Adventures with a Holley pt II

Now as I said there are only a relatively few cams available from Holley. They are all identified by colour and to me at least follow no specific trend. Is suspect they are the result of tuners playing around to find things that work. In actual fact the cams should be relatively easy to classify (and in fact there are a load of graphs online that show cam deflection as a function of throttle shaft rotation (see below).

As you can see some cams will clearly deliver less fuel than others while some deliver more fuel at small shaft rotations and others provide a more even delivery until the throttle is fully open. However, a note of caution in analysing these curves. The cams can be mounted using 1, 2, or even 3 different holes meaning that the start point will be different for different mountings. None of the graphs take this into account. This is probably because it is also possible to bend the arm that runs on the cam transferring the cam shape into fuel delivery. The cam fitted to the Moss setup was the black one which gives a pretty large total delivery. 

The data from the AFR showed that the engine was particularly weak at throttle opening from low speed (meaning that he throttle was being opened from almost closed). Immediate thought was that I needed more deliver at low throttle spindle rotation. Looking at the cam curves there seemed to be nothing that gave this although both blue and red were a little better. However substituting these made only small improvements. Then one of the other supercharged TR6 guys (thanks John) suggested turning the black cam around.. this means using the part of the cam that is not intended to be for metering the fuel pulse. However a close look at this part of the cam showed that the shape actually meant a large slug of fuel at low throttle opening.. (see data below. NB with 0.044" acelerator jet fitted) the bogging was reduced and the backfiring almost disappeared..

But it was still not good enough... I added the 0.050" acellerator jet and things improved further.

Looking again at the cam choice I realised that increasing the pump capacity to the larger pump would be the next step.. so I bought a larger pump kit.. Went to fit it and found that the carb already had it fitted... damn... money wasted! 

This was also interesting because this pump is not designed for use with the black cam, instead it has its own cams, brown and yellow... So I substituted the brown cam for the black one and things got even better.. Now only small hesitation when provoked (e.g. Punching the throttle from <1500 revs in 4th gear) and backfiring only occurred when warming up from REALLY cold weather.. job done I thought..