5 Liter w/ Turbo Build
08-04-2009, 05:47 AM
#31
Nordschleife Master
I posted photos of my mod that we made last week under the title GTS cooling mod. Search should find it. We did it to S4 heads with casting revision .1R and .4R, so it probably works on all S4 and GT heads. I don't know about early 32-valve heads, you'd have to get a junk head to test it with.
08-04-2009, 09:08 AM
#32
Man of many SIGs
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I posted photos of my mod that we made last week under the title GTS cooling mod. Search should find it. We did it to S4 heads with casting revision .1R and .4R, so it probably works on all S4 and GT heads. I don't know about early 32-valve heads, you'd have to get a junk head to test it with.
Thanks Tuomo
08-06-2009, 02:29 PM
#33
Man of many SIGs
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For Sc application there simply isn't perfect 928 engine. Not from factory anyway. One needs to select parts from 4 or 5 different engines to make best version possible using factory parts. Early '87 squirter block, '87-88 January S4 pistons preferably modified to have oil drain holes in skirts and lower compression tops, modified early 951 rods, '91-95 heads, GT style intake, crank scraper etc. All these parts together will result much better engine than any single stock engine can ever be.
Changes on S4 and GT pistons are interesting. I think there are several different piston configurations:
#1 Thick top, large compression area, weak skirt, no drain holes
#2 Thick top, large compression area, strong skirt, drain holes
#3 Thin top, large compression area, strong skirt, drain holes
#4 Thin top, small compression area, strong skirt, drain holes
Drain holes is not same thing as problematic not drilled all the way through oil ring drain hole in GTS pistons. These S4 drain holes refer to holes low down on skirts which allow excess oil to drain from plateau below wrist pin end.
Difference between thick and thin top thickness is about 1mm. Other 1mm comes from fact that bottom of thick top is 1mm further down from imaginary top line drawn above piston on its highest point. So thin top versions have two separate disadvantages on their tops which both separately are enough to make them less suitable for SC engine. Thick top is much better for modification and it allows clearly larger compression area on top before material becomes too thin. Difference is something like 8.2-8.3:1 CR for thick and 8.7-8.8:1 for thin when same thickness of material is left to piston top.
Strong skirt is obviously better skirt. But I think low compression is much more important for SC engines and having strong skirt. No oil drain holes is not important at all as they can be added to all versions which do not have them. Squirter blocks are more trouble than good on all NA engines so its better to save those blocks to SC builds. Especially those which have thick cylinder walls.
There are at least two different forged rod types. One is weaker than another. Stronger was mainly used in early 951 engines. Weaker was used in both later 951 and some 928. Best option is probably aftermarket set made to 928 specs. They are not that expensive, are easy to find and most importantly they are new parts which are probably much stronger than any Porsche version ever available.
'91-95 heads have extra cooling passages between exhaust ports. They are slightly better than earlier long bolt heads. Port matching to larger GT intake is yet another thing which isn't directly related to short vs long head bolt change.
#1 Thick top, large compression area, weak skirt, no drain holes
#2 Thick top, large compression area, strong skirt, drain holes
#3 Thin top, large compression area, strong skirt, drain holes
#4 Thin top, small compression area, strong skirt, drain holes
Drain holes is not same thing as problematic not drilled all the way through oil ring drain hole in GTS pistons. These S4 drain holes refer to holes low down on skirts which allow excess oil to drain from plateau below wrist pin end.
Difference between thick and thin top thickness is about 1mm. Other 1mm comes from fact that bottom of thick top is 1mm further down from imaginary top line drawn above piston on its highest point. So thin top versions have two separate disadvantages on their tops which both separately are enough to make them less suitable for SC engine. Thick top is much better for modification and it allows clearly larger compression area on top before material becomes too thin. Difference is something like 8.2-8.3:1 CR for thick and 8.7-8.8:1 for thin when same thickness of material is left to piston top.
Strong skirt is obviously better skirt. But I think low compression is much more important for SC engines and having strong skirt. No oil drain holes is not important at all as they can be added to all versions which do not have them. Squirter blocks are more trouble than good on all NA engines so its better to save those blocks to SC builds. Especially those which have thick cylinder walls.
There are at least two different forged rod types. One is weaker than another. Stronger was mainly used in early 951 engines. Weaker was used in both later 951 and some 928. Best option is probably aftermarket set made to 928 specs. They are not that expensive, are easy to find and most importantly they are new parts which are probably much stronger than any Porsche version ever available.
'91-95 heads have extra cooling passages between exhaust ports. They are slightly better than earlier long bolt heads. Port matching to larger GT intake is yet another thing which isn't directly related to short vs long head bolt change.
I would also like some info regarding the cooling mod (GTS style). I would like to do this to my 86 heads if possible.
What do you mean "weaker" style forged rods? Is there a flaw inherent in these rods or is the later design just beefier?
Thanks
Still waiting on this info....anyone?
BTW, I found this really cool Porsche training video regarding the 32 valve engine valve train.
http://video.yahoo.com/watch/4629118/12377608
08-06-2009, 05:16 PM
#34
In Your Face, Ace
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08-06-2009, 06:30 PM
#35
Man of many SIGs
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The difference is about 2mm if I remember our conversation correctly.If the stock 86 rods are forged then I may re-use them and go with new Woessner pistons w/ the ferostan coating. They are lighter than stock pistons by about 100 grams each and can run in our alusil blocks. Since I have a couple of scratched cyl's due to the broken valves that were bouncing around, it makes more sense to buy the new pistons. Especially if the stock rods are forged. The cyl. walls in this block are currently 8.66mm This would allow an overbore to 104mm bores and still have plenty of meat left for strength.
Abby, those Ti rods that I thought I had found for $2,200 a set.............well, lets just say I read it wrong. That was a price for ONE ROD!!!! WTF!!!
LOL I guess I can scratch that dream off my list.
08-07-2009, 12:53 AM
#36
Nordschleife Master
I found this chart on an ad for some Pauter rods on ebay: http://cgi.ebay.com/ebaymotors/Paute...4506.m20.l1116
Screen shot:
Screen shot:
08-11-2009, 01:51 AM
#37
Man of many SIGs
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Hypothetical question:
To run an aluminum piston in an alusil block, the piston needs to be coated. The stock coating is ferostan which is iron.
Another option is to run uncoated pistons but coat your bores with nicasil.
That being said, would it be possible to succesfully leave your engine bores uncoated but coat the pistons with nicasil? I don't know that there would be any cost advantage but it has piqued my curiosity.
Does anyone know the answer to this question?
To run an aluminum piston in an alusil block, the piston needs to be coated. The stock coating is ferostan which is iron.
Another option is to run uncoated pistons but coat your bores with nicasil.
That being said, would it be possible to succesfully leave your engine bores uncoated but coat the pistons with nicasil? I don't know that there would be any cost advantage but it has piqued my curiosity.
Does anyone know the answer to this question?
08-11-2009, 02:30 AM
#38
Three Wheelin'
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Location: In the boatyard installing the mast and engine, we don't need a crane, we harness the mesquito's! Yeah!
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Hypothetical question:
To run an aluminum piston in an alusil block, the piston needs to be coated. The stock coating is ferostan which is iron.
Another option is to run uncoated pistons but coat your bores with nicasil.
That being said, would it be possible to succesfully leave your engine bores uncoated but coat the pistons with nicasil? I don't know that there would be any cost advantage but it has piqued my curiosity.
Does anyone know the answer to this question?
To run an aluminum piston in an alusil block, the piston needs to be coated. The stock coating is ferostan which is iron.
Another option is to run uncoated pistons but coat your bores with nicasil.
That being said, would it be possible to succesfully leave your engine bores uncoated but coat the pistons with nicasil? I don't know that there would be any cost advantage but it has piqued my curiosity.
Does anyone know the answer to this question?
11-18-2009, 11:44 AM
#39
Man of many SIGs
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I'm resurecting this thread because there is alot of good info here. I had started another thread for this build at https://rennlist.com/forums/928-foru...questions.html
Does anyone have the cc #'s for a stock 951 piston?
Does anyone have the weight of a stock 951 piston?
Does anyone have the cc#'s for a stock 968 piston?
Does anyone have the weight of a stock 968 piston?
Are stock 968 pistons forged?
Does anyone have the cc #'s for a stock 951 piston?
Does anyone have the weight of a stock 951 piston?
Does anyone have the cc#'s for a stock 968 piston?
Does anyone have the weight of a stock 968 piston?
Are stock 968 pistons forged?
