what compression ratio
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From: Rexburg,Id
what compression ratio
Hey Guys; I'm rebuilding a 390 for my 66 F100. I bought an old truck with a 390, which turned-out to be a reman. engine with a variety of parts. It had a 360 crank, 428 rods, and 390 truck pistons (the ones with the dish and 4 valve reliefs, comoression height-1.78)
I just want something snappy, not pop your neck fast. I've changed to a 390 crank, and wondered what I'll end up with if I use the old pistons and cam (looks like new). I live at about 4800' elevation, and don't want to deal with pinging on unleaded fuel. Heads are ; Int. 2.027, Exh. 1.559, have been milled .010. Holley 600 carb. Thanks, in advance for your help! Brett
I just want something snappy, not pop your neck fast. I've changed to a 390 crank, and wondered what I'll end up with if I use the old pistons and cam (looks like new). I live at about 4800' elevation, and don't want to deal with pinging on unleaded fuel. Heads are ; Int. 2.027, Exh. 1.559, have been milled .010. Holley 600 carb. Thanks, in advance for your help! Brett
Last edited by biggut; Dec 23, 2004 at 06:40 PM.
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Egad. Lets see, that makes it a 360 with short rods. The compression height of those pistons is 1.776", and they're not 390 truck pistons, they're 390 car pistons and 360 truck pistons.
That would be extremely low compression if they did in fact use 428 rods. You probably have long rods in that motor. (long rods = 6.54" long, short rods = 6.488" long) The 428 used short rods.
If in fact you do have 428 rods and the above pistons the 390 crank will go in without problem. But if it were me, I'd check the deck clearance on the new setup. Get back to us with the deck clearance. Pop one piston and rod combo in it, set that one to TDC and measure it with a straightedge and feeler gauge.
That would be extremely low compression if they did in fact use 428 rods. You probably have long rods in that motor. (long rods = 6.54" long, short rods = 6.488" long) The 428 used short rods.
If in fact you do have 428 rods and the above pistons the 390 crank will go in without problem. But if it were me, I'd check the deck clearance on the new setup. Get back to us with the deck clearance. Pop one piston and rod combo in it, set that one to TDC and measure it with a straightedge and feeler gauge.
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Annihilator, the bore is.060 over. I hope to get the crank in this week, and then I'll do the deck clearance thing, and let you guys know what it is. Brett
Last edited by biggut; Dec 24, 2004 at 09:41 PM.
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Put the crank in today; (anyone else get in trouble for being in the shop on Christmas?) ran #1 piston up to TDC, and measured deck clearance with a straight-edge and feeler gage. It is between .019 and .020 to the top edge of the piston. Brett
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Thanks Rusty, I believe I'll put her together and see how she does. It'll probably be spring before I can put it in the truck, but I'll let you guys know how it works-out. Brett
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The truck pistons are the stock flat tops that all truck FE's had. The 428 rods will be the same as any other FE from a 360 to a 428 they all used the same length rod that was a 6.489. The 352 was the only od ball at 6.549. using the stock flat tops should give you somthing around 9.2-9.7:1 depending on the heads. this is enough to run regular unles you are running an agressive timing curve then it require around mid grade.