[77 cruiser]

Why do most do this?

4.155 x 3.875 = 420.33 round up to 421

4.155 x 3.75 = 406.77 round down to 406

 

[JWagner]

Can you cite your source for this info?

 

[77 cruiser]

This & Pat Kelleys.

http://www.wallaceracing.com/cid.php

I never tried to figure it the old fashion way.

 

[1966_L78]

Why do most do this?

4.155 x 3.875 = 420.33 round up to 421

4.155 x 3.75 = 406.77 round down to 406

Marketing...

Somewhere, someone determined that 421 sounded better than 420, etc...

How about when Chevrolet used "396" and "400" to denote the same "402" in 70+ cars and trucks???

Or manufacturers having new engines that are close to "nostalgic" engine sizes; 392 hemi, 5.0 litre Coyote, "427" LS...

How come some people like to tell you they have a 355, a 460 BB, a 402, when they really have an overbored 350/454/396? It because the want to impress people with the larger custom engine size (marketing)... I call then a "30-over 350" etc...

 

[animal69]

Real hot rodders always round down!