Philip Airey (Pma1010)
New member
Username: Pma1010
Post Number: 37
Registered: 7-2002
| | Posted on Thursday, November 07, 2002 - 1:17 pm: | |
I have searched through the archives but don't see a thread dealing with this topic.
Some of us I know have installed "modern" ignition systems on earlier cars. In my case I replaced the coils, distributors, microswitch et al with an Electromotive HPX from Nick S. While there are different systems available with different prices and functionality, the appeal for me was a one stop shop and Nick's reputation for support and experience (all of which has proven to be true, thanks Nick).
From time to time on other forums, the topic of ignition timing comes up - given the HPX is tunable for shape/advance with rpm (and, also for manifold vacuum with a MAP sensor).
While there is some inconsistency in the manuals, I read the stock advance curve to be 6 degrees BTDC at idle (3 ATDC with R1), progressing to 34 degrees BTDC at 5000 rpm. The timing graph then seems to advance to either 39 degrees BTDC at 6K (and then flattens) or, imputing from a combination of graphs in section L and section O, to 42 degrees at 6800 rpm before it flattens.
In general the recommendation from Nick has advocated more advance than stock on my 77 308. I can understand at some level that this could be appropriate, for example:
- car was originally set up for increasing emissions regs, particularly at idle, hence microswitch and R1, R2 points on US cars
- linear advance from rpm from the distributor versus "tunable" or at least non-linear, curves with more modern electronics
- advance solely a function of rpm in stock form versus available rpm and vacuum with HPX (and possibly other solutions).
- a probable bias to avoid detonation if a lower octance fuel had to be added etc
Having said that, I have not seen any dyno testing which would demonstrate, or at least suggest, advancing from the stock settings and if so, by how much.
Any perspectives?
Philip |