This style is at a consistent depth from side to side. Here is an example I collected form someplace - seems to be a work in progress (at least I hope so ): but in my mind, the amount is so minuscule, who cares.
The main reason for not doing a full relief was to preserve some compression. I've seen this most often on some of the flathead Harley street engines - it was NOT used on the KR race bikes to the best of my knowledge. This is where there are different relief depths between the intake and the exhaust. and still swears, cusses and bitches about it to this day (it is a dirty ass job!). This is an example from my friend 'RustyBucket' (fellow FlatCAD member) - it is from his very cool 276 cube full-house street flatty. This is typically done on a high-performance street flathead - where you want to improve the flow, but don't want to lose the compression or move the power band up too high. I'll show you a few examples before I detail what I did on the FlatCAD Bonneville engine: Not only is it to give space for flow, it is also to enable the intake charge to take as straight as path as possible to the bore (no going up, over and around as is the stock designs).Ģ) Relief Types or Styles: There are quite a few different styles of reliefs - from what I'll call 'partial' to 'full', "stepped" (where there are different depths on the intake versus exhaust side), etc. This is what relieving is all about - to ADD a new transfer area between the valve and the cylinder bore. it is gone! So - while the high-compression head achieved some compression, it actually hurts the flow in the "transfer area" - which is the area between the valves and the cylinder. Now - look at every high-compression head out there. Henry Ford accounted for it by making a rounded trough in the head - to let the gas go up, over and around.
This means that the intake charge has to go up/over the area between the valve and the cylinder and make two turns -> once to go up, then another time to turn back into the cylinder. The most important flow area of the valve (by the cylinder) is buried below the deck surface. What the canting does is it requires a depressed "pocket" on the cylinder side of the valve. the angles differ between manufacturers and even years of manufacturer. So read this if you want one mans opinion, if you don't believe in 'relieving a flathead' block, then what are you doing here anywayġ) General Theory Behind Relieving: If you look at the valve locations on flathead engines (Ford, Cadillac, etc) - you'll see that the valves are canted toward the bore. no shortage of debate, myths, examples, etc. There are as many beliefs and opinions on flathead relieving as there are bung-holes. What the Hell is a 'Relief' or Relieving Anyway - and Why Would You Do It? I sometimes take for granted all that I've learned and the many folks who have helped me learn. Okay gang, many of you know that I'm a bit obsessed with flatheads (of all sorts) and racing.