Race Engine Forum UK

Hello all,
I'm currently building a stage 2 Fiat 2L TC for my 124 CC coupe and an ignition specialist has recommended that I consider converting the standard Bosch electronic system (block mounted distributor) to a multi-spark CDI system.
The recommended unit is manufactured by Crane and replaces the Bosch electronic control unit but runs with the standard distributor with a modified Bosch coil.
Suggested settings are 12 deg (tickover) and 36 deg (5500 rpm), 98 RON will be used.
I'm told the system will burn all of the mixture (great for emissions!)

Engine specs are;
131 2L block, 84.6mm Borgo cast pistons, 10.9:1 CR, lightened rods
Beta 2L head, std valves, blueprinted seats, ported
Twin 45 DHLA, 37mm chokes, 145 main, 170 air, no 6 emulsion tube (NB; I was lucky enough to find this matched pair brand new in Melbourne, Australia.The
supplier has another pair if anyone is interested, they have a full range of Delorto spares as well)
124 BC 1608 cams (26/66 66/26)
Std exhaust system
Production Bosch electronic ignition

The car is for road use only at this stage and i'm looking to change the cams and exhaust system soon. I want to maintain driveability with a very strong mid range torque characteristic and decent top end power (aim is 170 bhp) at around 7000-7200 rpm but I'd also like to be able to rev it out past 8000 rpm occasionally (and yes i'm aware that triple valve springs, steel flywheel and forged pistons should be used at these revs; they are on the shopping list!)
To achieve these characteristics i'm considering using GC 3A cams and i'm also getting a custom 4-2-1 header made.

My queries are as follows;
1). What sort of improvement can I expect by converting to CDI multi-spark? How will the torque and power curves change?
2). Are the 3A cams the best choice based on my engine spec and requirements (and assuming I convert to CDI)?
3). The supplier said that the system will make hotter cams 'softer' and more driveable in the low to mid range, is this accurate?
4). Can anyone recommend a CDI system? Is the Crane system a good option?

Any feedback would be appreciated.

Regards,
Trent

Is CDI a Coil on plug system?
I was using Coil on plug from VW/Audi in my 16v 2.0l engine and it was reliable and accurate. I made it on Megasquirt EFI with 36-1 trigger wheel on the crankshaft. You may also run Megasquirt only in ignition control mode if you want to use carbs. It is quite easy to set up and also the cost is reasonable.

Thanks for your thoughts

The system i'm looking at is set up the same as the production Bosch inductive system (ie. not with separate coils on plugs) but the coil is different as the rate of discharge is much higher with CDI (capacitive discharge igntion)

From looking at the specs of the various Megaquirt systems they appear to be based on an inductive ignition system - whether running in igntion control mode (carbs) or not (EFI) - however i'm no expert

Trent, hi

3As will work fine on that setup but you will certainly need to dry-build and check pistons to valve clearance because they have quite a bit more lift at TDC than standard. 38mm chokes would be more powerful than 37mm and would be my pref choice.

You could actually run a single 3A inlet with OE ex cam with 37mm chokes - we did similar on the Lotus Lada (36mm chokes in fact). Less peak power, lower cost and terrific torque curve. The best results will come from a new ex manifold - built on car by a professional, the GC 3A cam characteristics I sent separately by email will give some good layouts and you should follow them whether you use a 3A pair or a single inlet cam.

Use GC springs and you may need top hats - depends on valve tip height which is 40.5mm std (tip to platform), the 3A base circle is 1mm further away.



G