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1995 GMC SIERRA SHORT BED MARK IV 454 700R4
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Discussion Starter · #1 ·
Recently got a set of PCE281.2034 Speedmaster heads. They are on Summit for $1,225.00 for a pair. I checked them over well. Casting seems flawless, bolt and spark plug holes all in alignment, with gaskets, and all threaded properly. They do not come with push rod guide plates or rocker studs. They do come with single springs with a dampner, not double springs as advertised. Quality springs with seats that fit over the bronze guides should be installed. That, along with setting spring height. The major surprise I got was that they were advertised with 119cc combustion chambers. I cc'd them twice to make sure and it's actually 127cc chambers. That will bring my compression down from 9.7 to 1 to 8.9 to 1. Had 116cc chambers on heads I was going to use. I wanted a streetable engine and 8.9 to 1 is great. The GM 454 HO engine has 8.75 to 1, along with an almost identical cam as the one I'm using. My dome volume on the 454 is -15.5cc 4.00 stroke. I will keep you informed!
 

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1995 GMC SIERRA SHORT BED MARK IV 454 700R4
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18 Posts
Discussion Starter · #3 ·
Speedmaster PCE281-2034 I have not given up on the heads. I fit a used 1027 Fel-Pro head gasket, 4.370 bore and .039, to it and the combustion chamber was larger than the compressed fire ring on the gasket. Made me scratch my head for a while. I did find out, when I called Speedmaster in California, you must use at least a 4.540 diameter head gasket on it. They are on the way. It makes perfect sense to use a larger bore gasket. The heads have bone stock valve springs, single with dampener, but, I already have a dual spring set up for them. The Intake valves are steel and the exhaust are stainless. I will be using those in my street performance application. Updates to follow.
 

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You’ll find all valves are some sort of stainless even the low cost valves intake and exhaust are usually made from 21N4 which is a very robust material.

Moving into the lower end of performance valves you start seeing a step up in the stainless alloy and a change in what’s used for intake NK-841/842 and exhaust of XH-424/426. As you get into competition engines the stainless alloy just keeps going up, especially for exhaust valves as they operate a lot hotter than intakes so this side requires a lot more attention. Going through Inconel pretty much ends the stainless family after this your headed to titanium. Titanium requires a whole different approach to the heads valve seats ordinary hardened iron or steel inserts are no longer compatible with the valve material.

Big thing you want to look for with stainless valves is ‘hard chrome stems’ most are. This is a flash plating process that adds a huge amount of stem and guide life in this hopefully low lubrication area. Again exhaust is the more critical stem and guide because not only is it hotter than the intake but sees pressure that want to both cook what little lube in in there and wants to blow it out. The intake running cooler and seeing manifold vacuum that want to pull lubrication into the stem to guide clearance lives a lot softer life.

So the trick if the engine is going to run hard is to beef up the exhaust valve material.

Bogie
 
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