Largest bore on a stock 318. Crank question also...

So what is the largest bore you gys have cut in a stock 69318 block? We are trying to get a 4" bore with our magnum xl 3.31 crank. We are trying to get in the 330-340 ci range.

Kasey

a buddy of mine has done a bunch of those. bored them to stock 340 bore.{not real high hp.}

I know of guys running the same set up with an x block and buzzing them 82-8500 making strong 450-500 hp on a 2bbl in their late models

Its all in the camshaft, compression, and the W2 head makes up the rest.

We are limited to compression, and no porting, but acid porting is accepted way of cleaning up casting flaws. the W2 flows 40 more CFM box stock over the Bowtie head allowed in the chevys. This thing is gonna sing.

our budget isnt alowing us to use an x block, or the R block thats legal. We have a 340 block laying around but cant bring ourselvs to possibly destroying a good block.


Kasey

If we offset grind the crank from the 2.00 chevy pin tothe 1.88 honda pin what can we get with the 3.31 crank.

KAsey

Why not put a stroker crank in it instead of the big bores? I guess if you ruin a 318 block you haven't lost much except the machining costs.

I've been thinking about this lately too! What to do with original forged 340 cranks? I was thinking offset grind to 1.88 and use the plentyful 6.3 rods from the used NASCAR shops. The piston weight needs to be less than 440g from what I understand from the rod makers. I believe 3.79 stroke may be doable starting with a non ground journal. Possibly use a Ford Windsor shelf piston.
I already have a 3.79 mopar crank that has to have the journals cut to 2". I have used Lentz 6.20 rods.
I hope to use them sometime this year.

Brad

I cant run over a stock 3.58 stroke.

I have been looking at used lentz, and corillo rods.

Kasey

Sonic test it.. I think it's a "your results may vary" deal there... I've heard of them going to 4" bores. Never a 4.04 but if it's thick enough why not?

What is the min the sonic should yield what .150?

Kasey

3.79 stroke may be doable starting with a non ground journal

Math: 2.125 - 1.88 = .245".
Assuming zero error/perfect alignment, the maximum stroke increase is .245", or 3.555".

.150" on the thrust axis makes me nervous.

318 3.91" > 340 4.04"
Result: 85% leakdown, poor oil control, high crankcase pressure.
Don't.