Hydro-idi
Full Access Member
We went back to the OEM camshaft and had new heads rebuilt to factory spec's as well. I sold the truck a couple weeks ago to father in law and it's a solid runner now. He will be towing a camper with it
Which cam?
- Thread starter 93MTF350
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We went back to the OEM camshaft and had new heads rebuilt to factory spec's as well. I sold the truck a couple weeks ago to father in law and it's a solid runner now. He will be towing a camper with it
Macrobb
Full Access Member
I want some more explanation, please. I can't see any reason why it would matter at all, provided you compensate on the upper side for the extra valve stem length.
The felpro and Victor Reinz gaskets aren't "decompression" gaskets exactly. They are perhaps .010 thicker than stock... but I once ran into a cheap set of Ford-spec NOS head gaskets, and they measured the same as the felpro ones I've used if I recall correctly. I'm guessing the .010 measurement comes from compression over time or something?
A guy, Jan, over on FTE came up with some "decompression" gaskets which are a good .040" thicker. Three layers of steel with 2 of good quality gasket material.
I bought a set and used them for a bit. It's /not/ a good idea:
1. IDIs don't like decompression. The engine will smoke and be harder to start when cold.
Oddly, I found that with the decompression gaskets, using glow plugs to start it worked /far/ better than ether when I was trying to get things to start the first time(manual setup here).
2. About 1,000 miles down the road, the gaskets leaked on me, leaking compression gasses into the coolant. Did not see coolant going the other way.
Apparently, you should re-torque the headstuds after a couple of heat-cycles, something that the felpro gaskets say you do *not* have to do.
I pulled the gaskets off and could not see any "problems" with them, or evidence that they failed. Put a new set of Felpro gaskets on it, and the problem went away.
Mind you, I put multiple layers of copper-coat on both sides of the gaskets, the underside of the head and the block, just to be sure. There's pictures over on FTE.
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Macrobb
Full Access Member
(double post - delete)
Hydro-idi
Full Access Member
When you remove that much material from the valves & seats, the valves will get a "knife edge" to them, which will cause both valve overheating issues and mushrooming. I ran my engine for about 500 miles when I knew something wasn't right. I tore engine apart and every valve seat was cracked in 1 or more places and valves were trashed. The valves were actually sucked into the cylinder head, hence the mushroom effect. This was with an additional .020 recession. I had to find new heads and replace all 16 valves.
Bottom line is when you remove that much material, your going to have problems. Factory specs are there for a reason.
Bottom line is when you remove that much material, your going to have problems. Factory specs are there for a reason.
Macrobb
Full Access Member
You removed material from the valves?
I'm talking about removing nothing from the valves, and just cutting the seat deeper into the head. Near as I can tell, the seat itself is a good 3/8" deep, so .020-.040" isn't going to make much difference.
The valves thickness, however... yeah, I can see why that would be an issue.
Hydro-idi
Full Access Member
Your right, shouldn't make much difference. After all, they are just specs that engineers had come up with when designing these engines. Please try it out on your engine and report back
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Macrobb
Full Access Member
Well, the engineers never designed it for a larger cam though. Or the doubling of factory HP and torque, so I can see some... creative interpreting of the numbers might need to be done.Your right, shouldn't make much difference. After all, they are just specs that engineers had come up with when designing these engines. Please try it out on your engine and report back
Anyway, I guess we'll see what happens when I do it. I still have the heads off my '88 which have a pretty mangled valve and seat from bashing it's way into the piston due to lack of clearance, so there isn't a whole lot to lose. They'll need new valve guides, too.
I am in a similar boat as to making a cam decision and await typ4's article. My first, and still current, leaning was towards the R&D stage 1 cam as it was tailored around forced induction. But sadly that's about the only recommendation I can add, and it's not much of one. I do want to point out however that Mahle has decompressed pistons available for both the 6.9 and 7.3. These have the wrist pin bore set .010" further in, increasing the clearance depth and decreasing compression ratio. Part number is 224-2190 for the 6.9's. I found them listed in the Mahle Aftermarket catalog. I will be watching this thread as it might answer very similar questions I might have myself.
I was told the typ4 cam is good with a turbo also. I remember seeing some dyno sheets comparing the two but can't remember where.
If you find those please post. I would really like to see them in comparison to each other.
Macrobb
Full Access Member
Now, I'm still not sure if the cam I bought from Typ4 was /actually/ a R&D cam(misgrind by the grindshop), but if it was actually a Typ4 cam, then:
I found that my Typ4 cam, when installed 1 tooth off like a R&D cam, degreed exactly like a R&D cam. I got the exact same numbers of lift, timing and duration.
So if my cam is typical, it might be as simple as getting one. If you install it straight up, you get more torque down low. If you install it 1 tooth off, you get more high end power.
I found that my Typ4 cam, when installed 1 tooth off like a R&D cam, degreed exactly like a R&D cam. I got the exact same numbers of lift, timing and duration.
So if my cam is typical, it might be as simple as getting one. If you install it straight up, you get more torque down low. If you install it 1 tooth off, you get more high end power.
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