1600HF Rubber gasket carburettor

[lancialulu]

Ralph

I know it is the carbs as I have swopped them onto my HF which runs 42s and has no problem in top normally but with the 35's has this curious strangling at 5000-5500. My HF has a redtop elctric pump and regulator as well so not fuel delivery problem (the 35's are intrinsically more fuel efficient anyway).

Tim

[Ed Levin]

Tim,

Frankly, it's not really a surprise that the 35s seem to run out of steam at 5000-5500. With 30mm venturis on a 1600, you should expect a power peak at only around 5500. To push the power peak to 6000, you'll need 32mm venturis, and to push the power peak to about 7000 requires 36mm venturis.

In other words, if it seems like it's strangling at around 5500, it's because it really is strangling at around 5500; the venturis simply aren't passing enough air to feed the engine at higher revs.

[lancialulu]

we agree!

[Lancia-hf]

regarding the sale of the white coupé with the campagnolo's. Last year on the Imola autojumble I saw the same wheels, refurbished Italian style (very very very thick coat of paint to diguise all the corrosion and cracks) being offered for 3000euro's. And sold for the same amount. So the car was only 3500. bargain!

[Peter de Wit]

Reading this with interest. I had an engine with top bhp at 7200revs. 45 carbs with relative SMALL venturi's. One piece inlet manifold. Internals could cope with more revs, but it just did not want to go beyond. This was an engine with uprated valve springs. At that time I also had another engine with similar spec but with OLD valve springs. That one never wanted to rev beyond 6200 or something. Massive torque, but just did not want to rev beyond it. Never figured out what restricted it so much. Could not have been the carbs. Inlet manifold was very nice one piece piece. Ports nicely matched, but std size. Also std size valves. My expectation is the valve train is a limiting factor as well. Together with the internal port diameters that were mentioned. I am at the verge of building a new stage rally engine. Still not sure what to aim for. An 8000rev 1600 doesn't seem to happen that easily.

I would opt for an affordable 135bhp engine as Tim has. I am sure a 1016 didn't produce it back then!

[Ed Levin]

It depends on how small those “small” venturis were, but it sounds as though your limiting factor was either the venturis or the jetting. Based on your max bhp at 7200, it sounds as though you were running 36mm (or maybe 34mm) venturis, High rpms require a high volume or air moving through the carbs, and the principal limiting factor for air volume is the venturi diameter. But too wide a venturi will cause the air flow to stall at lower velocities, which can kill torque and throttle response at lower revs. And, of course, a high volume or air needs to have enough fuel in the mixture, so it’s always possible that the venturis were large enough but the jetting was limiting you.

The other factors could be the length of the intake runners and the length of the intake trumpets. Very roughly speaking, the longer the total length of the intake track, the greater the torque but the lower the maximum rpms.

That said, if you’re building a stage rally engine, I’m not sure that you need or want an engine with very large venturis to support very high revs. I would suggest that throttle response and torque are more important characteristics on a rally stage than 8,000 rpm capability. So I’d be careful in sizing the venturis and tuning the set-up to balance the desire for greater power and higher revs with the real need to maintain sharp throttle response and good torque at mid-range revs.

[lancialulu]

Good torque band always wins corners according to most racing drivers!

Tim

[Peter de Wit]

Agree with both! Venturi's were 36mm. AFR was around 12 all the way up. Air correction jet seemed OK for high revs. So there was enough fuel. But I am sure if you put this size carbs on a stock engine, you will never get it above 6500 either. I wrote my part to introduce limitations in valve train as and additional problem we have.

As for torque, I took the Carlo Abarth route: VERY large inlet length with large bore carbs still give torque. Seems to work. And the secret for high revving engines is in the gearbox. A route I am not going to take again for budget reasons. But the CR gears do work!! Just make sure the synchro on first works since you need that for acute corners.

Having said the above. I would opt for the 135bhp engine Tim describes. Who sells the Holbay cams? Will keep informed.

[lancialulu]

Holbay was bought by a manager (name??) and still trades on under Colteracing

Try http://www.coltecracing.com/

I know the guy still has all the profiles!

Tim

[lancialulu]

The cams I have are T12V's or Tornado ref 147RH

Cam lift 6.63mm
Inlet 38/70
Exhaust 76/32

Hope this helps

Tim