390 Torque Build??
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390 Torque Build??
Got a old 1 ton dually short wheel base 360/4spd! Need more power was going to swap for a 390 can the 390 crank and rods work in the 360 block to get the stroke right? 390 stuff is getting hard to find, got one but block is busted. When building it up whats the best choice for cam and head work and piston choices to run this bad boy on the crap gas we have these days to not burn valves up! Aluminum intake and a Holley 750? Just need lots of torque to pull this old goose neck trailer around!
Any help and part numbers would be greatly appreciated!
Any help and part numbers would be greatly appreciated!
Hotshot
Joined: Apr 2009
Posts: 14,333
Likes: 247
From: Stanley, VA
Yes, to make a 360 into a 390 you must swap the crank and rods. The 390 rods are shorter to compensate for the longer stroke.
I would use the flat top 390 pistons, this should bump the compression up to around 9.5:1. The 360's piston actually sits down in the bore about .100" making for a really anemic CR.
If you're going for bottom end torque chose a cam that has higher lift and not so much duration and overlap. Most cam manufacturers have an "RV" cam in their product line. On the carb, with a 390, I'd stay more in the 600-650 cfm range.
On the heads, I would leave the ports and combustion chamber stock but one thing I would do, rebuild them for unleaded fuel. Have the valve guides replaced. Have hard seats installed on the exhaust side along with stainless steel exhaust valves. When I rebuilt my heads, they had already had a couple of valve jobs and the intake valve was starting to "sink" into the head. I had the shop install +.030" oversize head valves, this brought everything back to spec.
I would use the flat top 390 pistons, this should bump the compression up to around 9.5:1. The 360's piston actually sits down in the bore about .100" making for a really anemic CR.
If you're going for bottom end torque chose a cam that has higher lift and not so much duration and overlap. Most cam manufacturers have an "RV" cam in their product line. On the carb, with a 390, I'd stay more in the 600-650 cfm range.
On the heads, I would leave the ports and combustion chamber stock but one thing I would do, rebuild them for unleaded fuel. Have the valve guides replaced. Have hard seats installed on the exhaust side along with stainless steel exhaust valves. When I rebuilt my heads, they had already had a couple of valve jobs and the intake valve was starting to "sink" into the head. I had the shop install +.030" oversize head valves, this brought everything back to spec.
Hotshot
Joined: Apr 2009
Posts: 14,333
Likes: 247
From: Stanley, VA
If you do rebuild the heads, these people are really good on prices for the valves.http://www.sivalves.com/ I bought 8 stainless exhaust valves and 8 of their "seat saver" intake valves, these are the ones that have oversize heads. The 16 valves plus shipping ran around $80.00.
On the pistons, you want the ones with a 1.760" compression height not 1.660" and my personal preference is regular cast not the hypereutectic pistons. Hypereutectic pistons require a bigger ring end gap and, in my opinion, leads to more blow by. I used Silv-O-Lite 1131 pistons in my rebuild.
On the pistons, you want the ones with a 1.760" compression height not 1.660" and my personal preference is regular cast not the hypereutectic pistons. Hypereutectic pistons require a bigger ring end gap and, in my opinion, leads to more blow by. I used Silv-O-Lite 1131 pistons in my rebuild.
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