No idea Ron.

 

Hi Daim.
Thanks for the answer, but everything is new.
I don´t know, if my questions are for this thread, or for new thread, but are about compression and US/UK difference.
Yes I have UK engine with US specs. It is good message.
But somewhere in my head I still have the following questions.
Has a different compression ratio (and other US-ECU for UK engine with O2 sensors), effect on:
- fuel batch for injectors ?
- ignition timing (is really 18°BTDC ?)
- must I adapt US ECU with potentiometr for UK engine ?
- my car (EFI Lucas) work in P or N in open loop mode. I think ?
- can I switch US ECU DAC4585 with UK ECU with O2 sensors ? Is the pin assigment the same ? It make sense ?


Uff. Thanks for the answers.

 

Roman
I am assuming you want the car as simple and reliable as possible, and that you would prefer a UK spec system. If this is true, then:
If you do not need to have the O2 sensors, best idea is to get rid of them and fit a UK spec ECU that was for cars that did not have them; ie a 16CU version of the ECU for Lucas cars up to 1987. Loads on Ebay, or Roger Bywater from AJ6 Engineering will convert yours. Then all the open loop stuff etc etc disappears. Also remove all the air pump stuff, if your car has it.
I have recently helped a friend do this exact change and the car went really well. If you can afford it, buy the AJ6 enhanced ECU and large throttle bodies too. It transforms the car.

 

question; what was the comp, ratio of the early V12 around 1970/1971, in E type cars?

 

In Europe, 9:1, in North America 7.8:1.

 

.

jagboi; that is not completely true, there were some engines (probably UK only), that had over 10-1 comp. ratios, !

pic drawing from Jaguar of some info about pistons, .

notice piston with tight piston to head and large valve reliefs.

little known fact , is for the Pre-HE head , resurfacing deck face .050 thou. brings the effective ratio up about 2/3 tenths higher, best i can figure is my engine with 9-1 Euro pistons is around 9.2-1 now!

 

Not in the E Type Ron, as far as I know. There were a very few late XJS pre HEs that had a 10:I CR engine and a different, but not HE injection, called the P Digital. These made more torque and more power than the normal pre HEs and were sold in 1980 before the HE was launched. I have a feeling that page you uploaded is from Walter Hassan's most interesting booklet describing the V12 design and development process that led to the finalised production engine as first used in the E type and the XJ Saloons. For anyone's info, the Hassan booklet turns up on ebay regularly and is well worth buying.
https://www.ebay.co.uk/itm/Jaguar-V1...sAAOSwCkZZWhTj

 

Didn't the first year V12 E-types have high compression for all markets?

Just wondering.

Cheers
DD

 

Doug
If you look at the second page of Ron's photo of the Hassan book, he actually says the engine was developed on 10.6:1 CR and then subsequently the CR was reduced to 10:1 which was fine on 99 octane RON; then it was reduced further to accommodate much lower octane fuel, presumably for the USA market, as 99 was available everywhere at that time in the UK and Europe. It is not clear from his text whether these changes were made during development or after the engine was in a production car. So I googled the question and found Roger Bywater definitively saying the E type V12 was launched at a CR of 9:1 in 1971, with a lower CR for US and Canada.
Greg

 

it is quite possible that some early proto types may have had the experimental hi pistons.

UK only. if only i could find a good set of the pistons with the valve cutouts??

Nahh, may as well have custom pistons made , forged aluminum lighter weight, comp. ratio of my choice,, better ring selection(reduced frictional drag), thermal coating on crown , low drag skirt coating.
coatings to keep combustion temps, away from the cooling jackets, i dont want to end up with a small steam boiler!!

 

Hi Greg.
Thank for the answer. The assumption is correct. I just needed a little thrust down the hill
I still had in my head that the US Hess&Eisenhardt version will have value over time. But when and if, right? I'm 55 and I want to ride, not wait for money So I'm going into it.
Only one bad thing. My car is in "registration certificate" marked as Euro 1 car with catalysators. I must find the way change this to non-cat, or buy (AJ6) ECU for Europe with catalysators (I think, that is emission type G for Germany). Or was in UK ECU (Lucas ignition) with cats ? Workshop say, that UK version was without cats, type B. But ...
All other things are clear. Large throttle bodies will be good.
I have a little work to do in the spring

 

The workshop is correct, the UK was without cats until about 1993 or so. I'm pretty sure the ECU wiring was different between catalyist and non catalyist, so you'll have to match what wiring is in your car.

Looking back at your original question, you would need a USA market ECU to correctly run everything. Your fuel economy does seem bad, I would expect motorway economy ( say max speed 110 km/h) to be in the 12-13 L/100km range. When you are using as much fuel as that look at the vacuum advance mechanism to the distributor, it may not be getting proper vacuum. The dump valve can be a suspect. It's complex, make sure everything was hooked correctly when the engine was switched.

See a description here: http://www.jagweb.com/aj6eng/vacuum.php

 

Talk to Roger Bywater, he will be able to adjust your current ECU to what is required, no problem.

 

How do I identify this motor. I'm buying a 1980 xj12 first registered 6-6-1980. So there is a chance.
I haven't found anywhere online that specifies an engine code suffix etc.

Anyone?

 

The answer might be found here...with a bit of digging. Or contact Bywater directly

WELCOME TO AJ6 ENGINEERING / AJ6 Engineering

When you find out, let us know!

Cheers
DD

 

SOHC V-12 Engines

7Sxxxxx 5.3 Liter E-type
7P1001 5.3 Liter XJ12/Daimler Double SIx Series 1 w/carburetters
7P4000 5.3 Liter XJ12 & D6 Series 2 w/carburetters
7P25001 5.3 Liter XJ12 & D6 Series 2 w/fuel injection
7P42300 5.3 Liter XJ12 Series 3 Pre-HE (suffix ? = 9:1, suffix HA = 10:1)
7P45001 5.3 Liter XJ12 Series 3 HE
8S1001 5.3 Liter XJS non-H.E.
8S18001 5.3 Liter XJS H.E.

 

What would be the hp difference of the pre he American compression ratio to the higher euro spec compression? Would it be worth switching to higher comp pistons?

also what about the gutted or no cats? How much hp do you think you gain there?

 

From memory, the pre-HE high comp engines were rated at 272 SAE net HP and the low-comp versions with cats rated at 244 SAE Net HP. How accurate were the "advertised horsepower" ratings? That's a question for the ages. But, the above seems plausible.

Personally I don't think cat converters, providing they're not clogged, make as much of a difference as some would like to believe. More than a few have reported no 'seat of the pants' difference after gutting or removing them. A very unofficial and broad rule-of-thumb is that a 20 HP increase should be easily detectable by the driver. So my guess would be a 5-10 horsepower increase without cats.

Cheers
DD

 

Don't take this to the bank but it appears that 7P42300 is the beginning of "Lucas EFI" (as opposed to Bosch D Jetronic) but retained the older Lucas OPUS ignition (as opposed to Lucas CEI). The "HA" variant being the 10:1 hot rod engine

A bit less detail in the engine numbers here.

But if you have a pre-HE with the later EFI and the older ignition, and a build date from mid 1980 to early 1981, you might have the hit rod engine. I wonder if the "HA" suffix applies to the XJS as well?

Cheers
DD

 

The very earliest XKE’s, recognized by the Jaguar cast into the valve covers instead of the decal had 9.0-1 compression sent here to America.
About when the decal went on compression dropped back to 7.8-1