Yes, the Low Drag is one reason why I wonder why Sayer didn’t incorporate the more raked windscreen in the original E-type design. I’m sure he had a reason, I just wonder what it was.
Regarding the Kamm tail, while it wasn’t an active downforce type item, it was one of the first effective approaches to cutting down lift without a major impact on drag. None of the other cars in the list have this or other techniques to do the same as far as I know.
If Malcolm Sayer was well aware of the Kamm research, he didn’t let on to it. When Jaguar borrowed John Coombes’ 250 GTO for analysis in September 1962, Sayer wrote a aerodynamic report on it. Paragraph 3 of the report reads:
ROOF AND BOOTLID: This high-built wide flat back, of doubtful advantage, was largely responsible for the high side forces, and though it could not be measured, rear lift was undoubtedly high. See also item 4.
LIP ROUND BOOT REAR PANEL: Braking tests with and without this novel item showed that it did its intended job of stopping exhaust fumes from sweeping forward into windows and ventilators on over-run. It also, by slowing the flow over the boot and thus decreasing lift, reduced overall drag by some 5%.
(report reproduced in Philip Porter’s “Jaguar E-type - The Definitive History” pp.338-340)
It would seem Sayer attributed drag reduction properties to the spoiler, but not any anti-lift properties.
BTW the report indicated that the 250 GTO had 10 1/2% worse drag than the Low-Drag E-type, but was 7 1/2% better than the Coombes racing E-type (which is closest to a stock E-type.)
One can also contrast these approaches to that of the C2 Corvette, based on Bill Mitchell’s Stingray Racer. That car actually had a reverse airfoil shape with rounded lowers and flat upper. Maybe Mitchell thought it would act like a reverse wing and push downwards (just guessing), but it increased lift disastrously. The C2 also suffered from this. The C3 Vette, though it had worse drag, had much less lift.
Regarding the E-type top speed stock - well, if Jaguar had set the safe maximum engine speed to 6,000 rpm (which is about what you have to rev it to, to manage 150mph with a 3.07 final drive) then the 150mph factory speed claim sounds a lot more realistic as opposed to a managed one-off. Would a stock motor last long if revved to 6,000, even occasionally, let alone for a sustained period?
One more thing on the Kamm back - if Sayer’s pride blocked him from adopting it on the E-type, I’m glad of it. I cannot imagine the results if he had gone with function over form and chopped the E-type tail to counter lift. I think it was worth the tradeoff.
FWIW every XJ S1-S3 has a cut off E-type (2+2) tail. The mid-1960’s prototypes show the E-typish long tail that was cut, most likely due to practical reasons, and the finishing of the edge has a very minimal Kamm effect. Take a close look at a S1 or S2 XJ rear light detailing.
As I have only taken our XJ6C to about 190km/h (118mph) I don’t know how an XJ12 / Daimler Double Six would feel beyond 120mph or 130mph. Also I have been advised by a specialist that unless I add an oil cooler I should avoid driving the XJ6 faster than 180km/h for extended periods.
I would think that the high compression manual XJ6’s in Europe were driven like that all the time. We got “temporary” speed limits in 1972 and in 1973 the max allowed speed on our highways was permanently limited to 120km/h (75mph).
But it does have an overdrive, just as my ex Ser 1 E-type 4.2L 2+2 also had, being an auto to manual +o/d conversion, with the “Norman Dewis preferred” 1:3.31 final drive. (43/13)
The European E-types had the 1:3.07 final drive for the high speeds, AFAIK. (43/14)
European automatic cars had a 1:2.97 or a 1:2.88. (just like XJ-S’s)
My European sold XJ6C has the 3.54, which I believe most North American 4.2L E-types have, bit the O/D helps as it drops revs by 20%. (46/13)
I checked the measured data form the 1962 article and the recorded max speed driven across the same stretch both ways was 256.3km/h which is OVER 159mph!
Here’s a small copy of the data page. it also states that the test car had Dunlop R 5 race tires fitted (6.00 front, 6.50 rear), and for normal street driving the tire pressure was 2.2atm front and 2.2atm rear (32.33psi) BUT for “Sport” the setting was 3.2atm (48.5psi) front and from 3.2 up to 3.5atm rear (51.4psi).
They mention the speed ratio to rpm being 37.7km/h per 1.000 rpm with standard street tires, BUT also had recorded that with the fitted Dunlop R 5 racing tires the ratio was 42km/h per 1.000 rpm.
That would mean they were doing 6.100rpm at the recorded 256.3km/h (159.2mph) speed, but I think the rpm may have been a bit lower as the R 5 racing tires are not radial and thus they expand a bit at high speed.
That car was #860010 nicely featured driving in snow in the Chris Harvey “E-type End of an Era” book.
And AFAIK the normal 3.4, 3.8 and 4.2L XK engines did not blow up when driven hard. I know a 1967 car over here with the original owner who drive it like that all the time. he said the engine was replaced under warranty as it would leak cooling fluid after long runs at max speed during the first year of it’s life, but the replacement engine lasted well about 200.000kms and was first rebuilt in the early 2000’s. This is #1E16061.
Cheers!
Ps. This is copyright Auto, Motor & Sport (almost 60 years ago, so maybe the copyright has run out? 50+ years?)
1km with a standing start in 27.34 seconds, not bad!
Octane magazine did a test with car 860001 ( 1 VHP ) on the Autobahn for the Dec 2015 issue. It was restored but in completely stock configuration. If folks want to see the whole article and think it is ok to post a link here I will give it a try. Otherwise google …octane magazine e-type 150 mph test. It came up on this first line at least today. The title of the article is Taking It To the Max…
A few minutes later, David is calmly explaining how he got on.
‘I managed three runs in all. The second was the fastest; the first was
only 136-138 or so. They were all spoiled by traffic, however. When
you’re travelling at that speed you have to err on the side of caution.
You’re catching other traffic up quite quickly and you have to remember
that there’s no ABS, although the brakes felt strong and progressive.
There are also no aerodynamic aids – the car starts getting quite light
above 110mph and the steering becomes “power assisted”, so you have
to maintain a delicate touch. But the engine just seemed to get smoother
the higher it was revving. It was still pulling at 5000-5500rpm; I think I
saw 146mph at five-five, and it was still accelerating when I had to back
off because of cars and lorries in the distance.’
That’s good enough for us. We may not have quite hit that 150mph
target but we’ve come damn close, and we know the car had more to
give. Racelogic confirms later that the VBox recorded a maximum
velocity of 146.49mph and car owner Peter Neumark is delighted:
‘I thought it would do well to get to 135, maybe 138mph, so I’m
gobsmacked. Well done, David!’
The man himself is typically laidback about the whole experience.
‘The car felt absolutely super. It would comfortably have reached
150mph. Of that, I have absolutely no doubt.’
I believe the OM states, for my 4.2, that sustained periods above 5000 should be accompanied by an occasional slight lift off the pedal for a few seconds. For my car fitted with the 3.07 that would equate to 127mph. I have no idea whether the 4.2 would be good for 5500 for a long time. Talking bone stock engines here of course, and many of them these day with around 60k - 100k miles or higher.
No worries! I thought that if you feel a lift in the front at 9mph it is not an aerodynamic issue, but rather something wrong with the suspension & steering!
Just maybe LLoyd, I’ll now feel it at that higher speed? Does your car have all the shields in place, or did it before the air dam was fitted. I believe it was you who gave the thought, and dimensions, for the air dam1
Well it did work Larry but apparently I need to log in and all that and I already have enough email that I don’t read from Hotmail and yahoo. If you can copy paste that would work?
I thought that if you feel a lift in the front at 9mph it is not an aerodynamic issue, but rather something wrong with the suspension & steering!