Some of you guys have done amazing things to your cars and sing about outstanding HP gains. I'm 3 weeks into this XKR and out of a string of 911s, and would really like some kind of history of how to add an extra 50/100/200 HP to our cars without breaking either the bank or the cars. For discussion, can we focus on street HP instead of tracking?

 

Talk to Cambo or AlexJag. (Don't confuse the two, there is a feud ongoing)

 

Lets try to narrow down the target. What if we want to add 50-100HP to our SC car, what would it take to do that? Would adding 200HP cost twice as much?

Assuming that the old adage from road racing still holds...."All you need for more HP is more $$", there might be a sweet spot trade-off that we can find?

 

600hp = bust
4.2 sc with all the tweeks will fall short of 600hp..unless you like nitros.
Be happy with 500 and choose your tuner carefully.
WJ

 

Okay, so if 500 is a do-able number, that begs the question of what tuner does this enough to know his stuff. I'm in Alabama, so who's close that anybody knows about?

 

BTW, 500HP would pretty much meet a newer 911TT, but 520 would be better from a HP/weight relationship.

 

love the title of this thread. This should be interesting.

 

A tune from AlexJag,
Modified exhaust, (cats only) rest of exhaust is stock,
2.5" pulley,
Oil catch can,
This has me solidly in the 500 hp club.
I'm very happy. Low 12's in the 1/4 mile with 1.8s in 60'.
But with much stickier tires than the Goodyears I currently run 11's is possible. I'm certain you could squeeze more out of the 4.2 but reliability may become an issue.
600 HP is a bust.

 

Rick,
If 600HP is your goal, save your money and sell your 4.2L 2008 XKR with 90K miles and buy a low mileage 5.0L 2010-up XKR.

You'll need a limited-slip differential to put all that power to the pavement, and an E-diff is standard equipment on the 5.0L XKR. The 4.2L XKR did not come from the factory with a LSD, so you'll need an aftermarket LSD from Quaife or from an old Lincoln.

The 4.2L and 5.0L engines are very different. The 5.0L has much newer and improved technology, including a much better supercharger and direct injection. You'll never see 600HP out of the 4.2L, but that's easily doable with the 5.0L with upper and lower pulleys and the right tune - and no internal engine mods. And don't ask about headers - they don't exist - or a cold air box. The factory intakes are as good as it gets, and spending more money will only get marginally better results. No real bang for the buck.

If you decide to keep the 2008 XKR, know its limitations and enjoy what it is. Don't try to make it into something it's not.

Stuart

 

...as the man said, "A man's got to know his Limitations", and I've learned that 500 is the number for our 4.2L engines. Now the question of cost comes to the table, so what ballpark ranges are there for upping the HP by 50-100? Given that the engine has 90K miles already, these questions are more theoretical than planning, at least at the moment.
If post #8 is a good blueprint, what numbers of dollars are we talking about...roughly?

 

Why do you want more power? Just for fun or do you consider the stock setup too anemic? Unless you're trying to build a race car, I'd leave it alone. The 4.2's infinitely more reliable and less costly to maintain than the 5.0 but if you like the idea of big power numbers, the 5.0 will go over 700 if you want it to. Your engine has a decent amount of use, so increasing power's going to accelerate wear and tear. If you want reliability, I'd prepare yourself to spend a decent amount of money to replace all of the 14-15 year old seals, gaskets, and hoses. You'll need more free flowing exhaust, smaller supercharger pulley, colder spark plugs and a tune. You'll need stickier tires and a Quaife LSD wouldn't be a bad idea. Basic tunes will get you about 25-40 HP, more bespoke tunes CAN get you up to 100 or more. Also plan on dyno time to keep track of changes. You could also fit a larger supercharger at get as much as 200 HP more, but expect to spend $15-20K for the custom work.

 

Honestly, somebody mentioned 600HP and it caught my attention from an academic perspective. Comparing Porsche Turbos with their 485HP and $80K+ price tags (for 2008 models) it made me wonder what could be done with much less than that kind of money. I've loved speed forever, and live in an area where some opportunities exist to wring out a car for a little while. That said, I've had this car for 3 weeks and it hasn't gone over 85, and that was on the drive home.
Now that the suspension, brakes and everything else is fixed, my mind is wandering.

What you said about a dyno and regular visits to get a tune dialed in is probably the deal killer, because going back and forth to a city isn't my idea of a fun trip...for any reason.

 

When I bought my 2010 5.0L almost ten years ago, I had the Eurocharged tune and pulley done to my car, and I beilieve Eurocharged is in Texas, however they send you the tune and you load it yourself. You might give them a call. AlexJag, a forum member is in San Diego, I believe.

 

For the sake of interest and education for the rest of us, what if you had a stock XKR and wanted to spend $5K on it for speed. Not off-the-line speed, but highway passing speed. What would you do with your money?

Let's up that to $10,000, what would you do to get the most bang for the buck?

 

The basic bolt ons and tune already mentioned would be in that $5k range. For ten grand there’s really not much else for the 4.2. A custom fitted twin screw supercharger can be done for that $15-20k range I mentioned. But by that point you might as well get a 5 litre. As for the dyno, you could skip that but then you’ll never know what if any power increase there is. You could play with differential ratios and shift the power band to give you great top speed but the stock car is already capable of 160+ MPH.

If you want to have some fun and a project, I’d do the simple things and put money towards rebuilding older parts. Or save up and get the later version of the car.

 

Well-said. I can either add a lot of mods to my car or get a newer version. Adding mods usually reduces the street value, so it's tossing money down a hole if investment is a criterion. Addiing a SC to a 911 is about$15-20K, and our cars already have one, without the mods deduct.

Agreed on the 40HP increase....we can't feel it outside the 1/4 mile runs..

 

You can still enjoy the ride with an old Cougar, but that'll never compare to a newer Jaguar with less mileage and tighter, more reliable moving parts!

 

ah, grasshopper, this Jag is tight and sports a nice new Leaper, so I'm set for awhile Now that you've brought it up, though, the search for next year's toy begins!

 

You do realise that with all the added weight and wind resistance that leaper creates, you have already made your Jag slower?

 

hahahahahaa, okay, I give up trying to make the world a better-looking place