FAQ  •  Register  •  Login


Moderators: Curt!, Pa


old eagle

Posts: 1

Joined: Tue Sep 02, 2008 11:02 am

Post Fri Sep 12, 2008 3:19 pm


I concidder relieving the cylinders on my 1937 U. But what will I gain?

Not chasing 1/10 of seconds on the race track, just everyday useable torque to haul the bike up-hill against the wind with passeger and two weeks hollyday luggage at 70 mph.

Will relieving do the trick, will it be worth the work?

Old Eagle


Post Sat Sep 13, 2008 8:11 am

Re: Relieving

Relieving isn't going to do anything for torque, which almost entire a function of compression and displacement in mid-range. Breathing only helps torque when the engine is spinning relatively fast.
However: most cylinders have the seats recessed too far, and a light radius from the leading side of the cylinder surface blended into the factory relief cut is helpful, and only takes a few minutes. The exhaust is even more important - the head and cylinder temps go up when the exhaust valve is shrouded.

Tim 435

Posts: 745

Joined: Mon Sep 01, 2003 12:01 am

Location: Pa. , USA

Post Wed Sep 24, 2008 8:06 pm

Re: Relieving

Just remember old eagle what you take off you can't replace.
Vintage roadracing, Class C, AHRMA # 335


User avatar

Posts: 103

Joined: Sat Feb 05, 2005 1:01 am

Location: Switzerland

Post Sat Sep 27, 2008 4:19 am

Re: Relieving

Relieving will reduce the compression if you don't do anything else to increase compression. Reduced compression results in reduced torque. Relieving helps more in high RPM. As described by Panic, rounding off sharp edges will help avoiding hot-spots in the combustion chamber and will reduce pinging when you climb a hill.

Return to Big Twin Flatties

Who is online

Users browsing this forum: No registered users and 1 guest

Powered by phpBB © 2000, 2002, 2005, 2007, 2012 phpBB Group.