Hello Everyone:
I have a question. Can you increase the horsepower on a regular 5.0 XK non XKR? If so, how much can it be increased? How would do this?

Thanks for all your help.

JDog

 

I have a n/a 4.2 that has run a 13.6

revised tune, 100 cell cats , enlarged throttle body and x pipe

Free up your exhaust system and find some one that actually knows how to tune the direct injection system and you’ll have a really nice power plant

 

The easiest, cheapest and most responsible way to do what you ask is, and I'm totally serious here, is to sell the XK and buy an XKR. I'm an old hot rodder from way back and it was my job to make more power from everything I owned. I won't do that on an XK, it's not easy nor cheap to do it other than going XKR. Plus then, you can go up from there!

 

+1

This question is asked across our model forums with great regularity. Unless you have very deep pockets and specifically want the challenge, that is the answer.

Graham

 

Totally disagree on the deep pockets statement

revised tune, race cell cats and a x pipe isn't going to break the bank and it'll be a decent power upgrade more or less on par with a 4.2 xkr which is plenty

 

Thing is though, once you're on par with the 4.2 XKR, there's nowhere else to go. Also, that's not a huge upgrade from a 5.0 N/A.
Get a 5.0 XKR, there's still some more there to play with. 550 is easy with a tune and X-pipe with resonator delete. Add a pulley, cooler pump and a proper tune and you're around 600.
For me, and ever since I was a kid, there is no such thing as "...which is plenty". More power is ALWAYS better.

 

I found out it is possible to have too much horsepower. I had a '75 Porsche 911 that needed an engine rebuild. The 2.7 magnesium case was 170 flywheel horse from the factory. The max the magnesium case was capable of was 270 flywheel. The '75's were not worth the cost of a rebuild at the time so I installed a Turbo rotary 13b for less than the cost of a stock rebuild. Redline was 10,500 RPM Dynoed at 333 Rear Wheel Horsepower. It was not safe to floor it unless it was pointed straight ahead. Turn the steering wheel and the rear end came around. I will say that it was a LOT of fun.
The Turbo 13b is capable of over 1,000 flywheel horse.

 

What is "more or less"? In terms of 1/4 mile times, those mods will make it quicker on the strip but, with all other things being equal, a 300HP 4.2L normally aspirated XK with those mods won't have the low end torque or horsepower of a stock 420HP supercharged XKR. Those mods will be most noticeable at the highest RPMs. "... to make more power an engine needs to generate more torque, operate at higher rpm, or both."
https://www.caranddriver.com/news/a1...he-difference/

It's not "more or less". It's "more and less." That modded XK engine will have more HP than before, but still less than the XKR.

That will be most noticeable in normal, everyday street driving where torque matters.

I'm not saying that it's not worth doing those mods. What I am saying is don't expect it to drive like an XKR.

 

Those two statements completely negated each other.
My naturally aspirated P/S Mustang II has about 800 hp, 1100 on spray, and yes, the front end comes up on acceleration and if it the steering wheel was turned, the car still goes straight...... until the front comes down. NOT a good scenario.
Regardless, I stick with my original comment.

 

It was fun. But it was a handful to drive. It could get sideways way too easy. It was hard to put the power to the ground with narrow tires and non limited slip rear end. It was also my daily driver.

 

In 1983, a California jury decided that the Porsche 930 Turbo was too dangerous to drive.
https://www.upi.com/Archives/1983/06...4466425793600/

 

the op is talking about a 5.0 n/a not a 4.2 n/a so yes more or less power levels and torque levels wouldn't have a great amount of difference between a xkr 4.2 and 5.0 n/a

 

Steve,

I responded to your post about the mods you made to your 4.2L 2007 XKR. I was aware that the OP has a 5.0L and, although my comments were responsive to your post, the principles also apply to the 5.0L as well as any other internal combustion engine.

Stuart

 

For around $3k you can pickup about 30-40 BHP by getting a custom tune and a modification to the back end of your exhaust system. I did that on an 2012 XK vert. Although I don't have a before dyno sheet I have attached an after sheet.

 

In light of current prices of used 5.0L models and if power is an important factor, it simply makes more sense to put that $3K towards buying an XKR.

I'm not knocking the XK; it's a great car with plenty of power for most people most of the time. The XK is plenty fast and really doesn't need more power. But if you want more power, forget the XK and get the XKR. It's scary fast!

 

So in short we are telling him to save his 3k by firstly selling his car (most likely at a loss)
​​​​​​then trying to locate a relatively well priced xkr ...great advice ...well done .

​​​

 

Dude lives in Houston, he'll do fine. It may take a couple months, but it'll happen.

 

Steve,

I never said that the OP should sell his XK and buy an XKR. You did.

I simply presented some food for thought. Does it make more sense to spend $3,000 to modify an XK or put that money towards buying an XKR?

Many 5.0L XK/XKR models are currently for sale in the USA. It's possible to pay $3,000 or less over the price of an XK to buy an XKR. Search this site: https://www.cars.com/

Cheers!

Stuart

 

Ooooohhh! Oooooh!
That was me! I said first that he should sell and buy an XKR!
I'll take all the blame (credit) for that statement.

 

My ECU tune is way less than 3k , for a similar gain on NA car . Pm for pricing