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Triumph Spitfire Mk3 advance curve


Andy Moss
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I have measured the advance curve of my Mk3 Spitfire and find that it is a bit on the edge of what is described in the workshop manual.  Has very faint pinking (pinging) in the mid range, so was going to retard a bit.  Plotted how it matches the specification that was likely to be based on 4 star petrol and may be significantly unhelpful, but I do not know.  The car is completely standard and has new carbs and dizzy was reconditioned recently (no play in shaft), dwell checked too - all fine.  Car goes ok and I have no real complaints at the moment.  Interested in other peoples experiences and how this curve compares.  Was considering a 123-Ignition as per a really excellent article in courier magazine, but not sure it will be really that worthwhile.  What do you think?

805747591_SpitfireMK3advancecurve.jpg.115fbd006d39ea279ed9dc9a741daa34.jpg

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Your measured advance curve is at the retarded edge of the normal range, so wouldn't be expected to cause pinking, which can be caused by too much advance.

What fuel are you using? Standard 95 octane unleaded or super unleaded at 97-99 octane? As you imply, the engine was designed for 99 octane four star.

Nigel

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Nigel, 

Thanks for your reply and I totally agree.  It’s quite retarded and not really wanting to retard by much more unless that’s ok for modern fuel. tend to use 97 octane, ie super unleaded.
Perhaps somebody has a standard car that has had a rolling road session.  I’m tempted to book a session. 
cheers 

amo

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9 hours ago, Andy Moss said:

Perhaps somebody has a standard car that has had a rolling road session.  I’m tempted to book a session.

Someone local to me has a standard Mk3 (unlike my hacked-around one) and took it to a rolling road to be set up. He was very pleased with the results - as is to be expected when the chap at the rolling road was Pete Baldwin. If you have a local one with somebody of his calibre then it's recommended.

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1 hour ago, Pete Lewis said:

do  check as most dizzy curve test data is measured decelerating , not always made clear   this gives a very different curve to accelerating 

it might seem a bit strange and thats how we tested dizzy curves back on the rigs in the 79/80s 

just a thought  

Pete

Didn't know that, thank you Pete.

Nigel

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its quoted in some data sheets in the WSM   its not clear,  will have a browse of my lucas manual but the hysteresis of the centrifugal/ springs is  quite a varied curve going up the revs to that coming down   i dont know why this is the way they test as you feel the curve is more critical accelerating than the opposite 

some one knows ???

pete

 

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13 hours ago, Andy Moss said:

805747591_SpitfireMK3advancecurve.jpg.115fbd006d39ea279ed9dc9a741daa34.jpg

Andy,

I'd say from your chart that you need to check the operation of the advance mechanism.    Yours looks "sticky".

It should rapidly advance as the counterweights move out, then more slowly as revs increase as they stretch the springs.     Yours doesn't do the first,  then does the second, but erratically as if the weights are stuck.    Are both springs intact?   Do the weights move freely?

Gareth Thomas' book includes this chart, mostly 2L but inc. a Herald advance curve which should resemble one for a Spitfire:

 

John

Dizzie advance curves.jpg

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dizzy test data

page 6.321  supplement   in the wsm it quotes when decelerating for  13/60 herald  but not on the same page for mk3 spit   ....why 

pages 6.102/103 covers all/many and all are test decelerating  spit4   mk2 vitesse   Herald 1200/12/50/courier, 

and vacuum is also check   with a falling vacuum.

Pete

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1 hour ago, Pete Lewis said:

 in the wsm it quotes when decelerating for  13/60 herald  but not on the same page for mk3 spit   ....why

Lucas vs Delco? Perhaps the statement was less obvious on the Delco datasheet and the person copying the data into the WSM was being a bit verbatim.

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I took the base plate out of the dizzy and inspected the springs and weights. Weights were free to move, but I over cleaned, oiled and worked them around to check for any as you do.  Naturally, I over oiled it so will wipe the excess off the garage floor tomorrow. Checked the timing again, but not rechecked curve as it might be thought anti-social at 10pm. Noted that my draper tacho meter has died, so rev-counter accuracy will be used for the next curve. Also made a slightly softer advance spring that should increase the rate of advance. Might have a crack at trying to change the rate of advance in the lower revs by changing one of the springs. Alternatively, I’ll book a slot at the local rolling road and spring a cash haemorrhage.  Smile

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I have done the high to low curve and here is the result. I have also set the advance at 2000 rpm to ~16.5deg as that is mid way between the WSM limits. This gives a idle advance of about 11degs, which is lots more then the 6deg nominal.  Off to see how badly it pinks. Smile. 

3CC90F05-41C2-4298-BFBE-34C7F5EA6D01.jpeg
 

It goes really well, but has a slight pink at about 2500.  should  it really be ok at idle with 11 degrees of advance?  I’m really quite puzzled. 

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added the following - curves - seems that the decel curve wrong.

adv_curve_v3.jpg.ee9491fff7377fef341c66ff52fd3f79.jpg

wonder if I could play with the dizzy at each rpm to find mid point between too much advance and too much retard and try to tune to that curve.  I guess this is best done when the car is under load, so trip to rolling road might be best.

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Have ordered new RPM and Dwell meter after the Draper one broke. Need to have advance curve with same equipment before I start making changes. 
Incidentally, I got a draper one from Halfords, which would not measure rpm and flicked between random numbers. Took it back - it was awful. 

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