Where did my engine come from
 

Just purchased a 1960 MK2. Vin 125457DN, which translates to a 2.4 with OD. The car now has a 3.8L with engine number LA7877-9 (or could be and 8). From some research it seems it is a later 3.8 but anyway of knowing what car it came out of, like year, was it a MK2 or could it have been from an XK?

My car still has the 50:11 rear end and as far as I can tell the original Moss gearbox, but cannot see the number yet. We have not driven it year as just took delivery and doing all the safety checks.

Will post more info as we get familiar with the car.

Thanks

jjsandsms

It could also have come out of an S-type, a saloon based on the Mark 2, but with a revised back end and with independent rear suspension. Unlikely to have come from an XK, though, as so few of these were made with a 3.8.

https://www.jag-lovers.org/xk-lovers...y/engines.html

The LA prefix indicates a 3.8 Mk2 from the first years of production. The list made by Bernard Viart in the link above seems to be reliable. As you know, the engine number appears on the cylinder head (on the older cars) and the side of the block. One of them might show the final number more clearly. It's interesting as it indicates the compression ratio. 9:1 is not so common, though I think that, at one stage, several were exported to the US.

​​​​​​Welcome to the world of the Mk2 and congratulations on the car!

That axle ratio might make the car lively off the line, but cruising won't be very relaxed or economical. I'd try to find a 3.77 or 3.54 either as a complete axle or diff to swap.

3.8 S Type = Axle Ratio Axle ratio 3.54:1 with non-overdrive manual and automatic gearboxes ~ 3.77:1 with overdrive. These axles will take more torque.

That 50:11 or 4.55 rear axle is correct for a 2.4 overdrive model. However, you will be disappointed with the high revs and poor fuel economy with a 3.8 motor up front.
The 3.77 axle is ideal, but these can be difficult to find. The 3.54 axles are fairly common and I would not hesitate to fit one in a 3.8 car like yours.
Be aware that you might have the 3HA axel which was fitted to early 2.4 cars. That was later changed to the 4HA axel from chassis number 103507 (on overdrive 2.4 cars).
I am not sure about the changeability of the diff centres between the 3HA and 4HA.

I think the 9:1 compression was standard on cars for Canada/USA. Both of the Canadian delivery S Types I had were 9:1 engines.

We verified that the last number is indeed a 9 on the head and it appears it matched that on the block. That said does that preclude using premium. Luckily here in FLA we have stations that ell "rec-gas" which contains no alcohol with an octane RON of 90. We use it in a couple of other older cars we have with great results.

Yes we understand the need to sometime change the rear axle ratio. Are anxious to take it for a spin but waiting as we said on a safety check(s) and the plate. With the 50:11 and the 3.8 it should be a bit of a rocket ship starting out.

Gear linkage seems vague especially finding 1st over reverse!

I am sure there will be other surprises as we get to know the car. The biggest plus thus far is it is really a rust free chassis from the CA desert. Needs paint, weather-stripping etc., but does not appear to need any rust repairs.

Will post a few pics soon after we clean it up.

Thanks
jjsandsms

The trick for a Moss box is to not attempt to go into first first (if that makes sense). Go into second, then straight up to get first. That avoids accidentally selecting reverse.

With 9 to 1 use the highest octane you can find ~ from an oilco man. High speed knock is very difficult to hear by the untrained ear & even sometimes by the trained ear.

In the US, the average of RON plus MON, also known as AKI (Anti-Knock Index) is displayed on the pumps. Many other countries display only RON (Research Octane Number)

If you're going to Bonneville, 3.77 may give you the highest speed in od top. It was standard on manual overdrive cars in the day. 3.54 was standard on non-od and automatics. Modern cars tend to have higher gearing ; the manual 4.2 series 3 XJ used a 3.31 diff in spite of its greater weight and (in European spec) gave a spirited drive. A 3.54 or even 3.31 diff would work very well on a 3.8 Mk2. Starting in first gear would be fine as it's a stump pulling ratio. And as mentioned above, first gear synchronization and location is provided by a dip towards second.

I had a 3.8 E Type with the 4 speed Moss and it had been fitted with a 2.88 axle from an XJ6. It was quite nice to drive, brought the revs way down at highway speed, but it still had plenty of performance. More importantly, it reduced the amount of heat that came into the cabin.

In my S Type I have fitted a 5 speed overdrive gearbox and the overall ratio is 2.75 (OD ratio X axle ratio) and it's happy enough going through the Canadian Rockies with that axle. The XK engine has plenty of torque.

And my 1966 Canadian-market 3.8 is also 9:1

Canadian destined cars could obviously expect the universal availability of high octane fuel.

Yes, no problem at all with availability even then (now we can get up to 93-94 octane) but at most stations 91 is the premium blend. The range is 87, 89, 91, at most stations (depending on brand) and at some, the higher octane ratings in addition.
The problem comes in paying! regular (87 octane) is now $1.79 CAD per litre....I can remember when my father would drive out of his way to save $0.03 PER (Imperial) GALLON (4.4 litres) - but that was when an Imperial gallon of regular cost $0.36....hmmm come to think of it, that was in 1966, the year my Mk 2 was built. Now that same car gulps 91 octane at a rate that allows me to see the fuel gauge needle move.

From what I recall of tests from decades ago, round about 1980, the power and economy of the XK increased more rapidly with compression ratio than most other engines of the time. I think this was for 4.2 litre versions, but I'd guess others would be similar. It is in conflict with the How to Power Tune book. But with an XK, I'd go for the highest c.r. I felt I could achieve without problems from knock and retard the ignition if forced to use low octane fuel.

Years ago in the JCNA magazine I saw an article of a fellow who had pistons custom made for his Mark IX, that were similar to the Rob Beere pistons that change the shape of the combustion chamber. I've never been able to find that article again, so I'm going by memory. Basically he changed the piston tops so instead of creating vertical swirl as the OEM pistons do, it created horizontal swirl. This drastically reduces the tendency of a hemi engine to detonate and created a single flame front propagating outward, rather than two flame fronts that the standard pistons create. It enables a higher compression ratio for a given octane rating of fuel.

The XK's problem has always been that it breathes better than it burns, thus the need for relatively more ignition advance that other types of combustion chamber.

The obvious solution is to fit a bigger fuel tank, then the gauge doesn't go down as fast!

LOL!