Valve reliefs in a BB Chevy, Yes or No

[Ron Miller]

I searched for this topic with no luck, So I'm going to ask this question. I'm assembling a 454 2 bolt block, 0 deck, with a 4.280 bore. I have been thinking about adding valve reliefs on the block both intake & exhaust. I know this has been done before but I have never really heard of any real solid claims or gains. Has any body out their seen any solid gains with their engine on a dyno or increased in flow on a bench head stand. I have scribed the deck to match the chambers, and their is a obvious edge. I'm using a BB Chevy oval port true closed chamber head casting number 3872702. The heads have the 2.19 & 1.88 valves installed with major chamber un shrouding. The heads will be milled to at least .030, and no more than .060. When all done & said, I would like to see 9.5 compression ratio, no more than 10.5 with my flat top piston L 2377. So, I would like to hear all Good and Bad ideas on this topic.

Thanks for looking,

[bigjoe1]

I have done the chamfer in the top of the cylinder all my life. You only need to worry about the intake side, not the exhaust. I think it could be a very big deal on a serious engine, but your build is pretty mild, so it might be worth something like 10, maybe 15 HP- I do know on high HP engines ( 800-900 hp ) it can be worth 20 to 30 HP

JOE SHERMAN RACING

[rskrause]

I don't think there is any downside other than the time it takes to do it. I Certainly defer to Mr. Sherman re: the magnitude of any benefit.

Richard

[Ron Miller]

Joe & Richard,

Thanks for the replies and info. Looks like I will be grinding the intake reliefs today.

Thanks Again,

Ron

[MadBill]

Just make sure they don't go as deep as the top ring's upper travel limit.

[Ron Miller]

Just make sure they don't go as deep as the top ring's upper travel limit.

MadBill,

Thanks for the heads up ! I have that covered. I maid a simple tool with a 90 degree scribe. I set it - .030 from where the top ring will set at TDC.

Thanks Again for the reply,

Ron

P.S. Why do you call you self MadBill ??????? L.M.A.O.

[MadBill]

...P.S. Why do you call you self MadBill ??????? L.M.A.O.

My (still) best friend when we first met 50-odd years ago lived on a farm near our cottage. Over time his dad noticed that come July each year, things would start going badly wrong with their peaceful rural life: Grass fires, explosions, calls from the cops about a pair of VW's terrorizing a local subdivision... Somehow he associated the mayhem with my arrival for the summer and came up with the "Mad Bill" moniker and it has stuck all these years..

[BCLS776]

I have done the chamfer in the top of the cylinder all my life. You only need to worry about the intake side, not the exhaust. I think it could be a very big deal on a serious engine, but your build is pretty mild, so it might be worth something like 10, maybe 15 HP- I do know on high HP engines ( 800-900 hp ) it can be worth 20 to 30 HP

JOE SHERMAN RACING

I've seen blocks with just the intake side chamfered and some with both sides chamfered. Head gaskets often have a little bulge there too. Is it just a tiny bit more power to do the exhaust side, which is why some don't do it? Not worth the effort?

[bigjoe1]

The exhaust flow does NOT need the chanfer like the intake side does. It will just lower the compression


JOE SHEWRMAN RACING

[Eric68]

Not to hijack, but how much power do you gentlemen think a head with a chamber 4.500" across with a 2.30" valve would give up on a 4.310" bore? I'm looking at a substantial ledge on the intake side of the chamber.

I'm helping a friend upgrade from a 496 to a 555 short block. The heads on his 496 seem to be a much better fit for the bigger 4.560" bore.

[falcongeorge]

...P.S. Why do you call you self MadBill ??????? L.M.A.O.

My (still) best friend when we first met 50-odd years ago lived on a farm near our cottage. Over time his dad noticed that come July each year, things would start going badly wrong with their peaceful rural life: Grass fires, explosions, calls from the cops about a pair of VW's terrorizing a local subdivision... Somehow he associated the mayhem with my arrival for the summer and came up with the "Mad Bill" moniker and it has stuck all these years..

been wanting to ask that question myself. Great stuff...

[prostreetL-78]

Not to hijack, but how much power do you gentlemen think a head with a chamber 4.500" across with a 2.30" valve would give up on a 4.310" bore? I'm looking at a substantial ledge on the intake side of the chamber.

I'm helping a friend upgrade from a 496 to a 555 short block. The heads on his 496 seem to be a much better fit for the bigger 4.560" bore.

My Profiler 320`s flowed 18 cfm less on a 4.31 bore vs. 4.5" They have 2.300 intake valve also. Probably looking at 35 hp.

[shoedoos]

Watch out how far you notch the bore or you will be in for buying custom head gaskets...my two cents.

[pdq67]

A good thread and I did both valves on my Merlin cast-iron large ovals with 2.19"/1.88" valves back years ago. I do have a set of 8 Manley 2.300" valves for them but never put them in.

pdq67

[MotionMachine]

I don't think there is any downside other than the time it takes to do it. I Certainly defer to Mr. Sherman re: the magnitude of any benefit.

Richard

Takes no time at all, less than 30 seconds each

https://www.youtube.com/watch?v=uDc77irwo_Q