Hi all,

Am planning on doing a rolling road session in the near future, but in the interim am interested in peoples thoughts on ignition requirements changes when moving from a "normal" distributor to a megajolt system.

This post is a combination of what i've been doing as well as a few questions of the ausmini brains trust.......


Q1. - Any suggestions for how much LESS advance I would expect to run with a high power megajolt setup with 40thou plug gaps vs a standard distributor setup ?
Q2. - Does the current total advance of 37 degrees BTDC (Wide open throttle with no vacuum of course) seem crazy for a traditional distributor setup on a 998?



(basic specs of car:
-9.1 compression ratio
-98 octane fuel used (i hope)
-270 camshaft
-extractors and 1 3/4 single su with trumpet and unifilter sock aircleaner
-1100 head with worked chambers but standard ports
-lightened flywheel
-cooper s gear ratios and standard diff ratio for a 1967 morris mini deluxe.
- re-curved ignition developments bosch distributor
- was dyno-tuned with distributor 20 years ago!!
)

I did some analysis on my old Ignition Developments distributor that i have been running on the car for 20 years now.
These are the results.
- 7 degrees static / base timing,
- 30 degrees mechanical advance,
- 12 degrees vacuum advance.

Distributor system ignition curve looks like follows:

- Idle/ static: 7 degrees BTDC
- 1000rpm : 7 degrees BTDC
- 1300rpm : 12
- 1500rpm : 15
- 2000rpm : 19
- 2500rpm : 22
- 3000rpm : 27
- 3500rpm : 32
- 4000rpm : 35
- 42000pm : 37
Total advance: 37

Doesn't appear to have an issue with pinging at all with distributor setup as it is.. Have always been very pleased with how this "ignition developments" distributor worked.


Findings so far ....

Car ran well on the distributor system (other than it never idled and was sometimes hard to start - but that's probably more an issue with the 1 3/4 su and camshaft combo than anything else)

Have tried the "safe" megajolt maps and some of the "123dizzy" maps for "tuned 998 engines" (30 degree max total advance). Found that these megajolt maps had their ignition advance comes in a lot later in the rev range and there are some massive flatspots at around 3000rpm after a gear change...

I see the following advantages of the megajolt system so far;
- far easier cold starting
- much less ignition / points scatter at high revs (didn't realize how bad the dizzy was until i put the scope on it!)
- improved economy - as the vacuum advance changes are almost instant unlike a mechanical vacuum advance system and can change multiple times per second.


Setup so far on megajolt

I've been tweaking the megajolt curves to provide something close to my existing system and it's been an improvement on the generic "Safe" curves or "123 dizzy" maps for tuned 998 engines. But still not quite right yet.

I've dialed back by 1 to 2 degrees at all points indicated above (except at idle where i'm running 10 degrees) and at 4,200 upwards, running a total advance of only 34 degrees rather than 37.

My vacuum advance is coming in at 5 inches HG and fully deployed to up to 14 degress of vac advance at 10 inches Hg.

No indication of pinging (as far as i can tell).....


Q3. What are peoples view on ported vacuum vs. Manifold vacuum?

To my mind the manifold vacuum is the way to go for a megajolt system. Must say it's kind of weird to see 22 degrees advance at idle.. however that quickly drops to 10 as soon as i crack the throttle. So all good.


If anybody's interested I shall post up results after a session on the rolling road....

yep

_________________
did I tell you that I won a trophy?

yes, manifold vacuum is the one to use.

and i see around 20° with vacuum connected at idle, too. with a regular dizzy and factory 998ccm engine from the 1990s. no problem at all. if you worry you can write a map with 10° at the points where it idles.

i found that no map ever met my needs. ever played with it. normally the looked like modern ignition maps after that but give good power when needed and very good economy crusing our autobahn. so very worth the effort

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Rover 214 atm ....

Thanks KLAS, nice to confirm somebody else is using the manifold vacuum with their mini.

I'm happy to run the vacuum at idle too.

As i have read elsewhere it provides when idling, less heat, more efficient idling, smoother idle as at idle whilst NOT under load the mix is lean and thus more advance in the ignition is required.