"You can't supercharge an XK engine"

[Pigeon]

Mate of mine who has an XK120 replica has been told this more than once. Anyone here heard it? Doesn't make sense to me, strikes me that with an engine like the XK where you are pretty badly limited when it comes to increasing the RPM, a supercharger is the "kindest" option...

[Trooper2]

Supercharging tends to put extra pressure on the crank, caps, con rods and pistons, maybe they just can't be supercharged without some major modification.

[Pigeon]

But so does conventional tuning... if you increase the power without increasing the revs you must be increasing the combustion pressure...

[Mr Whippy]

Supercharging is a nicer way to get more power than more revs using CFM afaik.

Ie, better to add 20% more power at 3000rpm day to day driving, than rev to 3600rpm to get that extra 20% power.

Isn't it something like 75% of rod/crank loads are inertial from rpm's, so best to reduce the rpm's and up the loading if that makes sense

Dave

[tr7v8]

Turbo'd D type rep in Jaguar World mag the other day, using an SU, seemed to be quite powerful. The 4.2 would struggle to keep a head gasket in one piece but 3.4 & 3.8's would be more than strong enough.

[stevieturbo]

Mild performance forced induction setups, really dont load up the internals at all.
Yes, they can generate more heat, but thats the only real worry ( detonation aside....its obvious that needs to be avoided )

Unless the front of the crank was particularly feeble, I dont see why supercharging would be a problem....assuming heat/det are under control.

But turbocharging is probably the friendlier option for the engine in a low boost format.

[GavinPearson]

I don't think there's any debate about whether the engine can be supercharged. It can.

The debate needs to be on several points.

1) Will it package in the car? If it won't fit then that's no good.

2) Will the engine be able to last? Having seen the wierd deck arrangement on a 4.2 I would think that the head gasket would be very marginal, and a lot of work would be needed to get it to seal reliably if the engine was to make high torque. High power, low bmep would actually do the engine a favour as it would save the head gasket.

3) Is it worth the money. There is an awful lot of expense required to do this work and it might be better to fit tried and trusted tuning gear than undertake this task.

[Pigeon]

stevieturbo said:

Mild performance forced induction setups, really dont load up the internals at all.
Yes, they can generate more heat, but thats the only real worry ( detonation aside....its obvious that needs to be avoided )

Unless the front of the crank was particularly feeble, I dont see why supercharging would be a problem....assuming heat/det are under control.

But turbocharging is probably the friendlier option for the engine in a low boost format.

This is exactly the sort of reason I was puzzled by the statement. Though I'd have thought supercharging would be better for keeping control of possible heat problems.

[falcemob]

If you can make it fit it should work providing you have a half decent crank and get everything balanced properly. I've never had any head gasket problems with my 4.2s but have suffered major bearing problems due to balancing troubles although these turned out to be caused by clutch damage.
I've never seen a 4.2 throw a rod providing they aren't over revved.

[Jean A]

I'm also looking to build an XK 120 (Autotune) with some more power. I would like to have at least 300 hp. So I'm looking for a supercharge/turbocharge solution for the straight six. It seems not easy. but I found that Lynx did it already. So it must be possible.
If anyone has a clue ...
regards
Jean

[BB-Q]

Forced induction is easier on the internals than the same amount of power/torque using N/A power. This is mainly due to the fact then when making this power the rod is pushed down constantly through all four strokes as opposed to an N/A setup where the rod has to transition from compression to stretching forces as a vacuum is created in the cylinder during induction.

Turbocharging is by far the simplest option. Make a manifold, bolt a turbo on, bolt an injection manifold on the other side, Megasquirt it. Job done.

Supercharging requires you to have either very deep pockets or a tame machinist, as there will need to be pulleys made, etc. You also have the worry of the nose loading on the crank, as previously mentioned. My knowledge of Jag engines is not comprehensive unfortunately, so I can't advise in that regard- although I'm sure some searching of owners club forums etc. will get you the info you need.

I can help you with sizing a turbo or supercharger if that's of any use to you

[eliot]

BB-Q said:

Turbocharging is by far the simplest option. Make a manifold, bolt a turbo on, bolt an injection manifold on the other side, Megasquirt it. Job done.

That's not strictly true - overall from an engineering point of view they are about the same. If anything blowers are easier (from a person who's only ever tried turbos). I actually done turbo's because I considered it to be more difficult and fancied the challenge.

[Pigeon]

BB-Q said:

Forced induction is easier on the internals than the same amount of power/torque using N/A power.

Agreed

BB-Q said:

Turbocharging is by far the simplest option. Make a manifold, bolt a turbo on, bolt an injection manifold on the other side, Megasquirt it. Job done.

Supercharging requires you to have either very deep pockets or a tame machinist, as there will need to be pulleys made, etc. You also have the worry of the nose loading on the crank, as previously mentioned. My knowledge of Jag engines is not comprehensive unfortunately, so I can't advise in that regard- although I'm sure some searching of owners club forums etc. will get you the info you need.

Weelll...

I have a lathe, so making pulleys isn't too much of a problem. Bending large diameter pipework for a turbo manifold, OTOH, is much closer to my definition of "difficult" It's also significantly harder to develop a turbo installation to avoid lag and to counteract the inherent square-law boost characteristic, neither of which are problems with a positive-displacement crank-driven supercharger.

Also it's my friend's engine, not mine, and while you might get me to consider a turbo on the grounds of cost and availability compared to a Lysholm screw supercharger, there is no way on earth you'd get him to

BB-Q said:

I can help you with sizing a turbo or supercharger if that's of any use to you

Appreciated

I think this thread has probably now developed to the point where I can pass the link to my friend and see what he thinks...

[BB-Q]

Yes- I'm probably looking at it from a personal point of view. I don't have a lathe (sadly) but do have a welder!

[kenmorton]

Couple of links re: jag supercharging and general jag stuff:

http://www.jagweb.com/aj6eng/supercharge.html

http://www.jagweb.com/aj6eng/superchargers.php

http://www.jagweb.com/aj6eng

Defo worth talking to them.

Edited by kenmorton on Saturday 19th January 22:44

[Pigeon]

kenmorton said:

Couple of links re: jag supercharging and general jag stuff:

http://www.jagweb.com/aj6eng/supercharge.html

http://www.jagweb.com/aj6eng/superchargers.php

http://www.jagweb.com/aj6eng

Defo worth talking to them.

Sorry

It was from talking to them, and their lack of any offering for supercharging the XK, that the whole thread originated Highly amusing to see it come full circle...

[Jean A]

Pigeon said:

kenmorton said:

Couple of links re: jag supercharging and general jag stuff:

http://www.jagweb.com/aj6eng/supercharge.html

http://www.jagweb.com/aj6eng/superchargers.php

http://www.jagweb.com/aj6eng

Defo worth talking to them.

Sorry

It was from talking to them, and their lack of any offering for supercharging the XK, that the whole thread originated Highly amusing to see it come full circle...

So ... what's next. Is this the conclusion that an XK can't be charged ? I'll keep looking and keep you informed.
Does anyone has an idea about getting + 300 hp out of an XK. Without putting the mechanics to much at risk ? And without spending a fortune ?
Greetings from Belgium
Jean

[piquet]

Pigeon said:

kenmorton said:

Couple of links re: jag supercharging and general jag stuff:

http://www.jagweb.com/aj6eng/supercharge.html

http://www.jagweb.com/aj6eng/superchargers.php

http://www.jagweb.com/aj6eng

Defo worth talking to them.

Sorry

It was from talking to them, and their lack of any offering for supercharging the XK, that the whole thread originated Highly amusing to see it come full circle...

i've spoken to them a couple of times and emailed them and must say for all their expertise, they don;t seem to produce or sell anything special, they go on about supercharging but don;t offer kits or parts to do it for the xk,v12, aj6 or v8. Without liking to be rude being able to write a nice article on the subject is a world away from actually doing it and making it work. I did email them about a screw conversion to my xjr v8, they said they'd done it but decided it wasn't economical to offer it but they had produced 500bhp. If you look at the price of the parts from paramount i would have thought that people would pay 10k for 500bhp and once you've done it and got it working, surely it's not going to cost that much for the parts.

try talking to rob beere, i've spoken to him a couple of times and find him keen and helpful. He does do great N/A xk engines and i suspect would be interested in supercharging them

pk