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Old 05-07-2013, 06:23 AM
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Unshrouding block for valve.......

Anyone have any info on whether making a slight chamfer on the block to help unshroud the intake valve makes sense, or makes more flow/power? Ive done it before after seeing some buildups, but never saw anything that says it is really that effective. Sorta like the grooves (Singh) in the head to inprove squirt or the squish during power stroke. Ive seen it done on the head itself, and have done this too, mocking the head up on the block and scribing the bore on the head from the crankcase, then seeing how it was in relationship.....just curious....getting ready to build up my motor and want every little trick on it

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Old 05-07-2013, 06:33 AM
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are you building something like a 283 with 2.02 valves,or just looking where there is no need?Sometimes little tricks make a tiny improvement on very powerful engines.Maybe state all your plans and some ideas can be tossed into the pot. what are your goals,why are you looking where you are,is this just a low budget blue print or are you building an engine for class racing,,
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Old 05-07-2013, 09:32 AM
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Quote:
Originally Posted by BigMo View Post
Anyone have any info on whether making a slight chamfer on the block to help unshroud the intake valve makes sense, or makes more flow/power? Ive done it before after seeing some buildups, but never saw anything that says it is really that effective. Sorta like the grooves (Singh) in the head to inprove squirt or the squish during power stroke. Ive seen it done on the head itself, and have done this too, mocking the head up on the block and scribing the bore on the head from the crankcase, then seeing how it was in relationship.....just curious....getting ready to build up my motor and want every little trick on it
The idea behind a relief on the cylinder wall is more to provide clearance when using oversize valves that are tight to the cylinder wall than it is to provide for better breathing. Over the years I've found it's more power productive to avoid valves that overhang the bore wall instead use more lift sooner. For any cam that can mean using 1.6 or 1.7 rockers on a small block to really push the optimization of high and fast lift. However, I wouldn't use 1.7 on the street as they really put the lifter to lobe interface and the push rod under a lot of strain. Plus you have to have the porting to support this approach so this begs for high flow ports which again are not compatible with a strteet engine unless you are building a street racer for a purpose and are willing to live with the difficult driveability that brings.

Bogie
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Old 05-07-2013, 01:35 PM
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Never have done it, but I have to believe that relieving material on the cylinder wall (down to the top of the top ring) would help the flow coming in past the valve. It would be interesting to see some back to back dyno pulls.
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Old 05-07-2013, 02:43 PM
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This has been done by the factory (select Ford FE 427, BBC and small bore Pontiac in particular, might be others). There's surely the potential to help flow when large valves are used, especially at lower lifts and as long as the top ring isn't intruded on there's no real downside other than a slight loss of compression. I'd want to keep the cut well away from the top ring- something like a min. of 0.030".

Now, if someone were to go into a build w/this idea already in mind, pistons having the top ring lower on the piston could be fitted. Pistons having a high top ring placement- like some KBs- wouldn't be as advantageous to use if this were being done.

The larger the valve/closer the valve edge is to the wall of the bore, the more this will help. A 4" nominal bore using a 2.02" intake will have little use for it- I did this on a fairly radical 355 SBC and saw no gains before and after using identical parts, engine was apart for fresh rings only. Bigger valves using the stock valve placement in the head will benefit. Aftermarket heads sometimes juggle the valve placement in the head to help bore shrouding.

Put a head on the block w/a gasket in place (no need to torque it down) and scribe the bore onto the head and go from there to see just how much shrouding is going to happen w/the parts that are to be used. That will also show you if there's any overhang of the chambers (chamber wider than the bore, in other words).

Good luck.
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Old 05-07-2013, 03:09 PM
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just angle mill the head.
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Old 05-07-2013, 10:16 PM
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With all due respect, if the real issue is valve shrouding, angle milling wouldn't be my first choice. Angle milling can help flow, but can only help a slight amount w/shrouding, and in the process it introduces a whole 'nuther bunch of bother.
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Once you cut the angle on the deck of the head, you have changed the geometry of the intake face, the exhaust face, the valves, the bolt and cooling holes, and just about everything else.
More: Angle-Milling Cylinder Heads, or do a search for angle milling.

Moving the chamber wall away from the edge of the valve can help more than angle milling OR notching bores- depending on the chamber, obviously.
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Old 05-08-2013, 09:44 AM
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I have done this with Ford motors in the past, using the scribe the bore method with the head bolted onto a bare block. This is on a smallblock Chevy using 2.08 intakes..... and or course not getting into the ring area. Was just was wondering, out of curiosity more than anything else. Will be a 575+ motor, so I dont think the couple hp that might or might not be fournd will be an issue......
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Old 05-08-2013, 10:04 AM
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sounds like you are building a 383 making 1.5 hp/cube? solid roller,7,000 RPM,850 CFM 1 3/4 inch primary headers,10.5:1?
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Old 05-08-2013, 11:27 AM
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When a couple drag racing mechanics rebuilt my 327 (331 ci) now almost 25 year ago and put in the 2.02/1.60 valves (1.94/1.50 prior), they did this to the block.

The engine makes great power for what it is (>280 RWHP with a 327/350 hp hydraulic cam @ ~9.5:1 CR), so I think they were successful and knew what they were doing. But I don't think I've seen anyone else do this.
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Old 05-08-2013, 05:41 PM
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Quote:
Originally Posted by toddalin View Post
When a couple drag racing mechanics rebuilt my 327 (331 ci) now almost 25 year ago and put in the 2.02/1.60 valves (1.94/1.50 prior), they did this to the block.

The engine makes great power for what it is (>280 RWHP with a 327/350 hp hydraulic cam @ ~9.5:1 CR), so I think they were successful and knew what they were doing. But I don't think I've seen anyone else do this.
It's not uber common, but it has its place and most good tuners/builders are aware of the usefulness of it in the right application.
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Old 05-09-2013, 10:26 AM
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Thanks for the input folks.........Vinniekg2.....its a small block with 10.6, AFR 210 heads, healthy roller cam, forged and balanced rotating, will have Carbshop induction, estimated 575+ hp.....
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