Dizzy Advance curves ?

jp928

Well-Known Member
#1
Looking at a new dizzy for my rebuild. One from SimonBBC looks good, and affordable. Planning on a 9.35:1 CR 3.9L engine, with an SD1 front cover, so late drive gear will work. Most LR engines down here come with 8.13:1 CR, and I dont have its original dizzy anyway. I asked Simon about advance differences between different CR engines, and he just said it will work, dont worry - 35dlm8 . Do his units have any heat problems with the amplifier fitted to the dizzy body, like they did on RR in the past? Anybody with experience in th area can comment please? Hammil says a 3.9 should be good with a total advance of 34d, probably starting from a static 10d, assuming decent fuel rating.
thanks
 
#2
Will the dizzy have electronic (adjustable) advance or mechanical (springs)? Hammil is pretty good though just where the advance starts and finishes RPM wise is the real issue. Mechanical advance increases in a straight line while mapped electronic can have dips and flat parts in the line to avoid pinging etc.
 

jp928

Well-Known Member
#3
Not apparent , except they have solid state triggering instead of points. Must ask that question, but I thought my question would have elicited that detail.
 

cobraboy

Well-Known Member
#4
You also need to decide whether you are going to set up for ported or manifold vacuum, cue opening can of worms !
 

jp928

Well-Known Member
#5
Dont have car here now, but parts book indicates suffix D engines should have dizzy GEU952. The rest of the dizzy stuff is very confusing - lucas numbers without any idea which CR engine they suit. Anybody know what advance a GEU952 applies?
 
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roverp480

Active Member
#8
The Unipart numbers are a pain in the neck. They were never used by production and make tracking changes very complicated especially when comparing with subsequent Land Rover items as LR reverted to the old Rover numbers or changed them to new LR ones.
 

jp928

Well-Known Member
#9
Picked up a 10.5:1 dizzy, looked up the number and its advance curve. Since the advance specs rartely seem to use the same rpm points I found it easier to see whats going on by graphing the curves for 10.5 and 9.25 CR versions . The first part is pretty much identical, and then the 10.5 one is the same slope, but ~2 degrees higher. Its advance stop is marked "13d", which will be 26 crank degrees, so a static advance of 8-10d will be OK for a 3.5L, and 8d OK for the 3.9, if Hammill is to be believed. Might have to use 98Octane, but with the mileage I will be doing it wont be any pain.
 
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