View Single Post
beepbeep beepbeep is offline
beepbeep's Avatar
Join Date: Jun 2001
Location: Sweden
Posts: 5,771
Originally posted by hobieboy
Oops - my mistake

Here's the set up - I'm using MS to control both fuel & ignition. MS directly controls 6 ignition drivers (dwell & when to fire) directly; driving 6 coils to support my twn plug set up.

MS can only support wasted spark. And I'm using Mitsubishi/Diamond coils. According to spec I got, running dwell should be ~4.0ms.

The RPM trigger is via VR sensor mounted to the crank pulley.

Hmm...I believe I smell the problem here, depending on how you set up your ignition. If understand this correctly, you use six wastespark coils to lighten 12 plugs in total.

Now you migh and might not know this, but I'll write it anyway:

When using wastefire on twin-plugged 911 engine, you don't just connect each wastespark coil to it's own cylinder and call it a day. With other words, having one wastespark coil lighten two plugs in same cylinder is bad way of doing it as those plugs are connected in series and you will have twice the resistance to fire trough. If this is the case in your setup, there is no doubt why you have ignition problems on boost.

Correct way of wiring twin-plug 6-cylinder pancake motor with 6 wastefire coils is by multiplexing the coils so each coil fires one plug on cylinder that should fire and one plug on cylinder that is in exhaust phase.

Resistance across non-pressurized plug in exhaust phase-cylinder will be low, and this way majority of spark energy will be transfered to cylinder that has mixture in it (plugs being connected in series trough the coil). So effectivly, you will be (almost) chanelling energy from two coils into one cylinder, instead of dividing energy from one coil to try to lighten two plugs in pressurized enviroment.

Now....did you or did you not multiplex the wires??

One twin-plug coil trying to lighten the mixture trough two plugs in single boosted cylinder will have helluva time to do so, regardless of dwell. You will need very big coils indeed to do so. It's much smarter just to rearrange the connections and let two coils work for one cylinder instead of having one coil just waste it's energy in non-firing cylinder.
Thank you for your time,

Last edited by beepbeep; 11-01-2006 at 01:08 AM..
Old 11-01-2006, 01:04 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #13 (permalink)