8 replies to this topic

[Raz]

:erm: Hi guys Whats your thoughts on removing the dizzy vacume pipe and blocking it off .........only i have been told by a garage that they are a waste of time and they always block them off ...anyone out there done this and was it any benefit if so why is it better to block it off
Cheers Raz

[The Matt]

Some cars don't have a vacuum advance, some do.
They are there for a reason though! It alters the timing depending on how much vacuum there is in the inlet manifold. I would leave it connected myself.

[Guess-Works.com]

Here's the deal...

Vacuum advanced dizzy's are used on most everyday road cars, what happens is when you are cruising, you are at part throttle, which induces a vacuum in the inlet manifold, this is used as a means of altering the advance on the timing which further improves fuel consumption and economy. Blocking the vac will just loose you that added economy.

Vacuum-less Dizzys are generally for performance vehicles, where not too much time is spent on part throttle, thust making the vacuum absolutely pointless, and have a more agressive advance curve.

[Sprocket]

Or, Vacuum advance is removed when total advance is too much for the tune of the engine.

Get the car on a rolling road with a decent operator and let him make that decision. :cheese:

If the engine is in standard to mild tune, then its probably worth keeping the vac advance for fuel economy. When the engine starts to get into serious tune then a change of distributer is on the cards, of which, Aldon, seem to have got that area covered.

There are reasons for its removal. The reason below not many people know about, unless like me you've spoken to Burlen Fuel systems and got them to look up the tech drawings.

Not all vacuum take offs on the SU carbs are the same. There is 'throttle edge depression' and also 'manifold depression'. Throttle edge depression is less than manifold depression, so if like me you changed the HIF38 with throttle edge to a HIF44 with manifold depression then the vac advance is wrong and why it was removed, as too much total advance in the wrong place. Complicated, I know :nugget: .

[Tarks]

HMMM CAN OF WORMS! SPRINGS TO MIND IM GETTING MINE RR'D VERY SOON!

[Sprocket]

IM GETTING MINE RR'D VERY SOON!

Can not stress this any more, even on the slightest mod such as air filter and exhaust back box

[AlexM]

Can not stress this any more, even on the slightest mod such as air filter and exhaust back box

What if your car is injection?

What can they do if you can't map the ECU?

[Sprocket]

Can not stress this any more, even on the slightest mod such as air filter and exhaust back box

What if your car is injection?

What can they do if you can't map the ECU?

If the injection system is operating correctly then it tunes itself ( dont think there are many of those, still summit wrong with mine) which is the biggest advantage of the system. You are however restricted to the program in the ecu which is set up for ecconomy rather that all out power, this is the bit you can't change and most tuners would like to. The only thing you have to do is ensure the whole system is working correctly and that means no missfire or eratic idle. :fear:

There is a limit though. I spoke to a chap that had tuned his SPi engine to a point, where, when he floored the accelerator, the injector was unable to provide enough fuel and melted the piston crowns within seconds. This was the point he removed the injection and fitted twin 1 1/2" SU's, retaining the ecu for the ignition and alarm.

I think his engine spec was some thing like 1293, 267 or 277 duration cam, big valve head, 1.5 ratio rockers, K&N, tubular manifold and straight through box