Most folks brag about WOT power increases but part throttle is where most cars live 99% of their lives. The curse of drive by wire setup like ours is it's terribly easy to trick your butt meter into thinking you've gained a lot down low when the tune just opened the throttle more at lower inputs.

The tune I had in my Lincoln LS did more to the transmission timing and performance than engine performance and still made the car a lot more fun to drive.

 

See Cambo's posting above, it mentions steve_k's 4.2L XK, with a tune.

 

Contrary to popular belief with a few simple mods the n/a 4.2 is highly tunable.

With the new corrected tune for the enlarged throttle body and larger bore diameter mid pipe I'm hoping to squeeze out a few more hp, hopefully a 13.4/13.5 e.t can be had.

 

Post before & after dynos.

 

It's a bit hard to post a before dyno when the car is already mechanically modified...

The 1/4 mile results are more real-world than a dyno anyhow, nobody can deny that our cars are making considerably more power than stock;

My XKR to go from 13.184 @ 106.68mph to 12.646 @ 113.97mph
Steve's XK to go from 14.5 @ 95mph to 13.7 @ 101mph

You don't get that from just 10 horsepower more...

And frankly, if I did post up another dyno sheet, it would probably be heckled again by the internet experts for one reason or another, or the (real) numbers would be lower than the inflated unrealistic numbers that people expect to see.

We have a saying here in Australia, that American horses seem to be smaller than our ones, dyno sheets always seem to show higher numbers in America...

The 1/4 mile tells the story, i'm yet to see a 4.2L XKR run close to my numbers.

 

The XK 4.2 normally aspirated engine gains around 7% on bhp and torque. The gains may not be that large in numbers, and I'd never set false expectations, but what matters more than the numbers is the behaviour of the engine. What is most noticeable on this (and most n/a engines) is improved responsiveness and low-rev flexibility. Typically that's what most owners are after, even on the turbo-charged or supercharged engines. In practical terms it means the car is quicker off the line pulling into fast flowing traffic etc from a side-road or when needing a quick response for over-taking, and that the engine has a stronger pull at lower revs. If the car didn't give a shove in the back before it won't after the remap but the performance gains are noticeable.

All that being said, the ECU on the 4.2 needs to be removed for the remap and it is a particularly nasty ECU to open and to make the connections necessary for a remap. If it was an OBD job for £225 I'd recommend it highly but because of the complexity involved doing this particular engine the price is typically around £495 so whether you consider that good value or not is a very personal thing. It really depends where you feel you want to see the improvements.

 

Sounds like a figure that's been plucked out of the air.

No it doesn't. I've flashed Steve's XK and my XKR several times. KessV2 does not require removal of the PCM from the car, it's done over the OBD port. I'd expect the guy who runs the "Remapper Certification courses" to know this....

 

What a crazy world we live in when dyno charts have more of a bearing than actual timeslips.
Ridiculous

 

Paul until you can actually tune a 4.2 xkr and xk to run similar e.t's I'd be very skeptical of the information you provide on this forum.

Also as Cambo stated the ecu does not need to be removed, a corrected tune can be uploaded via the odb port
Good research

 

Well ... shoot. It sounds as if it does in fact help with performance increases, but now we're collectively at odds on the process involved: to ODB or not to ODB, that is the question ...

At 10 model years old and 70,000 miles, my warranty is my wallet. Time to find an expert in the Midwest or someplace worth driving towards. It's winter here, and I feel the need ... the need for speed!

Thanks everyone for your input!

 

Caution beware LoudHog it obviously comes down to the correct tuner only then will it be worth it

 

I can guarantee that I can do both a 14 second run and maybe a low 13 second run with out doing a thing to my car. Track prep, ambient temperature and reaction time alone can make more than a 1 second difference in e.t. Try hooking up summer tires when it is 40 f outside. Guaranteed a 14 second pass if you are lucky. Now a 70 degree day it will hook up and you will lose a second off your e.t. 95 degrees and you will be back to mid to low 13’s. All on the same tune mind you. So to say at the track is the only way to measure power improvements is not factual. There are simply to many variables. Why do F1, NASCAR, DTM etc etc etc All use either engine dyno’s or chassis dyno’s
The only fair way is a run with the car at normal operating temperature on the stock tune, then install the tune and run it again on the same day within an hour or so. I do not think there is a more accurate way to do it.

 

That comment is completely bass ackwards to what I've found to be reality. Give me mine shaft air on a cold day with decent track prep and I'll show you amazing numbers. Come back on a 95 degree day for a mediocre performance.

My XKR came alive when the temps dropped below 50 degrees and it loves sub 40 degree weather. My '93 Paxton blown 5.0 stang would break the tires loose in fourth gear pushing 12 psi out of a 6 psi (summer) blower. It made 390 RWHP in 90` heat and ran 11.79 @ 119 mph in warm weather.

Elapsed time is really a moot point because for a street car you are only concerned with the MPH. Trap speed indicates power. Time to get there measures efficiency.

 

Not sure what tires you have on your car Rancharo50, maybe all seasons or something similar that work better in cold temps but with my car in 40 f weather and summer tires the car will smoke them all the way to 3rd gear. Maybe you are referring to drag slicks. Thus slower time slips in cold weather due to very limited traction. In warm temps it will hook up and go faster with the same summer tires, in hot temps it will hook up but go slower. Yes the car feels faster in cold temps and I am sure it has more torque but, my point is that traction is very limited in cold temps with summer tires and the car won’t necessarily go faster due to limited traction. Hence my argument that drag racing results does not guarantee that your car has more hp or less after a tune. Again too many variables. Traction, reaction time, track prep and driver skill are far more important to a faster et. Especially at grass roots hobbyist levels that probably 99 % of us are.
60-120mph times are probably more indicative of additional power.

 

I had my 12 NA vert dynod after installing a Myna exhaust and having ECU Tuning group perform a tune. the BHP was 438hp as opposed to stock at 375 bhp. If you like to see the dyno sheet I can post it. About a 16% improvement. Unfortunately I didn't dyno the car before the modifications were. made.

 

Haven't you got a 5.0L XKR-S?, stock it would do a low-mid 12 @ 117mph with my 68 year old mother behind the wheel.

But do you just want impressive dyno numbers or do you actually want your car to accellerate faster? I know what i'd prefer...

I had my XJR on three different dyno's and it made 300rwhp, 321rwhp & 340rwhp. Yet somehow it always consistently trapped 106mph +/- at the track. Tells me that the dyno's were not accurate or comparable, but the trap speed is.

But if a variance of 40rhwp or ~13% is acceptable, then yeah, chassis dyno's are great!

Just to be 100% clear, the progression on my XKR was;

13.184 @ 106.68mph, 1.950 60ft
12.943 @ 111.57mph with a 1.998 60ft
12.646 @ 113.97mph with a 1.975 60ft

60ft times (i.e. traction) were about as consistent as you can get
And the reaction times aren't included in the ET

I did a lot of ~109mph passes after fixing the cats & before the modified tune went in.

Put the trap speeds in here ET-MPH-HP Calculator and have a laugh.

It's pretty ironic that 4200lbs and 109mph = 419hp, given what the 4.2 XKR was rated from the factory....

Yes it's 4200lbs with me in it (i'm a fat *******, and I weighed the car at the track).

Let's look at some other's, our mate Richard with his stock 2010 XKR, he's not as heavy as me LOL, he trapped 115.41 & 115.73, https://www.jaguarforums.com/forum/x...2/#post1833461

5.0L XKR with 510hp, 4120lbs = 115.63mph, amazingly close eh?

A 5.0L XKR-S with 550hp, 4120lbs = 118.5mph, which is what's been reported for the R-S, from several sources.

Make it 595hp and you've got 121.7mph, which nobody seems to have acheived yet, despite throwing money at tunes & pulleys, perhaps all these tuners have been selling snake oil???

Lend me a 5.0L XKR for a week i'll make it do 11.9 @ 121mph

 

I am 67kg's on a bad day.

There are 9 weeks until my next track day so an XKR-S X-pipe, smaller top supercharger pulley (waiting to be fitted) and a tune with dyno runs at each stage might be achievable before then.

The question is, what order should I upgrade in? I would be interesting in putting a tune on a standard XKR to see what is the best that can be achieved with just that then add the X pipe and retune, then the smaller pulley and retune.

 

I'd do the x pipe first. I thought it made a difference to performance and the sound is wicked.

With my xkr on the stock tyres and with just the x-pipe installed the main problem was traction even at 80kph, so if I was wanting more speed out of it I'd be going x-pipe first then tyres and maybe looking at aftermarket struts in the back.

I should add that I dont have the most finesse when I am launching, and when I have interference from dts or traction control I have an overwhelming urge to press harder on the accelerator...

 

Referring to the NA as I was, we have - generally - nothing. So post before & after timeslips if that's all that become available.

Summary: post ANYTHING rather than nothing other than "tuner" claims about this % or that %.

 

A buddy of mine spent 14K on Dinan tune for his 750 BMW. The numbers sounds impressive as is the torque. The cross brace is also the intake... All that said, Dinan does not post how much faster you'll go. He says there is little improvement, some on the highway... More power is not linear to going faster after a certain point. 120+ HP or something like and still on OEM brakes... I would do brakes over HP...