Compression Ratio XJ750Turbo

[Kneggie]

Hi All,
Following a comment from Axel on Facebook, here I will explain what I mean by the Compression Ratio from the normal 750 11M engine to the CR of the 11T engine. Initially I had used a foot and head gasket from Athena, because the original is bad or not available. The thickness of the gaskets are both 1.2mm. The standard thickness of the 750 base and head gasket are 0.3 and 0.9 mm respectively. The difference in thickness of the gaskets are: 2.4 - 1.1 = 1.3 mm. So the combustion chamber volume increases with the area of ​​the cylinder with the 1.3 mm height. The stroke and bore dimensions are: 56.4 and 65 mm. The stroke volume is 3.13159x3.25^2x5.64=187.15. The CR 9.2:1 => 187.15:9.2=20.34 cc. With the 1.3mm enlargement of the packings, the volume above the piston increases by 0.13x3.14159x3.25^2=4.31cc. The new CR is now: 20.34+4.32=24.65cc => 187.15:24.65=7.59. So the new CR is many times lower than the 8.2:1. Since I still had to replace the base gasket because it burst open during the first assembly and after 2000 km the O-rings also failed. Am I going to replace the base gasket for an original, which I bought in Florida last year. The CR is now higher but does not exceed 8.2:1. The thickness differences in the base gasket are 0.9-0.2=0.7mm and the head gasket is 1.2-0.9=0.3mm. I won't do the calculation again, but the new CR will now be 7.9:1.
Cheers, Dirk

[turboadmin]

Hi Dirk, with a lower compression ratio you can use more boost pressure!

Did you ever measure the actual compression pressure on an original 650 and 750 (4KO and 11M) engine and on the turbo engine (11T)?

[Kneggie]

Yes, I have measured the compression pressure, but due to the pollution in the combustion chamber, the compression pressure increases.
According to the workshop manual, the compression pressure must be between 7 and 10 bar, as standard it must be 8.5 bar.
My 650; 11T has a compression pressure of 10 bar. A measurement by the American President of the American Turbo Club measuring 12 bar, this engine had driven 160,000 km. So the measured pressure doesn't say much.
Before I disassembled my 750 T I also measured this pressure was 7 bar. The CV is of course lower than the 11T.

Ja, ich habe den Kompressionsdruck gemessen, aber durch die Verschmutzung im Brennraum steigt der Kompressionsdruck.
Laut Werkstatthandbuch muss der Kompressionsdruck zwischen 7 und 10 bar liegen, standardmäßig muss er 8,5 bar betragen. Meine 650; 11T hat einen Kompressionsdruck von 10 bar. Eine Messung des amerikanischen Präsidenten des American Turbo Club mit 12 bar, dieser Motor hatte eine Laufleistung von 160.000 km. Der gemessene Druck sagt also nicht viel aus.
Bevor ich meine 750 T zerlegt habe, habe ich auch gemessen, dass dieser Druck 7 bar betrug. Das Verdichtungsverhältnis ist natürlich geringer als beim 11T.