Hello all, so took the 4.2 XKR down to my local dyno today and look to be down on power and massively on torque.. I've had the reduced s/c pulley, exhaust and quaife diff added - supposedly the car also has a nap but I'm now very dubious. Any idea what it could be and how I can get more torque/hp? Thanks

 

It looks pretty close to stock to me. Altitude, temperature, humidity all play a part.

A SC pulley and exhaust don't help without a proper tune.

You need a tune.

 

Thanks, can you think of anything to add some more power alongside the tune? I thought stock torque was around 560ft

 

Stock 4.2L XKR torque is 413 lb.-ft. @4,000 RPMs. From my sales brochure dated 05/08.



You could also use an X-pipe and less restrictive, high-flow catalytic converters but would need a tune. Get a custom tune once, after you've done all the mechanical mods.

 

And let’s not forget there is a difference between theoretical yield vs actual yield. I’ve not ever considered it but I know a few that went down the path of blueprinting the engine. Anyone here? That exercise was horribly expensive and only exposed mediocre gains.

Despite @Cee Jay ’s comments ;-), I prefer the look of my ‘07... now imagine it with the 5.0 SC... hmmm.

 

Thanks all I will take it away and see what I can do!

 

I've "Blueprinted" many, many engines. It isn't what you probably think. Blueprinting is merely Recording all the clearances and bearing/ring/bore sizes. Since all tolerances must be withing specs anyway, just Writing Those Measurements Down is what BLUEPRINTING actually is.
Now, doing a GOOD engine build is getting all those numbers as close as possible To Each Other and in the either TIGHT or LOOSE side of things is where the POWER is. That's not blueprinting. That's doing a Good Build.

 

Looks close to stock for power but Don't think that torque curve is right unless it was done in third gear instead of fourth. What dyno machine used?

 

Agree here, Iherve a 7.5% reduced pulley, no backbox and K&N's fitted, when dyno'd it had lost 17 horses.

Have been told that a decent tune will see a minimum of 50bhp increase over stock and in the map they.can tweak max gains for all my mods.

Will be getting it done when temps come back up, but even as it is straight line me stamping on the loud pedal up to 100mph will make the back end twitch out momentarily before the e-diff reigns things back in

 

Must admit I'm very grateful for my quaife diff..

 

True Mike but then you are comparing a (what I beleive is) an open diff on a 4.2 with that of the quaife. It will be a night and day difference.

My (albeit limited) knowledge of e-diffs is that whilst you will still see an advantage with rhe quaife in certain driving conditions it won't be as pronounced.

Only someone that's an replaced an e-diff running XKR with a quaife can really comment.

Also a comparison of your results with your quaife on a drag run compared to a standard 4.2 R will be the real proof

 

Indeed.. I will need to get it on the strip at some point. Having come from a stock 4.2 R To this one I must admit this feels a lot better on launch

 

Will have to politely disagree . I'm still running stock open differential and street tires and have the fastest 0 to 60 times on 4.2lit cars , I'm even beating stock 5.0 cars including 5.0 XKR-S on 0-60 . Check out the screen shot and my time on the bottom, 4.05 or 3.8 with 1 ft rollout vs 4.26 for 5.0 XKRs. So I suspect lsd Will only make a difference If there are substantial traction loss, And I'm sure lsd will make launches a lot more consistent but not faster. Key for running fast with open differential is sticky tires.

 

Sheet Alex, no need to be polite, point I was making is, if he were to have his car mapped/modded like yours and he wasn't achieving your results you are then the quaife was a complete waste of money.

Make.sense now?

 

That one makes sense to me. But I would argue the diff is good for more than just the straights..

 

Yea and I get that . I'm sure LSD would improve drivability drastically during lower traction events such as turns, wet road or worn out tires. My point was it won't make you any faster unless you are traction limited on your take off, which I'm still not even with more power. That being said I would love to get LSD unit at one point to experience the difference, wish they were a bit cheaper for experiments sake.

 

as I have been saying it's not going to make any difference if I have LSD or open differential , If we would be comparing straight line acceleration numbers

 

What tyres do you use then because my 4.2 XKR was hopeless at launches and that was with Michelin Pilot Super Sports? I think that a limited slip diff would have made a big difference.

 

I don’t have drag strip slips to back it up but when I went from the stock diff to the Quaife, the difference in launch traction was night and day, from not being able to get traction in 1st to almost no loss of traction was quite noticeable and afterwards changing to Sport Cup 2 tires warm and sticky no issues whatsoever.

 

Well I should add to my post above that "sticky tires make a difference" This is on my setup where my alignment is right and adjusted for straight line acceleration, suspension is in the right place, and ECU tuning is dialed in for right power delivery in 1 st gear, with this combination and PS4 Michelin tires, traction is good. Now that being said I would love to try LSD to see if I can improve some