I am considering relocating the alternator to the air pump bracket (removing the air injection system).
Two advantages that I can see. 1) easier access to the alternator and 2) one less drive belt dragging on the engine.
I seem recall reading about someone doing this years ago but can't find it now. Any special considerations, insights, thoughts, or recommendations?
Thanks

 

I did it a couple of years ago. I got a CS style alternator from Summit Racing. I wanted to make sure the electric fans had enough power. I had to get a new pulley. The alternator came with a 10mm pulley and it needs a 13mm, or 3/8” and 1/2” respectively. I had to put some spacers behind the alt to fill the gap on the bracket. Belt tensioner and belt are stock.
It doesn’t put out a huge amount of power at idle, but as soon as the car is moving it’s fine. I tried a smaller pulley to make it spin faster. Then it charges at idle but is really charging at speed and that seemed overkill.

 

A bigger alternator pulley would make the alternator spin slower, not faster.

An alternator only puts out as much power as is required of it, if you have 125 A alternator, and the battery and accessories, only need 40 amps, the alt will only put out 40 amps no matter how fast you turn it

Doug

 

I said bigger, I meant smaller. I'm sure there's a size that would give optimum performance, but I decided that it was good enough. I was judging the output by the gauge on the dash, rather than actually putting a meter on the battery.

 

Maybe its the Aussie in me.

BUT

I never liked that relocation.

I ditched the air injection on one of them, the other 2 "no got", found the proper Jag idler bracket/bearing assembly, as from a NO air pump car, went 115Amp Bosch, from XJ40, swapped the pulley for the 11A V belt, and left it down where it was.

I liked the extra room around that top hose etc, and thinkng about it as I scribe this, that was 1994, and I have NOT touched that thing since.

The Efans came the next week, and the extra room, just got warmer and fuzzier.

All the electrical junk, AB14, Resistor Pack, starter relay, cruise bellows, etc etc ALL moved out of the engine bay, now we're cooking.

Compact A/C Compressor, DAMN, now I can actually SEE the #1 spark plugs, and get at them easily, how good is this V12.

All that finished in 1995, and again NEVER been there again.

Do it ALL, do it RIGHT, repeat in 30 years, is what I have said, but I reckon 40 might be the case here.
Too many owners do the bit at a time method, what a waste of drinking time, really.

 

If you want to give away the air pump, then you need this:
https://www.ebay.com/itm/224317336952

If you also remove the air ramp, it is necessary to solve the blinding of the air holes at the injectors.

 

Absolutely!

If you need to repair/replace one moving item, do them all, otherwise, you just keep going back in. Esp on a car that requires moving a lot of other stuff to get to what you want.

If one item goes bad, others are shortly to follow.

If your water pump/starter/alternator/air pump/AC compressor, goes bad, do them ALL at that time. AND all new hoses.

One item rarely mentioned, people NEVER rebuild their distributors, this should be done when everything else is done. Replace bearings or bushings, vacuum can, and all that hardened grease on any mechanical moving parts like a centrifugal advance.



Doug

 

I agree, the distributor is actually very simple to work on and usually really needs at least a good cleaning and oiling.
That alone will add power/ fuel mileage.
But there is more.
If you look at the compression and timing curve of British engines compared to American engines, you will see the added power potential.
This will shock most of you. But the British premium gasoline is rated at 100 octane while American gasoline is only rated at 93 octane yet they are both the” same” just different ways of rating them.
The following is conjecture on my part. Jaguar had only a tiny handful have engineers working on the engines. I believe they made a mistake. Accordingly we got lower compression and less timing advance in our distributor. You see the difference in power ratings.
I’ve driven right hand drive Jaguars imported from England and they run fine on our gasoline even with more compression and timing advance.

 

General rule of thumb:

10* initial static advance and dizzy centrifugal advance should be full in between 2500 and 3000 RPM.

Max advance depends on the motor design, but around 35-36 degrees total is common. That is typical performance curve for a US V8 motor with wedge combustion chamber. Note that advance curve may increase your NOX emissions, if that applies to your location.

More efficient combustion chamber designs may need only 32* max advance.

Doug

 

Look at the curve on the HE distributor. That is because the HE head has so many sharp turns in the combustion chamber.
Each turn reduces power. That’s why the HE makes the same power with 11.5-1 compression ratio as the pre HE does with only 7.8-1 compression. All of the factory race motors started with a version of the PreHE head. (And high compression ) Unlike the HE when the valve opened on the PreHE air and fuel flowed straight out in a swirl into a combustion chamber in the piston. A hemispherical combustion chamber.
HE doesn’t mean High energy or anything like it. It means HELP EMISSIONS.(ok not officially). But it came out just as California was making emissions stricter. If Jaguar had lost the ability to sell in California that was more than 25% of their whole market. They would have gone broke.
The May fireball combustion chamber is similar to the early (1936 -1952) Buick Fireball combustion chamber. Designed to run extremely lean without misfiring.
The HE didn’t make the whole fuel mileage improvement itself. Actually that was a slow piece by piece improvement as development improved. The original BORG Warner transmission had a 4 % slip rate compared to the GM Turbo 400 of only 2% that happened 3/4 of 1977 in the mean time the size of the fuel injectors was decreased ( making less wasted gasoline) and the original Bosch system was replaced by the Lucas system which also improved fuel Mileage. The original 3.07-1 or 3.31-1 final drive was replaced with the 2.88-1 ratio, slowing the engine down at freeway speeds about the same time.
BECAUSE of the fuel crisis in that period sales of the XJS had dropped below 1000 in 1979. With similar results for the XJ12. So instead of marketing cleaner emissions they made a big deal of improved fuel mileage starting in 1981
yhat and steadily improving build quality greatly increased sales.

 

Part of the reason the XKE is so beloved is that polished engine when you open the bonnet.
Open the bonnet on an XJS AND ALL YOU SEE is a mess of TUBES AND WIRES AND HOSES. Topped by an antique, ugly AC compressor. Replace that with a modern compact one out of the V
Eliminate the ugly by tucking them behind or underneath. Bundle the wires into neat loams. Don’t hang them across the top of the engine because it’s a little cheaper that way. Then polish up the engine and others will recognize what a beautiful engine the V12 is.
You can even eliminate the distributor like the later 6.0 ‘s did, which really makes the engine stunning.
Forget originality for once. ( that was at a low time in Jaguars history, owned by BMHC ). Show that beautiful engine off. It’s there, just covered by cost accountants money saving attempts.

 

Funny you should mention that.

I took the XJS to local Saturday morning car get together we have every week, today. (it finally runs well enough to drive it places)

A couple people said open the hood, I've never seen a V12 motor.

I said, "I'll open the hood, but you can't see the motor because of all the mess on top of it".

I will say it is a smooth riding quiet car, and you don't feel any engine vibes.

Doug