Do I need to bore over 30 to put in pistons?

[Billla]

Originally Posted by Blue71LWB

I'm thinking of putting in some flat top pistons in my inline 250. I feel the engine is fine , but I was told I would need to have it bored if I was going to go with new pistons. I really don't want to bore the block. So will it be OK , to put in new ones without boring ?

Pistons come in different oversizes - .010, .020, .030 and so on. Somtimes there is an .002 or .003 piston as what's called a "high limit" piston - allowing a new piston to be installed after a quick flexi-hone if there's minimal bore wear.

It all starts with a bore measurement - the bore determines what your options are. Once the largest bore size is known, then you know what your options are. Sometimes the inline 6's show little or no bore wear even after 100's of thousands of miles.

[Billla]

Originally Posted by Sammy

Speaking about boring engines. Sm block 350's for example. Some folks are going 60 over. Doesn't that cut pretty close to water jackets? Until recently I had never heard of going 60 over. Now several shops do a 60 over bore. Old school was always stop at 30 over( 283/327's).

Your shop can complete a sonic test to ensure the bore walls can handle an .060 overbore. Doing it blind IMHO you've got a 1 in 4 chance of hitting the jacket. The issue isn't just wall thickness, but also core shift - the wall thikness may not be completely concentric with the bore center, i.e. one side may be far thicker than the other based on bore centerline.

[Blue71LWB]

Thanks fellas,
For some reason I was leary of having it bored. I'll just ask around and take it to the most respected shop around here (when I get it out) , and go with a min bore.

Thanks again.

[RACINJASON22]

Originally Posted by EAST SIDE LOW LIFE

**********************************************************

I agree with Sammy!!! I would think more then 40 over on a 350 is the begining of leaving the comfort zone. Some old 283s were bored as much as 80 over but I would not go more then 60 over if it were mine. 327 same thing 60 over is fine but a 350 40 over max.

Where is longhorn Man when you need him.

esll.

Hey EAST SIDE LOWLIFE why is it in your opinion OK to bore a 327 .060 and not a 350. They both have the same bore 4". Large journal 327's use the same block as the 350 so they can be bored the same IMO. Just wanted to clairify.

RJ22

[EAST SIDE LOW LIFE]

Originally Posted by RACINJASON22

Hey EAST SIDE LOWLIFE why is it in your opinion OK to bore a 327 .060 and not a 350. They both have the same bore 4". Large journal 327's use the same block as the 350 so they can be bored the same IMO. Just wanted to clairify.

RJ22

**********************************************************

First off If it were my 350 cu. I would only go through this if I was restoring a truck and this were my original engine. If this were the case I would be more concerned about decking the block as in most cases this has neg. effects on the #s.

Less meat more chances of failure. That's what machine shops have told me .... maybe I'm just afraid of all the power that is going to result by the 60 over bore! Or maybe I do not like to take chances of taking things to the max and having a melt down.

Now you being of a different opinion I can respect. That's the beauty of this hobby of ours. We all get to do our own thing.

esll.

['68OrangeSunshine]

I've got Badger pistons in my 292. My machinist set me up with them. They are cast pistons. If you want forged pistons you have to go to Arias or Ross, but they're spendy. You might get a line on them at www.inliners.org.
TRW doesn't make them anymore.

[Billla]

Originally Posted by EAST SIDE LOW LIFE

maybe I'm just afraid of all the power that is going to result by the 60 over bore!

350 + .060 overbore = 10.8 CID = ~11 HP @ 1 HP/CID. I wouldn't lose any sleep over this one :-D

The only reason to bore an engine IMHO is to establish the correct piston/bore clearance and ensure a square bore (i.e., no taper). The CID increase on a stock block (not the aftermarket ones that you can bore out huge) is minimal. If you can buy a piston and establish a reasonable clearance, square bore and the right surface with a hone, go for it.

[PanelDeland]

I would go minimal overbore as suggested.The first thing though is to determine what you can get in the way of pistons without going custom.The options may be limited and could play a part in your decision.Since the 250 hasn't been built in many years there may not be as many choices since the demand has dropped.I also agree on a better cam,the cam reps will be able to help you more on that,make sure to have as many of the specs to give them as possible.Use good qulity head gaskets since the standard compression ratio is about 8.00:1 and the new will be higher.You may also need to run a better grade of fuel(higher octane)since compression will be higher.Since you are going to a 4 barrel you will want a better exhaust also maybe headers or a split manifold.

[EAST SIDE LOW LIFE]

Originally Posted by Billla

350 + .060 overbore = 10.8 CID = ~11 HP @ 1 HP/CID. I wouldn't lose any sleep over this one :-D

The only reason to bore an engine IMHO is to establish the correct piston/bore clearance and ensure a square bore (i.e., no taper). The CID increase on a stock block (not the aftermarket ones that you can bore out huge) is minimal. If you can buy a piston and establish a reasonable clearance, square bore and the right surface with a hone, go for it.

**********************************************************

Was I being serious ....

esll.


I've done rebuilds On very expensive # correct engines and the school of thought that I come from is to error is human .... when there is NO' second chance I have always have chosen to error on the side of caution. Old habbits are hard to break. Yet to blow something up or have something that does not work right when it's finished ..... at this point one should not be scratching their head .... what the heck went wrong??? Know what I mean!