3.58" cranks in 318 with 308 heads and stock height pistons (318 mains)

[cudaracer]

Anyone do this?

If I use stock height 318 pistons, with the 3.58" stroke, the pistons stick above deck by 0.051", but with the larger open chamber 308 heads, I am seeing that I would get right where I want to be with CR, and a thick gasket.

Thoughts?

P2V is obviously a concern, so reliefs are a must.

[cudaracer]

Just found out that silverlite makes flat pistons with a 1.685" CH, so with that 360 stroke, it puts me at 0.030" below deck. 

Best part is, they are cheap cast pistons, good enough for my 390hp target.  CR goes way up because of longer stroke too.  And my torque target is now 440ftlbs.

yeeehaaaa

[72bluNblu]

The pistons are the biggest deal with that combo. It used to be that custom pistons were needed for that application, so I'd be sure to check that the pistons you're looking at will work.

Other than that, its just the costs on turning down the 360 crank to 318 mains. Keep in mind you'll need external balance rotating gear to go with it. Also, check those 308's for chamber size. The set I have checked out at 65cc's, so they may not be as big as you think.

Any reason you're not just going with a 4" stroker crank other than cost? Usually the custom piston issue makes the whole thing pretty close to a wash price-wise.

[cudaracer]

Crank is a stroker ready to go, with 318 mains.

Piston is for 67-77 dodge 318 trucks, available in several over-bores.

This is the PERFECT solution for 318 increases, and my CR is raised to 10:1.


Just wondering if my stock rods will be strong enough for 440 ftlbs.

Also, do I need to run special fuel for 10:1

[RzeroB]

I know I have been "hibernating" from the hobby for a while, but I didn't know you could turn a 360 crank's 2.81" mains down to 2.50" to fit into a 318? I thought that I read somewhere long ago that said it made the journal too thin over the oil passages hence weakening the crank. Like I said, I'm not up on the latest info, so maybe what I remember is now outdated info. Just curious as to how it will work out.
 

[cudaracer]

They sell 318 stroker kits right, both 4" and 3.58" stroke.


That's how.

Ready to go.

Hughes even has them

[Road_Runner]

This is EXACTLY the combo I've asked about here previously.  My thing is that if I decide to stay with the original 318 in my 73 I'd like to 'hide' more power in a stock looking package.  This stroker yields 348 c.i. with an almost perfect 89-90% stroke to bore ratio.  I have a set of 302 heads which are the later swirl port 318 heads which I'd have to open up for the extra cubes but would still look stock and I could even run a stock 340 intake if I wanted.  I'd be very interested if you end up doing this so keep us updated with your build & results.

Later, Jim

[cudaracer]

So far I have found the crank selling for $350 and the cast pistons for about $277 at Jegs.

Here are the specs for piston:

http://www.kb-silvolite.com/test/silv-o-lite/spistons.php?action=details&S_id=52

Here are the specs for crank:

http://www.moparsupercenter.com/crankshaft-cast-iron-3-58-stroke-318-340-mainp5007257.html


This appears to be the perfect setup for the 318 to seriously boost torque, keep piston weight down, boost displacement to 348ci, and for low cost.  I will keep same rods, but the crank and pistons are heavy duty relative to stock 318.  Or should I replace the rods as well, seeing as how I will be near 400hp, and much more torque.

[Chryco Psycho]

The only issue I can see is with the piston .058 above deck the combustion chamber in the head has to bigger in diameter than the piston at least .020 int the chamber , with quench @ 10:1 comp you should be able to run premium pump gas .

[cudaracer]

^


Read my second post, I found the right piston with a lower comp height that will put piston at 0.031" inside bore and get me just over 10:1.


It's the perfect combo.

[Chryco Psycho]

 
 Sorry I didn't read the whole thread

[cudaracer]

My concern now is piston to valve clearance. 
These appear to be flat pistons with no dimples at 31 thousand in the bore.  My cam is 0.477 lift on intake, which is the closest point if I recall.

Anyone have a similar setup?  How can I know, without purchasing them?

[HP2]

During the overlap cycle with both valves open may be the tightest pinch point with the piston. I didn't do all the math to see where this combo is, but it certainly is dependant upon your particular block height, gasket thickness, the piston location, and chamber volume on how close everything gets. I've never found a block that was exactly at spec for any variety of dimensions, except bores and bearings. You might be able to flycut valve reliefs if needed, but that is a wild card with a flat top cast piston as you don't know how thick the tops are.

So the crank and pistons are $627. Figure $75 each for main and rod bearings. $100 for rings. $75 for rod bolts, $200 for installing the new bolts and resizing the rods and you're almost $1200 into the crank kit and that is without any balancing work at all on a cast iron crank and cast pistons. For another $700 you can get a 390 crank kit with forged pistons and a cast steel crank that is all balanced and ready to install. But, it is your coin and your labor so you need to do what works for you.

[brads70]

Where are the ring lands during all this? Just thought I'd throw that out there?

[PlumCraZRT]

Where are the ring lands during all this? Just thought I'd throw that out there?

That was my first thought on the .050" out of the hole piston...

Later in the thread he mentions that he found a piston that leaves him .030" in the hole.