dang!

[Warrioreater400ex]

i just got my 300 back from teh shop today, we really burnt the engine up, anyways, it got bored .20 over, and has new piston, rings, sleeves, and valves, anyways, since now its a 320ex, i rode it, but of course im still breakin it in, so i didnt max it or anything, but it has a VERY noticeable difference in speed and acceleration! i was kind of amazed. but anyways, now i just gotta sell that beast! then ill be debt free!

not tryin to be a mean guy but just cause you bore it .20 onve dosen't make it a 320,first off a 300 ex has 282cc. i belive,boring it .20 over is nowhere near enough to bump the dissplacment that high,some one correct me if i'm wrong

[Tommy 17]

ya i know what u mean mines a 406 and i think it went from a 397... its only bored .40... mayb a 300 is more...

[beerock]

there is some sort of formula to figure out.

the stock bore on my bike is 66mm my bore is at 67.50 right now and some how tat equates to 257cc

stock is 246, im 11cc higher!!

I dontknow how to get the cc, maybe you multiply the bore and the stroke?

[Guy400]

There is a formula for finding displacement and it's the following:

pi (3.14159) divided by 4, times bore times bore times stroke times # of cylinders.

For the 300EX above the stock bore and stroke is 74mmx65.5mm. A .020" overbore equals .508mm. So...

3.14159 divided by 4 = .7853975
His bore is now 74.508

.7853975 * 74.508 * 74.508 * 65.5 * 1= 285585 cubic mm
Move your decimal point to convert from millimeters to centimeters and you've got 285.585 cc's.

[Tommy 17]

thank god somones smart i am still seeing if mines really 406:huh :huh :huh

[400exRacerX]

Well going from a 397cc (400ex displacement stock) to a 416cc motor is boring the motor .80 over.

[Chef]

ok, so if i did this right, my displacement is 472.806 mm?

89mm bore
76mm stroke

89mmx76mm

did i do tat right?

[Guy400]

In the immortal words of Ed McMahon, "You are correct sir!"

[Warrioreater400ex]

hahah sorry, i didnt know bout all that stuff....... phew too complicated for my brain! :p

Guy, are you showing off again? No seriously, where did you find out that was the formula?

[Guy400]

Originally posted by Fourstrokefan
Guy, are you showing off again? No seriously, where did you find out that was the formula? It's from my old hot rodding days! Some things you just never forget. Now, my wife's middle name? That's another story...

[Scott]

It's called geometry. Displacement is the volume of the cylinder. For compression ratio you have to include the volume of the combustion chamber as well. And if I remember right, Guy already posted that formula on another thread...

Bore = diameter
stroke = length

Volume of a cylinder = pi * radius * radius * length

Radius is diameter/2


And to think it's been 15 years since I took high school geometry, and I still remember it...

[Guy400]

Compression ratio can be found using this formula:
To make the formula look less confusing I'll make some symbols.

CR=compression ratio
D=single cylinder displacement
Vh=volume of the head in cc's
Vd=volume of the deck

CR= D + Vh + Vd\ Vh + Vd

Now, this formula is assuming you're running flat top pistons with no valve reliefs. Most all piston manufacturers include documentation, if asked, on your specific piston as to how it will effect deck volume and combustion chamber volume. For instance, a domed piston will obviously reduce combustion chamber volume thus increasing compression. Also, you can't forget to include the head gasket thickness into your equation and add that to either your combustion chamber volume or deck height, it really doesn't matter for the math above. I had a real sweet chart that showed the conversion of various gasket thicknesses to cubic centimeters in relation to bore size but I've seemingly misplaced it:(

But anyway, if you "cc" your head at say, 50cc's put you've got a domed piston displacing 10cc's you're going to need to use 40cc's as your number for Vh.

At any rate, there's the formula for figuring compression ratio.

["BLAHH"300!!]

IF JACK HAS A PIE WITH 15 SLICES AT 10 INCHES ACROSS
AND
BETTY HAS A PIE WITH 26 SLICES AT 10 INCHES ACROSS

WHO HAS THE BIGGER PIE:rolleyes: :p

[knighttime]

does

[quadfamily]

Yeah, I was real disapointed when I found out that boring my 300EX .080 over will still only make it 297cc. I was hoping that it would at least be an even 300cc. Bummer! I'm doing .080 because that's supposedly the largest overbore you can safely go on the stock sleeve. Haven't done it yet so I can't tell you how it runs. By the way, it's an 11:1 wiseco from Four Stroke Tech.

["BLAHH"300!!]

YOUR A
- ------>> -GENIOUSE- <<-----

Well I have something to say here, allthough it may feel like it has more power by just going .20 over but infact it may just be that you think it has more power because you know that you have added a mod to it, like when people get a loud pipe and it seems like it has more power but it realy doesn't. Maybe it is noticable but I am just saying...........Don't take this the wrong way, i hope you all get what Im trying to say.:huh