Please read this writeup before buying any inletmanifold that are too long...
Tuning and such..

Best regards
Ole mobeck

 

This was an interesting series of tests and dyno runs of various length intake trumpets and their affect on power and torque:
https://www.emeraldm3d.com/articles/...length-intake/

 

Most interesting, and it all coincides with what is in Chapter 6 (about induction) in Roger Bywater's book: Engine Technology for the Modern World. Which is why variable length inlet manifolds and variable cam timing is so effective on modern engines. My own belief is that you will find it very hard to improve on the OEM inlet manifold if you want a tractable road car with a flat torque curve.
The manual gearbox the OP intends to fit will have by far the biggest effect on performance!

 

I remember reading this article in Practical Performance car a few years ago, there used to be a regular section called “ Walkers Workshop” I think Dave Walker is now retired and his business partner runs Emerald.

 

Typed a response to this several times and deleted as 'liable to provoke' ... but I think sharing is warranted ...

Fancy manifolds - waste of money they don't work on the V12 regardless of claims - got this from the racing community - and that includes Rogers modified ones because they make sense only on 'race' cars and make road cars painful in traffic. TWR did make some improved manifolds that are improvements on the factory, Don Miles has the tooling and still makes them in small batches

Larger throttle bodies - waste of money they only serve to add noise.

Tubular headers - don't do it without serious attention to underbonnet temperature management - you should consider the header sacrificial if you wrap it, effective ceramic treatment is seriously expensive (don't be fooled by the ceramic in a can garbage)

For cars with no catalytic remove the centre exhaust, for cars with them remove the rears. A larger exhaust is pointless unless you fix the inlets

Sequential injection - pointless on anything but a highly tuned motor

If you really want to replace the ECU and use the Ford coil packs there's a lot to consider - Emerald K6 would be my choice but to get all the benefits the distributor has to go especially if you go for more air in and more out - that also means modifying the fueling system because stock pressure too low and designed to to be throttle managed only, the fuel rail is also a bit on the small side - TWR I believe had an underbonnet reservoir / pressure 'reserve' vessel. The best you will get is semi sequential. I don't know of any that can handle more than one MAP / MAF or Lambda probe (doesn't mean there aren't any) which precludes the use on a Jaguar V12 because each bank is independent.

I'd recommend sticking to one of the 'kits' from the likes of Mobeck but don't forget that this is only part of the story - I'd budget at least £7k

Lot to think about - and whether you can feel the benefits would likely be one of those audiophile type conversations - the transmission alone will make a huge difference personally I wouldn't go manual but would aim for a ZF HP26 - if I had 10k to burn - I don't. Modern sequential transmissions eat manuals for lunch, they aren't the slush boxes of the 90's.

 

Ben
How do we contact Don Miles, or are you talking about race manifolds?
My own experience is that Roger Bywater's super enhanced ECU and large throttle bodies made a HUGE difference to my car, and most definitely not an imagined one.
I was spinning the wheels in the wet from a "normal" traffic light start, and the acceleration and performance from 80 to 130 mph was night and day better, the car was seriously quick at three figure speeds after the kit was installed. It turned the car into something far, far faster and more eager. And I promise you it is not just the proud owner's impression, a couple of professional road testers drove it recently and were amazed. But the V12 MUST be caned regularly, many of them are so babied by their owners that they nevr really loosen up, I believe.

I totally agree with you about everything else you wrote, though!

 

Has a facebook page, he is currently building a group C Jaguar aka the Silk Cut Jaguar.

For some reason Facebook links don't work - search for TWR facebook - groupo number is 1432458440324391

I may have a super enhanced ECU available next year - one day I will post the why ...

 

No problem at all. What you write is not unreasonable. I’m still building up parts and deciding what I go for so it’s good to hear different opinions etc.

I have messaged Don to ask what manifolds he offers, although would imagine the 6.0 manifold is probably quite good still compared to a 5.3, looks like he also offers fuel rails, although it’s easy enough to make some up if needed, at the moment the 6.0 push fit fuel rail seems fine to me and takes relatively modern injectors etc

Also can understand that a larger set of tubular exhaust manifolds/headers can take up more space in the engine bay and be a large heat source, I guess I’d get them ceramic coated if I did have some, maybe cast manifolds are ok.

 

Don can take some time to respond but he will - he has just done a run of 3 pairs of manifolds but I know for sure one pair is already paid for you will need to tell him what you want or take what he has - he can do any text you want (for a price) - the fuel rails are designed to reduce pulsing in the fuel line not sure if he does fittings for the later Bosch injectors but you can just get the rails and DIY it though you may struggle to find the bore that Don seems to have sourced

 

Ben
What advantage do these manifolds give, would you say?

 

according to Don increased airflow but clearly I have no dyno numbers or engineering data on flow rates, I did do some research and the math gets complicated, you can actually make airflow worse into the cylinder if you remove metal in the wrong places.

Don recommended based on the work I've done on the exhaust side, to compliment improved exhaust flow, reckons the throttle butterfly's can still flow enough. I don't know if they're recommended unless you're going to improve fuelling - he reckons an increase of 2 psi is required so potentially up to 40psi given that Jaguar is 36 plus or minus 2, the increase isn't easily achieved with a standard Jaguar return regulator - gets complicated fast - the 'aftermarket' ECU is used to adjust injector pulse duration which the standard ECU cannot do - nor even Roger's super enhanced that I currently have fitted.

The TWR performance manifolds are 36mm at the heads opening to 41 at the larger plenum so larger than standard Jaguar items, apparently it is the side of the manifold feeding the ports in the head that are the restriction as hinted at by Roger B,

I don't know what the Zytek does but I believe that setup retains the distributor as a mechanism for engine speed sensing

This could all be snake oil of course but can't be distrusting and cynical all the time - just most of it -

Don Miles fuel rails ....

 

All very interesting stuff, those manifolds do look nice

The heads on my engine are standard, maybe some porting is needed to get the best out of the manifold? The ports would at the minimum need to be enlarged/matched?

Finally took delivery of the engine and other bits.

it was a 6 hour round trip to look at the car but the seller was kind enough to deliver the engine and other parts to me today.

I’m rather pleased that my engine has a crank position sensor bracket, should make fitting a trigger wheel a lot easier….

 

At this point I have no plans to port heads though I do have a good pair of heads and cams. The engine is back in the car and really I don't have any plans to pull it out again unless I suddenly get crazy rich and replace the transmission- and I have thought about it - but I don't want manual - would not have said that 40 years ago but arthritis and other ailments abound with age - hard enough to get in and out of the car with any dignity need this car to be fun not self abuse.

 

what do you mean by “sequential”?

dual clutch transmissions without torque converters are amazing. These “eat manuals”.

in any sporting situation(lapping etc.), you dont want a torque converter.

 

And that is essentially what I mean.

The HP26 / HP28 are solid performers too even with a torque converter - had the HP26 in my SV8 and that was close on 500bhp - was also my XJ but that was a rather lame 300bhp - neither are a patch on the box in my Audi in response terms which is a 7 speed 'DSG' or S Tronic as Audi call it - but they're leaps and bounds better than the TH400 and derivatives track use excepted - that said I had plenty of fun with the SV8. I first encountered the DSG in a Passat R36 - I've been sold on them ever since.

I just cannot at this stage justify the hassle of making one fit into the XJS - but there are ways to get a HP26 into one.

I don't think you can buy a performance car (that isn't an EV) that has a manual these days.

 

I’ll be sticking with a manual. I have the ZF 8 Speed in my F Pace SVR daily and it is amazing, but I want the involvement of a manual and would not want the hassle of re-inventing the wheel to fit and programme such a modern auto.

 

Putting a manual in an xjs is pretty easy. Thr install is part of the fun for me.

way better highway cruising too.

.68 5th and 3.73 final drive.

(still could use about 100hp more however)

 

All the Jaguar inlet manifolds from 75 to the very last in 97 are basically the same. Internal bore of the runners about 33mm for the whole length. the main differences are the logo on the to of the plenum replacing the ribs and the change in outside lugs to mount the late 'O' ring injector rails. So when Jaguar / TWR did the 6L engine the very same jnlet manifold went on effectively reducing flow by 13% but not a real problem for the low revs being used generally with the auto box. The manifolds I am making (remaking) were designed and made by TWR in period for better air flow and performance. They were used on the Group A XJS's and were intended to go on the 6L XJR15 which used basically an XJR-s engine. BUT the tooling had vanished from Stones Foundry. I tracked the tooling down over 15 years and acquired it pre COVID and have had a number of sets made for customers. They flow about 30% better than stock as made.. There are various online calculators online which will back up TWRs findings that the stock Throttle Body is good for upto 8500rpm on the 5.3L engine and about 7750rpm on the 6L If you have a larger v12 then the revs are lower and you may then fit TB's with the 4.2i butterfly with advantage. The even larger AJ6 TBs are simply too big just as the Lister 4 TB system is also grasping at straws. The 33mm runners are the restriction and the number and size of throttle bodies does not resolve the problem. These manifolds are 36mm at the head face opening to 41mm at the plenum so are cast up trumpets in effect. Std heads can be opened up to this (this is the diameter of the ID on the standard gasket) with the heads in situ. If you are interested drop me a line donmariamiles@gmail.com I also do the new CV14 injectors (green or grey) at £550 a set, these are the barbed with pipr type not the late 'O' ring type.

 

Don
I am interested and will PM you. What will the inlets do for a standard 5.3 litre engine please, and at what revs will it do it? I mean, will it allow higher revs with advantage, or better power throughout the rev range as a result of better breathing?

 

Are these fuel rails currently available?