DIY Improvement to Performance & Economy of AJ16 Engines

[AndyStodart]

I can understand people's potential scepticism just reading the title of this thread. Could there really be a cheap and simple modification that improves both performance and fuel economy? If it was that simple why didn't Jaguar do it?
Well the reasons are quite complex, but I will try to explain them.

When I worked at Jaguar between 1988 and 1995 it was std policy to map the ignition timing 3 degrees retarded from borderline knock on a mid-limit compression ratio engine, at all speeds and load where the engine was knock limited. The ignition timing to achieve borderline knock was determined by running the engine steady state on a dynamometer at each speed and load until the combustion chamber temperatures were fully stabilised. This is not a condition that tends to happen in normal driving in the UK where it is difficult to operate the engine at wide open throttle for more than a few seconds at a time, during which time the temperatures due not reach their high stabilised values.

Consequently the lower temperatures that occur during normal driving mean that the mapped ignition timing is significantly retarded from the level at which knock would occur.

A couple of years ago I designed a revised crank sensor bracket to take advantage of this situation. It was initially designed for the AJ16 engine and moved the position of the crank sensor with respect to the engine. As a result the signal to the engine ECU which should indicate when each piston is at TDC is generated 5degrees early.

Consequently each ignition event generated by the ECU occurs 5degrees earlier than the mapped value. It's a bit like advancing a distributor in the days when they contained contact breaker (unlike the one on an AJ6 engine). The extra ignition advance increases the performance at all speeds and load where the engine was deemed to be knock limited when tested on the dynamometer. I initially implemented my bracket on the AJ16 engine as the engine management system on this engine also has a knock sensing system, which I helped to develop.

This meant that in extreme circumstances should the extra 5 degrees cause any knock, then the system would simply retard the ignition timing out of knock. This bracket proved very successful and I have now sold over 340 of them.

A couple of years ago I was asked to produce a couple of brackets for some AJ6 engines which were fitted to race cars running on super unleaded fuel. At the customer's request, the bracket was designed with an extra 7 degrees of ignition advance. The two engines fitted with these brackets went on to complete a season's racing and the cars they powered were quite successful in their class in terms of performance. This was quite a severe test of an AJ6 engine to run at this level of ignition advance.

I was then asked by another Jaguar owner to design a bracket for AJ6 engines. Having produced a batch of these brackets which provides an extra 5 degrees of advance I thought I would offer these to other owners as well.

It takes under an hour to replace the std bracket with one of my brackets using nothing more than std tools. In fact, if like me you have had a lot of pratice, you can do it in 15mins on an AJ16SC engine which is the most complicated installation due to the neeed to remove the SC drive belt tensioner.

If you would like any more information about these revised crank sensor brackets for either AJ16 or AJ6 engines then feel free to email my wife Helen, who deals with any enquiries, on helenstodart@gmail.com

[ptjs1]

Andy,

Tks for this useful post in the XJ40 / X300 section and also for now giving the the same opportunity to owners of AJ6 engines. As you know, I picked up one of the AJ16 brackets from you for my XJS but still haven't got around to fitting it as I wanted to do some immediate back to back performance tests so I could write it up for the mag. Your post will now make me get off my backside and fit it in the next few weeks!

I will also copy this thread and duplicate it in the XJS section of the BB for XJS owners to also benefit. Hope that's ok with you.

Cheers

Paul Sinnott

[AndyStodart]

Hi Paul,
That's fine with me.

[YoungX300]

I know nothing about anything of a mechanical nature on my car, but I wondered if you could quote just how much performance and economy are increased by?

[AndyStodart]

One owner fitted one of these brackets to a 4.0L naturally aspirated engine and claimed it increased power output by 20bhp on a chassis dyno test. I have not personally performed such a test, but everyone who fits these brackets says that they can definitely feel the difference.

[naki]

Andy, have you started making these again now? last time i emailed with you, you had decided to not make anymore?

i would like one for my 1992MY XJR Manual (VIN 665307).
let me know if thats possible.

thanks

[YoungX300]

I also fancy one for my 1997 3.2 sport manual, what would be the price of one of your kits?

[Popsjag]

Hi Naki & YoungX300,

If you email Helen ( helenstodart@gmail.com ), she will tell you how much & how to pay.

Regards,

Steve.

[davidr]

Andy - for an AJ16, how does this affect the interaction between the crankshaft position sensor (that we are moving) and the camshaft position sensor (ie the one where the distributor would be on the AJ6)?
Should the camshaft position sensor stay where it is (ie the dimple in the centre of the sight glass at TDC) or should it be advanced 5 degrees?
Regards
David

[ptjs1]

David,

On an AJ16, the Engine Position Sensor (as I believe it's formally called?) only serves to help the engine fire at start. It does nothing after that. Because the Crank Sensor has one notch missing to indicate TDC but can't indicate which stroke cylinder 1 is on, the Engine Position Sensor merely helps the ecu to know whether it's on a compression stroke or an exhaust stroke. Otherwise, the engine would need to turn over longer before the ecu worked out when it knows that cylinder 1 needs to fire.

So, fitting Andy's bracket doesn't need a change on the EPS position.

Paul

[davidr]

Thanks Paul. I've ordered one so we'll see!!

[davidr]

My new bracket arrived yesterday but after I'd left for the run up to the Kemble breakfast meeting. I managed to escape 'er indoors' gaze for a short while yesterday evening so I went out to the workshop and fitted it.
It took me about 45 minutes to do including taking some photos, cleaning up parts and having a chat with my neighbour who dropped in to see what I was up to.
Wasn't very hard to do. Just 2 bolts to undo the sensor bracket and then pull it off the dowels. Unplug the sensor and pull the whole thing out. Then one bolt to undo the sensor from the bracket and put it on the new one. position the new bracket with sensor attached, do up the 2 bolts and plug the sensor back in and there you are!
I haven't got any further than starting the car to check it still ran ( which it did!) so I'll have to give the car a drive later today and report back.
Sorry to leave on a cliff-hanger!!

PS I did this on my 1995 XJS Celebration. I know this is the X300 forum but the process is the same!

PPS. I did take some photos but despite repeated attempts I can't get this bloody site to upload them! See previous exasperated posts on the subject!!

[Brakebuster]

there is no hope for you is there David ,


email them to me and i will post em for you , lol

BB

[ptjs1]

David,

If you want to send me the pictures, I'll get them put in a gallery under your account here on the website.

Would be good if you also put your post and pics in the same named thread that is in the XJS section of the Bulletin Board.

Paul

[davidr]

Another attempt to post my photos - this time using my laptop instead of the ipad.
I think it might have worked!!
I tell you - its taken longer buggering about trying to get these pictures loaded than to do the job on the car!!
Maybe I'm better with a spanner than a keyboard!! (or maybe this could be made much much easier!!)