Im looking into buying some pop up pistons for my Y block but want to buy 91 pump gas. I have 113 heads street ported and polished with 5thou decked, .30 over bore and 5 thou decked off the block. I dont understand the math to know how much compression to achieve to buy premiem gas at any local station.

Look fast, drive slow!

You can use this online calculator:  http://www.csgnetwork.com/compcalc.html 

I plugged in some values.  3.78 bore, 3.3 stroke, compressed gasket .043, chamber volume 72cc, Head gasket diameter 4.00, Deck clearance .025, and 10 cc dome.  CR would be 9.04:1.  It would probably run well on regular, definitely would on 89 octane.  All assuming the block is 292.

Enter your own accurate values, i.e. chamber volume and deck clearance after measuring.

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.

Thanks for the quick reply. Yes its a C1AE 292 block. Stock crank cleaned up at .20 under. Ill check it out on my computer. Does the timing have anything to do with with the gas it takes? Advanced timing mean higher grade. Im gonna run three 94's with an MSD or a Stock distributor with that adaptor replacing the points. Depends on the cash flow. In your experiance how much horsepower roughly would this engine produce? 240? I port matched the stock exhaust to also match the 113 heads. Im using a 573 edelbrock intake. Oh before I forget the heads have stock rockers and I plan to get a mild cam from John mummert with a true roller timing chain if it affects any calcuation on the math.

Look fast, drive slow!

My guess on the HP would be 275.  Others have more experience with high output engines though.  The valve timing, dictated by the cam chosen, will increase or decrease dynamic compression/cranking compression.  A mild cam like the Isky e4, combined with a static CR of 9.2, should still allow regular gas.  Ted made a really neat chart about this on a similar query I made several years ago.  I'll try to find it.

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.

Here is the thread:  http://www.y-blocksforever.com/forums/Topic57116-3-1.aspx 

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.