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'99 996s
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82 Posts
Discussion Starter #1
The time came to refresh the heads of the old 996. Looking at the cost of replacing 8 valve guides, It was nearly a wash to pick up a set of low milage s4r heads and put them on the 996.

It turned out easier than I thought. Heads, timing belt covers, timing belt backing plates, and 93 tooth timing belts were the only things I needed to accquire.

The banjo oil fittings in the heads needed to be drilled and tapped from M8 to M10 x 1.0. The head studs needed to be shortened by 10 mm give or take (have dremmel will cut) Installation was straight forward. Squish setting didn't change. The intermediate exhaust pipe moved back slightly and one small screw on the verticle head near the timing mark, which I don't know what it was for, need to be removed so the oil breather tank would fit.

Put it all back together and she came to life on the third revolution!

The final pieces of the puzzle to figure out are the radiator bracket and V piece. But she's back on the road.
 

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Did you put your old cams in the new heads? The intake cams are not the same. Shorter duration on the 4V Monster and ST heads.
 

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'99 996s
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Discussion Starter #5
Did you put your old cams in the new heads? The intake cams are not the same. Shorter duration on the 4V Monster and ST heads.
The new to me heads were nearly complete. Came with cams, valves, rockers... just needed to add my valve covers and coolant fittings.

So i have the 10 degree shorter duration intake camshafts of the ST/ 4V monster series, 251 vs 261. So when I time the camshafts this winter I think I'll need to go with 114/110 centerlines vs the 996's 110/110 centerlines. But this time the job's going to be much easier. The s4s head's came with adjustable pullies. No more offset woodruff keys!
 

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I've always liked the power delivery of my ST4s, from reading about it, it seems some of that can be attributed to those shorter duration cams. Never road a 996 with the "normal" cams, so I can't compare. Interested in hearing what you think. Are you going to update your fuel map to suit?
 

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'99 996s
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82 Posts
Discussion Starter #7
I've always liked the power delivery of my ST4s, from reading about it, it seems some of that can be attributed to those shorter duration cams. Never road a 996 with the "normal" cams, so I can't compare. Interested in hearing what you think. Are you going to update your fuel map to suit?
I really don't feel much difference from the factory 996 cam timing. I can tell you I am down on midrange from 110/110 cam timing on stock 996 cams. I didn't measure to know where my current cam time is now. I do know when I change it I will have to update my fueling. I will then need to find someone in northern New England that can program the old FIM chips.

Its only the second day of test runs with the heads. I haven't had it above 7K very often. I keep running out of road on my daily commute!
 
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