Question about overbore?

[Anonymous]

My overbore just went from .30 to .40...

is that significant enough to make any difference to CR?
curious if I should make any adjustments?

 

[Anlushac11]

8)

Yes it will make a bit of a difference. To see how much go to the Falcon handbook webpage and use their compression calculator and enter in specs for the stock bore and then same specs for .040" overbore. At bottom it should give you the estimated compression ratio and the estimated horsepower.

http://falconperformance.sundog.net/compcalculator.asp

 

[Anonymous]

Well I am not the greatest at these things...

and I am not sure about some of the other measurements...

but if you increase the bore alone...
that takes the CR over 10.4:1.....

 

[CZLN6]

Howdy Jimbo:

An extra .010" overbore may increase displacement by one cubic inch. That alone will not change CR very much at all.

If you'll give me your critical dimensions I'll run the figures for you. I will need bore, stroke, chamber volume in cc, deck height and compressed head gasket thickness.

Adios, David

 

[Anonymous]

Thanks David, I actually hung with the machinist today for a couple of hours while he was boring the block... way cool.

He explained it all to me.. but he has most of the measurements, as I am in his hands now... and that is better than mine.

But, yes, he said he will compensate for the increased bore and still get me into the 9.5:1 range....

 

[Anlushac11]

8)

I even put the link to the configurator in the post. Im not sure how to have made it any easier.

Even if you started at 3.68" bore(stock) and bore it .040" and stock CR of 8.4:1 the compression calculator showed it only increased the CR to 8.8:1

 

[Anonymous]

8)

I even put the link to the configurator in the post. Im not sure how to have made it any easier.

Even if you started at 3.68" bore(stock) and bore it .040" and stock CR of 8.4:1 the compression calculator showed it only increased the CR to 8.8:1

Well for someone like me even that could be a challenge.... I had the decimal point in the wrong place.... instead of 3.72 for a CR of 8.8:1 I put in 4.08 for a CR of 10.4:1 :roll:

Like I said I am not the greatest at the math side of this, which is why I asked in the first place.

 

[xctasy]

A simple mistake, Jim. But that really made me think....

a 408 thou over bore sounds just great on a engine that has only 365 thou between cylinders.


Imagine a 245 cube six with 80 thou over Chevy Pistons? The bore holes would make the block look like an Audi badge!

 

[Anlushac11]

8)

I even put the link to the configurator in the post. Im not sure how to have made it any easier.

Even if you started at 3.68" bore(stock) and bore it .040" and stock CR of 8.4:1 the compression calculator showed it only increased the CR to 8.8:1

Well for someone like me even that could be a challenge.... I had the decimal point in the wrong place.... instead of 3.72 for a CR of 8.8:1 I put in 4.08 for a CR of 10.4:1 :roll:

Like I said I am not the greatest at the math side of this, which is why I asked in the first place.

I assumed it was a typo

Had me worried because I ran many combinations trying to figure out how you came up with a 10.4:1 CR with an overbore.

It happens...but never to me...no sir... :roll:

 

[Anonymous]

LOL.......