Re: Big block exhaust valve/cylinder wall clearance
[Re: lancer493]
#2869404
01/05/21 04:38 PM
01/05/21 04:38 PM
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Joined: Jan 2003
Posts: 14,492 So. Burlington, Vt.
fast68plymouth
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 14,492
So. Burlington, Vt.
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.030” radial clearance from the exhaust valve to the bore wouldn’t bother me.
Since the valve and bore are not on parallel lines...... and the direction that the valve is moving vs where it is in the bore...... as the lift increases, the clearance decreases.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: Big block exhaust valve/cylinder wall clearance
[Re: lancer493]
#2869461
01/05/21 06:46 PM
01/05/21 06:46 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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it is too close to the top ring territory
How close? Even a 1/16" radius will help some.
Boffin Emeritus
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Re: Big block exhaust valve/cylinder wall clearance
[Re: fast68plymouth]
#2869481
01/05/21 07:55 PM
01/05/21 07:55 PM
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Joined: Aug 2003
Posts: 43,126 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,126
Bend,OR USA
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.030” radial clearance from the exhaust valve to the bore wouldn’t bother me.
Since the valve and bore are not on parallel lines...... and the direction that the valve is moving vs where it is in the bore...... as the lift increases, the clearance decreases. I've ran less with no bent valves or witness marks on the valves or block, you should check all 8 exhaust valves in the head your going to use on the side of the block your going to run them on to make sure what you have on all of them
Last edited by Cab_Burge; 01/05/21 07:55 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Big block exhaust valve/cylinder wall clearance
[Re: lancer493]
#2869668
01/06/21 12:38 PM
01/06/21 12:38 PM
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Joined: Mar 2007
Posts: 3,277 West Coast, USA
jbc426
master
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master
Joined: Mar 2007
Posts: 3,277
West Coast, USA
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I've often wondered about the notching of the top of the cylinder to match the contours of the cylinder head and the possible effects on flow related to this unshrouding. I would think there should be some video or technical papers of the flow changes by researchers somewhere.There were masses of research as far back as WW1 in the aircraft engine research files.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's 1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: Big block exhaust valve/cylinder wall clearance
[Re: lancer493]
#2871737
01/09/21 04:14 PM
01/09/21 04:14 PM
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Joined: Jun 2012
Posts: 1,899 MYRTLE BEACH SOUTH CAROLINA
ek3
top fuel
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top fuel
Joined: Jun 2012
Posts: 1,899
MYRTLE BEACH SOUTH CAROLINA
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Re-installed heads w/only all the exhaust valves w/checking springs installed. No pushrods, and mechanically opened each valve to the maximimum valve lift that this camshaft has. This allowed me to turn the crankshaft get the throws out of the way for realworld accurate measurements between the cylinder wall and the exhaust valve. Sounds corny but used a measured paper clip as a wire gauge (.029") and each valve had very close to the same clearance allowing the paper clip to slide easily through between the wall and the valve. Increase the valve lift and the clearance goes away quickly.Not high tech but pretty darn accurate.I used .690" as my lift number. Ithink a.750- .800 lift cam (actual) would have trouble here in this 4.350" bore. I talked with the tech dept at Hughes engines,(where the heads were purchased and ported) and they said the've had no complaints at that bore. Just doesn't look like any camshaft upgrades at this bore. Thanks for all the input here. Bill any chance you can move the heads up the block ? offset dowel pins .015-.030 " reduce the intake manifold with a side cut.... ? maybe move the valves // angles..
Last edited by ek3; 01/09/21 04:17 PM.
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