Custom dizzy rebuild
Discussion
I'm about to send my dizzy to the Distributor Doctor for him to remove the existing gubbins and to set it up with a specific specification as far as the weights, springs and thus advance characteristics are concerned.
Both the original (I think) dizzy on my car, and a nearly new replacement that I bought last year, have around only 12-14 degrees of mechanical advance, and talking to him, he said he could set it up any way I wanted, and also for a very reasonable cost.
Bearing in mind that I want to run the car on full manifold vacuum, I was thinking of asking for around 20 degrees mechanical advance and say 10 degrees of vacuum advance, setting it up at 8 degrees at 950 rpm with the vacuum disconnected, to give 18 degrees with vacuum connected, maxing out at 28-30 degrees at 4k rpm, without vacuum. Should it have more than 20 degrees and if so, how would you set it up so that there was a reasonable amount of safety from the risk of detonation?
Is this also an opportunity to get him to dial in a specific advance curve between these limits, ie sharp rise, linear rise, inverse rise etc. Is that possible or am I overreaching as far as the practical possibilities?
Both the original (I think) dizzy on my car, and a nearly new replacement that I bought last year, have around only 12-14 degrees of mechanical advance, and talking to him, he said he could set it up any way I wanted, and also for a very reasonable cost.
Bearing in mind that I want to run the car on full manifold vacuum, I was thinking of asking for around 20 degrees mechanical advance and say 10 degrees of vacuum advance, setting it up at 8 degrees at 950 rpm with the vacuum disconnected, to give 18 degrees with vacuum connected, maxing out at 28-30 degrees at 4k rpm, without vacuum. Should it have more than 20 degrees and if so, how would you set it up so that there was a reasonable amount of safety from the risk of detonation?
Is this also an opportunity to get him to dial in a specific advance curve between these limits, ie sharp rise, linear rise, inverse rise etc. Is that possible or am I overreaching as far as the practical possibilities?
Thanks, Mark, it is interesting reading.
Martin at Distributor Doctor told me that 2 degrees is often found to be added or lost when he tests the total advance of a Lucas dizzy, from the number stamped on one of the weights. As you know, an '8' stamp signifies a maximum advance of 16 degrees but in my case, I was below a few degrees below this.
He said he has charts for the standard curves, but also said there are no standard charts for TVR's, which is not a surprise, although as he often is asked by customers to build dizzys to specific instructions for race engines, he was quite happy to talk about different characteristics and options.
It would be interesting to see what sort of chart those who have mapped their own ecus have found, and to see if there is a common theme there in the way they set up the advance after their own testing.
Martin at Distributor Doctor told me that 2 degrees is often found to be added or lost when he tests the total advance of a Lucas dizzy, from the number stamped on one of the weights. As you know, an '8' stamp signifies a maximum advance of 16 degrees but in my case, I was below a few degrees below this.
He said he has charts for the standard curves, but also said there are no standard charts for TVR's, which is not a surprise, although as he often is asked by customers to build dizzys to specific instructions for race engines, he was quite happy to talk about different characteristics and options.
It would be interesting to see what sort of chart those who have mapped their own ecus have found, and to see if there is a common theme there in the way they set up the advance after their own testing.
I already measured the dizzy angles in this way and again, even though it showed an 8, this method also confirmed what the adjustable strobe was telling me, that it was only giving me about 14 degrees of movement.
To dremmel off 3mm more from the weight as you said should not be to much of a problem as you say, but where Martin charges about 40 quid to recalibrate it with different weights and springs (over the phone quote, mind), I prefer to do it that way.
To dremmel off 3mm more from the weight as you said should not be to much of a problem as you say, but where Martin charges about 40 quid to recalibrate it with different weights and springs (over the phone quote, mind), I prefer to do it that way.
Thanks Dave, that's great information, exactly what I needed. I will move ahead with 20 degrees of mechanical with an aggressive curve as described.
With 15 degrees of vacuum advance, will it still idle at around 18 degrees if set at 10, vac disconnected?
I assume that raising the idle from its ECU governed 950 rpm to the 1000 rpm you recommend, is by clamping the stepper hose and using the base idle screw while setting the dizzy. Which would mean my getting it changed in the map for it to stay at 1000 rpm afterwards, which can be done and burnt back into the eprom.
On my already running nicely car on map 2 and this improved dizzy and full manifold vacuum, I'm going to also add a wideband lambda and guage, so I can also tweak the afm a little too, and hopefully bring this old 60s v8 a little bit closer to the levels those with modern Ecus are experiencing.
I resigned myself to the fact that for this car, without the services of a local experienced ecu installer and mapper, it was not worth the risk in ripping it all out and diy fitting a new system, that might have ended up with me being not that much better off if I cocked it up.
With 15 degrees of vacuum advance, will it still idle at around 18 degrees if set at 10, vac disconnected?
I assume that raising the idle from its ECU governed 950 rpm to the 1000 rpm you recommend, is by clamping the stepper hose and using the base idle screw while setting the dizzy. Which would mean my getting it changed in the map for it to stay at 1000 rpm afterwards, which can be done and burnt back into the eprom.
On my already running nicely car on map 2 and this improved dizzy and full manifold vacuum, I'm going to also add a wideband lambda and guage, so I can also tweak the afm a little too, and hopefully bring this old 60s v8 a little bit closer to the levels those with modern Ecus are experiencing.
I resigned myself to the fact that for this car, without the services of a local experienced ecu installer and mapper, it was not worth the risk in ripping it all out and diy fitting a new system, that might have ended up with me being not that much better off if I cocked it up.
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