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Adding A Vac Unit To An Alden Yellow

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#1 absx2


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Posted 06 December 2017 - 08:11 PM

I have a Alden 100AY to fit to a +.060" 998 with a Piper 270 cam and I have retro fitted a vacuum unit from a standard 998 dizzy but now i`m not sure if Alden have different curves for vac and non vac.


Does anyone have the answer please ?

#2 KernowCooper



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Posted 06 December 2017 - 11:15 PM

I spoke to Aldon direct last year and they sent me the curves for the yellow and the red and there was only one curve for each so no different curve for Vac/Non Vac.


The curves are here on TMF in the FAQs

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Edited by KernowCooper, 06 December 2017 - 11:16 PM.

#3 Cooperman


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Posted 06 December 2017 - 11:18 PM

I don't think that will work. Any distributor without a vac advance will be curved for a specific spec. engine, so adding a vac unit will simply change the curve to something completely different.

Best bet is to speak with Aldon, give them your engine spec and be advised as to what will work best. They are very good at doing this.

#4 absx2


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Posted 07 December 2017 - 07:31 PM

Thanks chaps

#5 carbon


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Posted 07 December 2017 - 07:38 PM

Absx2 - there are also lot of differences between apparently identical vac advance cans. The three variables are:

- start vacuum, when it starts to advance, in inches mercury

- end vacuum, when it stops advancing, in inches mercury

- total vacuum advance, in distributor degrees


These are normally stamped on the can, for example 3-10-8 would be:

- start vacuum is 3 inches mercury

- end vacuum is 10 inches mercury

- total vacuum advance is 8 distributor degrees


So at full advance this vacuum can would give you an extra 16 degrees of crank advance. For a fast road build I would recommend avoiding cans with much more than 16 degrees of crank advance, just to be on the safe side.

#6 absx2


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Posted 08 December 2017 - 05:01 PM

Thanks guys. 

I called Aldon today and unfortunately for me he confirmed that there is a difference between the curves on the vac and non vac so if I wish to keep the vac unit I will need to return it for recalibration along with my engine spec.


Is the vac unit worth the bother I wonder ?

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