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#1 rolling road figures

Posted: Mon Jun 24, 2019 10:03 pm
by 265bhp
has anyone put their car onto a rolling road ?

I am fully aware that the 265 figure was an optimistic one back in the day....but am curious to know what sort of values have truly been achieved (in standard form that is)

all the best

#2 Re: rolling road figures

Posted: Mon Jun 24, 2019 10:57 pm
by Heuer
I took my OTS to Hi Tech Motorsports in Coventry and they measured ~280 bhp and ~ 340 lb/ft IIRC. Engine is not standard though as it had 9.5:1 compression and trick cams. SU carbs with UO needles, EDIS ignition and ITG air filter.

#3 Re: rolling road figures

Posted: Tue Jun 25, 2019 7:15 am
by Gfhug
FWIW my car showed at the wheels 160 bhp at 4000 rpm.


#4 Re: rolling road figures

Posted: Tue Jun 25, 2019 10:50 pm
by Turnip
Heuer wrote:
Mon Jun 24, 2019 10:57 pm
280 bhp and 340 lb/ft.
Rear wheel or crankshaft?
My engine has 8:1 pistons, UO needles and an ITG filter. Apart from that it's pretty standard.
When setting up the 123 Tune dizzy we got 170hp (RW) between 4000 and 4500. It tapered off after that.
170 RW HP equates to about 205 at the crank.
FWIW, the rolling road guy reckoned that even the more tricked up XK engines he sees usually only produce another 20hp or so.

Peak torque is around 225 - 230 ft-lb between 2500 and 4000 rpm.


#5 Re: rolling road figures

Posted: Tue Jun 25, 2019 11:19 pm
by 265bhp
Interesting...I know it’s all somewhat subjective and so on...but just for my own knowledge..was the 265 meant to be at the crank or the the wheels...?..either way it’s one heck of a difference...

#6 Re: rolling road figures

Posted: Wed Jun 26, 2019 12:16 am
by abowie
I got about 150hp at 3000 at the wheels on my 4.2 coupe. Didn't push the brand new engine harder than that.

#7 Re: rolling road figures

Posted: Wed Jun 26, 2019 1:05 am
by chrisfell
“was the 265 meant to be at the crank or the the wheels..”

Er,... neither. To say it was an estimate is being charitable, it was a lie. Not even with all ancillaries removed and separately powered (water pump, oil pump, as well as alternator/dynamo) would the gross output get close to 265. A good 4.2 engine, properly built, with manifolds matched, a free flowing exhaust and minimal air filtration and perfectly tuned would produce an honest 200 bhp, no more. ( Source: Jenks, circa 1970).

#8 Re: rolling road figures

Posted: Wed Jun 26, 2019 1:54 am
by PeterCrespin
I'd go with those figures Chris. The most powerful XK was the EFI big valve 4.2 with electronic ignition which developed about 220 on a good day. And I do mean literally on a good day, as ambient temp and air pressure need to be corrected for.

Since there is no such thing as directly measuring horsepower, the 4.2 was calculated to develop the same ponies as the 3.8 despite greater torque, by using a lower rpm figure.

Next time there's an Angus bash you should organize a mobile rolling road and work out a pecking order that is believable. By relating engine spec to outcomes it should also be easy to parse which mods deliver the best bang per buck. It would also confirm if David's OTS engine can deliver 50% more torque from the same capacity by raising the CR by 1.5 points and fancy cams with associated breathing tweeks.

#9 Re: rolling road figures

Posted: Wed Jun 26, 2019 10:29 am
by Heuer
My adventures with understanding the output of my car started when CMC asked if they could put it on the Hi-Tech Motorsport rolling road so they could properly set the cams and SU needles. This was the final result back in 2008:

After fitting the EDIS/Megajolt this is the graph from my in-car Road-Dyno:

I should explain that to use the device you start rolling in 2nd gear at walking pace and then floor the throttle, hence the sharp rise from about 1,500 rpm.

I decided to go back to Hi-Tech and see if they could smooth out the curves:

This is the 'at the wheels' graph produced in 2012, the last of eight runs with tweaking in between. The timing was retarded by 5° amongst other things:

According to Hi-Tech you can add 17% to 20% to get 'at the flywheel' figures. All runs done with Shell V-Power 99 octane.

#10 Re: rolling road figures

Posted: Wed Jun 26, 2019 7:22 pm
by politeperson
Dave Walker and his team have rolling roaded plenty of E types at Emerald in Watton. His figures seem pretty accurate as the Dyno is re-calibrated at least every 6 months.

They reckon a really strong 4.2 is around 180 bhp at the wheels, most are in the 160 range apparently.

Still plenty for a 1,200kg vehicle.

It is the torque figures that make the car pick up and go down the road.

I reckon the 265 bhp figure is in the cloudy realms of motoring journalism for most cars. Most motoring journalist I know haven't a clue what the relationship between torque and BHP means. They all seem to recycle each others rumors and are experts and copying and pasting as far as I can see.

My silver E is 240 bhp at the wheels and it goes like stink, thats all I can say. The torque is strong. To get that kind of power was not particularly cheap, many racers spend much much more than me.

I have the original engine to go back in to WYO shortly. That will be interesting as it has a balanced bottom end by John Everard and a new cylinder head by Neil Brown, D type cams, 185 psi on each cylinder with a big valve gas flowed head. The cylinder head was new old stock believe it or not.

Anyway, this is where I am performance-wise for now, see you at Goodwwod next week I hope.

#11 Re: rolling road figures

Posted: Wed Jun 26, 2019 9:25 pm
by H7OB
I think the pure numeric value of HP or torque is less significant as dynos vary from one to another. Whats more important is how much better a skilled dyno operator can make your car run, relative to its potential. We all know that midrange tractability and torque is what makes our cars faster in the real world rather than max BHP. After a few bedding in miles Im planning to have mine set up soon. Years ago I used Peter Burgess for my Vegantune big valve Elan Plus 2. Hes noted more for his knowledge on SUs but my little Dellorto fed twin cam felt so much crisper, livelier and smoother than when I arrived. Undoubtedly the best value Id ever spent for the best part of a 10% improvement throughout the rev range. He was far more interested in the before and after, rather than the numbers themselves and the difference was instantly obvious. Ill report back once the E has enjoyed the same!

BTW James, yours sounds epic! :salute:

#12 Re: rolling road figures

Posted: Wed Jun 26, 2019 10:06 pm
by Heuer
All very interesting but apochryphal tales do not count. If you have empirical figures please produce them for scrutiny.

#13 Re: rolling road figures

Posted: Wed Jun 26, 2019 10:23 pm
by 265bhp
neat bit of overtaking James....your car sounded well....:salute:

#14 Re: rolling road figures

Posted: Thu Jun 27, 2019 7:52 am
by politeperson
Thanks chaps.

Yes, I was going to bottle it, then I changed my mind.



#15 Re: rolling road figures

Posted: Fri Jun 28, 2019 10:47 am
by Tom W
Great video James.

I’m very interested in your modifications to get the figures you have David. What cams do you have? Have you made any other changes to the cylinder head such as larger valves or porting/gas flowing, or changes to the valve springs to allow more lift without coil binding?

#16 Re: rolling road figures

Posted: Fri Jun 28, 2019 1:55 pm
by Heuer
Engine was built in 1999 by VSE to their VSE02 fast road spec:

Inlet cam was a modified L2 and exhaust cam was L2B. 9.5:1 compression. Cast manifolds to 1.75" exhaust, straight through silencers. Ignition is EDIS/Megajolt with bespoke map. SU carb's with UO needles and ITG air filter attached to stock plenum.

VSE expected to see 283bhp at 4,900 rpm and 300-310 lb/ft of torque after run-in.

#17 Re: rolling road figures

Posted: Mon Jul 01, 2019 2:00 am
by Sarthe72
Obviously not rolling road, but two before and after graphs. I feel that the lesser figures are pretty representative of a standard engine.


#18 Re: rolling road figures

Posted: Mon Jul 01, 2019 8:38 am
by Heuer
That huge torque dip between 2,250 and 2,750 rpm is a consequence of using tubular manifold, big bore exhaust and truck cams. My engine was the same and the only quick fix was to install 1.75" venturi's in the silences. You can see it in my first graph. Longer term experimentation showed careful cam timing, reverting to the stock intake plenum (with ITG filter) and installing EDIS/Megajolt with custom map was able to mitigate the issue.

Another game of consequences with an E-Type!

#19 Re: rolling road figures

Posted: Mon Jul 01, 2019 9:58 am
by H7OB
The ITG Maxogen filter inside the standard canister, with UE needles seem to be well regarded. Would this still be worth doing on a standard engine? Don’t want to ruin the real world drivability.

#20 Re: rolling road figures

Posted: Mon Jul 01, 2019 10:42 am
by Heuer
Just buy the correct Maxogen filter and push it into the nose of the plenum. No need to use the canister. Full details here:

According to the Factory you can expect about 6% more power by deleting the "air silencer". Not bad for the money. Putting straight through exhaust silencers in will yield a 10% improvement. UE needles required. Do not go beyond 1.75" pipes and do not use tubular manifolds as they will cause a power drop. Bling at the expense of performance :banghead: