Not trying to start a debate. REALLY!!
I am curious though. Why did Jaguar rate the 3.8 at 265HP. And make no change to the 4.2?
This defies logic to me. Adding 25 cubic inches, maintaining 9/1 compression, maintaining cam dwell and lift, should easily add 20 HP. Was the 3.8 exaggerated?, is the 4.2 suppressed? There is an acknowledgement of torque increases.
Anyway I find this a puzzle, and I guess I could shake the internet, but I would just end up here anyway. So what’s the deal?
Should we tell him?
They lied…
Cheers,
LLynn 
That’s what it looks like. The front end? Or the back?
That means more HP at the same RPM. But the 3.8 had a higher redline, meaning the same HP at lower torque.
But yes, they lied. Others did too. The most powerful XK engine was the later EFI 4.2, which still didn’t produce 265 HP. IMHO.
I just woukd assume the HP/ torque curve would both raise some. Maybe cross a little earlier on the 4.2. Who has the real dyno numbers?
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.
Yes, I can understand the effect of 1969. It’s the early 4.2 that has me curious. As a long time Rodder, builder. I am aware of understating, and over stating HP to suit a political, and sales climate. I find this one just Wierd.
Marketing. The E Type is still claimed as a production car with a top speed of 150mph. Yes…a specially prepared version may have nudged the magic number…but the one available to the public…not possible. But ask “the Internet”…and falsehood is fact.
I do not remember this one from 2015 being much if any different from stock. Sounds like it was still accelerating when they had to back off due to traffic conditions.
David
68 E-type FHC
From the article:
"The car’s engine was even dyno-tested on a rolling road "
It’s a shame they didn’t disclose the dyno results.
I’m more curious what real flywheel numbers are.
Unlikely to be “stock” …and the article is cautious to avoid too much investigation on the issue. The combination of the high drag coefficient of about 0.44 with the frontal area of 17.5 sq ft requires more power than the “stock” engine provides. I think the E type that did the original run had a highly modified motor and possibly some drag reduction modifications …possibly underbody fairing…??
…teeny, tiny little advert-influenced horsepowers…
IIRC, the factory ensured the engine was as good as it could be made at that time. The run was made,without over riders and side mirror(s).
I dynoed exactly one XK, 3.8 flavor, tri-carbed, dead stock engine: at 5000’, uncorrected: I saw 198 HP, 200 ft-lbs torque.
Not by very much. I had Tweety to 138 (5th wheel-measured) mph, and though still “accelerating,” it twerent by much, and the front wheels were beginning to be more like wind vanes, rather than road tires, firmly planted.
I ran out of brass ba…!
Karl
Re-read Robert’s answer and you may understand. Horse power is never measured, it is calculated.
It is calculated from torque and time (expressed as RPM).
Therefore, if the 4.2 reaches the same power as the 3.8 but at lower rpm, it is clearly a more powerful engine and there is no mystery to solve.
Nick, where do you get that the siamesed barrels and different crank spacing were the reason for the red line change? They would not in themselves alter primary engine component loads, whereas the heavier piston loads would certainly have an effect. The 4.2 crank has different harmonics and damper.
OK, but wouldn’t you expect an increase in HP at an additional 500 rpm?
Heh heh…yes…marketing speak “as good as it could be made at the time” translates to “highly modified motor”…I imagine Mr Lyons telling the salesmen and mechanics…“Chaps…make sure this car achieves 150mph. Let me know how you get on.” There would have been some late nights.
Naughty they!
I have both 3.8 and 4.2 series 1 cars. They are quite different to drive but the difference really is in low down torque rather than absolute power.
In the 4.2, you just put your foot down anywhere in the rev range and the car accelerates.
When I drive the 3.8 I put my foot down low down and I am always disappointed. You need to drive it higher in the rev range.