Cubic Inches

Reply Subscribe

Thread Tools

Search this Thread

Aug 26, 2014 | 01:16 PM

mtntop1

Thread Starter

Mountain Pass

Joined: May 2005

Posts: 209

Likes: 0

From: Arizona

Cubic Inches

If I bore a 302cu in .30 over what will the new cubic inches be. Also approximately how much torque improvement.

Aug 26, 2014 | 02:06 PM

85e150

Super Moderator

Joined: Apr 2004

Posts: 34,475

Likes: 2,800

That gives you a 306 and probably no measurable difference in power. You gain 4 CI, but you lose just a tick of compression.

Is this just a clean up bore during a rebuild?

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

Aug 26, 2014 | 04:46 PM

xlt4wd90

Lead Driver

Joined: Sep 2003

Posts: 7,013

Likes: 205

From: SoCal

Wouldn't boring out the cylinder GAIN a tick of compression? It's squeezing a little more volume into the same combustion chamber.

Aug 27, 2014 | 12:40 AM

85e150

Super Moderator

Joined: Apr 2004

Posts: 34,475

Likes: 2,800

Bigger space and VE is not 100%. Marginal VE is even lower. Plus you usually have a bigger head gasket gap.

Aug 28, 2014 | 11:07 PM

SDDL-UP

Laughing Gas

Joined: Sep 2013

Posts: 1,112

Likes: 101

From: North Idaho

Yes, you gain compression by increasing the bore.

Aug 29, 2014 | 12:39 AM

85e150

Super Moderator

Joined: Apr 2004

Posts: 34,475

Likes: 2,800

Checked a couple of static CR calculators. You are correct, you get a bit of a boost in CR with a bigger bore, all else being the same.

Dynamic compression....not sure, but given the marginal volumetric efficiency, I don't see how you gain cylinder pressure while running. I suppose there is a standard, known calculation for that as well, but I don't feel like looking it up and proving myself wrong again.

Op hasn't been back yet.....