So the brave among us started the performance discussion (go Squirrel!)... now up to the newbie to ask the stupid one that didn't need to be asked....

What can you do to a 4.2 V8 (short of trading it in and buying the STR that you wanted but didn't get - for whatever reason).

I have a very basic 2003 S-Type 4.2 V8 - I believe with some performance suspension upgrades but memory fails me now (bought it from the gent here in Dallas that sells hundreds used).

I would like to just get a *wheee* bit more juice out of the engine (and maybe drop the ride a bit -- but that's a different thread).

Any and all comments wholeheartedly encouraged!

 

Start w/ a cold air kit
A cat back exhaust
Lowering springs
Dyno tune.....https://www.jaguarforums.com/forum/s...ad.php?t=33009

 

Thanks very much for the response! Yet another guy with an STR... I have no idea why I didn't go STR when I got mine. (voice inside head -- I remember why - you were afraid you would wrap it around a tree -- or get 3 tickets a week after you test drove it) Oh yeah. I remember now....

So for a green bean like me, where would you recommend learning/shopping for all this stuff? (note - I'm not an idiot about cars -- we tore down my 327 in my 63 impala years ago -- it's just my jag confuses the he77 out of me!)

thanks again!

 

The 4.2 has steel cylinder liners, so you could bore it out fairly easily, and shave the head for a bit of extra displacement and compression.

You could always go for a port and polish on the heads, bigger valves or add material to the cams and have them reshaped.

Lower your gearing for the best kick in the pants, bang for the buck. Decrease your wheel and tire size, and you will lower the gearing as well.

A 50-100 shot of nitrous is fun and cheap

I recommend for DR racing in Arizona for headwork and cam regrinds. they have done an amazing job with 3000gt's and those are some bitchy finicky cars.

 

So have you found out anything on a gear swap to lets say 3.55's in teh rear end of an STR there Viscoussquirrel?

 

To be Honest, I haven't been looking for the STR. I have an N/A Xk8 So most of what I research revolves around that or the XKR.

 

You could use one of the K&N CAIs for the 03 & up Thunderbird. There is also supposed to be some company out there that has a long tube header/high flow cat combo that can fit the S-Type (to the tune of $800.00!LOL!!). Now it's my understanding that these will give you minimal horsepower increase with a major loss of low-down torque, so unless your REALLY boosting the power output, that's probably a waste of time & money. Oh, and you could get the ECU reprogrammed ($1000.00), but if the dealer has to reflash your ECU, (for a tsb for instance,) that'll wipe it out and you'll have to get it done again. As far as gears go, keep watching this space.
Hope this helps.

 

OK, I'm bumping an old thread here, but I've been seriously considering adding a nitrous system to my XK8's 4.2 engine. I've seen some "dry" systems for under $500 that inject the nitrous ahead of the MAF so that the ECU automatically increases the fuel flow and there is no need to tap into the fuel line. They say they can add up to 35 horsepower. But then I could do a "wet" system that installs in the throttle body. That alone scares me a little because I don't exactly know how to do that. It will give a lot more horsepower, though. So, the question becomes how much additional HP can a N/A 4.2 liter engine handle before it gives up the ghost? I don't want to get anywhere near that limit. Are there significant differences between the 4.2 supercharged and the 4.2 N/A engines that allow the S/C engine to handle the extra power? Did Jaguar engineer different connecting rods, cranks, and pistons for the XKR? (I know the heads are different). If the engine components are generally interchangeable, I figure the N/A should be able to easily handle an extra 100 HP.

I'm taking a big trip in about a week, but when I get back I'm thinking about adding the H-pipe, maybe removing the two mufflers in front of the axle, and adding a nitrous system. And yes, I know that nitrous isn't street legal, but I'm not really big believer in that law. I mean, if I'm doing something dangerous with the nitrous, like street racing, then bust me for it. But as long as I'm a safe and sane driver, who cares if I have a nitrous system connected to the car?

 

Hey Reverend make a 2nd thought prior to applying NOS into your ride .
I had seen a blown out LS7 engine from using NOS . You should have seen pistons and crankcase of it .
They told me it was an overboost stuff and the car churned out more than 800 HPs when the NOS was on .

 

Nos is perfectly safe if used correctly and tuned properly. It's the dumbasses that blow their engines that have no clue how to use it.

I think the heads are the same, the Xkr uses different pistons with lower compression and I think stronger forged connecting rods.

 

AFAIK the crank is Cast not forged. That could be an issue. Otherwise, as previously stated an instant hundred horse added to the motor is a shock to the internals so make sure all is tuned properly to avoid fragging the engine.

 

As far as tuning is concerned, wouldn't a wet kit be better?

 

Hmmm... for some reason I was thinking they lowered the compression by using different heads. I guess they could also lower it by using shorter connecting rods. That would prevent the piston from going up so far in the cylinder. If that's the case, what other differences are there between the N/A and S/C engines? Could I just install the shorter connecting rods, bolt on the supercharger, and have a 400 hp engine?

Actually, that sounds kinda expensive.

 

The connecting rods are the same length. The reduced compression comes from the pistons being dished which gives more volume for the mixture being compressed thus lowering the compression ratio.

It would be cheaper and easier to just sell the XK8 and buy an R than trying to covert one.

 

Yeah... after mentioning it I started thinking about it. I have a friend who owns a junkyard and I've asked him to keep an eye out for any XKRs that come through. If I could get a wrecked XKR it might be cost effective to take the engine and brakes and then resell my engine and the rest of the XKR, but I don't think I'll be rebuilding an engines.

 

If you would like to keep the AJV8 Naturally aspirated there is no cheap-quick way to get power but it is possible.
The AJ37 of AM5 Aston Martin engine is an evolution of the AJV8 I was involved in. I developed it from a high performance higher revving back room laboratory 4.4 version of the AJ26!

Anyway- back to your question: I would get rid of the exhaust manifolding and replace it. If it's an AJ27 or AJ26 its an inadequate log manifold- compromised for both package and emissions (catalyst light off). If its an AJ34 you have- the grouping of the cylinders is correct- it connects cylinders that fire 270 degrees apart (and each bank of exhaust manifold look assymetric) but the seperation and primary and secondary lengths are far too short. I would do a tuned length manifold- similar to those used on BMW M motors- such as the V10 unit in the M5. Aim for primary lengths of around 850mm from head flange and about 400 mm secondarys. This will give a nice spread of torque.
The air box losses could be made lower at the expense of a noisy and boomy intake. As stock the earlier engine at peak power has about a 70 mbar pressure drop and the later model (rear fed on the XK cars unlike the front fed AJ33s and AJ36s) had around 50 mbar loss. You want to get this down to about 30 m bars (AJ33 in the XJ and AJ36 in S type are around 30 mbar) and then you're doing well.

Your exhaust back pressure is around just under 500 mbar as standard, if you don't mind a bit more noise- I would target a system that drop the back pressure down to the 300 mbar region (this is BMW M5 territory and Aston Martin V8 territory).

The inlet valves are a healthy size on the Jag V8 and they are very light. The ports as standard are slightly better on the AJ27 in terms of flow vs the AJ33 (thanks to the efforts of an utterly useless Austrian consultancy thats full of themselves) but the AJ33 has more metal to fettle and port the heads. I would eliminate all the squish of the AJ33 heads in the chamber- it shrouds the flow and was poorly conceived by an consultancy outfit who are focused on diesel development but THINK they know about gasolines

Once the peak flow number is up at 0.72 (flow coefficient relative to the inner seat diameter) you know you're doing well- epecially if you've kept the port volumes small. As stock the AJ33s flow at around 0.58 at peak valve lift.

Next I would go for some healthy cams- no need to go too agressive, a nice 256 cam profile with about 11.1 mms of peak lift is ample for both intake and exhaust- just like the Aston Martin V8 uses.
After all of the above you would have spent thousands, and only gone up in power to around 360- 370 Bhp at peak power with a much peakier engine (you won't be at the astons 380 Bhp + becuase the intake runners of the stock Jaguar are too long and narrow). You won't have lost much low speed torque and could have actually gained due to the exhaust manifolding upgrades not possible by OEms due to emissions bollox.
However this engine wont make anywhere near the low speed torque of a super charged V8!!

 

Sorry for some reason I thought you were driving an XK8 (AJ34)- most of my comments still apply- just ignore the part about the intake system loss- you're already very low on that front!

 

Do the dished pistons in a SC engine result in it being a non-interference engine?

 

I have run NOS systems in a few of my cars in the past...
they are fun and your right they are fairly safe if used and setup properly..
what most people dont under staind about it is that the systems are designed for quick 8 to 10 second burst's... even setup properly hold the button down much longer than that and your going to melt a piston or your compression ring's..(i,e the extra power that 75 shot gives you also gives you another 250 to 400deg F cumbustion temp gain )

another problem I've seen is valve's sticking open and causing some problem's..

In my option a turbo charger or supercharger setup with a good tune is the way to go...

 

have a 2006 super v8. in the last 6 months . mina gallery. intake/pully and back exhaust. big diff. the combo stated to add 50-60 hp from mina. the car really breaths better and more accel. just had complete tune up and put new hi-flow cats on. the car has a deeper growl and the power just flows. should be running betwenn 470-485 hp and over 500 ft/lb of touque. I am going to get the car dyno'd soon.
When I got the car 2 yrs ago I thought it moved well, but after the mods. I realized how restrictive the old exhaust was. I am not got to change foward muffers because I don't want the car to be loud. any one have any expirence with ecu reprograming.
arden had a replacement ecu but I think its a lot of $$.