Your opinion about induction and ignition

Hello, I am new on this forum and also new with Jaguar V12 engines. I have done a lot of research about this topic, but i have hard time deciding which route to take. I have 89 XJ-S that has been sitting since 2010, my plan is to take out the engine and go trough it with new seals and gaskets or any issues that i find with it. Since all the rubber and hoses need replacing i can’t decide what to do with fuel and spark. I am certaint that i dont want to use factory ecu, distributor. Also i kinda want to do custom wiring like painless kit or something similar. I want to erase cruise and AC and other unneccesary items for me.

  1. Go with Weber carburetors, dream come true, they sound and look cool. Probably the cheapest option, i can get manifolds and find 40IDFs preowned from ebay and rebuild them. Then comes to issue with spark, how to go distributorless? Can you tune Webers on jaguar V12 to pass smog?

  2. Megasquirt, rebuild factory fuel rails and injectors, go distributorless, not that expensive on first sight. The thing is i have no experience with standalone ECUs, how to set them up and i imagine its going to be costly to get them tuned.

  3. Buy complete fuel injection solution like Mobek is selling, pricey but works from the box. Only downside is that you got to cough up a lot of dough in a single purchase and you get to have no fun building it yourself.

What would you do in my situation?

Welcome to the best Jag community on planet Earth!

Well, in my situation–one that involves decades of self-induced ‘fun’–I’d unreservedly head for #3.

It would help to know where on the planet you are.

EU, Estonia, everything is expensive to ship from anywhere with taxes and postage. Im leaning more towards Webers. Im a carburetor guy, have had luck with dcoe webers on volvos and dgev webers on old subaru ea boxer engines.
I think this route will let the enginw breathe better as well (getting large throttle bodies for injection will also add up monet).

If you’re already planning to fit a distributorless digital ignition (a big step forward), it seems like a really strange idea to fit carbs (a massive step backwards). Given the engine is already fuel-injected, why not just improve on what is there?


Webers on an XJS is a major retrograde step.

Megasquirt has been used very rarely and you will have trouble finding people to help you.

Mobeck is expensive, but perhaps ideal aftermarket because Mr Mobeck can answer questions. You seem to have questions.

I would do the seals and gaskets and hoses as you describe and get it running as-is before attempting to address shortcomings real or imagined. You are proposing to change too much stuff at once which is a recipe for never getting it going. Replace one system at a time, if you find your suspicions about stock ECU/ignition to be correct.


Thank you everyone for feedback!
I got no experience with the stock car myself, but so far the research ive done shows that after all these years stock systems can be really unreliable, wiring that has been eaten by mice or heat cracked, overly complicated cooling or heating systems, idle valve, you name it. I would like to tackle these issues head on and improve on them before rebuilding stock stuff. Also i feel like the car is bit sleepy as stock for my taste, i want to fab better exhaust system, taller rear gearing, so why not make it breathe a little better to suit other supporting mods.

Plenty of people have already gone this route and you can simply copy their work. Just search on this list and you’ll see plenty of posts by myself or Philip Lochner.

Weber is indeed a retrograde step. Not only will fuel economy be worse, but it will be harder to tune. The Megasquirt is self tuning.

kind regards

1 Like

Plenty is you two, and nobody has published ‘The Book” like Kirby Palm has on the standard system. Everyone has some completely different variation too. It’s a research project, compared with Mobek.


Please don’t troll - just give Alvar your experiences of aftermarket induction and ignition systems, rather than denigrate others’ successful efforts.

kind regards


My experience is that there is insufficient information and helpful advice for the amateur to even remotely consider megasquirt. It is exponentially more of a project than mobek or stock. This is after reviewing all information and posts available over the years when considering this for a 1992 with bad ECU. It wasn’t going to be cheap either.

If cheap is a primary criteria I think nothing beats getting it running as per original.


Oddly enough Webers seem to be rare on these engines and most of you are suggesting its a downgrade. I am a young male and i enjoy snappy throttle response and high revs, not looking to save gas or take my jag on a peaceful sunday stroll, but i do need to pass smog in order to drive around legally.
Mobek has put together an amazing system with quality parts, its just the price for me is like a 5 month salary in my country and i would prefer to buy some of this now, some of this later, so buying megasquirt parts once in a month would probably suit me better.
Also so far from the feedback you guys have been giving me, seems like stock system is not that bad either. I guess its not bad for keeping it stock, but what happens when the mods start coming in?

You’ll play hell doing so with carbs, and much less hell with decent EFI.

1 Like

As I understand what others have posted about Webers on the v12, they work well mostly only at high rpm. The problem is that a v12 road car spends 95% of its time at low rpm, so Webers only really make sense for a race car.

kind regards



The stock ECU, especially the 16CU is quite reliable and I wouldn’t bother changing it. The only weak link is the ignition amplifier.
Save your money and effort, for other upgrades that can improve performance, but most important reliability… Already rebuilding a V12 is a big and expensive task.
The gearbox for example can be tweaked to make the car more sportive.
Distributor-less system, yes, go for it, technology has advanced quite a lot since then and I think it’s worth it.
Renew all injection wiring in the engine bay, yes indeed.
The Lutz mod and a single pass radiator would make for a more robust cooling system.
Full flow oil cooling.
Upgraded gaskets and banjo bolts…
Download Kirbert’s Book, the list is long.

See, and I consider the AB14 ignition amp one of the car’s best features! Common as dirt, cheap to fix.

Other than that, I agree with your assessment.

For performance, I wonder what would happen if you increased the lift of the intake valve but not the exhaust valve? Increasing the lift of the exhaust valve is supposedly problematic because it’s a weird pocketed valve and increasing the lift can cause it to perform worse rather than better. The intake is conventional, though, so boosting the lift should be beneficial. So, increase the lift of the intake valve and increase the duration of the exhaust valve.

1 Like

one of the reason for that is the limited height available for the trumpets

short trumpets are good for high rpm
longer trumpets would bring more low down torque, but wont fit under the hood

or you’ll need some serious modifications

1 Like

Oh, I bet those 12 trumpets provide some glorious music on acceleration!

Thank you for the tips!
Single pass radiator does not look like a good idea unless you make your cooling system reverse flow.
What is Lutz mod?
Who is Kirbert and where can i find his book?

by this fellow JL-er