EFI or Carbs.

Jag designed the V12 to use the EFI but even though they delayed introducing the new V12 for almost 2 years it was never ready. So at the last minute they cobbled in a 4 carb manifold and released it.   It took an additional 3 years and then they had to use a Bosch system out of the VW Rabbit x 3  (3x4=12)  It took Lucas until 1977 before they released their own EFI. 
   It made 13 more horsepower than the carbs did and got maybe a 1 or 2 mpg better gas mileage. 
 

   The problem today is parts. Only a few thousand EFI systems were made until the 1980's. Parts in Junkyards are  40+ years old  and not inventoried by anyone.   They whole system doesn't use a single microchip. It's all transistors soldered on a board and by now some of those soldered connections are pretty badly corroded.  
        
Carb  parts are readily available. (From a GRM advertizer ) 

Didn't you say Webers? This is for the granddaughter?

Either the granddaughter is going to be one awesome mechanic or she'll have a cool boyfriend she met on her semester in Europe.

Kudos to you, Mr. V12!

Nah!
      Webers don't really work very well on Jag V12's. They look really impressive but when you close the hood the intake throats are less  than 3/4" from the hood.  ( there isn't room for filters either) 

Air doesn't like making that sharp a turn. So you've  spent more than $3-4,000  for not a lot of power gain.    Group 44 made 450 hp using the stock carb setup.  
        Besides this one is for me.   

For you?  Carbs. All day long. 

Series 1 SWB V12? Fantasic. 

In reply to frenchyd :

Like the 240Z - the go to is Webers but you do some damage with warmed over stock carbs.  

I dig where you're shoveling 

In reply to Datsun310Guy :

I'm thinking for towing purposes.  I mean the thing has more power than a 454  even on carbs. 

TR7 said:

Series 1 SWB V12? Fantasic. 

I just think a Jaguar pulling a Jaguar race car would be cool. 

Patton Machine makes EFI conversion kits for Stromberg carbs.  Use the stock intake and carb bodies, but get the tunability of EFI.

In reply to JoeTR6 :

That interests me but I'm not sure what I'd get.  I mean I'd still need to use a Megasquirt  with all that development time.  
     Because the 40+ year old EFI isn't adjustable in any way. It either works or it doesn't. Given Jaguar and Lucas's development,  reliability is extremely iffy.  Frankly they'd run a few thousand off and then change.  Run a few thousand more and change.  That continued as long as the V12 was in production. 
   The manifold / hardware for EFI remains basically the same  for its entire 22 year production life. 
    Mobeck makes a plug and play system but like the factory system it's not adjustable.   Flex fuel would be an absolute requirement for me.  

There is a similar issue with EFI parts for Volvos, although not quite as bad. As such, converting them to Megasquirt is pretty straightforward - it also helps there is a vendor who sells what is essentially a plug & play kit to convert the Bosch D-Jet EFI to Megasquirt (although at ~$3K, it's not cheap).  It comes pre-programmed since the general parameters for a B20 are well established.  It does help the B20 D-Jet is a (approximately) port injection system, similar to modern cars and most of the components are essentially the same. 

Although I say it without having done it myself, it seems like the newest Megasquirt systems are fairly simple to set up for an engine to get it running, then it's just a matter of fine tuning.  Seems a lot easier to deal with than getting multiple carbs all synchronized. 

Did any company ever make a Jag V12 manifold to use "American" style 2 BBl or 4 BBL carbs? A 3x2 "6-Pack" set up on a V12 sounds cool.  

All I see is a John's Cars ad in Hemmings when I look at that Jag.

In reply to ddavidv :

Im going to have to disagree, I think those early V12 cars are kinda special because of that engine. 

In reply to ddavidv :

I understand. The EFI is not simple. Plus with all those hoses, wires ,  even air conditioning for the fuel line, it looks scary as heck. look at Group 44's  engines.  Neat,  clean, simple.  The XKE which won SCCA  B Production in the run offs against all those Corvettes and Cobra's using the stock carburetors.  The XJS which won the IMSA  Championship  against Corvettes Camaro's BMW's and turbo'd Porsche's  using Webers. Then over at the 24 hours of LeMans where in 1988 they beat the best Porsche had. 
    
Unlike later OBD2 EFI you actually need to be a decent mechanic to figure it out.  
 Yet if you put in a Chevy V8 you start out by losing 100 horsepower+. Guess nobody has told you the old 350 Chevy  only had 160 net horsepower?  
  The little 326 cu in V12  on carbs actually makes 7 horsepower more  than a big block 454 and on EFI the V12 makes 30 horsepower more than the 454. 
 The carbs are lawn mower simple to work on. They are the simplest  carb I've ever worked on.   Yes there are 4 of them but  the linkage is very easy.  Nearly impossible to screw up. Combined they are bigger than a Holley dominator. 
       A professional swap to install a Chevy small block will cost you $20,000 which should give you an idea of just how hard it actually is. 
     Then you've got to figure out how to get the lost power back.  

In reply to TR7 :

Exactly. The factory did a messy job of putting it in the car, though it didn't get tidied up until the early 1990's. But that series is called the best, most reliable probably because of how clean its installed. 

Megasquirt made from scratch. Just something different. E-Type efi. https://www.youtube.com/watch?v=giQasJo7ftI

The answer is obviously EFI that looks like carbs.

Ian F (Forum Supporter) said:

There is a similar issue with EFI parts for Volvos, although not quite as bad. As such, converting them to Megasquirt is pretty straightforward - it also helps there is a vendor who sells what is essentially a plug & play kit to convert the Bosch D-Jet EFI to Megasquirt (although at ~$3K, it's not cheap).  It comes pre-programmed since the general parameters for a B20 are well established.  It does help the B20 D-Jet is a (approximately) port injection system, similar to modern cars and most of the components are essentially the same. 

Although I say it without having done it myself, it seems like the newest Megasquirt systems are fairly simple to set up for an engine to get it running, then it's just a matter of fine tuning.  Seems a lot easier to deal with than getting multiple carbs all synchronized. 

Did any company ever make a Jag V12 manifold to use "American" style 2 BBl or 4 BBL carbs? A 3x2 "6-Pack" set up on a V12 sounds cool.  

The Jaguar V12 EFI manifold was used in both the XJ12 & XJS V12 from 1975-1996  I'm guessing a bit,  but there were over 230,000 made in that period.  Over 1/2 of which came here to America.  I've got 3 of them myself and only one carb manifold ( with carbs).  Rebuild kits are readily available. And not terribly expensive.  It takes about 5 minutes per carb to rebuild them assuming the throttle shafts aren't worn out. And I'm not exaggerating. They really are lawn mower simple. 
   Regarding synchronizing 4 carbs instead of 2  throttle bodies. ( it's ultra important to synchronize  the EFI ) It's a cake walk.  There is a device called a unisyn  that anyone who tuned up British carbs  bought.  Mine is probably from the 1960's.  So simple to use I don't remember if they sent instructions  with it.  Uber intuitive.  
    Once set ( either EFI or carbs ) you don't need to mess with it again  until someone messes with it.  I've rebuilt engines and put the carbs back on and in checking everything was spot on.  ( it takes about a minute per carb to check they are exactly perfect.  Adjusting can take maybe 15-20 minutes to synchronize all 4 carbs. 
     Against that there would be the whole time required to wire the Megasquirt in. ( 2-3 days? )  the factory puts the ECU in the trunk. And since it's a 1972 it won't have any wiring going there.   The carbs use a air of double headed SU fuel pumps putting out about 2.5 PSI  while the EFI uses a single SU fuel pump putting out 30 psi. But the gas tanks would need to be modified to take the fuel return lines. ( and fuel return lines bent up and installed) 

The  time spent  to tune EFi? I have no clue, I do know the Megasquirt is self learning.  But part of what makes a Megasquirt better than the factory unit is the ability to adjust.  I can also add a simple sensor to the fuel line and have the ability to use flex fuel.  
  E85 will easily gain 15-20%  more power ( important for the towing I intend to do ). since the compression is so high.  Stock it's 11.5-1 and  that gets me around 320 DIN net  horsepower compared to 237 DIN net horsepower for carbs.  
      Plus all that alcohol means the engine will be massively cooler running. ( again very important for towing). 
    OK fuel mileage with E85 is going to be bad. On carbs premium ( at my local station) is $4.39/9  while E85 is as low as $3.09/9  

$98.80 a full fill -up

to $46.20  that's over a $50 savings per fill-up 

  The premium might average 12 mpg  compared to 8? mpg?  To go the same 500 miles. $131.25 on E85 vs premium at $183.33    
 So I'd save $52 using E85 on a 500 mile trip over using  premium.  Oops, I forgot Towing. Better cut mileage in 1/2.  So I'd save $104 
    

In reply to frenchyd :

Just summing things up.
 Using carbs is the simple, cheap answer. 4 rebuild kits  1/2 hour to rebuild and synchronize them? ($200)  Can use the car right away.  237 horsepower DIN net.  ( 454 Chevy makes 230 SAE Net )  towing the Jaguar race car  500 miles?  $ 350 

    EFI using Megasquirt  it will take about $500 worth of DIY Autotune, wiring etc to install it. ( I have the manifolds etc. and the Megasquirt ). Plus the gas tanks (2) conversion. And 30 psi fuel pump. Plus fabricating return fuel line.  (?$500?!!) and $50? for a fuel sensor. To have flex fueL.  E85 gets me to 320 hp. DIN net  plus seriously cooler running.   Traveling 500 miles $ $262  $88 less 

This is Grass Roots  it could go either way......

To put it even simpler. 
  Towing gas money  to the 2000 Challenge Race.

Carbs $3,300

EFI.      $1,050 

In reply to frenchyd :

Right. 
 

Except carbs are in your wheelhouse, and EFI is not.  
 

You are doing mental gymnastics to talk yourself into something you don't actually want. 
 

What's the cost of an EFI car that never actually runs, or takes a very long time and a lot of frustration to accomplish?

Those are all good points.  I do happen to agree that carbs are simple.  
Except I understand the need to remain mentally alert as I age. ( approaching 75) 
      This summer I'll be getting the EFI working on my XJS.   I think I've studied it enough and have all my questions already answered.  Absolutely it will be challenging.   But I believe I can.
      So doing the XKE V12  race car and then the XJ 12  will be simply more of the same.  
 

  If things go as I plan. (If?)  my wife will retire 1&1/2 years from now. Which allows  me to retire myself. ( a big reason I'm still working is so she won't feel like the load is on her alone). 

  Once retired,  I'd like to tow the XKE down to the $2000 challenge.  On a special light weight (500#)  trailer I'll build for the XKE.  Pulled by the XJ12.  
 

  So I have an incentive  to accept a challenge that will push me out of my comfort zone.  
     On the other hand,  boy are carbs the EZ button.  

One other minor point.  
     Carbs on a V12 even if I replace the camshafts with reground ones and get another  whole .100 lift From the stock .375 lift.  Might get me to 460 hp. 
       While EFI with turbo and reground cams  I should be in the neighborhood of 650 hp. 

  I'd much rather have that when I get to the Challenge. I know I don't stand a chance against the Nelsons. ( or probably anybody else set up for the drag race).  But it should be fun.  

In reply to frenchyd :

Why do you ask for people's opinions then argue with their responses?  You already know what you want to do. Do it. 
 

My OPINION is that you will be happier with carbs, and I have no idea why you would need or want turbos and 650 hp on a tow vehicle. But you don't want my opinion.  
 

I'd also never start a 2nd EFI Megasquirt project before finishing my first, but that's just me. And you don't want my opinion.