frenchyd
frenchyd UltimaDork
12/21/21 2:25 p.m.

Carbs or EFI?  
   Texts and calls to SVRA  remain unanswered.  I've tried to put the XJS in group 6 where it properly belongs. It was designed prior to the 1972 cut off (1968) built on a 1968 chassis, with an engine introduced in 1971. Delayed due to Jaguar/BLMH merger and development  problems with the EFI . 
      Anyway. If I wind up in group 10 where EFI is the norm  does the LS intake have a mechanical linkage?  What about the Atlas? What size are they?  

 

 

 

 

 

 

Tom1200
Tom1200 UltraDork
12/21/21 2:28 p.m.

In reply to frenchyd :

I mean this in the nicest possible way; who cares where SVRA classes it.

Put it together with the things you know and like and run it.............fun will be had by all.

Saron81
Saron81 Dork
12/21/21 2:36 p.m.

This is pretty easy for classification... the only Group 6 Jag sports car is the XKE. 
Your car is newer than the cut off date (by several years) and it came with carburetors.. Trying to argue otherwise isn't going to make you any friends. Likely why your inquiries remain unanswered, lol. 
 

frenchyd
frenchyd UltimaDork
12/21/21 3:04 p.m.

In reply to Saron81 : No sorry,  the XJS always had EFI    Only the XKE and pre 1975 sedan had carbs.  Since the sedan uses the XJS chassis and all suspension/mechanical parts.  It's really a moot point.   
I wish I could find my old XKE series111 that's lighter ( the V12 is 30 pounds lighter than the 4.2 six cylinder) and pushes much less air.  

 

frenchyd
frenchyd UltimaDork
12/21/21 3:06 p.m.
Tom1200 said:

In reply to frenchyd :

I mean this in the nicest possible way; who cares where SVRA classes it.

Put it together with the things you know and like and run it.............fun will be had by all.

You are right.  I just wanted to play with the TransAm cars etc. but they tend to run group 6,10,&12 together. So I'll get to play with them anyway. 

Driven5
Driven5 UberDork
12/21/21 7:44 p.m.
frenchyd said:

I've tried to put the XJS in group 6 where it properly belongs. It was designed prior to the 1972 cut off (1968) built on a 1968 chassis, with an engine introduced in 1971. Delayed due to Jaguar/BLMH merger and development  problems with the EFI . 

As I read it, your argument for where it 'properly belongs' would only hold water if you were asking to run a carburetted Series I sedan in Group 6... But does not apply at all for an XJS. The cutoff is for series production date of that make and model. Period. End of story. Not the designed date. Not the series production date of different models on a similar platform. Not the original engine production date as used in other models. The fact that the XJS was only ever offered with EFI, but the EFI wasn't offered at all until well after the cutoff only reinforces that this is nothing more than wishful thinking. You can't simply backdate a car introduced in 1975, with 1975 technology, into its 1972 racing configuration.

frenchyd
frenchyd UltimaDork
12/22/21 6:26 a.m.

In reply to Driven5 :

I've accepted that, hence I'm going to use EFI and gain what I can. ( which is a lot) 
   Now I need to know what LS  or Atlas engines had cable or mechanical linkage. The reason is the early EFI was based on 3 Bosch VW Rabbit units ganged together.  Those are all analog based.  It's easier to swap intakes to Chevy since those are all digital and the Megasquirt doesn't have any problem translating them.  
   Group 44 built 3 different XJS's.  A 1976, -1978, and a fiberglass and tube frame one.  All 3 were legal. And each was lighter than the earlier. 

  The last one was able to move the engine back 8 inches which changed the weight bias significantly to rear.  Thus front tires lasted 2 times as long.  Plus it had a Franklin Quick change. 
     That plus I see very little participation of group 10 or 12 so they tend to put them in will group 6.   My reason to be in Group 6 was so I could play with other TransAm cars.  If they run them together what do I care which group we are in?  

DeadSkunk  (Warren)
DeadSkunk (Warren) UltimaDork
12/22/21 9:05 a.m.

In reply to frenchyd :

If you are asking about cable throttle linkages Frenchy, the early LS engines had them. My Challenge motor is a 2003 and it was electronic by then, so you're looking for earlier 1998-2002 I think. You can bolt early 3-bolt cable throttle bodies to later 3-bolt manifolds, too. That's what I'll be doing. As for Atlas engines I don't know.

Edit: Are you thinking of using LS throttle bodies on the Jag motor? Like, one for each cylinder bank?

Furious_E (Forum Supporter)
Furious_E (Forum Supporter) GRM+ Memberand UltraDork
12/22/21 9:14 a.m.

In reply to frenchyd :

4th gen F body should all be cable throttle body, truck motors as well up through 03 I think, not sure what year the vans changed to DBW but I think they hung on longer than the trucks by a couple years, all C5 and later Corvettes are drive by wire. Also important to consider is three bolt vs four bolt mounting pattern. I THINK all factory DBC throttle bodies were the three bolt pattern and 78mm bore, although DBC four bolt throttle bodies are common on the aftermarket in various sizes. 

frenchyd
frenchyd UltimaDork
12/22/21 10:54 a.m.

In reply to DeadSkunk (Warren) :

Yes I'm thinking Chevy's  are about 75mm which is close to Jaguars.  There are larger Jaguars available so I know bigger will work.  I'm not sure how to input signals from 2 units.
     The "crank" sensor on Jaguars is a Hall effect trigger on the back side of the distributor rotor. Except later after Ford bought them out they went to an actual crank sensor.    
      Since they are batch fired it really doesn't need a cam sensor input does it?  
        

frenchyd
frenchyd UltimaDork
12/22/21 11:00 a.m.
Furious_E (Forum Supporter) said:

In reply to frenchyd :

4th gen F body should all be cable throttle body, truck motors as well up through 03 I think, not sure what year the vans changed to DBW but I think they hung on longer than the trucks by a couple years, all C5 and later Corvettes are drive by wire. Also important to consider is three bolt vs four bolt mounting pattern. I THINK all factory DBC throttle bodies were the three bolt pattern and 78mm bore, although DBC four bolt throttle bodies are common on the aftermarket in various sizes. 

Pop the hood and look for a linkage with a cable instead of a wire going to it?   Heck I'm pretty creative. Maybe I can even convert drive by wire to solid linkage?  
  I wonder if I can even add OBD2  to the system?   

frenchyd
frenchyd UltimaDork
12/22/21 11:10 a.m.

In reply to DeadSkunk (Warren) :

Since I'll be in group 10 or even 12 I wonder what other improvements I can do?  Trans Am is very sticky about 15x10 rims and original style wheels. 
    Maybe I should start thinking about 17x10's. (13's in the rear) Since they will actually fit under the stock fenders. Or with the Group 44 flairs. Go even bigger?   

frenchyd
frenchyd UltimaDork
12/25/21 12:33 p.m.
Saron81 said:

This is pretty easy for classification... the only Group 6 Jag sports car is the XKE. 
Your car is newer than the cut off date (by several years) and it came with carburetors.. Trying to argue otherwise isn't going to make you any friends. Likely why your inquiries remain unanswered, lol. 
 

    Since I have molds for an XKE. I wonder if SVRA would let me run in group 6?      
 Group 44 won the run offs in 1976 with a V12.  I can pretty closely replicate the XKE front subframe  and yes the V12 will fit in a series 1 or 2 chassis.  

RXBeetle
RXBeetle Reader
12/25/21 6:40 p.m.
frenchyd said:

In reply to DeadSkunk (Warren) :

Yes I'm thinking Chevy's  are about 75mm which is close to Jaguars.  There are larger Jaguars available so I know bigger will work.  I'm not sure how to input signals from 2 units.
     The "crank" sensor on Jaguars is a Hall effect trigger on the back side of the distributor rotor. Except later after Ford bought them out they went to an actual crank sensor.    
      Since they are batch fired it really doesn't need a cam sensor input does it?  
        

Something like this looks like it has all the right pieces to run dual throttles with adjustments. Maybe not the right lengths but it's a good starting point to adapt as needed. 
https://throttle.motorcyclepartsi.com/motorcycle-parts-u01-4-125-bk-universal-split-dual.html

frenchyd
frenchyd UltimaDork
12/26/21 11:42 a.m.
Saron81 said:

This is pretty easy for classification... the only Group 6 Jag sports car is the XKE. 
Your car is newer than the cut off date (by several years) and it came with carburetors.. Trying to argue otherwise isn't going to make you any friends. Likely why your inquiries remain unanswered, lol. 
 

Actually not.  The XKE ( which as you point out  allowed in group 6) was built up through 1974 and sold as new in 1975& 76 since the XJS was developed and built earlier it wasn't released until 1975 it actually overlapped the XKE.  
     Nor did it ever come with carburetors.
in order to race TransAm Group 44 petitioned SCCA to grant them the use of Weber carbs.  The EFI had no means of adapting to different fueling needs since it basically used 3 VW rabbit units ( Bosch) ganged together. 
    Retrofitting the earlier carbs was my suggestion to fit with group 6  and the common 4 barrel carbs. Using the 4 single barrel SU carbs.  
  Weight, technology, power, and size wise the  XJS is a natural fit in group 6. 
    Since SVRA tends to run group 6,10, & 12 together it's a moot point.  I don't race for trophy's but for fun.   

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