XK6 4.2 engine

[DonkeyApple]

What sort of power can be extracted from these with a bit of basic work these days?

I seem to recall that going from double SUs to triple was good for about 10%? But is there much else?

[lowdrag]

My 4.2 has 300 bhp ands wears profiled cams and triple Webers amongst other things.

[DonkeyApple]

lowdrag said:

My 4.2 has 300 bhp ands wears profiled cams and triple Webers amongst other things.

Have you trade any/much torque for the bhp? And is it silly money?

I'm assuming that for an engine that has been around for so long that there are basically a series of steps to eek out more power and that they are proven paths with proven, escalating costs.

Ie, does something like cleaning the engine up, adding triple SUs and a different cam give you a noticeable gain over 70s figures for a sensible outlay?

[lowdrag]

Depends what you define as "sensible". Here is the dyno graphs so you can see that we gained in power and torque:-

[mph]

The S3 XJ6 had the largest inlet valves of the 4.2 range.

An earlier head can be modified to take the larger valves and along with some different cams and blending of the ports a well assembled XK 4.2 engine should give around 250 hp with a nice flat torque curve, which is what you want on a heavy saloon.

VSE charge £700 + VAT to upgrade their standard rebuild to a higher performance for road use, which I'm assuming is the approximate cost to carry out something similar to the above.

[Flying Phil]

Pure Automotive porn!

[gruffalo]

DonkeyApple said:

What sort of power can be extracted from these with a bit of basic work these days?

I seem to recall that going from double SUs to triple was good for about 10%? But is there much else?

You can't tease like that, come on spill the beans, what are you up to?;-)

[DonkeyApple]

Was just pondering this situation: http://www.pistonheads.com/gassing/topic.asp?h=0&a...

http://www.angliacarauctions.co.uk/en/classic-auct...

[Huntsman]

DonkeyApple said:

Was just pondering this situation: http://www.pistonheads.com/gassing/topic.asp?h=0&a...

http://www.angliacarauctions.co.uk/en/classic-auct...

Bad times....

(Actually, a 240 looks a good target for a powerful 4.2)

[Bobo W]

Out of interest In Phil Llewelyn's article in the latest Octane he talks about the merits of Mk 1's and 2's but says his ideal option would be a standard looking Series 1 XJ 4.2 with fast road engine, stiffened suspension and vented discs which I have to say does appeal

[DonkeyApple]

Huntsman said:

DonkeyApple said:

Was just pondering this situation: http://www.pistonheads.com/gassing/topic.asp?h=0&a...

http://www.angliacarauctions.co.uk/en/classic-auct...

Bad times....

(Actually, a 240 looks a good target for a powerful 4.2)

Once I saw my grandfather's old car was coming up for auction the other day, I raised this with my father who has reminded me of the effort and money he invested in keeping it working both while my grandfather and then myself owned it. He also told me that Gerry spent some money on it also while he had it.

So, in short, at the start of last weekend I was reckoning on a golden opportunity to buy back the car and then have the suspension, brakes and engine brought up to date but ended the weekend with the idea pretty kaput. Which has been a bit of a shame.

Plus, I've emailed the chap who owns it and he hasn't responded.

[mph]

Bobo W said:

Out of interest In Phil Llewelyn's article in the latest Octane he talks about the merits of Mk 1's and 2's but says his ideal option would be a standard looking Series 1 XJ 4.2 with fast road engine, stiffened suspension and vented discs which I have to say does appeal

I'd tend to agree, and all can be completed relatively cheaply.

The three-speed auto would spoil the fun to some extent, and to replace it is a bit costly.

[hidetheelephants]

mph said:

I'd tend to agree, and all can be completed relatively cheaply.

The three-speed auto would spoil the fun to some extent, and to replace it is a bit costly.

Swap the BW slushmatic for a ZF 4HP22? Extra ratio and a much more sophisticated unit, and plenty available used.

[anonymous-user]

When I had an Interceptor I found the classic three speed Chrysler Torqueflight box to be smooth but mega wasteful of power and fuel, but quotes for conversions to four and five speed boxes were very spenner. A four speed would be attractive in my Series One Daimler Sov, but, apart from having electronic ignition (points mean no prizes), the car is very original (it doesn't even have wing or door mirrors) and so maybe I should just keep it as is, transmission wise I don't plan to drive it a lot anyway.

[DonkeyApple]

hidetheelephants said:

mph said:

I'd tend to agree, and all can be completed relatively cheaply.

The three-speed auto would spoil the fun to some extent, and to replace it is a bit costly.

Swap the BW slushmatic for a ZF 4HP22? Extra ratio and a much more sophisticated unit, and plenty available used.

They used both the 4HP and the US 4L60 unit so the conversion from the torqueflite isn't difficult just time consuming.

It's the sort of job someone is going to be charging over £5k for and that's an awful lot of fuel. I think if was going to go down that road I would go manual instead and get even better fuel and performance benefits.

[mph]

DonkeyApple said:

They used both the 4HP and the US 4L60 unit so the conversion from the torqueflite isn't difficult just time consuming.

It's the sort of job someone is going to be charging over £5k for and that's an awful lot of fuel. I think if was going to go down that road I would go manual instead and get even better fuel and performance benefits.

I've looked into this before and although the box itself isn't expensive the rest of the kit is. The only company I've found that supplies the lot wants around £5k and then you've got to get it fitted. If it could be done a bit cheaper I'd certainly consider it for my XJ 4.2 Coupe.

http://www.gwautos.com/

The manual with overdrive is obviously another option, but I do wonder if the car would be a bit overgeared with the diff ratio of an auto car ? I've actually got a manual overdrive box to play with but I'm not sure yet.

I had a five speed manual in my S3 XJ6 and although it certainly benefitted the fuel consumption it somehow didn't feel right in an XJ.

[DonkeyApple]

The cheapest way for an auto upgrade is to probably find a donor in a scrappy and strip what you need. It's probably one of those jobs that if you have loads of spare time and a decent workshop then you can do it yourself for not very much but the moment you need to employ someone to do it the economics go out the window?

I imagine finding a manual donor quite unlikely? But what's actually needed? As you say the boxes aren't expensive and a good shop will chop and weld a bell housing if required and bespoke propshafts aren't expensive or brackets. I'm guessing there are just lots of fiddly things?

[JohnBlackWatson]

My XJ Coupe is currently with XJ Restorations and part of the work they are be doing is to fit a 700R4 gearbox using the quarterbreed kit from John's cars in the US.

All parts were located in the US and the cost so far is approx £2500 including all shipping and customs fees.

The car has just come out of paint (its the one in ammonite grey on the XJ Restoration facebook pages) and we expect it to be on the road around April when it will be tax exempt.

I've also had the suspension and brakes uprated so definitely looking forward to getting the car back.

Will post an update when I get the car back and know how it drives after the mods.

[mph]

JohnBlackWatson said:

My XJ Coupe is currently with XJ Restorations and part of the work they are be doing is to fit a 700R4 gearbox using the quarterbreed kit from John's cars in the US.

All parts were located in the US and the cost so far is approx £2500 including all shipping and customs fees.

I'd forgotten about the Quarterbreed kit, I looked at it years ago but it didn't include the gearbox etc, as I recall. For the £2500 do you get everything to complete the conversion, including the gearbox ?

[DonkeyApple]

JohnBlackWatson said:

My XJ Coupe is currently with XJ Restorations and part of the work they are be doing is to fit a 700R4 gearbox using the quarterbreed kit from John's cars in the US.

All parts were located in the US and the cost so far is approx £2500 including all shipping and customs fees.

The car has just come out of paint (its the one in ammonite grey on the XJ Restoration facebook pages) and we expect it to be on the road around April when it will be tax exempt.

I've also had the suspension and brakes uprated so definitely looking forward to getting the car back.

Will post an update when I get the car back and know how it drives after the mods.

Do you mind me asking if you looked at KWE before settling on XJ Restorations?

There seem to be a few XJ restorers nowadays.