Hey folks,

I think I've only made one post on here but am an avid lurker and I want to first say thanks for the wealth of info that's here on the x27. I have an 85 v12 parts car I purchased it cheap and got it running. The car is very tired, rusty (it's originally from ohio) and was very neglected. It's not worth saving. The motor needs new seals, vacuum lines, injectors, valve clearance job, water pump, etc.

Last week I pulled to motor out of the car because I will be using it in a one off replica. my username should give away what that is. It will be paired up to a t5 and 8.8 rear end. I'm planning to retain the original lucas injection but I'd like to bring it down to the bare essentials for aesthetic reasons. It is pretty basic already as far as I can tell. I will replace any corroded wiring, all connectors, new looming, new injector harness.

So what is really needed to run the lucas system?

ECU/ vacuum line to MAP
Injectors
FPR (Aftermarket-single)
air intake temperature
coolant temp sensor to ECU
ignition amplifier
injector resistor
throttle potentiometer
full throttle switch (I can't locate it)


What I will delete or already have:

air pump
air rails
silly dual FPR
over run valves
power steering pump
oil cooler???

I would like to remove the injector resistor and replace the injectors with low impedance injectors if there's a simple replacement because I need to replace the injectors anyways.

Another thing I'd like to do is relocate the throttle bodies to the front of the intake plenums. The original throttle linkage really bothers me visually and the side draft throttles will likely cause fitment issues with the inner wheel wells. I will build new sheet metal plenums with similar volume and weld them to the factory runners if I go this route. Is the original throttle potentiometer a 0-5v like a more modern TPS?

I've read the original oil cooler really does not do much, what are my replacement options? weld AN bungs on the feed and return and use a generic oil cooler and custom lines? The car will be street driven exclusively and if it's not necessary I will delete it.

Alternator- I'd like to relocate it to the valley on the front of the motor. Has anyone done this for a street application and if so, what alternator did you use as well as the pulley, and tensioner?

Thanks in advance for the help, I know this is a lot of questions in one post but hopefully it can make for a healthy discussion and hopefully I won't be given too much grief for not restoring the car, just the engine.

 

Welcome to the forum 275nart,

Plenty of Jaguars died from rust over here in the UK and been completely scrapped so it's good to hear your making use of the superb V12 engine.

I've approved your post so it's now open for other members to respond.

Graham

 

The XJS injectors are already low resistance (R), sorry for my analness but impedance (Z) is a totally incorrect term. I know everyone uses it, but they obviously do not what impedance is.

The Lucas ECU has separate pick and hold outputs for the injectors. The resistor pack is needed on the hold line to keep the injectors open. They provide current limiting, you will fry the Lucas ECU if you remove them.

The only way to remove the resistors and use low R injectors is to change the ECU and use PWM to limit current.

Plenums - The stock ones are way too small. You can use the stock runners, cut the plenum off and use 100x100 square section, weld the TB to the front.

 

Why use the Lucas EFI if you're prepared to do all that work? Dirch ut (it isn't that sophisticated as it may seem) and use say Megasquish or so... That is tunable and I bet with a few little tweaks and different injectors, you'd have more than the factory power output (depending on year, market and emissions code from 268-295 bhp).

 

Thank you Graham for approving the thread. These engines are great, I agree! Hopefully this car can donate its parts for use in someone else's restoration project.

Thanks for the clarification. I will be mounting the ECU on the passenger floorboard and it would be okay to relocate the resistor pack there as well, I just thought there may be a way to eliminate it by using different injectors. But it sounds like it does more than some of the Mitsubishi/Chrysler injector resistor packs I'm familiar with.

I am familiar with stand alone EMS (AEM, MS and Haltech) and use an AEM EMS in one of my cars. I don't know if there's a huge performance advantage to be gained from using megasquirt unless I were to do individual throttles, electronic ignition with individual coils, or use some kind of forced induction. The ECU won't be seeing more fuel and air or internal modifications as the car I'm building will weight around 2500 pounds. Freeing up the exhaust for the sound alone is a no-brainer though!

Thank you everyone for your replies so far.

 

Warren
What sort of performance gain do you estimate that increasing the plenum size would bring to an HE motor?
Greg

 

I don't know for sure It was my engine guy who suggested it. he has done a few mostly on pre-he. I'll be doing this to my engine so I'll let you know

 

I wonder if it will more just change the power band or would the runners have to be shortened as well? I'd be interested in seeing photos of that engine.

On my 4cyl turbo car I had a fabricator friend make a custom intake with shortened runners, a large tapered plenum, and a 90mm throttle body. This shifted the powerband from 4500-6000 to 5500-7000. Obviously a forced induction application will react differently to these changes.

 

This is the sort of thing I'm aiming for.

 

That setup still has the sidemounted TBs.

Afaik shorter intakes will result in a generally low torque figure. That is why many modern 4 cylinder have variable length intakes so that at low revs the engine has a usable amount of torque. Adding to the fact, that the 5.3l has a short stroke, I am sure that shortening the intakerunners will cause the characteristics of the engine to be somewhat offset, that it will be gutless at low rpms where as at high rpms you'll see it wanting to rev higher and higher.

Moving the TBS to the fronts will also cause an uneven aircharge in each cylinder, as the most rear cylinders will probably have a fair bit less air than the fronts will. Afaik BMW and Benz only did that to have a bit less hassle on the sides...

But that is all in my opinion and afaik...

 

Maybe throw the dizzy in there too for good measure.

Yes. TPS is 0-5V.

I'd not want to add to the sufficient heat already in that block. An aftermarket oil cooler would be my choice.

 

The plenum on the Jag V12 is too small, increasing its size to 100x100mm improves throttle response. Shortening the runners will move the torque up the RPM band. The problem with the stock intake manifold is the runners are too big for the stock 5.3L RPM band, which is why the same manifolds on the 6.0L work much better.

Moving the TB's to the front improves the air distribution to each runner, because the TB's are not pointed to the centre runners. Another thing while the manifold is apart work can be done to make each runner equal in volume. And a small bell mouth to move the entrance away from the plenum wall, air will move slowest at the wall.

This is a pre-HE and made 500hp @ 7500rpm out of 6.0L

 

I think a big problem with the V12 was it hampered by the 3 speed automatic. Since the OP has indicated he intends to run a 5 speed manual I'd be tempted to use the engine as is and see if that's good enough.

Take a look at what the 1993-97 XJ12 cars used, they had forward mounted air filters, but kept the throttle bodies where they are.

Full throttle switch is right by the "turntable" for the throttle rods, it's activated by the throttle cable.

 

This should tell you lots about the EFI system: http://www.jagrepair.com/images/Elec...ance%20S58.pdf

 

Was mainly posting because of the simplified fuel rail and throttle linkage relocation. Looks sexy side draft TB's or not!

My experience has been the same with short runner intakes. Tapering the plenum is common on turbo inline 4 and 6 engines to get proper flow to the rear cylinders although I wonder if it's all that important on an N/A application.

Hah, yes that would be a good thing wouldn't it? I'm in the Charlotte area as well.

Good lord those intakes are giant. I am 100% okay with having a more rev happy motor with the power band shifted up. The 5 speed and 3.73 rear will really help move things along I'm hoping too.


300hp/300tq with short gearing should be plenty. The car will weigh about 1000 pounds less than the xjs too. The main priority for me here is dressing down the motor while still having good drive-ability.

Thanks for this, you have no idea how much this helps.

I was able to remove the engine harness, ECU etc yesterday. I've never seen a 20 foot engine harness!

 

There has been a great deal written about the OEM oil cooling on the V12. There are two types of OEM systems: 1) Bypass flow and 2) Full flow. Bypass flow was fitted until about 1987 when full flow oil cooling became the norm. The difference is that Bypass flow cools some of the oil pump output, while full flow moves it all through the oil cooler. People have theorised that the bypass system does not do much and does not cool the oil much.


I have the bypass system on my car, and I have measured oil temperatures at various points in the engine, summer fast road use being the norm for the test. I have proved that the bypass system cools the oil very effectively, there being about a 20 C drop across the cooler. Also I have measured that oil temps on my car do not exceed 85C, and that this temp is everywhere the same apart from the oil cooler return pipe. So sump, filter, oil distribution block in the V, oil cooler intake are all at 85C max temps. I run 5W 30 or 40 fully synthetic Shell helix.


The original engine designer's technical paper about the V12 indicated that the oil is responsible for about 30% of engine cooling. So my view is that oil cooling is very important for the V12, and it would be risky to get rid of it.
Good luck with the project, really interesting.
Greg

 

Indeed, that is what is basically the common norm. Such "massive" engines produce an AWFUL lot of heat as a byproduct of the internal combustion. Watercooled engines do manage to cope with heat well but the oil is still mostly the hotest fluid in the car...

Even aircooled VW boxers had oilcoolers...

 

Don't forget the vacuum line too, that's how the ECU senses load.

 

Great to know Greg. Thanks for your input. I had read conflicting information on this. It's not like it's expensive or time consuming to retrofit an aftermarket cooler on there with new stainless lines so I will definitely go ahead with that.


Got it, and the vacuum pulse regulator? that goes in line before the ecu.

 

Yes, that plastic piece is a pulsation dampener. Smooths out the signal to the ECU.