It is my understanding that this engine's static timing should be set to 10 degrees BTDC, in order to get the engine started after a major overhaul.

I would like to know what the "total advance" should be, using a dial-back timing light at about 3,000 RPM, where the distributor's mechanical advance reaches its maximum.

For example, I set this dynamic timing on my MGA as follows: Start with 10 degree BTDC at about 500RPM (before the mechanical timing advance becomes active). Then, disconnect the vacuum line to the distributor, rev the engine to 3,000 RPM and set the timing to 32 degrees BTDC.

I appreciate receiving your input.

Hans

 

Hans

See Attached curves
40617A distributor OEM for XKE` 4.2?

"Jaguar used the advance unit in the Series 1 XKE 3.8 and 4.2 models. Due to the differences in the two engines, the advance rates of the distributors and vacuum units were different. If you are not sure which you have, check the parts manual for the part number of the distributor. As a rough guide, the 3.8 distributor has a mechanical advance of 13 degrees which translates to 26 crankshaft degrees. Add initial timing of 10 degrees and you get a total of 36.
The 4.2 uses an 11 degree mechanical advance curve for a total of 32 degrees using initial timing of 10. The difference is because the 3.8 cylinders match the chambers in the head."

XKE appears to be 32-33 degree at 3000 RPM Vacuum capped off. Probably based on 98 octane fuel... so 31-32 degrees if you have low 90's fuel octane as only option.
Rgds
David

 

Hi David
Many thanks for your reply and the detailed information. This makes all sense to me. But I wanted some confirmation first. You know, after screening all posts which have to do with the Jag's ignition timing, I was slightly surprised that all other threads inquire and respond only to the basic, static timing, whether it is 0 or 5 or 10 BTDC. It is my understanding that this is good to get the engine started, especially after a rebuild. However, it is not optimal without knowing and addressing the dynamic timing especially with the vacuum off and at the point the mechanical timing-advance has reached its maximum, i.e. around 3,00 - 3,500 RPM.

Because I spent about 3.5 years restoring my '56 MGA, I received countless hints and advices from the forum members on MGexp.com. However, most beneficial was Barney *******, the "MGA-Guru" (MGAguru.com), an automotive engineer who spent the past 40-50 years dissecting the MGA from the front to the back, writing thousands of technical reports and providing countless advices for greenhorns like me. Thus, I quickly scrolled through his library regarding dynamic timing advice and found some real good information. I think you would enjoy reading it, so I attached a copy.

I think something like that would be appreciated by many Jag owners to further optimize the engine performance. What do you think? I am certainly not the ideal person to draft such a threat since English isn't my mother tongue ( I am Swiss).

Thank you again, David, for your prompt and exact response. Have a nice weekend,

Regards, Hans

 

Hans,
I did the research for retrofitting a Distributor from a late XJ6 to a mid 60's 3.8S (also had a 68 XKE)... The Jag. shop that I use, when a lift is needed, sets the timing of a XJ6 at 3000 rpm 33 degrees... They don't need to remove vacuum hose and plug as at 3000 RPM there is no vacuum advance, also this covers weak springs, worn posts etc. in an older distributor. They adjust idle with a CO machine (sensor in tailpipe), then set Idle RPM and they are done.
So on the 3.8S, I did the research to get right timing at 3000 and let idle fall where ever. Took everything back to pre-smog numbers then dialed in tuning. Many talk about advancing 2 degrees at a time with a test drive, to you get pinging, then back of a degree or two. I am more inclined to do the research and select the critical function to be right.
Thank you for doc, I have added it to my Library.
Rgds
David