7 replies to this topic

[absx2]

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 ?

[KernowCooper]

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

Attached Files

•  Aldon Dist Adv Curves.jpg   36.19K   19 downloads

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

[Cooperman]

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.

[absx2]

Thanks chaps

[carbon]

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.

[absx2]

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 ?

[KernowCooper]

Well seems the advice I got was wrong last year ? sorry about that, the advantage of running a vac unit on the road is, increased mpg, and more engine torque on a part throttle, if your running on the road then yes use a vacuum unit

[Spider]

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 ?

 

I find this 'odd' I gotta say.

 

Usually, the mechanical advance is sorted and then vacuum, if wanted, is done 'on top of' the mechanical advance.

 

Mechanical Advance is worked out on Wide Open Throttle, under which conditions there is no or very little vacuum and this curve is the same whether vacuum is fitted or not.