Idle vac varies from engine to engine in teh same brand, model.

Your figure is a tad low, but I reckon a degree or 2 of timing advance will lift that significantly.

Any engine that has little use, as most V12's are sadly, that vac figure you have is normal.

A D Jetronic engine with a vac leak would run like a dog, simple.

Lift that timing,as I mentioned, and see what happens. The PreHE can run some serious advance with NO issues.

The cam chain stretch is also something to check when and if you really want to venture inside that engine. Definately NOT for the feint hearted.

 

Thanks Grant....that makes me feel a lot better. I had not heard before that the pre-HE is OK with additional advance. I might play around with that this weekend.

 

Vacum. One of my favorite words and the concept it represents. so very useful, and yet not understood by many.


As to the matter at hand, I would be more concerned as to whether the needle on the guage is steady or swings wildly A bit of a wiggle is normal. Values are another issiue or even a non issue.


Carl

 

 

This I wrote for the HE, but it the same for ANY engine, in ANY market.

Trimming the timing on a running V12.pdf

Have fun.

 

 

Thanks again Grant....reporting back after playing with the timing. I advanced the timing quite a bit but did not have the courage to take it up to where I could hear pinging as you suggest in the writeup. Worried with the V12's small cylinders and all the air noise at speed that I might miss it. Anyway...vacuum has increased to 16 in HG at idle and it runs much better.I was having dead spots in the acceleration at light load and part throttle and the occasional intake "pop". It seems to be running great and the engine feels very lively. I really appreciate you sharing your experience.
John

 

John,

Well done.

Always fun going outside the box.

That "pinging" is more a HE thing, with their 12.5:1 comp ratio, things are really on the edge.

The PreHE is 9:1 and you can really wind that timing up, but it will soon become apparent when you are too far, as it runs roughish.

If you are happy with what you have, again, well done, now drive it like you stole it, and it will settle even more. Our PreHE gets pounded, and survived 2 teenagers learning to drive in "Him", and now at nearly 600K kms, still thunders at the red line with no complaints.