im going to need to bore my engine over. does anyone have a suggestion? .020 .030 .040 .060? any one better than another? my first instinct it .060 because its the biggest, haha. does anyone know what these different bores would increase the ci to? thanks

Usually I'd say bore the engine out to the smallest bore that you can get away with. If you can end up with a good cyl wall with .020 over, do .020 over. That way in 100k miles if you need to bore it again you can. If you're going for a big bore engine you can go with .120 over or so without any block fill and technically up to about .2 to .3 over with fill, but that's a bit over the top for your motor probably.

To figure out the displacement, use this equation, it will get you close enough:
CID = 8 (the number of cyls) x bore^2 (squared) x stroke x .7854
CID = 8 x 4.3^2 (stock bore) x 4.303 x .7854 = 500ci
CID = 8 x 4.32^2 (new bore .020 over) x 4.303 x .7854 = 504.5ci

im going to need to bore my engine over. does anyone have a suggestion? .020 .030 .040 .060? any one better than another? my first instinct it .060 because its the biggest, haha. does anyone know what these different bores would increase the ci to? thanks

It may come down to what pistons are available. Smaller is actually better. It gives you more options in the future if you need to bore it again. Plus on some engines the bigger bore thins out the cylinder walls such that the combustion chamber heat begins to heat up the coolant a lot more.

When I had my GN rebuilt there was a shortage of .030 pistons so I had to go .040 over, which on the 3.8L block is the max. If I need to rebuild it again I may have to get another bock. Also, the car runs considerably hotter - I had to put a bigger radiator and bigger fans in it. I'm not sure if the Caddy blocks have this issue tho.

Jim

davesdeville,

Can you work one for me? (boring the 500 .030 over). I just don't understand the equation and can't get it to come out as anything near 500. Boy do I feel stupid!:cookoo:

yeah,i agree with terrible one. i am not terrific at math. what is "^"? thanks.

yeah,i agree with terrible one. i am not terrific at math. what is "^"? thanks.

The "^" is "to the power of" or in this case 'squared'.

Jim

I just want to know how many cubic inches I will end up with:rolleyes:

.020 = 505
.030 = 507
.040 = 509
.060 = 514

Thanks

so, if i bored .020 over i would have a 476, right?
i think i did the equation right.

sounds correct

i did all the math so i figured id share so you guys dont have to. here it goes.
472
.020 = 476
.030 = 478.2
.040 = 480.4
.060 = 484.9

and im fairly sure my math is right. thanks for the equation dave.

Thank Google.

And come on guys, I got a D in Algebra I, and a D- (actually an F, but I went to class 4 extra days and did extra work for a D-) in Algebra II, but I still got that equation.

well, i havent taken a math class in 2 1/2 years so everything i learned is basically gone, haha

I suck at math. That's okay though because nice people one the forums can work out my displacement equations. :)

I'm no math whiz either, but I am a geek. I popped the formula into Excel and referenced a cell with the overbore value in it (.020, .030, .040, .060). I just changed the value in that cell and the output changed. I'm sure there's a web page somewhere that has a similar tool - but you have to know the input values (standard bore, overbore and stroke).

Jim

I'm no math whiz either, but I am a geek. I popped the formula into Excel and referenced a cell with the overbore value in it (.020, .030, .040, .060). I just changed the value in that cell and the output changed. I'm sure there's a web page somewhere that has a similar tool - but you have to know the input values (standard bore, overbore and stroke).

Jim

Or you can just store the equation in your TI :2thumbs:

JTraik how is your project coming?