea by looking at the head ID casting. N42, N47, E31, etc. The edge will be close to the the symbols.

This one looks uncut. Holy moly on that price.

https://jdm-car-parts.com/products/e31-head-for-datsun-240z-series-1-nos?srsltid=AfmBOooSCQQdZA1flBbQstx-oCBt4adJYn9eX779z2gKvZTRaaYCqXZE

Didn't read all.. Just wanted to ad, use a self made copper head gasket, you can use them over and over!!

read: Copper Topper | The Ins and Outs of Copper Head Gaskets - DSPORT Magazine

It's an N42 head. I have other heads as well for comparison so I'll take a look today.

Edited April 17Apr 17 by Seppi72
Added verbiage

If the guy used flat tops in a bored and stroked block the N42's small chamber might have given a too-high compression ratio. Maybe he added a gasket to lower it.

Cylinder pressures would be illuminating. Not sure you'd want to try to measure them with the front cover off but it might be possible. Interesting puzzle.

What would you consider to high?

I would think anything much above 10:1 as too high and a good cam would help with dynamic compression

Before i started on my 280zx restore with a L28/N42 engine and N42 head i measured the compression and after 1-2 years of standing still it was a good 10-10,4 : 1 so... This was on a original euro version 280zx. (For use with the high octane fuel available, leadfree offcourse.)