Those short stubby inlets were made originally by mangoletsi, they still do them I believe.
They are real nasty and some have tight bends to adapt the Jaguar spacings of the ports to Webber carb spacings. I know guys who have lost power and tractability having spent £3000+ fitting these babies. The inlets are shortened(not good) from std mainly in the name of keeping the carb height low. Better if you can get them are the taller ones made in the USA originally for GP44, far better flow and keeps the inlet length. Down side it the increased height unless you fit 90 degree bends. The webbers are also nasty, especially when you go backwards from injection to carbs that few can sort.
Got a spare brand new set if anyone wants them.

 

i have heard they look pretty, but dont run as well as factory inlet manifolds&TBs.

i do think its more the cyl. head inlet port shape& valve, that limits max air flow!

i had my manifolds Extrude honed,both runners and plenums, and it opened them up around
1/8-1/4" all the way thru, and took out a lot of humps and bump protrusions! 6MM oversize TBs, K&N filters.
i ported the head ports & bowls,(45yrs of porting must have learned something), added 3MM oversize valves(bought from Lanky,Grp44), lightened,backcut, and polished stems, 3 angle seats blended into bowls, plus resurfaced the head deck .050 to put the valves deeper into the bore.
as and after thought i shoulda/coulda, relieved the top of liner where valves come close, for more open area near the flow pinch point at liner!!!

ported exhaust manifolds, and had them thermal coated in&out for heat retention ,to help keep velocites up, for more scavenge effects! 2 1/2" down pipes into 2 mufflers then one large 5" outlet all on one side,(YUP its loud), sound nice at 6500-7000 revs.

for breathing on 5.3? pre-HE, i dont know what would be better(except turbocharging).

like allen said toward the end of things, Jag couldnt keep up with the turbo cars(Porsche,Volvo,etc.).
so they moved on to Group C racing,4 valve engines etc, even then they met with severe competion from turbo cars!

are you listening cal?

darn i feel like a school teacher again, headed a college level engine lab. in Daytona FL. for 6yrs!

 

almost forgot thermal coated the full chamber surface of the head deck,coated the exhaust ports, all valves top and bottom, piston tops, all in the process of heat control(dont want any overheated engines,and may as well use the heat for something).

i dont think anything in my engine is factory stock!


when i was doing my engine 94-95,i talked to Lanky grp44, and he said they did not have any coatings or extrude-ing available in the early mid 80s, rumors that it would be later on. F1 stuff.
and agreed that it had some merit to it!

 

The pictures from the Webcon website don't look like there is a bend in them, but i'll take your word for it.

I wasn't suggesting to go with carbs though. Those are EFI throttle bodies that fit where the Weber's would have gone.

 

the length from air in to inlet valve is to short, ram effect doesnt occur till way up in rpm! long cross runners are the way to go

mid range torque is far more important, that can be had with long cross runners, or tall ones that stick out thru there hood about a foot. with a plenum on top(dont forget the plenum).
short runners if you are driving along in 4-5th gear at 40mph, quickly open throttle car would gasp and hesitate even with EFI, course if you are doing 120mph it could,maybe pull ok, but you have lost the race already, and there aint enough road to make it up!

and you could shift down, but by then you are still losing, believe me been there done that!

but they do look kool, and may scare the competion.

 

i posted this pic i took around 1985-87 at daytona 24,

grp 44 car in paddock area, with top open! notice the length from head to trumpet inlet, gotta be 16-18 inches, and counting the port length another 4-5", ther stuff was all magnesium with slide throttle plates.
today cars run a big plenum chamber over the trumpets, there is power available in the proper plenum!

those were the great days!!

 

G'Day Gent's
I have being reading this thread with a great deal of interest. Next year some time I will be rebuilding a 5.3HE spare motor I have and fitting a 5speed to it that I already have again, all will be done outside the car and then just a complete swap when ready.
I am planning on just replacing rings and bearings in the bottom but doing a little head work, I am even contemplating trying to build a set of stainless extractors . Now what really is interesting is the talk about the inlets, my intention was to go down the path of ITB's, but now I'm starting to have second thoughts. This is a road car, its not going to see a track, and probably will never see high speed as there is nowhere in Oz legally to do it, but I do want the capability of it.
This is what I was thinking of originally, will fit nicely under the hood, even with a custom filters above.

 

Have you got Allan Scott's book? if not get yourself a copy. I got mine on eBay for about $50. TWR did a lot of development work for the V12 road car for Jaguar and a lot of this information is in the book. It will give you a starting point.

From What Allan was saying most of the power they made in the road engine was exhaust and cold air intake related. When they installed the GrpA inlet manifolds they lost power in the 3000-4000 rpm range and did not make power until after 6500rpm, NOT what you want in a road car.

As you ar in Australia talk to Norman Lutz from the E Type factory in Melbourne. he has a lot of information and can supply parts at a much better cost than most. I bought my 6.0L engine and 4L60 adptor from him for about $3600.

 

I will keep an eye out for the book. Im ok for parts for now as I have the complete conversion kit for the 5 speed and pedal box to suit, and two complete 5.3's but I will definetly bookmark Norman Lutz from the E Type factory if I need anything else.
I would see more torque down low as more beneficial to me in a road car, don't know about 500hp but 350 to 400 would be nice, just enough to turn heads.

 

The HE V12 has a much wider torque curve than the flat head. 400 would be easy with 6.0L I think 350-380 for the 5.3 should be doable without spending a fortune, especially if you use aftermarket ECU with ignition control.

 

Just sticking to the original subject I came across this group.
Jaguar XJS-GT
420hp and 600hp with nox is not a bad claim, but why are they going back to carbs?

Has anyone gone down the path of direct to head throttle bodies and curving and extending the inlets to match the plenum?
or maybe these people have something better. Custom Plenum Creations - Home

 

all i can say is build it the way you think is best, and see what happens, nitrous is another crutch to make power(and it does), but engines have a tendency to blow up, dramaticly!

have seen so many,have lost count, i have installed nitrous kits, but without any warrenty of any kind!
forced induction will make more power also ,but it easier to keep under control!

i'm kinda gettin older so i like things that last.

 

I am no great fan of Nox, nor am I a fan of FI unless its bolted to a side of a diesel, not quite the same thing, which I own 3 off. Personally I beleive that the v12 should be left naturaly aspireted. when you see makers like Holden/Chev getting 480+ hp at the rear out of their ls2/3 motors with no FI, there has to be hope for the V12.
The biggest thing I have noticed so far is the lack of exhaust design due to space. a decent set of tuned headers would work wonders but how would you get them in there. If anyone has header plans I would love to see them. Or if anyone manufactures them at not a Kings Ransom price let me know.

 

Although you can pick up a good set of headers for a GM LS or Ford Coyote motor for under $300, you won't find a set of Jag V12 headers for less than $2,000.

 

Look up twr and group 44 racing they both where around 550/600? Also check out the silkcut Jaguar.

 

Calvin if turbos are kept on the smaller side it will be very streetable and might get better mpg than stock if set right.now if you put on turbos that will scare small children and have a mouth tennis ball size then it will have some lag but there's ways around that too. Your other route is a procharger which are quite snappy on throttle response and pull through the rpm band nicely. I originally wanted too go that route

 

just dawned on me, i built my whole Jaguar, and didnt even have a computor!

did it all with just common sense!

course there is no such thing as common sense, its just last centuries new ideas!

 

what kinds of pistons did you use ron? stock pistons? because I did notice they didn't have valve reliefs in them

 

yes stock european 9-1 pistons, with my head work, very slight reduction in the valve relief area, guessin comes out around 9.2-1 ratio.

its all i could get in 1994, no computor DUH!, oh i could have had made a set of customs, but i was walking slow as to what would work and what wouldnt,bought pistons before i knew grp44 well enough to communicate, they had some 10.5s but i felt for street use maybe to much!

i built my car around the idea it would make a nice street cruiser,not a race car, i still think my cams are to much, dont really start pulling till after 4000revs, and lets be honest i dont drive around all day long at 4000rpm!

there is a big difference between fantasy and reality(MAYBE)!

 

in 1995 i found a stroker crank 8mm longer forged billet, but $2500. american dollars plus shipping,NOPE not affordable for me.

then,and i know me once i get started, custom pistons,bore and shape to be decided(not much to go on), custom rings unobtainable then, and even thought about light weight con rods(aluminum).

lightened & knife edged crank counter weights, redesigned oil passages, shot peened , and nitrided bearing surfaces, and all that and i would only have a rotating assembly!!

i used the SDS because the factory 1978 fi system was just useless for me!

as you will find out,it is a never ending labor of love, i'm still not finished completely.

if i were going to do it over,TODAY, it would be a nice smooth running torquey turbo engine, start making usable torque by 1700-1900rpm, and a GM 6 speed auto! as you are aware jag dont breath well, so forced induction will overcome some of the short comings of the ports and valve arraingments, flat head or HE!

altho the Audi V12 diesel thing would be a great challenge for me,id love it,new territory, new concepts, out with the old and in with the new! YUP sounds like i gotta win the lotto.

many new ideas are available today, that were not back 20yrs ago.