T18skyguy
Eugene, OR
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Joined: 12/13/2004
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If you take the exhaust manifold and lay it on a completely flat surface(like a plate of glass), you should not be able to insert a feeler gauge any larger than .01 inch around any of the ports. Any larger than that then no gasket will seal it indefinitely and you must have it planed or buy a new manifold. The .01 spec is a Ford spec but the 454 probably isn't much different. If it's out of spec check the head at that area and look for erosion as that could be a problem area for you. I would agree that there's no better time to go to headers then now, especially if your gonna keep the rig.
Retired Anesthetist. Pilot with mechanic/inspection ratings.1996 Jayco C 22 foot with 460/Banks Powerpak/Bilsteins.Wife and daughter. Two cats which control my life. 1975 Ford F-250, 84 Coupe Deville, Thorp T18, tons of tools and tons of junk.
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sum1
So-Cal
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Joined: 11/07/2005
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zed1k wrote:I didnt hone the cylinders sorry WHEW! 
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1fastdad
mo.
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Joined: 08/27/2007
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Unfortunately those cast iron manifolds are a real problem. They do make stainless steel replacements but they aren't cheap. Like everyone said you are probably better off getting a good set of ceramic coated headers they don't rust and they will increase performance and mileage.
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RJsfishin
Winston Or.
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Joined: 10/16/2007
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T18skyguy wrote:If you take the exhaust manifold and lay it on a completely flat surface(like a plate of glass), you should not be able to insert a feeler gauge any larger than .01 inch around any of the ports. Any larger than that then no gasket will seal it indefinitely and you must have it planed or buy a new manifold. The .01 spec is a Ford spec but the 454 probably isn't much different. If it's out of spec check the head at that area and look for erosion as that could be a problem area for you. I would agree that there's no better time to go to headers then now, especially if your gonna keep the rig.
.01 ?
Is that like .010 or ten thousanths ? That seems like a lot.
Rich
'98 Flair, 454, Onan Microlite 4k, Intel PD 9155 w/ wizard, Sta-power 1500 watt Inv, 2 6v batts, ammeters, KingDome/sat, Oly Catalytic Heat, hauling 2 Bent Bikes and sometimes towing a Tracker F&S boat.
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zed1k
NS, Canada
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Joined: 05/23/2008
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Wow, this is a great forum, I am definatly going to have the head machined, and I am going to look into headers as well.
Thanks
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T18skyguy
Eugene, OR
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Joined: 12/13/2004
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RJsfishin wrote:T18skyguy wrote:If you take the exhaust manifold and lay it on a completely flat surface(like a plate of glass), you should not be able to insert a feeler gauge any larger than .01 inch around any of the ports. Any larger than that then no gasket will seal it indefinitely and you must have it planed or buy a new manifold. The .01 spec is a Ford spec but the 454 probably isn't much different. If it's out of spec check the head at that area and look for erosion as that could be a problem area for you. I would agree that there's no better time to go to headers then now, especially if your gonna keep the rig.
.01 ?
Is that like .010 or ten thousanths ? That seems like a lot.
It's .01 or 1/100th of an inch. If the gap is any larger than that then there's not enough "crush" on the gasket and it blows out.
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Mike Hohnstein
Germantown, Wi
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Joined: 01/04/2004
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Much valid information has been posted on this thread. However, tubular headers are not automatically the best option. Tubular headers flow advantages are at higher engine speeds, that's why they are used in racing applications. In the short term it would be wise to opitimize the lower engine speed characteristics of a given engine combination. Consider the fact that truckers are dropping their road speeds, and gaining significant milage numbers. I personally like cruising along at 80+ mph, but it's not really cost effective in the best of times.
The GM P30 shop manual recommends using a graphite paste between the head surface and manifold flange, to allow the two surfaces to move indepentantly, reducing manifold stress and cracking.
There is a place for tubular headers, but they need to have a thick flange, 3/8" minimum and that means expensive.
Last week we 'remanifolded' a GM TopKick with 7.0 engine and 30k GVW.
Both OEM manifolds were cracked, miles on chassis 32k. Local dealer had both manifolds and all fasteners and studs, total cost $607. The replacement manifolds differed from the OEM as the flange surface was slit between cylinders, futher isolating the manifold from heat related stresses. I chose the Victor graphite manifold gasket as it will NOT burn out as long as torque and sealing pressure are maintained. The real key to success is using grade 8 fasteners and maintaining torque, and allowing the manifold surface to flex somewhat using graphite in some form.
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AlanB
Sierra Vista, AZ
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Joined: 11/18/2002
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There are headers specifically for lower RPM high torque applications. They have longer tubes with small diameters. Some older motorhomes with small engines came that way from the factory, it works well. (LeSharo, with a Puegote 4 cyl? I think.)
AlanB
2002 Holiday Rambler Imperial 40PKDD Cummins ISL
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BluegrassBill
Woodland, Wa. USA
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Joined: 05/24/2003
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Do the Headers. Your engine will thank you for them. Thorley, Gibson and of course top-O-the line Bank$ make long tube high torque systems for RV's.
Bill
Bill & Kathy Francis
95 Itasca Sunrise 29RQ,P32 454 Chevy, Banks,ECM chip.Safe-T-Plus, Bilsteins, Super Steer Bell Crank, Stewart Stage 1 Waterpump, Severe Duty Fan Clutch, OilGuard Bypass Filter, Coolant Filter. Rear Tracbar. 1-5/8" Front Swaybar.
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bill h
el segundo
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Joined: 08/02/2001
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I'm a header fan, but if you do manifolds, mill them flat and use no gasket, just a graphite paste. And use a splash shield on the right side like the left has. Without it, the right rear exhaust and plug leads get real hot. Studs shear, etc.
Bill and Susan
84 Barth 30 tag powered by ht502/Thorley, Gear Vendors OD
Siamese Calvin and Airedale Hobbes
4WD Toyota toad
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