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Oct 18, 2003 | 05:42 PM

stratton

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From: so cal

scary cr

hey guys i've been building a 390for my work truck
have short block and parts ready for assembly
have a 68 360 block bored .040 over with silvolite 1130's
crane 343801 cam and rebuilt heads with mildly ported exhaust
390 crank and rods edelbrock performer intake and holley 650 cfm carb flowtech headers

i plugged my numbers into the compression ratio calculator and came up with almost 12 to 1
please tell me i missed something this is way to high i don't even know if it would run opinions?

also where can i order a new set of head bolts?

Oct 18, 2003 | 05:53 PM

Ratsmoker

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From: Missouri

Welcome to FTE!!!
What is the compression height and dish(cc) for those pistons"? It takes domed pistons or a lot of shaving to make a 390 have 12:1 so yes you figured in something wrong somewhere. New head bolts can be ordered through www.summitracing.com for about $50. You should be able to get the stock cheapies at autozone for a little less.

Last edited by Ratsmoker; Oct 18, 2003 at 06:30 PM.

Oct 18, 2003 | 06:23 PM

Ratsmoker

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From: Missouri

I did some research and found your piston specs.

You have a 3.784" stroke. Divide this by two. (1.892). Add 6.488" for the rod length and 1.76 for the compression height. This will give you 10.14. The FE deck heighth is 10.17. This puts the piston .030 below the deck. The 1130 pistons have a 19cc dish to them. Your head gaskets have a 10cc displacement if you are using the standard felpros. Your heads displace about 67cc. This gives you roughly 8.95:1 compression with your 4.09 bore.

Last edited by Ratsmoker; Oct 18, 2003 at 06:25 PM.

Oct 18, 2003 | 06:36 PM

Jarlaxle

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From: New England

Any part store will have head bolts. If you're as paranoid as I am, order a set from ARP & never worry about them.

If ratsmoker's figuring is right (and I have no reason to think it isn't), that's just about perfect for a street engine--and should live happily on 89 octane gas.

Oct 18, 2003 | 06:45 PM

Ratsmoker

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From: Missouri

I think I know where you messed up stratton. In most online compression calculators you need to enter the piston dish as -19cc not 19cc. Also the FE head gasket is not round so I just add 10.1cc to the chamber volume and enter the gasket thickness as .0001.

Oct 19, 2003 | 04:34 PM

FE427TP

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From: yes

plus odds are the heads have bigger chambers than they were supposed to anyways unless you've cc'ed them it's probably safe to assume on the large side of their range

Oct 20, 2003 | 08:08 AM

stratton

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From: so cal

thanks alot guys i got a little flipped out there appreciate the help couldn't do this without fte

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Oct 20, 2003 | 08:29 AM

Ratsmoker

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From: Missouri

Thanks and you are welcome! I wish I would have used head studs. I got the ARP bolts. I don't know what I was thinking. They don't cost any more than the regular bolts.

Oct 20, 2003 | 06:33 PM

#10

FE427TP

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From: yes

Quote:

Originally posted by Ratsmoker
Thanks and you are welcome! I wish I would have used head studs. I got the ARP bolts. I don't know what I was thinking. They don't cost any more than the regular bolts.

that you may want to remove the heads someday?

Oct 21, 2003 | 06:11 AM

#11

William

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From: Sun River St. George

Head removal on an engine that used studs to mount the cylinder heads used to be a problem. That was before ARP came along. Their studs go in hand tight and can actually be installed with the head sitting on the block. Later when its time for head removal the ARP studs can be removed by hand and if they get sticky a little allen wrench can be used. With the ease of use and clamping pressure of studs verses bolts, I cannot understand why anyone would use bolts? The only issue I have encountered with ARP studs on FE motors is oil pan clearance on the number 5 main cap. In that case I use two ARP bolts and the rest studs. Fe's are so massive on the bottom I feel this small compromise is OKAY!

Oct 21, 2003 | 07:45 AM

#12

Ratsmoker

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From: Missouri

I covered my engine in a garbage bag and popped the number 5 stud ends through. I ground them flush with the nut. It worked great and stopped metal shavings from getting in the engine.