944 pistons for hybrid engine?
05-23-2007 | 02:20 PM
#31
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From: Penn State
Originally Posted by mark kibort
the pistons are from an 85-86 US. you can tell by the little dish in the middle of the piston. on an S4 it is very large, and hence the reason you can use the S4 pistons for a hybrid motor. this means the heads on an S4 have a lot less CCs. so, an interesting rebuild would be using an 85 block with S4 heads to bump the compression to 12:1. plus you get the larger valves of the S4 heads and by using the 85 cams (same as GT) you get the best performance package of the stock components. I dont think anyone has ever done this yet.
Mk
Mk
I've got all the parts lying here just no time to assemble it yet.
05-23-2007 | 04:22 PM
#32
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From: Trondheim, Norway
so to sum things up, S4 block and Euro S/S2 heads combined will give a lowish CR, especially when adding the CCs for the necessary piston cut-outs. So to get a proper CR for N/A I will need to shave off the heads. This will make the valves go deeper, requiring even deeper piston cuts.
And there are no known EuroS/S4 hybrids built yet. So I have to figure it all out for myself. Currently I'm more of a shock-replacer than an engine-developer, but hey, how hard can it be? And I have approximately zero spare time. I think I'll go for it!
MM
And there are no known EuroS/S4 hybrids built yet. So I have to figure it all out for myself. Currently I'm more of a shock-replacer than an engine-developer, but hey, how hard can it be? And I have approximately zero spare time. I think I'll go for it!
MM
05-23-2007 | 04:30 PM
#33
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From: saratoga, ca
i think shaving the heads could effect valve timing( that much) not to metion the valves would be pushing down that much farther now. as it is now, the valve reliefs only allow for about .3" . when a belt skips teeth, the max lift being near .45", causes the valves to hit. I dont think i would want that gap narrowed any further.
best just to change out the pistons to 85s, since you have to cut the valve reliefs anyway. you are talking about a $500 set of pistons, vs doing head work that may or may not do the deed.
mk
best just to change out the pistons to 85s, since you have to cut the valve reliefs anyway. you are talking about a $500 set of pistons, vs doing head work that may or may not do the deed.
mk
Originally Posted by gruffalo
so to sum things up, S4 block and Euro S/S2 heads combined will give a lowish CR, especially when adding the CCs for the necessary piston cut-outs. So to get a proper CR for N/A I will need to shave off the heads. This will make the valves go deeper, requiring even deeper piston cuts.
And there are no known EuroS/S4 hybrids built yet. So I have to figure it all out for myself. Currently I'm more of a shock-replacer than an engine-developer, but hey, how hard can it be? And I have approximately zero spare time. I think I'll go for it!
MM
And there are no known EuroS/S4 hybrids built yet. So I have to figure it all out for myself. Currently I'm more of a shock-replacer than an engine-developer, but hey, how hard can it be? And I have approximately zero spare time. I think I'll go for it!
MM
05-23-2007 | 05:40 PM
#34
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From: Trondheim, Norway
Originally Posted by mark kibort
i think shaving the heads could effect valve timing( that much) not to metion the valves would be pushing down that much farther now. as it is now, the valve reliefs only allow for about .3" . when a belt skips teeth, the max lift being near .45", causes the valves to hit. I dont think i would want that gap narrowed any further.
best just to change out the pistons to 85s, since you have to cut the valve reliefs anyway. you are talking about a $500 set of pistons, vs doing head work that may or may not do the deed.
mk
best just to change out the pistons to 85s, since you have to cut the valve reliefs anyway. you are talking about a $500 set of pistons, vs doing head work that may or may not do the deed.
mk
05-24-2007 | 07:50 AM
#35
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From: Denmark
Originally Posted by Vilhuer
Friend is building engine for Rotrex SC. Reasoning behind using 951 was that they are build for boost. Piston tops are better suited for high temps and possibly piston diameter is more cone shaped that in NA pistons allowing more heat expansion.
Idea of having top 2mm of cylinder bore exposed when mixture is ignited don't sound very wise to me. What happens to then walls if there is even small problems in timing or engine knocks?
Idea of having top 2mm of cylinder bore exposed when mixture is ignited don't sound very wise to me. What happens to then walls if there is even small problems in timing or engine knocks?
Last edited by 928DK; 05-24-2007 at 09:31 AM.
