• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

What size would a 1275cc bored .030 be

Share this page

6

68Sprite

Jedi Hopeful
Offline
I just picked up a 1275 with 30 thou 21251 pistons in it, what size would that make this motor now. I know 20 over is 1293cc and 40 over is 1310 or 1312cc

New1275003.jpg

New1275002.jpg

New1275001.jpg
 
based on you knowns of .020 and .040 over. I took
1293-1275=18
18/2=9
9cc per .010 of overbore
9x3=27
1275+27=1302

Now for the real answer..
V= ((Pi x R x R) x H) x 4(cyl)

V=Volume
Pi=3.141
R=radius (bore/2)
H=Height (stroke)



70.61mm x 81.28mm = stoke bore and stroke
Ref: https://www.austin-healeys.com/spritespecs.htm#Engine

7.061cm x 8.128cm = 1273.11cc


<u>+.030 overbore</u>

71.372mm x 81.28mm

7.1372cm x 8.128cm = 1300.7364cc


mark
 
Gotta ask,

What size, make amd model tire is that mounted on your cosmic wheel in the background?

Is that a Sumitomo 175/50-13 ? HTR 200?

Jay
 
Wow, thanks for the answer Mark. I don't think the .030 over piston is very common.

Jay, the tires are Nexen N2000 175/60/R13 on 13 x 5 1/2 Cosmics. The tread wear rating is 380 Traction A and Temp A. I got them of off https://www.tires-easy.com, they were around $30 a piece if I remember right. They are directional and have a cool modern tread pattern if you like that sort of thing. They ride much quiter and smoother than the Sumitumo 175/50/R13's that I have mounted on the stock steel wheels. Let me know if you need more pics. Chris
 
Back
Top