a 390

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RPMLegends18

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When people talk about 390s, is it a stroker 318? I put 390 in the search tool but that didnt really help me. Because that is a huge gain in cubes...well at least it sounds like it is
 
cool thanks for the info...now to do some google searching and homework to really figure out a stroker motor. As I dont really know to much about them. Or if someone can provide a dumbed up explanation. Because with the longer stroke it makes the piston move further in the bore (right?) but wouldnt that push the piston up into the head? Or are different rods used? I would like to do this to my 318 some time done the road
 
I recommend reading this book. It has A LOT of good information in it.

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How To Build Big Inch Mopar Small Blocks
 
RPMLegends18 said:
Or if someone can provide a dumbed up explanation. Because with the longer stroke it makes the piston move further in the bore (right?) but wouldnt that push the piston up into the head? Or are different rods used? I would like to do this to my 318 some time done the road
Click to expand...

Yes, the longer stroke will move the rod and piston up closer to the head. In the case of the 4 inch arm, yea, it would move the OE piston right up and out of the block.

The stroker engine will use the OE length rod. The piston becomes shorter in it's height above the pin making it shorter and lighter. The draw back is sometimes the rings end up in the pin area. Not so great, but workable.

I DO NOT KNOW IF THIS IS THE CASE WITH THE 318 - 390

With 390 cubes, you use ported 340-360 heads or preped Edelbrock heads. 1-3/4 headers, etc.......

Check with "Speedomotive" in Ca. for help. I do beileve they have a 318 - 390 kits and parts. I'm not sure who else has stuff for this, but it's out there.
 
KB make forged pistons for the 318 to 390 conversion, they offer a flat top for high compression and a dish piston for pump gas engines. With a 4 inch stroke the LA engine's tall deck there is no problem with the ring being in the wrist pin.

In fact the small block mopar tall deck and raised cam is a perfect engine to stroke. With the proper I beam rods there is no clearance problems at all...
 
thanks for all the info guys. See that is the part were it got me confused, I didnt know that it used a shorter piston above the wrist pin. I will defiantly have to pick that book up and do some reading. Is there any mods to the actual block for the bigger crank stroke? I checked out the Speedomotive website, and for the base 318 to 391 stroker kit is $1350, but then there are all these other upgrades to go along with it. Could you get away with just getting the base kit or what upgrades would you guys suggest? I also have a set of 360 heads off my old motor that would be the perfect candidate. They are from a 76 Dodge Powerwagon, I will pull the numbers off the heads and share that with you guys. This 318 that is in my car now is pretty fresh. I just built it about 4,000 miles ago. Its been cleaned .030 over, stock rods, new flat top pistons, and a purple cam (Adv. Duration 284/284, Lift .484/.484) would that cam be usable in a stroker application?
 
rumblefish360 said:
Depends on the Con rods used.
Click to expand...


there are two I beam rods that are generally used, Eagle 5140 I beam rods, and Scat 4340 I beam rods.

the scats are made of a stronger steel and they are both about the same price.

H beams will generally require the bottom of the bores to be notched for the rod bolts to clear...

Stock rods can be used and they will require a notch to clear the rods bolts also....usually by the time you have them resized and a good set of rod bolts installed, the price of the new I beams is not that much different.
 
Sounds like a decent plan. You'll need to replace the pistons and/or rods. Not all 318 pistons are created equal although all years used a 6.123" long rod.

The 67-69 318 pistons have a wrist pin to piston crown height of 1.759" and the pistons sit .036" below the block deck at the top of the stroke.
The 70-71 318 pistons have a wrist pin to piston crown height of 1.750 and the pistons sit .060" below the block deck at the top of the stroke.
The 72-86 318 pistons have a wrist pin to piston crown height of 1.739 and the pistons sit .056" below the block deck at the top of the stroke.

Running the stroke from 3.31 to 4.00 is enough to jam even the late model pistons into the heads with a stock rod.
 
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