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Old 01-14-2011, 08:17 PM
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383 head gasket thickness

I currently own a 383 stroker in a truck that I am about to sell here shortly but in order to appeal to buyers I would like to advertise it with the ability to run on 87 octane. Right now the engine will only run on 93 or higher without spark knock. I would like to know what thickness gasket will allow the engine to run on low grade octane. Just to let yall know I did not assemble the heads so I don't know the thickness of the gasket used, everything else I did myself. Heads are double hump heads with 2.02 intake.

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Old 01-14-2011, 10:08 PM
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You have more than gasket thickness to worry about. Using a thicker gasket COULD actually promote increased detonation. You have to know how far the pistons are down the hole and the current gasket thickness to determine if you can go that route. You need to know your quench area before you make a move.
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Old 01-15-2011, 09:37 PM
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Absolutely correct.

You likely have flat top pistons being it's not oem pistons, but you need
to first know if they're at 0 deck height (even with the top of the block)
at top center.

Then what your combustion chamber looks like - if it's relatively open
and without quench area you won't have much of a chance of running
87, even if you were to lower compression like the above says.

To combat detonation you need around .040 between the top of the
piston (not dish a ring around the outside edge but a flat area on much
of the top of the piston) that corresponds to a flat area in the comb
chamber in the head. If your pistons are even with the top of the deck,
then you can run i.e. an .039 compressed head gasket thickness. If the
piston is down in the hole you need to use a thinner gasket to keep
the top of the piston to comb chamber flat area to around 040.

Here's a good compression ratio calculator.


If you go to the "calculator" link on that page there are other good
calculators that help you fill in information if you are missing info on
one of the components.
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Old 01-15-2011, 11:41 PM
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you need to supply all of your engine's specs before you go swapping out parts. You can run 15.1 compression on 87 octane with the right cam. You can also have to run a 9.5 compression on 107 octane with the wrong cam. You need information like this

Bore, Stroke, Cam Duration, intake valve closing points abdc at .050, combustion chamber volume, piston volume, deck height, gasket specs. There is a lot more that needs to be known before you just go slapping on a thicker head gasket and end up lowering your compression ratio and still have to run on 93 octane.

Running 87 octane over 93 octane you talking a few bucks different at each fill up, running 93 in my 383 isn't a big concern to me because it is just a weekend warrior and I always have my car to drive
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