*Moved to X308 Forums* Sorry about that :/


Hello everyone,

Just curious as to how much horsepower you can possibly achieve with modifications for a 1998 Jaguar XJR?

I would like to have around 500rwhp if that's even possible.

If that is possible, how much would it cost to get it done?

Thanks.

 

As was linked in the X300 forum, you can't really go past Avos's Kenne Bell twin screw upgrade
https://www.jaguarforums.com/forum/p...xtra-hp-42059/

There are other avenues you can go down, it really depends whether you want to do lots of smaller upgrades yourself over time, or if you just want to spend the money up front and do it once.

If you want to do it yourself, you can upgrade the SC pulleys, redo the intake, throttle body, port the SC, add water and/or methanol injection, or even nitrous. Then there are diff and transmission upgrades as well.

But if you have the cash and just want to walk away with 500hp, talk to Avos

 

500 is attainable.

What is your budget?

How much can/do you want to do yourself?

Have you installed a nitrous kit before?

 

Basic mods (supercharger pulleys, intercoolers, intake, exhuast, tune, methanol injection) on the stock blower seem to yield about 420-450 whp on the top end.

The twin screw kits seem to be capable of around 500 whp on the 4.0s pretty easily. This is the easiest way to serious power, but it's a healthy chunk of change up front.

It's going to cost a ton to go much bigger than 600 whp. You'll need a custom fuel system to keep up, a standalone to manage it properly, and I'd start to worry about the strength of the bottom end at that point, so you'd probably be looking at custom pistons and rods at a minimum.

 

We spoke via PM once before, and your recommendations were top notch!

Budget is $5,000

I don't want to do much myself.

No, I have not. Is this safe on the engine? If so, how big of a shot can I run through it?

Thanks!

 

No matter which route you take you absolutely MUST change the head gaskets to stronger ones as the stock '98 composite ones cannot handle 500 rwhp.

I think your only real option is to contact Lawson at PowerHause or however you spell it and ask him about his Nitrous kits and how he retards the timing when using nitrous.

You will NEED upgraded head gaskets, and a stronger rear end.

The Twin Screw cannot added to a car and have it running well anywhere near $5K.

 

The twin screw setup will cost you about twice that, if you're paying someone else to install. Probably more...

 

I actually wouldn't mind spending $10,000 + if I could get it around 600 rwhp.

I just need someone who can do it here in the states.. Buckhead?

 

I think if you aimed for 550 with the TS kit you won't be disappointed. 600 is easier with a 4.2, so add a couple of grand more for the new engine.

It's not like anyone ever dyno's their car to get a true figure anyway, or they add in a 'transmission loss factor' which is just a made up number.

Go for a drive in a TS equipped car, I guarantee you won't be left wanting more, no matter what the quoted power figure is

 

I'd like to see a real world performance run of a TS equipped car calculating out to 600 RWHP, not just a piece of paper. Then I would like to see the build list and cost for that. There is a lot of other high $ work that would have to be done to get to 600 RWHP.

As Foghorn Leghorn said :
If I remember correctly, Steve M's 11.9x run calculates to somewhere around 530-550 flywheel hp. This is the figure that has been proven.

 

If you are talking about 700+bhp ( 600rwhp ) you have to rebuild the car, ie. use a different block, custom made forged internals for bigger capacity , TS Kit, fully ported heads, new cams, all new fuling system including bigger pumps, FPR, bigger fuel injectors two wideband lambdas, high flow cats, catback exhaust wath/meth kit etc, stronger differential and LSD, some upgrades to the transmission, upgrade to suspension and brakes....well, we are talking many times the $10K. Please remember that your car is AJ26, so it has not all the same potential for big power than AJ27s.

If you are ok with about 520-550bhp ( 430-455rwhp ) you can do it with TS Kit quite easily but still reserve at least $15K+ . If you want 600bhp from 4.0 AJ26, you need to do something for cams and heads.

I have not seen any Eaton powered 4.0 Jaguars over 450bhp dyno chart.

Nitrous is another way but I would not say it's real power if that's your only modification.

 

'Flywheel hp' really bugs me. It's a made up figure!

"hmmm, I got 400hp at the wheels, I better add 15% for drivetrain loss. That's 460hp. Wait, that's not a nice round number, lets use 20% instead, just to be safe, now I have 500hp!"

WD, I would suggest the dyno run you have is too low, rather than Avos's being too high. I've had my car dyno'd as well, and twice I got 240rwkw, which is roughly 320hp at the wheels.
I wouldn't presume to guess what my engine would make on a stand with nothing attached to it. That figure is meaningless to me.

With a TS I would expect anywhere from 300 to 350rwkw, or 400-467hp, and like I said, who's going to be upset with that?


Drag times can be varied too. I've seen one car do a 14 flat with lower pulley only. The owner had done the mod after running 14.2's the year before. Tyres, track conditions, fuel, and of course the driver all vary, even day to day...

 

True, actual performances can lie on the low side only...but if one get's a low run, they can always try again, or if they need to, can try to blow smoke and make excuses.

One could not run Steve M's 11.9 with less than over 500 flywheel hp. That was real world proof.

On a separate note, If you go with buckhead, I would write the very detailed liquidated damags clause in the written contract such that they get paid 100% if they deliver on the agreed upon date, and that # decreases significantly as time goes on. They don't exactly have a good track record on this board for hitting their projected delivery dates...

 

We have used 17% loss with the 722.6 MB transmission.

 

Going by that, I have 374hp at the fly, not bad for a 12yo car that had 380 from the factory

Sadly I haven't had the chance to get to a drag strip. Well, I have, but my tyres cost roughly half of what you guys are spending on entire cars!
Hopefully one day I'll be able to though.

Failing that, when I do get around to TB and intake mods, I'll be able to put the car onto the same dyno that I pulled two 240rwkw runs, and get a real figure for the improvements.

FYI, this is the dyno that was used
STM | Speedtech Motorsport - Performance Vehicle Specialists - EVO 1-9 | STi | HOLDEN | Nissan
They have a worldwide reputation, and even a few world records on the drag strip.
Not saying their dyno is magical, just that it is consistent, and has been backed up with real world results

 

This =

 

What was your dyno figure?
I need to get out and see what mine will do that run in. Still impressive though Like I said earlier, chasing numbers is a silly game, Do the work, get the results, drive your car. That's what matters

 

I totally agree, it is how it drives for you in real life that matters.

Unfortunately, I did not get a dyno while in that configuration, and just sold that car last month to make room in the garage for my latest little roller skate, a 2000 lb miata which I've just installed a 10 psi eaton, and am in the process of installing a Mega Squirt stand alone and Nitrous Little toy car looks basically stock but will be 9.x lbs per rwhp by the end of this month and pulls a full G in the corners.

 

Too bad I couldn't get my car to your location and pay for you to work on it! That video was quite impressive! MUST. ACHIEVE. THE. SAME.

 

If you'd been lucky, you could've just bought it, and saved yourself a whole lot of trouble