Paul,
My 85 Series III ran on regular. All my other Series III’s required 94
octane. My 90 Majestic requires 92 Octane.
Here are the compression pressures from my Shop Manual for XJ40’s 86-94,
2.9, 3.2, 3.6 and 4.0
2.9L Europe 210 to 230 lbf/in2
2.9L Rest of World 200- 220 lbf/in2
3.6L Europe and North America 160 - 170 lbf/in2
3/6L Rest of World 150 - 160 lbf/in2
3.2 and 4.0 160-170 lbf/in2
Compression Ratios
3.2L 9.75:1
4.0 9.5:1
2.9L Europe 12.6:1
2.9L Rest of World 11.17:1
3.6L Europe and N. America 9.6:1
3.6L Rest of World 8.2:1
My Drivers Manual for my 1990 Majestic says it has a 9.5:1 compression
ratio which agrees with my shop manual.
Does this answer the question? It looks like the limp wristed 2.9 had
the highest compression ratio while the 4.0 and 3.6 ratios are so close
that an engine with oversized pistons and liners could have more or less
depending on what you had. I think the Word High Compression is a
rather meaningless term when you have the actual numbers quote above.
Right?
Since Jaguar offered Grade A and Grade B Piston (smallest 3.6L Grade A
Piston was 90.960 largest grade be with 0.20 oversize (available) added
was 91.007) the displacement could vary considerably but I would think
the compression ratio would be the same.
If you wanted to spice up a 4.0 - 3.58 automatic differential ratio, you
could buy a 3.2 Automatic Differential - 4.09 ratio which would give you
a lot more off the line speed but knock down the top speed from 147 or
so. 3.6 automatic differential ratios were 3.54:1 But hey who wants to
drag LOL.
The lenght of the piston rods center to center on the 3.2 were 175.285
and the 4.0 was 164.42
The bore and stroke is
3.2 91x83
4.0 91x102
2.9 91x74.8
3.6 91x92
This should be enough technical specs right?
Now, my question is has anyone ever rebuilt a 4.0 with over size pistons
and liners and changed to the 4.0 rear end?
AttyDallas wrote:
In reply to a message from Jay sent Fri 25 Jul 2003:
Did anyone ever answer Dave’s original question?
what are the compression ratios on the low vs. high comp
engines? is the difference due to different piston size, stroke
length, etc.?
as to the low compression version, did it not require premium
octane fuel?
–
&:-)) Paul '88 XJ6 VDP 127k (and '90 XJS coupe on way
Garland, Texas, United States
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