The great British ART of detuning Jaguar engines by Mr Bywater, AJ6 Engineering

OR This is a quaint little story to show how using common sense , a bit of brains, very little cash, avoiding buying bullshit stuff from unscrupulous vendors, we can improve the original 6 cylinder XJS so much, to make it faster, nicer to drive and use 1 gallon every 60 miles less gas than it's thirsty heavyweight cousin.


This was how the car (3.6L XJS) arrived. 1007mb (high) 16C good.
It was so so bad, we took another shot at it to get the scale right. 
On top of it the driveability was hopeless with a bad dead spot on the throttle making it absolutely horrible to drive round town.
The AJ6 toilet ECU was supposed to correct precisely this problem which it manifestly fails to do.
The moral of the tale! You can always pay money to go slower, and because it's noiser it feels faster! 
Then blag in front of your mates because you got more money than sense.
It's a big hit on the cred stakes if someone then comes along to show you, you just got RIPPED off, so rather than eat humble pie, you have to start slagging us off.....it's easier.
Pity cos rolling roads don't lie, & I didn't take any money to do this test, unlike Mr Bywater.

It was still not looking funny but showing about 195Bhp from an engine which is supposed to give 221. 
Owner was depressive after shelling out successively for ECU, buying performance air filter, and going to his local Jaguar dealer who only made things worse!
Of course if we took the uncorrected rolling road figures, it would all be fine like they do in the UK.
This way it's easy to claim fictitious increases of 10 or 20bhp!
I just call that bullshit!

This is when we start to do a little playing around. hmmm! Is it impossible for a Jaguar dealer even to set the ignition advance right after giving them in excess of 200 quid and 4hours work?
I measured a small power increase, but as you can see, all is not well below 3000rpm with that typical NASTY Jaguar AJ6 kink.

Just for fun we advanced the ignition too far, and you can see the clear onset of detonation. NASTY! better not do that too long!
Funnily enough with all that AJ6 engineering toilet the car was still pinking at correct advance at low RPM. Does that start to tell you something? On top of that the exhaust was LOUD and very tiring to drive any distance. Basically what in Germany they call a "lemon"!

This is where we started to tart up the power output. Guess how we did it?
We got all the stuff from AJ6 engineering and threw it in the bin.
AND Guess what else? We got a 25 bhp POWER INCREASE.
I like power increases, so do customers.
All this took under 1hour and a mere 70 Euros, for the rolling road.
THIS ROLLING ROAD DOESN'T LIE. 
Our standard engine is now producing what seems to be 225bhp, which seems good enough for a 200 000kms 20 year old engine to me.
However I know we can get more and make the car a dream to drive.


THIS IS NOT LYING EITHER!
This was on the way home, but after fitting our next modification, 
which consists of adding silencers not removing them.
Here we actually start getting POWER increases over the original and as you will see, some super driveability improvements...
If the stuff we threw away is anything to go by, this car should leave a AJ6 engineering modified V12 car for dead even with a 6.0L engine.

Can you spot something? Well the scale is different, but with our VERY TRICK exhaust modification we suddenly make a load more torque and the engine breathes better. 
More power everywhere, and on our test a week later we were saddled with bad weather and 991mb which is LOW.
However our test engine was now making 235Bhp, which is kool, and no signs 
whatever of pinking at 991mb,so you can imagine the rest.
MY job is designing exhausts. I get paid for that.
Peak power was also 500rpm higher up at 5400rpm.
We are starting to remove that horrible dead spot around 3000rpm, and there's no horrible loud crackly exhaust, just GRUNT.
Now why are they all using that stuff in the club racing series in the UK? Because someone high up TOLD THEM like sheep....Roger Bywater is a "very respected tuner". ?political correctness,- forget it,- that's just STUPID.
Well....if losing 40bhp and making a noisy exhaust is respectable then I will say BEEEUUUHHHH to that too (!), but I sure as eggs is eggs, am not going to pay a couple of grand for the privilege.
MAYBE, just maybe....if you fit the rest of his toilet, you might get BACK the power you originally lost...but even that is far from sure.

Another shining example of what NOT to do. 
The inlet tract is already miles too long. 
Shell out another shed load of wedge to get another unproved untested, but certain power DECREASE.
Wanna bet me the price of this dumbass performance "improvement"?
Don't forget, trumpets are invariably used in inlet tracts to get a velocity increase in a place where you need it,- usually just before a constriction like in the choke tube of a weber carburettor.
The primary purpose is to get the carburettor to work properly and atomise fuel. This mod and the ones below do NOTHING.
Strangely, because AJ6 Engineering obviously understand nothing whatever about engine preparation, he/they have been insisting for years no power increase will come from working on the head.
That's strange it's EXACTLY what we do next, and even stranger, we get another MONSTER power increase, again without touching the bottom end and with absolutely standard cams and valves.

Yet another totally dumb idea.
This is a total waste of time because the cam timing is very short and so are the original cast exhaust manifolds. 
The exhaust manifolds and associated valves are wrong in this engine.
However we always knew the guys on Jaguar exhausts knew Zilch about design, and the latest V8 ones are no exception. Prediluvian, is the word. 
Now what was Mr Bywater doing at Jaguar all those years ago? I heard something to do with making a project with a lamer alloy engine that produces really poor power (?!)
If you understand what's going on, then you can correct it. 
Obviously the STUPID idea in the head of the guy who did this is;- "DUUHHH", manifold is too short, so let's make it a mile long!! And then let's sell this toilet for a pile of money calling it "PLUS TORQUE". 
Better call it "PLUS TALK" and "MINUS MONEY" and "MINUS HORSEPOWER"!

The final chapter showing KK modifications from England
Bore out your Air flow meter! Would be more useful to bore out your nostrils in fact. Enables tuners to think clearer.

Most of us use handkerchiefs for this, but if you insist in using a lathe, then the result can hurt a good deal more than just your pocket!
The main way to get more power from a (slightly) constricted inlet tract is to get the head to breathe better then raise the compression, and improve combustion.
Or has no-one ever thought of that in England any more?

Ohh.. duh you can of course slag us off, and say our work costs too much, (unlikely) and in any case carry on using your thirsty old engine with a semi blown head gasket, and put the extra money you would save in the fuel tank.....

Then next time a healthy 3.6L XJS or XJ40 comes up in your mirror, we gently suggest you move over to let us past because it is probably using less fuel than you do, going  30km/h faster.

Bad porting Bad inlet manifold Dreadful mismatches Horrible inlet ports
Chain Tensioners? A little bit of work later Sorting out the passage Better ports not too big!


HOW WE GET SERIOUS GRUNT.

No 1 RULE

There is NO substitute for a really professional engine builder,  NO substitute for a head which develops power and burns properly. No substitute for proper evaluation with precise figures, not bullshit.
POWER is ALWAYS in the head. no where else!
Our philosophy is different, this engine doesn't work, there has to be a reason, we only have to find it!

No 2 Rule

There is no substitute for observation, even if you don't like what you see!
There is no such thing as cretinous resonant effect when they don't exist.
No flow bench testing the inlet manifold or cutting it open! 
These are signs of desperation.

No 3 Rule

Always treat manufacturers with a good dose of disrespect, they probably did it that way for a bodge!
Here are one or two of the problems,-
The inlet manifold to port matching to begin with, is simply diabolically bad!
The camshafts are extremely mild and far from optimal.
The chamber is the wrong shape and the valves too small.
The ports are all the wrong shape, and the engine has all the wrong length runners.

No 4 Rule

Removing several pounds of aluminium from the head will not harm it, weaken it or poison anyone.
You have to start somewhere of course and this consists of porting the head properly, then you match the gasket, then you match the inlet manifold. LOADS of hours, but we are here to transform the engine not mess around.
According to AJ6 engineering, AJ6cylinder heads..nothing can or should be done..

No 5 Rule

The AJ6 head thing, was developed in the 70s and has a LEYLAND lo-gogo dancer on it, - you know the company that developed and sold crown jewels like the Allegro and Marina! 
Any engine with 92mm stroke is going to have maximum torque beginning at Diesel rpm figures.
Ignore anyone who says it can't be done, they are talking total rot! 
On top of this we have to move 1.6T with that torque and we don't need 102mm stroke to do it!
This means if we do our job right we will get near maximum torque around 1400rpm.
So let's aim for it!

Theory confirmed

Our conversions work and here are the figures!
 Check our power graphs, and this is with totally STANDARD camshafts.
We make a power band a mile wide, 1400-6400 rpm, collossal torque everywhere, and a car which is infinitely faster and more agreeable to drive than any V12,- with only 260 bhp!- (but most poorly maintained V12 HE have no more), 

If Cosworth had done Jaguar's design, no doubt it would have been a classic like the Mercedes, Opel or Ford YB.
So the head is rubbish, the camshaft design is 50 years old and the exhaust is from the stone age!
That's why we liked it.
We redesigned all the weak points and it even becomes a respectable race engine!

Now let's compare,- V12s are they better?
You like to go back to a flat and lifeless 50bhp/L, nothing below 3000rpm due to that silly short 70mm stroke?
Constrictions just about everywhere, a totally cretin injection system, a ruinous fuel bill?
A brief burst of gas guzzling life, to about 5000rpm?

Inescapable conclusions

Mr Bywater must have learnt about tuning from the Allegro....
Here's the other theory,-
Bullshit people long enough, get a major UK club and a few web sites in the world to give you rave reviews, ignore or rubbish other people's work..... then hide all this "progress" under "electronic management"..
Heard it before?
 

The timing chain system which tends to get noisy and clattery on this engine. it took years messing about for Jaguar to try to correct this, but never really succeeded. Luckily it never goes wrong even when rev'ed to 8000 rpm + This is the tricky bit, get that stupid manifold to sit flat on the head, without blowing around the corners. The steel shim gaskets are a pain, and the manifold often cracks or warps. Gaskets we use seem to cure the problem, but they need to be done up real tight Some people seem to be unconvinced of the validity of our work and whether or not the standard ECU can deliver more power. Well here's a nice lesson in combustion efficiency. Better combustion, same fuel equals more power less waste.