The Triumph Dolomite Club - Discussion Forum

The Number One Club for owners of Triumph's range of small saloons from the 1960s and 1970s.
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PostPosted: Wed Apr 27, 2016 1:56 pm 
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Joined: Sun Mar 16, 2008 2:52 pm
Posts: 1870
Hello Track-day / rally guys. I've been doing some dynamic measurements on Lucas coils / ignition systems for another thread, and I have found a problem. Now I can understand why modern cars use ignition coils mounted on the spark plugs, but what do you use for 6,000 rpm 4 cylinder engines ?
Am I right in saying this is 200 sparks / second at the coil output ?
Thanks ,

PostPosted: Wed Apr 27, 2016 6:54 pm 
TDC Shropshire Area Organiser

Joined: Sun Aug 21, 2011 4:12 pm
Posts: 4407
Location: Highley, Shropshire
The Carledo revs to 6800rpm before the rev limiter cuts in. The engine has a distributor cap, rotor arm, plug leads and a single coil.
Triggering is by a toothed wheel inside the crankcase and timing controlled by ECU, but you are only interested in the coil right?
That is a standard Cavalier/Astra/Carlton coil, one of those funny shaped aircooled ones so beloved of GM. Even where mine is mounted on the bulkhead above the exhaust and below the fan motor I have had no problems at all. I've got several spare ones about the place, I'll clean one up and see if there is any writing on it to say what it is and what it does!
My maths says 200 sparks/second at 6k too - so we're both right or both wrong!


2 door '73 Toledo with Vauxhall Carlton engine OWF 797M (The Carledo)
Vermillion (and Rust) Sprint Auto EGP 247T (The Dolomega)
'91 Cavalier 2ltr 8v auto
'95 Cavalier 2ltr 16v auto
Spectrum Auto Services, Servicing, Repairs, MOT prep. Apprentice served Triumph Specialist for 40 years and home of Maverick Triumph.PM for more info or quotes.

PostPosted: Thu Apr 28, 2016 12:35 am 
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Joined: Fri Oct 06, 2006 8:57 am
Posts: 500
Location: Auckland, New Zealand
Interesting topic. I keep the rev limiter around 7400 but actual change points based on dyno curves are 6600 from gear to overdrive and then to gear, or 7200 gear to gear (1-2 or 2-3).

Apart from magnetronic sitting in the distributor and mechanical advance filed to go to 32 degrees (10ish at tickover), my system is basically standard using a ballast resistor coil. I can't tell the difference between a very old original or new Bosch, both appear to perform equally well. I've stopped using the in-loom resistor wire and now go straight from the fuse box to a separate resistor bolted to the offside suspension turret, then to coil. Standard cap or top entry 'Mini' version, rotor, leads feeding NGK BP7EFS plugs with 33 thou gap. Currently back on a very old original cap as the last Bosch one I bought came with a broken centre contact that caused high end misfire and starting difficulties.

The wire from the coil that feeds the standard rev counter now feeds the auxillary rev counter, strobe type change light and the rev limiter.

Dyno curves didn't show any unexpected drop off that might indicate lack of spark at high revs. I run 45 Dellortos but suspect the dyno curve would improve at top end if I could be bothered to change to 48s (if I could ever find any).

I can't change much of the ignition as I need to stick within the classic rules I race under, but interested in any ideas as to how I might improve the basic system (ie no ECU etc).


PS - my maths are also the same

PostPosted: Fri May 06, 2016 6:35 pm 
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Joined: Tue Jun 28, 2011 5:01 pm
Posts: 2130
Location: Dorset
I use a 40thou gap on BP6EFS plugs but might go to 7s.
DLB105 coil, magnecor leads, ambassador cap, magnetronic ignition.

Dan Brown


CA18DET Turbo Sprint - 280hp
Toledo Race Car

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