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Author Topic: 318 cylinder boring  (Read 5935 times)

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spike

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318 cylinder boring
« on: November 02, 2012, 22:27:25 »

lookin at buyin the strocker kit for my truck here real soon, and to build the 390 stroker the 318 has to be bored .30 over
but for the same price as teh 390 kit, i can get the 392 kit, but for teh 392 it has to be bored .40 over
would .40 over be too much? the site lists a 396 which is .60 over :o

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Re: 318 cylinder boring
« Reply #1 on: November 02, 2012, 23:15:39 »

0.40" over isn't too much at all.
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270SE

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Re: 318 cylinder boring
« Reply #2 on: November 03, 2012, 03:25:04 »

It's all the same price. I'd stick to .030.
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fifthcrunch

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Re: 318 cylinder boring
« Reply #3 on: November 03, 2012, 05:23:11 »

I second the motion to stick to .030.  If your block has just a little core shift, .040 could be too much.  I have read a lot that says anything beyond .030 is taking a chance.  Nice to have the extra cubes, but it would be a gamble.
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M_Body_Coupe

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Re: 318 cylinder boring
« Reply #4 on: November 03, 2012, 07:56:22 »

Heck, 0.030" is already a big 'large'...lol...seriously, if the shop has a sonic tester at the very least make sure they use it and check it over.

My shop would not go over 0.020" because they wanted to cylinder walls as thick as possible for my intended use. The thicker they are, the less they flex, the more they allow the rings to really seal the combustion chamber.

The question I would ask: do I need 0.030" cut to clean up the bores, or is it that the standard kit sizing is available in the 0.030" only?
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Ice Cold

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Re: 318 cylinder boring
« Reply #5 on: November 03, 2012, 07:59:15 »

Could sleeve the cylnders, then go nuts on the bore.
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spike

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Re: 318 cylinder boring
« Reply #6 on: November 03, 2012, 08:42:08 »

the standard bore for a 390 stroker is .30 over
i wouldnt think .40 over would be too much as its only .10" more
but i figured id get everyones opinion as ive never dont this type of build before and i wanna get the most outta this 318  :evil:

M_Body_Coupe

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Re: 318 cylinder boring
« Reply #7 on: November 03, 2012, 08:47:43 »

the standard bore for a 390 stroker is .30 over
i wouldnt think .40 over would be too much as its only .10" more

Just remember that when Mopar went to the lighter thin wall castings the meat from around the cylinders got thinned out...I still recommend the sonic test scan for wall thickness...but 0.040" over??? Nah..don't go there...your cubic inches are already coming from the bigger stroke, and as- is you're going to put more pressure against the wall due to the larger stroke...
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270SE

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Re: 318 cylinder boring
« Reply #8 on: November 03, 2012, 08:55:40 »

The standard size pistons are likely just as cheap, and .020 might be as well.

Up to .030 was okay without sonic checking as long as all appeared right. Over .030 had to be sonic checked. Another thing to think about- if it needed to clean up .030 later at .030 it'd be .060 which is still readily available. .070 would be a big stretch for a factory block and might have cooling issues.

Bore has little to do with making power. You're not going to be gaining a lot of power by having 2 more ci from a larger bore, and it really does hurt the reliability that much more that if it doesn't need it- don't do it since you aren't racing.
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CudaZappa

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Re: 318 cylinder boring
« Reply #9 on: November 03, 2012, 08:58:48 »

Heck, 0.030" is already a big 'large'...lol...seriously, if the shop has a sonic tester at the very least make sure they use it and check it over.

My shop would not go over 0.020" because they wanted to cylinder walls as thick as possible for my intended use. The thicker they are, the less they flex, the more they allow the rings to really seal the combustion chamber.

The question I would ask: do I need 0.030" cut to clean up the bores, or is it that the standard kit sizing is available in the 0.030" only?

^^^ I agree.
Thicker walls make more power than the cubes they generate.  Go as small on the overbore as possible.  The function of the wall thickness vs. strength gets rather weak the more you bore it.  If you can only get .030" pistons then go .030" over.  If .020" are readily available, go that route.  It's a good rule of thumb to ALWAYS sonic check your block because God only knows the core shift.  Its generally considered safe at .030 over, though.
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spike

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Re: 318 cylinder boring
« Reply #10 on: November 03, 2012, 09:06:16 »

ok you guys convinced me to stick to .30"
and i planed on having the block all checked out before i have work done
another question that im sure you guys will take as a no brainer, but im new at engine building
should i spend the extra $650 for the forged crank and billet H-beam rods?

79dodge4ever

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Re: 318 cylinder boring
« Reply #11 on: November 03, 2012, 10:49:14 »

ok you guys convinced me to stick to .30"
and i planed on having the block all checked out before i have work done
another question that im sure you guys will take as a no brainer, but im new at engine building
should i spend the extra $650 for the forged crank and billet H-beam rods?

very much so; also I believe the block has to be clearanced for the crank to fit without hitting
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Re: 318 cylinder boring
« Reply #12 on: November 03, 2012, 10:54:06 »

BPE and K1 make 4.15 and 4.25 stroke crankshafts, so you can go bigger than 390. My buddy built a 318 bored 30 over with the 4.15 stroker crank. He used a scat 6.20 length rod and I forget which piston but it wasn't anymore expensive than your average 390 stroker kit and its like 20 cubes bigger.
« Last Edit: November 03, 2012, 10:58:09 by efriedrich »
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spike

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Re: 318 cylinder boring
« Reply #13 on: November 03, 2012, 10:57:05 »

well i wouldnt want to bore it out any more then .40", but im sticking to .30" over
since ill be driving it daily a lot with some long road trips and off roading, i want it to last

270SE

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Re: 318 cylinder boring
« Reply #14 on: November 03, 2012, 18:07:11 »

The bigger strokes require an aftermarket oil pan. If you've got one, for the 4.25 you have to mod it. If not, then you have to buy one, which will add another couple hundred to the price most likely.

If the block needs reboring, stick to .030 over. If the walls aren't worn enough to need it, see about standard bore.

The block must be clearance for the crank, ground a bit at the bottom.

If you aren't doing 4.15 or 4.25, aren't going to go over 6,500, aren't going to have over 11 psi, aren't going to run over a 150 shot, the cast crank should be fine. Rods and piston are a better idea to spend on.
« Last Edit: November 03, 2012, 18:09:33 by 270SE »
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