Longrodding a 390?
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New User
Joined: Apr 2003
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Longrodding a 390?
hey there all. I am having a dillemma about deciding whether to replace my 360 Crank & rods w/ 390 or to get a 390 crank and use 360 rods with milled pistons. Has anyone done this and what might be the advantage/disadvantage to this. i also think that I need to have the block milled/notched for rod/stroke clearance at the bottom of the cylinder. I've heard this provides LOTS of torque, but how might it affect overall torque range? Any input is greatly appreciated. Also, who was it that said they had 390 crank & Rods ready to go for 200.00? Do you still have available? Thanks-Eric
Post Fiend
Joined: Feb 2001
Posts: 6,624
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From: Missouri
There is very little difference in length. You would not even notice the difference. The 390 rod is much stronger than the long rod though. You would not need to notch the block to do it.
Engines with very short rods tend to make more off - idle power. Engines with very long rods make more power for the rest of the RPM range thoguh. This is becasue short rods accelerate the pistons more at TDC and this will increase scavenging during the overlap period. This really doesn't apply to your situation though.
If you are going to drive this engine like you stole it then you will want to find the 390 rods and put ARP bolts in them. For just a commuter vehicle you will be fine with the 360 rods.
Engines with very short rods tend to make more off - idle power. Engines with very long rods make more power for the rest of the RPM range thoguh. This is becasue short rods accelerate the pistons more at TDC and this will increase scavenging during the overlap period. This really doesn't apply to your situation though.
If you are going to drive this engine like you stole it then you will want to find the 390 rods and put ARP bolts in them. For just a commuter vehicle you will be fine with the 360 rods.
Elder User
Joined: May 2002
Posts: 799
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Yup, the 390 rods are much heftier and confidence-inspiring. I didn't appreciate that fact until I had them side-by-side. I did the complete 360-to-390 conversion and like it. I'm still working out a few bugs, though -- like what's the best time for truck errands so I don't wake up the neighbors with all the noise. ;-)
Next evolution of this thing will include quieter mufflers.
Next evolution of this thing will include quieter mufflers.
Freshman User
Joined: Jan 2004
Posts: 32
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From: Miami
The biggest advantage would be piston dwell. Piston Dwell will free up a few horseys. I don't truely feel a long rod is that much weaker than a short rod engine. If you keep HP Moderate say 400Max HP, but more like 350 or less build. But if you have to get new pistons (highly recommended), and still need a crank, then look for a crank and rod combo. They are out there. If all else fails ask seller of crank if They have rods also.
All in all a short rod set up is more for peace of mind on a mild build. 390's have been built and ran with success with long rods. Some even in race situatuations.
Scotty
All in all a short rod set up is more for peace of mind on a mild build. 390's have been built and ran with success with long rods. Some even in race situatuations.
Scotty
