Valve reliefs in a BB Chevy, Yes or No

[Schurkey]

Aside from unshrouding flow, wouldn't these chamfers also funnel combustion pressure to the top ring--sort of like gas-ported piston crowns?

The downside is that when the top ring is closest to the chamfer(s), the cylinder pressure hasn't peaked yet.

[Neal Arnold]

Definitely would not build any BBC without doing both reliefs!

Most gaskets have the same spread in those areas, so it helps laying it out.

The top ring should be down in pretty good but definitely measure where it sits and just start laying it back.

As far as gains 100% it will benefit the efficiency of the engine.

[gnicholson]

this is a 9 year old thread.

[MadBill]

But we still have BBCs, so...

[Newold1]

My experiences on smaller bore BBC's from 4.00" to 4.310" is that depending on intake valve size the side bore relief can help flow on the intake side especially at low lift flows but is is also very dependent on camshaft timing and cylinder head used. On the exhaust side depending on the cylinder head used it does not seem to make a big difference even with a 1.88" valve because with the lesser exhaust valve cant and the piston is further down the bore on exhaust openings. On big bore BBC's 4.350 to 4.625" it tends to be a poor return on time and expense. JME