24 replies to this topic

[Gremlin]

What are the advantages and disadvantages of blocking up both ends of the vacuum advance pipe on a standard 998 with standard ignition, and then what would change as I'm thinking of changing to an electronic inginition?

[jaydee]

You car will have the worst MPG if you block it 

[Gremlin]

You car will have the worst MPG if you block it 

Any gain in power? or torque?

[jaydee]

Nope sorry

vacuum advance increase advance as you release the throttle to give better part throttle ingition

[6joshh6]

Pretty pointless unless you have a race car with a modified advanced curve. If you want to look at modding your dizzy I'd look at Des Hammill's 'how to power tune your mini', which has a nice easy to read section on the topic. You can generally pick up a copy from your local library 

 

[krusher74]

 

You car will have the worst MPG if you block it 

Any gain in power? or torque?

 

You need to do some reading on spark timing, so you understand what vac and centrifugal advance are actually doing.

 

The centrifugal advance is sensing the engines rpm and altering spark advance in turn

 

The vac advance is sensing engine load and altering spark advance in turn

 

There basically the oldskool version of a modern engines ECU ignition map.

 

you want you engine firing at the right time to burn the petrol most completely and use that bang pushing the piston, take awy thins like vac advance on road car and you taking away an engine sensor for the distributor.

[KernowCooper]

All road cars need vacuum advance Vizard and Calver go to great lenghts to say so in their articles, without vacuum on a road engine = no plus and many minus issues

[ucchockey]

Does this include electronic ignition. I have an Aldon red dizzy running electronic ignition but it doesn't have vacuum advance. What disadvantage would I be getting?

[KernowCooper]

A Aldon Red is a Race Spec Distributor and not the best curve for road use, What spec is your engine? to warrant a Aldon Red

 

Qoute@Calver

modified A-series dizzies - the Aldon duo - 'Yellow' and 'red'. The yellow dizzy has a reasonably gently advancing ignition curve to cope with almost anything road orientated. The red dizzy has an 'immediate' advance curve that comes in with a bang and is all over by around 4,000rpm and this dizzy is only suitable for race use

 

The Aldon red is indeed a full race dizzy as above, it's designed to run with cams of around 300 degree's and a compression ratio over 11:1. As such it runs a LOT of static advance and isn't really suitable for the road or a smaller cam. You'd be better of with a Aldon Yellow.

 

 

Just curious how much static advance are you running? if it not a lot to adoid pinking on the road i doubt it anywhere near right, The leaflet that came with my aldon yellow list the red as follows

 

Aldon Red  649,  296, 300 cams and up and Race Use

Edited by KernowCooper, 07 July 2013 - 11:27 PM.

[ucchockey]

Lol. Not a race engine. Ops.
Got the dizzy years ago when I was young and clueless and never thought about it since. It was rolling roaded at Aldon with the red dizzy on it and I remember at the time the bloke muttered something about advance curves.
It's a 1293 mini sport engine with stage 2 head, fast road cam and twin hs4 carbs. Seems to run pretty well but maybe would be better with a different dizzy then.
Would it involve a lot of re-tuning etc to change it?
Does vacuum advance work the same with electronic ignition?
Does the yellow dizzy have vac advance?
I sometimes get to a stage where I think I know what I'm on about and then something like this comes up and I realise I know very little. Doh!

[KernowCooper]

Would it involve a lot of re-tuning etc to change it? No buy a aldon yellow and fit and set timing to 10degs at 1000rpm with vac disconnected

Does vacuum advance work the same with electronic ignition? Yes it does exactly the same

Does the yellow dizzy have vac advance? You can buy the Aldon Yellow without for a mild engine used in competition or like mine with for road use.

 

I know people say buying a Aldon is still a guess on the manufactures behalf, but as Calver and Vizard pointed out they have run their dyno for hundreds of hours over a 30 yr period on just about every spec engine constructed so they draw on this when making a distributor

Edited by KernowCooper, 07 July 2013 - 11:56 PM.

[KernowCooper]

Road use Vacuum Advance every time.

[Captain Mainwaring]

You can buy the Aldon Yellow with or without vacuum advance...........

 

That's the mistake....never give the customer a choice. 

[ucchockey]

Cheers for comprehensive answers guys.

[krusher74]

If you do go to a yellow with vac another rolling road session would be in order, if they have set up fueling to suit the red it might be on the rich power side, A retune with cruise on the lean side would work with the yellow/vac.

 

If you have 12.5/13 to 1 fuel across the whole needle it probably not going to like/need the extra advance. 

 

probably 2/5mpgs at cruise out there for you to gain.