Boring a 351c

[c9zx]

If .113 is the min. you should be good to go. I should always be so lucky. Chuck

 

[71ponymaster]

Im usually not lucky at all. Its not done an runnin yet...

 

[rpmcarter]

the only advice I would offer is sending a request for information on the finished product by email. Not a face to face conversation...because people tend to tell you what you want to hear. If by email they commit to a tolerance/performance/reliability standard, you have it in writing vs a "hearsay" conversation. With that said I've always been lead to believe the 351 has thin walls and .30 to .40 is the most reliable. In addition it gives you "tolerance" opportunities if changes need to be made. Go .60 and your DONE!

 

[Mister 4x4]

The thing I'm having a hard time getting my head around is the idea that .020" - the thickness of 2 or 3 sheets of aluminum foil - makes such a huge difference in the survivability of an engine.

I get it that "more metal is more better." I'm not disputing that, or the trend of engines being more prone to blowing up with larger bores. It's just mind-boggling to me that with consideration to all of the pressures, friction, heat, stress, et al, that engines go through, 3 sheets of aluminum foil can make all the difference.

Another question: if .113" is "good to go" for milling off another .020", then what is the absolute engineered minimum tolerance for cylinder wall thickness? If it's less than .093", then I think it's safe to say from an engineering perspective that Clevelands indeed do not have "thin" walls and is just another unfounded altruism propagated most likely by some Camaro guys.

 

[TommyK]

I would just like to point out that when you bore a cylinder .020" over you are only reducing the wall thickness of the cylinder by .010".

Also, my understanding of the term "thin wall casting" is it refers to the modern casting technique developed in the 40's and 50's to manufacture cast iron blocks. It is not a direct reference to the cylinder wall thickness of a particular family of blocks. The thin wall casting technique was developed to improve the quality and accuracy of the castings while making them lighter at the same time.

The anecdotal evidence regarding Clevelands is that .040" is the max safe over bore. That doesn't mean a Cleveland can't be bored larger with good results. As Chuck pointed out it is all about the wall thickness on the thrust side of the (thinnest) cylinder.

This has been discussed at length over the years on the FE forum as well as the 460 forum. The advice with regard to a 460 is that .060" is the generally accepted safe max overbore but many blocks when sonic checked can go .080 while some can go as far as .120".

 

[Mister 4x4]

I would just like to point out that when you bore a cylinder .020" over you are only reducing the wall thickness of the cylinder by .010".

Also, my understanding of the term "thin wall casting" is it refers to the modern casting technique developed in the 40's and 50's to manufacture cast iron blocks. It is not a direct reference to the cylinder wall thickness of a particular family of blocks. The thin wall casting technique was developed to improve the quality and accuracy of the castings while making them lighter at the same time.

The anecdotal evidence regarding Clevelands is that .040" is the max safe over bore. That doesn't mean a Cleveland can't be bored larger with good results. As Chuck pointed out it is all about the wall thickness on the thrust side of the (thinnest) cylinder.

This has been discussed at length over the years on the FE forum as well as the 460 forum. The advice with regard to a 460 is that .060" is the generally accepted safe max overbore but many blocks when sonic checked can go .080 while some can go as far as .120".

Good points, Tommy! ::thumb::

I'd forgotten that boring .020" diametrically only yields .010" of material from the radius of the bore. So technically, the thinnest the material will get on 71ponymaster's block is .103", rather than .093".

Still amazed that 1/10th of an inch can still stand-up to the hellish environment inside our engines, though. :-/

 

[71ponymaster]

The smallest thickness i found is .132. Its .040 over an wore to .043ish. So takin it to .060 will only change that .132 thicknes down to right at 1/8th an inch. Which accordin to my machinist is as thin as u wanna go

The issue w these blocks is sometimes the bores arent centered to the water jackets. Which i proved w my sonic testin. I had thicknesses as high as well over 1/4 in. An the castings vary so u never know just how much meat u got

 

[Mister 4x4]

Hey, I'm just glad you got good news. ::thumb::

Good luck with it - I know I'm not unhappy with mine [so far].

 

[Paul of MO]

On a Cleveland it is not really a failure issue but a cooling issue. The thinner you go the hotter the water jackets get and the harder it gets to dump the excess heat. It is an exponential relationship.

With the availability of low cost high quality aluminum radiators and other modern cooling aids it is not that big of a deal anymore.

We ran several 60 over Cleveland's in the 70's on the street and they all got hot - not overheating but hotter than they should. Any off the shelf temp thermostat would open quickly and then stay open. Even with the best coolant, a 30lb cap, and electric fans the engines would run very close to overheating. So what - we had fun!

I have built race motors that were punched out to 120 over and never had a block failure - we did epoxy the blocks up to the freeze plugs.

We have a 100 over filled block that I would not hesitate to use in a street car but why? With iron heads and a mild street cam it will not make any more HP than a stock bore block. It can handle 1200 hp all day long and should be used for that.

60 over will clean up all but the worst worn or rusted blocks.

- Paul

 

[71ponymaster]

Ya ne too. Mr 4x4. Ty an u too

Ya an aluminum radiator was in the plan already. Clevelands seem to run a fine line when it comes to temperature

 

[Kit Sullivan]

"Boring a 351 Cleveland" is easy...just tell it all about how fart can exhausts and leaf-blower electric superchargers make jap-cars into 10-second street cars. That would bore anbody!

 

[69 Rustang]

I am late chiming in, but I am one of the .060 over guys and been running it hard like that for a lot of years. I've actually been hoping it would come apart or something as then I can justify a stroker motor with the wife.

 

[rpmcarter]

Well I believe we can safely say this topic has a conclusion..... yea ya can and no ya shouldn't :s

 

[Mister 4x4]

"Boring a 351 Cleveland" is easy...just tell it all about how fart can exhausts and leaf-blower electric superchargers make jap-cars into 10-second street cars. That would bore anbody!

rofl Nice! ::thumb::

 

[Mister 4x4]

Well I believe we can safely say this topic has a conclusion..... yea ya can and no ya shouldn't :s

I'm still not convinced that the "no, ya shouldn't" part is as much the "gospel truth," as much as a "bad experience passed around the shops and pits over the years." They wouldn't have such a selection of .060" pistons and rings available from the various vendors if that were the case.

Fact: .060" is the limit for machining - simply because there's nowhere left to go... either in removing more metal, or finding slugs & rings to fill the larger bores.

Rumor: .060" Clevelands will have overheating issues and eventually grenade as a result - so far, not any more or less frequent than any other engine that could potential suffer from over boring.

Just sayin'