Race Engine Forum UK

Good Day Guy,

May I start by adding my thanks to the all the others for providing such an informative site.

I am having some difficulty in deciding on what carburetion to use on a 1600cc cvh engine. Due to the nature of the sport, we are restricted to two chokes maximum, one twin-choke, two single or split carbs. At present I have a 34 DMTR with modified chokes to 27mm. I have managed to get hold of a single 40/45 Sidedraft manifold for this engine and was wondering what your opinion would be of this alternative setup? Would it be worth me buying a single 40/45 DCOE and what calibrations would you recommend as a starting point? The engine needs to be able to pull cleanly from standstill many times during the course of an event.

The engine spec is as follows:-

Head modified by Mike Tanski
42.7mm Inlet Valves
37,1mm Exhaust Valves
10.4:1 CR
280 degree solid lifter cam 3070/70/30 with 10.9mm valve lift
maniflow exhaust manifold.


Many Thanks,
Derwyn Roberts

Interesting question Derwyn, because the last proviso 'must pull from a standstill many times..' is very relevant.

This is going to be more a function of the cams (head work and CR sounds fine) than anything. Will it pull away cleanly on any carburettor? You'll find this out quite quickly. Certainly all competition cams that I know of tend to 'take away from the bottom and add on at the top'. And they do this because they invariably rely on overlapping to generate good cylinder filling, and overlapping only works really well at high engine speeds.

So, what you'll find is that if you can keep the carb air velocity high by running small carb and small chokes it will be more tractable where you appear to want it. Sure the 40DCOE on, say, anything from 28mm to 34mm chokes (about the biggest I'd fit in 40's although 36mm are listed by Weber) will ramp up the torque overall but I doubt it will be as good from tickover. I definitely would not go 45 DCOE on that setup.

I'd like to know about the event type really. You might be better off going for a 32/36DGV (the Formula Ford crossflow carb). And you might be better off doing some back to back tests before you settle on a final spec.

Come back to me on this.

GC[/i]