I own a 1968 series 1.5 E-Type OTS. I was at an event this weekend and someone commented that the redline on my tach was 5500, which is what the 3.8 E-Types should be and that my 4.2 should have a redline of 5000. As there is no clock in my tach I doubt it came from a 3.8 at some time in its life.
Can anyone share some knowledge with me about this please? I have posted a picture of my tach, is this a replacement or original?
5500 is correct for a '68 Series 1.5. Your commenter was mistaken.
As Doug says, it’s just one of those “trick questions” that the E-Type has a habit of generating. The Series 2s went back to 5K, but 5500 is correct for the S1.5s.
My '68 S1.5 2+2 tach and speedo are the same as yours.
Does anyone know why the redline was dropped for the Series 2? The engine itself was not changed, so I am guessing it was because it went from three carbs to two.
I think we can safely blame the marketing department for their, erm, exaggerations. When the 4.2 debuted the redline was reduced from 5500 to 5000 because cylinder/piston/crank main spacing was no longer equidistant, which made sense. However, when the Series 1.5 made the scene for the 1968 model year the redline mysteriously went back to 5500 and then quietly reverted back to 5000 in the 1969 Series 2. There is no feasible engineering explanation I’m aware of for that single year exception, but maybe it helped to sell cars in the US that had their horsepower throttled by new Federal emissions regs.
Somewhere in the recesses of my mind, I recall being told by a long time Jaguar mechanic that the crankshafts in the 4.2 could not not withstand continuous, high speed runs at 5300 RPM or more. The problem arose with long (10 minute or so) flat out runs. If I recall correctly, the redlines for the 3.4 and 3.8 XK engines bounced around a bit as well.
I believe the manual talks about easing off the throttle for a few seconds when doing flat out running for extended periods.
Yes, the 4.2 Driver’s Handbook has always cautioned against revs over 5,000 rpm. In the “Performance Data” tables with speed\rpm ratios, they write:
“It is recommended that engine revolutions in excess of 5,000 per minute should not be exceeded for long periods. Therefore, if travelling at sustained high speed on motorways, the accelerator pedal should be released occasionally to allow the car to overrun for a few seconds.”
(bold as printed in the handbook)
Dave
Interesting. I did not know the red line number varied. Here are the pages from my owner’s manual.
David
68 E-type FHC
I have always wondered what-on-earth this practice is actually supposed to accomplish…to let the rod bolts catch their breath?!
I think it also had to do with the massively much heavier flywheels of the later 4.2 over the 3.8.
Awhhhh. An owners manual well oiled from it’s rear main seal. Imagine that!!!
