Some of you may remember that the heart of my 03 is out and torn down with a scuffed cylinder wall.
Here is my dilema:
Bore the bad cylinder, buy one piston, full set of rings and put it back together...OR do I bore all 6 and spend the $$ on pistons.
What would the increase in cubic inches be for a 20 or 40 over bore ?
Would there be any real h.p. gain ? I'm guessing less than 10 hp???
I'm just lookin at the cost of the pistons and trying to make a desicion.
Thanks, Dan

 

Most will agree that in horsepower, there is no substitute for cubic inches. But just 20 or 40 over isn't going to make a huge difference without supporting mods. Save the money and go with a cam and springs, ect. It will net more HP in the long run compred to just boring it out. JMO

 

bored may not gain a whole lot but, bored them all and install shaved pistons and you will.

I say it depends on what you're doing. Do you plan to pull or race with it.... towing or economy in mind ? Or, how much do you want o spend? You could sleeve that one cylinder and buy one piston for a lot less than doing the whole job. You could do the whole job though with some hp gain and a little more peace of mind.

 

Well. I drive it everyday (when it has an engine in it). I do pull heavy loads quite often, but i also like to show up the ricers from light to light. (evene thought the 6spd makes it a little harder)
Would I have to sleave it if a 20 or 40 over will do it ? I've read that you can bore just one and be fine ??? I think most of the scuff is attached piston material.

 

that's actually what the service manual says to do if you fry a cylinder. It even shows you how to do the whole sleeve job. Cummins has all the parts to do it.

The .20 and .40 are the minimum and maximum bored that can be done. You can only bored the cylinder twice and those are the specs.

You can't bored just one cylinder unless you plan to sleeve it. One reason for the sleeve... to bring the truck back to stock compression after having to bored one cylinder.

I guess you could bored it and fill the gap with huge rings but, probably not the best idea.

 

Well on past posts, I have been told that the Cummins pistons all weigh the same. SO, if that is the case...could I bore 1 cylinder and just use the oversize piston ?
Someone told me that the compression would be off and that this would mess things up, But I am sure that not all 6 cylinders see the exact same combustion even on a stock engine.
What's your take on that ??

 

I don't know that would be the case. There's no way a larger piston is going to weigh the same as a smaller one. It would throw off the balance of the crank and that wouldn't be good.

I'm no expert on this but, I'm sure you either bored them all or bored one and sleeve it

 

Bore all and all get new pistons or bore and sleeve the bad one. Do not bore 1 cylinder and install 1 over sized piston.
Good luck,
Topper

 

Hello,

For any type of daily driver you absolutely can clean up the bore to the next size and put the appropriate size piston in. Racers do it all the time too. It is done every day. The overbore piston may weigh slightly more or maybe not. Many manufacturers make them weigh the same. The balance pad on the bottom is just slightly machined. If it's not done by the manufacture any machine shop can do it. It is how pistons weights are equalized in the first place. There is almost no increase in HP. An overbore of 0.02" will get you under 5 cubic inches total if it is done on all cylinders so it's a waste. Actually it thins the cylinder walls and can lead to less power due to poorer ring seal. Most damage easily cleans up at a 0.02" overbore. I would not hesitate an instant.

Damon

 

Bore X Bore X Stroke X Cylinders X .7854 = Cubic inches.