I installed a pair of 028 sandwich gaskets, I do not recall whose they were. At 11/1, they blew out in less than a year.
040 FellPros have been fine from 10.7 to 11.3
BTW;
What SBM has 8.6 Scr?
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My 2cents;
A 318 engine at a true 8.6, would have a total combustion chamber volume of 85.7cc.. Assuming an 020 steel gasket of 3.9 cc, that is a basic of 81.8 ..
Swapping to an 028 of 5.5cc, the volume changes to 87.3 and Scr to 8.46, and yur never gunna know the difference.
The FelPro is, IIRC 8.9cc, changing the total volume to 90.7 , and the Scr to 8.2
You can notice that at WOT at or near the torque peak and after.
The rest of the time, NOT at WOT, your engine is operating on EFFECTIVE Scr, which could be as low as 4/1, maybe even less, so, your thin headgasket at this time, is pointless.
In any case, Scr is just a tool to get the pressure up, which is the real measure of WOT performance. I have never measured a stock lo-compression 318 with more than 140psi, and almost never have I seen more than 135psi @900 ft elevation.
87 gas will support 155psi at WOT, with even a modicum of care in assembly... and up to 165 is possible with 91 gas, in a tight quench design.
But again, that throttle on top of your intake, can reduce that to 90psi or even less, at idle........ never mind that 10% of your pressure could be leaking past your old worn out rings.
Lets say your thin gaskets might get you up to 135psi at 4% leakdown, on a fresh build, but your tired rings/bores are at 10%, thus the math says your pressure might actually come in at 126psi.
The point is this, at your performance level, chasing a .14 point of compression is pretty much a waste of time.
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If you have a 318, with over 130 psi,
IMHO, the best place to put your money is into a higher than stock stall convertor, and/or performance rear gears. A 2800 really woke up my lo-compression-318. The 4bbl and free-flowing exhaust, was just icing on top.
If I was taking the heads off anyway, well then I would mill the crap off them.
But then;
If I was taking the heads off to have them rebuilt, well then I'd also get some higher compression pistons installed; I mean I'm already buying over $200 bucks worth of gaskets, so I'm only doing it once.
BTW;
While cruising at 65, your engine is heavily throttled, thus operating at a very modest pressure level, meaning, that any Scr change is pretty much meaningless....... while cruising. A reduced cruise-rpm is more effective, and driving slower, is even more effective. Which is the opposite of adding a hi-stall and performance gears. Thus for economy, I have found that a bigger engine, cruising at a lower rpm, is a better idea. You get more torque, more power, more performance, and with a reduced cruise rpm, you get more mpgs.
Just saying.
This all goes out the window tho, when you start stuffing big cams into them, and rather rapidly I might add.. On my personal 11/1 carb'd 360; I've seen just one bigger cam-size drop an easy 1/3 fuel economy; and 3.5 cam-sizes smaller, nearly triple it's economy.
And, overdrive is a real game-changer.
Jus saying.
