Octane, and 928 heads.
07-15-2004, 02:08 AM
#1
Nordschleife Master
Thread Starter
Octane, and 928 heads.
When Porsche was useing the 16v Euro heads, they ran a rather traditional wedge shaped combustion chamber with an aluminum head. IIRC, it's not a quench style head. A 9:1 nominal CR was rated for 87 octane fuel(CLC/AKI). A 10:1 nominal CR was rated for 91 octane fuel (CLC/AKI) This is comperable to the heads in other vehicals, and the run similer CRs at similer octane rateings.
When Porsche switched to the 32valve head, they did some extensive modernization to it. They switched to a hemispherical combustion chamber, and as I understand it, a quench style head. The CR and fuel octane rateings are the same. The 9.3:1 86 Euro 32valve engine is suppost to drink 87 octane. The US 86, with it's 10:1 CR is suppost to drink 91 octane.
My understanding is it's rather similer to the heads in Catilacs Northstar engine. Also, as I understand it it's rather similer to some other hemispherical, quench style import heads. They seem to run about a CR point higher for a given octane rateing of fuel. Some where around 10:1 for 87, and 11:1 for 91. Hum.
Does anyone here offer a good reason as to why Porsche would leave that kind of thing on the table? Expecaly in the early 90s?
When Porsche switched to the 32valve head, they did some extensive modernization to it. They switched to a hemispherical combustion chamber, and as I understand it, a quench style head. The CR and fuel octane rateings are the same. The 9.3:1 86 Euro 32valve engine is suppost to drink 87 octane. The US 86, with it's 10:1 CR is suppost to drink 91 octane.
My understanding is it's rather similer to the heads in Catilacs Northstar engine. Also, as I understand it it's rather similer to some other hemispherical, quench style import heads. They seem to run about a CR point higher for a given octane rateing of fuel. Some where around 10:1 for 87, and 11:1 for 91. Hum.
Does anyone here offer a good reason as to why Porsche would leave that kind of thing on the table? Expecaly in the early 90s?
07-15-2004, 03:27 PM
#4
Nordschleife Master
Thread Starter
heinrich, read your WSM. In 1986 prosche was building 3 motors.
1. 4.7l, 16v 310 hp engine, we like to call the Euro S2
2. 5.0l 32v 288 hp engine, we often call the US S3
3. 5.0l 32v 280 hp engine sold outside the us. At best as I can tell, the only thing diffrent from the US 32v engine, and the ROW 32v engine, was the nominal CR, and the octane rateing of the fuel. This apperently lowered the maximum hp by 8hp.
Notice, I usualy wrote, "nominal CR", as thats what the factory put in their books. Why it doesn't work out to the exact CR, I'm unsure, BUT thats what they put in their books.
Sorry about misspelling Cadillac. My fingers got crossed up.
1. 4.7l, 16v 310 hp engine, we like to call the Euro S2
2. 5.0l 32v 288 hp engine, we often call the US S3
3. 5.0l 32v 280 hp engine sold outside the us. At best as I can tell, the only thing diffrent from the US 32v engine, and the ROW 32v engine, was the nominal CR, and the octane rateing of the fuel. This apperently lowered the maximum hp by 8hp.
Notice, I usualy wrote, "nominal CR", as thats what the factory put in their books. Why it doesn't work out to the exact CR, I'm unsure, BUT thats what they put in their books.
Sorry about misspelling Cadillac. My fingers got crossed up.
