boreing an engine

[matt11583]

i understand the basic concept to boring out an engine to get more displacement. my question is how exactly do you bore it. what is getting cut back and how do u know how much you can cut back. basically i want to understand more about what happens to the engine when you bore it out, and what has to be done after it is done. any imput about this or any links to help me better understand it would be appreciated. thanks

[JustSayGo]

Boring cylinders oversize does not add much CID. You can do the math if you know the bore X stroke of an engine and the ammount the bore is increased. Boring is done to correct worn tapered cylinders so that new oversize pistons can be fit to new engine clearance tollerance that will allow the rings to do the best job possible of sealing compression.

In the days of inline engines it was fairly common for garages to have boring bars. Boring bars are centered and clamped down over the cylinder and use a cutting tool run by an electric motor that feeds down the cylinder. One or more cylinders could be bored without removing the engine from the vehicle. Then a rigid hone turned with a drill motor was used to fit oversize pistons to the correct final clearance.

Boring and honing machines have become more sophisticated and expensive over the years and are now found at machine shops. The new machines still do the same thing but measuring accuracy is built in and improved design allows greater accuracy of top to bottom dimensions, centering, roundness and of course production speed has been increased.

When high performance cylinders are bored a steel deck plate that looks something like the headgasket but is at least 1'' thick is bolted in place with the headbolts to distort the cylinders the same way that they will be distorted when the cylinder heads are torqued down. Deck plates allow cylinders to be a little straiter and more round after the engine is assembled.

Honing machines use stones that move in and out of the bore creating the desired crosshatch patern and stop at the correct measurement.

The machines also have recirculating water soluble oil constantly washing and cooling their tools and the engine block as it is being machined.

[matt11583]

ok...i understand how to bore it but why is it that people will say, for instance they can bore a chevy 350 to 383. if it doesnt add much CID how does that work....or r they talkin about something different and i am very confused???

[TheSilentChamber]

You stroke a 350 to a 383. Stroking is putting a larger crank/differnt length rods/differnt pistons in an engine to increase the displacement.

[curtis73]

Right.

For instance, my 454 cid engine with a 0.060" overbore (commonly called 60-over) yeilds 467 cubic inches.

A 350 with a .030" overbore yeilds 355.

Have fun with this calculator...
http://www.bgsoflex.com/displacement.html

[534BC]

A lot of engines can be bored "blindly" up to 1/16 " and lots of piston makers offer oversizes in that same amount. This is mainly done for service life and should be done only to the next required size by wear.

Some engines can be bored a lot more, but should have the thickness of the cylinder walls tested to ensure adequate thickness there. This type of boring is done for displacement increase (power) and uses up all the "lives" of the engine.

Oops, I struck water jacket, time for a sleeve.

Typically older engine can go a bit more than newer engines.

[matt11583]

thanks...that makes a lot more sense now....but in the calculater link curtis gave...what is the piston oversize value mearsuring??? i think i understand the rest. if you wanted to stroke an engine out, you would get shorter rods, and a stronger crankshaft along with stronger, bigger pistons??? right??

[matt11583]

thanks...that makes a lot more sense now....but in the calculater link curtis gave...what is the piston oversize value mearsuring??? i think i understand the rest. if you wanted to stroke an engine out, you would get shorter rods, and a stronger crankshaft along with stronger, bigger pistons??? right??

[534BC]

It is the value of the "increase" , In His example on the Chevy a value of .06 is put in and gives 13 more cubic inches.

[534BC]

If "stroking" an engine something in the set-up has to be reduced 1/2 the amount of the stroke increase to keep the same piston height. It can be a shorter rod, shorter piston,ect.

A "stroked" crank is weaker than when it started usually, but a purchased "stroker" crank can be a lot stronger than the stocker it replaced.

One tip is that an increase in bore size does more good than a stroke increase of the same amount, yet engines typically can handle a bigger increase on the stroke and if you can do both that would be great.

[534BC]

I think maybe Curtis has a Caddy 500 with dimensions of 4.3 x 4.3 = 500 cid

Playing with the calculator if He bored his engine .14 He'd get 533 cid and would smoke me if I sroked my engine .14 I'd only get 516 cid. Not only does the bore increase add more cid, but it also "means" more or does more good.