Lovely, beautifully made. Have H&S been able to supply any power improvement figures? And would we be talking at pretty high revs? I do hope you will post your impressions once it is all fitted. Removing the centre boxes does help power, but on the only car I have heard with it done, it did make the car far noisier, at least from the outside where I was.
Greg

 

The OEM inlet manifolds are not as bad as you might think. The V12 Aston Martin engine, which is very powerful and efficient being basically two Ford Zetec V6s welded together, has a manifold that is almost the same.



+According to Roger Bywater (he of AJ6 Engineering fame) in his book Engine Technology for the Modern World, at road car revs, say up to 5500, neither the inlets nor the exhaust manifolds restrict power. At racing revs, naturally they do to an extent, as TWR confirmed (see Allan Scott's book on the racing TWR XJSs). But even the racing TWR cars had to use the OEM exhaust and inlet manifolds, and although they fettled them as far as they could internally, that was the limit possible under the rules; yet their engine made 500 BHP or nearly so. Mind you, they used pre-HE heads!
I agree that improved breathing makes a noticeable difference to the V12 in our cars even at road car revs above 3000 or so, but for really big gains at road car revs (as in the 60/70 BHP levels) I still believe the HE head is the real restriction.
Greg

 

Hi Greg, they didn't provide any performance increase figures and I think you're correct in that it's likely to be high up the rev range that any real performance benefit is felt. I will certainly provide some feedback once she's all back together again.
As for the sound, it's a bit of suck it and see really. We're essentially replacing (at this stage) from the headers back to just in front of the IRS, we're currently contemplating the size of pipe to use which of course also has an impact, but if its sounds too loud we could always re-instate a mid silencer (albeit a less restrictive one). She's a keeper so i'm happy to experiment over time ;-)

 

Hey Everyone,


It has been a while sinceI posted on this thread and it's good to see it come back to life. In regardsto performance enhancements from a properly tuned set of headers, relative tothe stock configuration, there will be a performance increase. How much? Only adyno will tell, but my hunch is that it would be worth the investment for someapplications. The more the performance mods to the engine, the greater the %increase. I size and build header parts every day for a living and I can tellyou, with confidence, by incorporating some of the following designparticulars, there will be a fairly beneficial improvement over the originalmanifolds:

• Proper primarytube size
• Stepped headerdesign
• Primary tubelength
• Merge collectors
• Accurately sizingthe merge in the collector
• A transitionalmerge after the minor merge point in the collector
• Length ofsecondary on the collector
  
  
  When dialed in, there willbe a worthwhile improvement, but it will take some work. Quite honestly, Ialways felt it would be a great project to take on, but we don’t build headersanymore, just header fabrication components.
  A little off topic, but Ithought it would be interesting. Here is a set of headers we built years agofor a Jaguar XJ13 kit car.

Header for a XJ13

 

I fitted AJ6 Engineering's silencer substitute pipes to my 93 6.0ltr 2+2 convertible. At the same time, I intended to 'gut' the catalysts but Roger Bywater discouraged me from doing so, saying that it would likely cause my car to fail the emissions test come MOT time.

My car has Marelli/Lucas engine management so that may 'react' differently to the Zytec engine management on your XJR-S but I will be interested to hear how you fare on the emissions test come MOT time.

The H&S manifolds look fabulous by the way & whilst my car is undergoing some work at the moment, I couldn't really afford/justify the cost (sadly) amongst all the other work that is being carried out.

Rgds.

A.

 

https://www.jaguarforums.com/forum/x...ssions-169599/

I think it should be here, too.

 

[QUOTE=Greg in France;1619111]The OEM inlet manifolds are not as bad as you might think. The V12 Aston Martin engine, which is very powerful and efficient being basically two Ford Zetec V6s welded together, has a manifold that is almost the same.



+According to Roger Bywater (he of AJ6 Engineering fame) in his book Engine Technology for the Modern World, at road car revs, say up to 5500, neither the inlets nor the exhaust manifolds restrict power. At racing revs, naturally they do to an extent, as TWR confirmed (see Allan Scott's book on the racing TWR XJSs). But even the racing TWR cars had to use the OEM exhaust and inlet manifolds, and although they fettled them as far as they could internally, that was the limit possible under the rules; yet their engine made 500 BHP or nearly so. Mind you, they used pre-HE heads!
I agree that improved breathing makes a noticeable difference to the V12 in our cars even at road car revs above 3000 or so, but for really big gains at road car revs (as in the 60/70 BHP levels) I still believe the HE head is the real restriction.
Greg[/QUOTE

Hi Greg, I think we may have to agree to disagree over this point.

Regarding the Aston manifold the runners appear to be significantly larger diameter and whilst also apparently unequal lengths perhaps not to the same degree as V12 Jaguar.

On the other points whilst I know a little about Roger Bywater's work at Jaguar on the basis of engine data I have seen where V12 was on dynomometer the airflow and volumetric efficiency increases as expected up to peak torque at about 3000rpm then falls drastically thereafter.
If airflow increases could match engine requirements at higher revs by maintaining % volumetric efficiency there would be potential for significant power increase at 5500 - 6000 rpm.

Other data on inlet manifold flow capability that I saw showed significant differences from one runner to another, again hardly ideal.

The 6.0 for example has cylinder capacity of 500cc, each cylinder needs to flow equal amounts.

Additionally even if the standard inlet manifold was optimal for the 5.3l then fitting identical unit on 6.0l wouldn't likely have sufficient flow capability unless serious reserve I.e oversized for 5.3

The design ethos for V12 production engine in terms of power output was a rather conservative target of having standard output of V12 production engine to equal highest output of tuned 6 cylinder previous generation.

So having a 5.3l V12 equal at tuned 3.8l six isn't that ambitious, hence in my opinion the limitations of standard engines.

That said I still believe 400bhp is achievable from normally aspirated 6.0 with HE head and 450 to 500bhp with same engine if turbo charged.
Totally convinced that despite packing limitations with twin turbo on XJS V12 it's got to be the way to go for anyone seeking large increases in usable torque and power.

​​​​​​​

 

We do not completely disagree about many of your interesting points Paul, and particularly so with your points about a fairly conservative design brief. However I believe the real limiting factor is the intake and exhaust valve positioning and the chamber shape on the HE, not the inlet manifolds. The HE configuration mitigates against efficient high rev cylinder filling, but I had thought it was quite Ok to about 5000 RPM. I am not so sure about your criticisms of the inlet manifolds, as TWR got 500 BHP from damn near standard ones (just a bit of fettling here and there). Albeit with pre HE heads, but identical inlet manifolds, Allan Scott's data in a graph on page 310 of his book, which compares several configurations, shows peak power for the baseline standard setup at 5250 RPM and an as good as flat torque curve from 2259 to 5000 RPM on the graph on the next page. if your points about the HE falling off at high revs are correct, it cannot be the manifolds, can it?

I also feel it is not really a fair criticism (even if true) with hindsight to hold a conservative strategy against a road car engine that was developed in the late 1960s, the injection version of which was developed and marketed in the XJS in 1975. What looks a rather medium output today, was mind-blowingly powerful in 1975, with road car brakes and tyres only just able to keep up - let alone the roads and the drivers!

I still feel as a road car engine the Jaguar V12 is among the most, if not THE most delightful engine to drive behind. Now of course love is blind, but even so, that is something you cannot say with a straight face about any other 1960s era engine.
Greg

 

I will admit that the Austin manifold is similar to the Jaguar manifold..

in that both have a throttle body and a plenum and 6 runners...

but saying they are the same is like saying my childs five finger hand is equal to Mike Tyson's five fingered Hand and should be able to knock some one out ....

AM verse Jaguar Plenum
runners
shorter ----- longer
thicker ----- thin
throttle to plenum
cone ------- just stuck in the side

internally I would have to have a look inside
but with the differences above I would expect that
the Austin set up would make more torque at a higher RPM and more HP
and the Jaguar would make it where is does around 2800 rpm
I have the VE number for the stock set up for the Jaguar it peaks at 79% at 2800 to 3000 rpm than then falls off to 69.05 at 5550rpm where the max Hp is... and above that if fall off to 60% at 6000 rpm and 44.5% at 6500rpm that cuts the torque tp 169.5 at 6500rpm giving you only about 210 Hp at that engine speed.. (running out of PUFF)
torque and Hp number are for the 5.3 liter...
running the VE numbers with the 6.0 displacement confirms that they are correct for both engines and the increase in engine displacement is the reason for the increase in torque and HP
I have ran them for warrjons 6.7 liter engine but they will not be correct because of the improvements he has completed on his head(s)
I am hoping that there will be a 3 to 8 % increase in the VE percentages because of his un shrouding of the intake valves (10% would be nice 15% would be heaven)
Warrjon's 6775.1cc with out touching the heads would produce
352hp @5550 rpm
382lb/ft @2800 rpm
with a 10% increase in VE from his head work about
420 HP @ 5550 rpm
420 lbs/ft @ 2800 rpm
new plenum any one?

 

Jon, i agree, i think Norm Lutz has done some serious mods to the factory plenums, and internal trumpets added. says over 500hp with his other mods!

again pre HE heads!

i have found that driving a car with more torque than HP is more enjoyable and fun, like passing or pulling away from a traffic stop!

greg makes some valid points also!

Paul59 , a no brainer, of course a pressurized inlet manifold will increase torque and HP,

it changes all the VE mods completly, like big ports ,big valves ,valve shrouding, big TBs, even the header debates, camshaft timing,ETC all things change.

ok i have built some supercharged and turbocharged engines, quite easily just increasing a measured 10psig in the inlet will run circles around modded hi VE engine!

just a stock engine(in good condition) will be amazing with 10/15 PISG.

 

I'll chime in on this.

The difference between the Aston and Jag V12 intake manifold is more than just runners. If you look at the distance between the end runners and the manifold wall the Aston manifold is much deeper. This distance should be at least 1.5 times the runner diameter for proper breathing. Which is why Norm designed the Lutz manifold, this on a bored 5.3L (6.0L) pre-HE made 500hp in an XJS.

The intake runners are not the restriction they are about 1.5sq" which would put the torque peak for a 5.3L at 4800rpm. The pinch point is in the head at the valve guide where it narrows to 1.0sq" approx, which will put the torque peak around 3500rpm, which is very close to the claimed figure of 3200rpm (in my car). So upgrading the intake manifold without opening out the ports in the head will have zero effect.

Headers in an XJS will not have a huge effect as there is not enough room for proper tuned length pipes. Best solution for a road car is to replicate what TWR did with the XJS GrpA in a tubular design.

 

Warren
What did the Lutz manifold look like, please? And is there anything that can be done about the pinch point you describe?
Greg

 

Squared off like the Aston manifold, 100x100mm for road use, Norm moved the TB to the front but that could remain OEM if needed.

I'll take a pic of my manifold tomorrow and photoshop a mockup. My plan is eventually make a new intake manifold out of my favorite material - Fiberglass, as an exact replica of the Jaguar manifold with equal length runners and larger plenum.

 

I have a couple in the garage of the DB9.<br/>Handles for gates thought to do.

 

see Warren's post here, I believe the photo is of the Lutz inlet manifold
https://www.jaguarforums.com/forum/xjs-x27-32/so-has-anyone-actually-made-500bhp-v12-pre-
he-95447/page34/#post1536977

also regarding Roger Bywater's claim that inlet manifold didn't limit 5.3l breathing I wonder why AJ6 engineering used to market an alternative inlet manifold that was highly regarded (apart from some quality control issues) by those who have more experience than I

AJ6 manifold (long discontinued)



from image posted by Ronbros

 

Here is a mockup of what Norm suggested to me, it's 100x100 box section, cut the runners off and weld/braze on the box section, he suggested moving the TB to the front. You could add to the runners to make them all the same length, like AJ6 did, except the AJ6 have the trumpets too close to the wall restricting flow.

But all this is mute as the restriction to flow is the narrowest cross section which is at the valve guide. To fix this you need to get in there with a grinder and open out the port and remove some of the boss NOT THE GUIDE, When I did mine I found over 1mm difference in diameter. between the largest and smallest. This amounts to about 0.1sq" in cross section. I could have gone larger but erred on the small size, I figured I can get back in there with the grinder at a later date if it's still too small.

 

Warren
Thanks for the illustration. Have you any idea what did the manifold mod do for power and at what RPM?
Greg

 

6.0L pre-HE 70mmx95mm 500hp at 7500rpm in an XJS built for 300km/h cruising

 

Where to find a picture of the TWR XJS GrpA headers?

DB7's headers is 32mm dia internal. XJS v12 will be 36-37 mm.

 

There is a pic in Allan Scott's book. What they did was to cast manifolds that kept the exhaust separate until they merged at the down pipe.

This pic is of e-Type headers, they would fit and do the job. and could be fabricated from pipe.


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