cudaracer2

Struggling for long time on what to do with my 318. I love keeping the original block, but stroker options cost plenty.

Until now. I have dug up a solution that should work for far less.

So far I have found a 3.58" crank new selling for $350 and stock bore cast pistons for about $277 at Jegs with the correct comp height of 1.658" which places the flat piston top 0.031" below deck, up from the 0.081" stock distance. CR also goes way up because of larger stroke, so that flat piston nets me over 10:1 with a 66cc chamber. Quench is good to, and it's hard to beat a flat top piston -- minimal surface area.

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 very 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 I wonder, seeing as how I will be near 400hp, and much more torque.

Thoughts or experiences?

bigblock

REPLACE THE RODS.

Coronet 500

Welcome. You'll want pistons with valve notches. Having them close to the head and more than a small stock cam will give you clearance issues, and yes 318 rods are puny.

cudaracer2

CRAP......well, that shoots down my plans then. Are you sure I need pockets, seeing how it is still 0.031" below the deck? I have a med lift cam, 0.477 / 0.480" of lift, with no issue, but 0.081" in the bore. Will 0.050" less clearance really be an issue?


I have to imagine that machining those pistons will cost a fortune.

Coronet 500

On my son's piece together magnum .047" in the hole actual .461" int, .451" exh lift simulated .035" gasket, exh was tight. The intake was .054"valve to piston clearance ATDC "chasing the piston". With a simulated .067" gasket int clearance increased to .097" with .469" lift on that lobe, exh increased to most over .100".

The differences in the lifts was due to varying rocker ratios and a used cam with advertised .480" lift.

When you get tight with larger durations the place to check closely is intake ATDC when it is "chasing the piston".

cudaracer2

Valve diameter obviously compounds the problem, as I am at 1.88" intake......thus a 2.02" valve would be worse.


Anybody know what it takes to machine piston nothces?

Gorts 5th

well with valves that big you have to go large CI.
i know that it'll run with large valves but at what velocity/V.E. ?
is this pro stock your running or a street car
you don't need valves that large to get 400 hp out of this.
What about one of the TRW piston/gasket rebuild kits? they have 9-10-1 CR
With a good lunati cam 400 hp is very possible 1.2 1.5 hp per C.I.

cudaracer2

I am looking for lots of torque, so stroker is the solution. less than 400 hp is fine, and I am not even going with headers, just dakota 360 manifolds.

Coronet 500

Your thoughts on valve size are spot on. Those numbers were with a 1.78" intake valve, 1.5" exh valve, magnum shortblock,flat tappet, LA 302 heads with external oiling, ie."pieced together".

I would seriously start looking for notched pistons with that deck height your looking for.

Coronet 500

Here's a thought, a neat build I always wanted to try. KB 165, 283c.i. chev +.060"(3.935"bore) 1.805"C.H. piston, crank turned to 2.1" 6" long chev rods, ends up .005" below deck.

I don't think the aluminum or steel know if it's in a chev or dodge and you get to buy inexpensive parts and make good compression.

Gorts 5th

Food for thought
i have read this several times and i will follow the rule, Geometry is geometry.
he main reason I stick with Lunati is Harold , he was the one of the first to take advantage of the wider Mopar lifter & increase the ramp speed accordingly although I am sure Mopar engineers understood the advantages in the 50s when they designed the V8 engines . Harold started UltraDyne & I could see the advantage of using UltraDyne cams years ago , but UltraDyne went out of business & I printed their online catalog before it was removed from the internet . Hes was hired by Lunati at the time he closed his own business , Ulradyne . Since then many have copied him with Mopar specific grinds having more lift at the same duration . Most Comp Cams designs for Mopar are copied from the small block Chev, you can find the exact same grind in both the Mopar & small block sections although they are starting to change , the SBC has a very short rod ratio & needs a totally different cam than the Mopar , it is just lazy to copy the SBC design for Mopar . Harold has created a whole new series of cams for Lunati for all makes of engines which is sold as VooDoo as well most of the UntraDyne profiles can be found in the Lunati catalog still . There is a section around pg 185 with various lobe profiles in Hyd & Solid lobes specifically for the 904 lifter Mopars & AMC

Further to this is the Chev is a short rod engine with a 1.45 rod ratio
Mopar is typically in the 1.7 - 1.8 range with much longer rods .
This changes a number of things , @ both TDC & BTC the piston moves much slower & actually stops for a longer period of time this does 2 things it allows more time for complete burn of the fuel & moves away slower allowing more time for the pressure to work on the piston which results in increased torque & decreased fuel consumption ! If you have driven an older GM pick up you are lucky to get 9 MPG while a 440 can get into the teens & sometimes into the 20s , the best I have done so far is 24 mpg in a 440 Challenger on the highway & 512 " strokers pushing high teens on the highway even with dynoed stupid power .
The downside to long rod engines is the intake , the piston moves away slower so the engine tends to pull less hard on incoming air flow . Ever notice that the 440 Port is only slightly larger than the Chev small block while the 454 , 455 , 460 even the 351 boss have Huge intake ports ? The trick is velocity , by using a smaller port the air speed in the port is higher so the air flow is kept moving even when the valve is closed building pressure behind the valve & creating a mild supercharging effect . conversely the short rod engines pull air better so having a bigger port with more air available makes sense .
Back to the cam choice do you really think a cam designed for a short rod engine is ideal in a long rod engine ?

Gorts 5th

Apparently the short chetty rod's and the mopar heads won't work together
the geometry of the LA. is different than chetty and furd
and that's why the LA. design is better.
quit trying to copy chetty and furd!
chetties are chet and furds block traffic!

Jrod2011

I was looking at KB flat tops for my 318 as well and the sell ones with a 5cc valve relief that shouldn't affect your compression ratio to much but will help with proper valve clearance. You want to stay .100 above the piston if possible with the valves.