removing rev limiter from a distributor????.......
Discussion
I have a 1983 1.5 alfa boxer twin-carb engine form an alfa-sud fitted to my kit car, which is rev limited to 6000rpm, which can be annoying, I have been told I can remove the rev limiter and rev it to around 8000rpm.....I'm lead to belive the rev limit gizmo is located in the distributor rotor arm and is some kind of centrifugal device which breaks the circuit when at 6000rpm.......does this sound right to anyone?....... or is it done some other way?......where is is, and how do I disable it!
F.M said:
It`s usually a little spring on top of the rotor arm which under centerfrugal force at high rpm, breaks the contact between the rotor arm & the cap......
The centrifugal mechansim actualy fires the opposite plug which will be near the end of it's exhaust stroke. Because this plug requires a much lower voltage to ionise, the plug the rotor is pointing at does not fire. The solution is the same though, remove or jam the mechanism. That said I'm really not convinced the Sud engine is safe to 8k on a stock bottom end.Breaking the HT circuit to prevent a spark is never a good idea, the resulting very high voltages can cause insulation breakdown and is very hard on the igntion amplifiers.
F.M said:
It`s usually a little spring on top of the rotor arm which under centerfrugal force at high rpm, breaks the contact between the rotor arm & the cap......
The centrifugal mechansim actualy fires the opposite plug which will be near the end of it's exhaust stroke. Because this plug requires a much lower voltage to ionise, the plug the rotor is pointing at does not fire. The solution is the same though, remove or jam the mechanism. That said I'm really not convinced the Sud engine is safe to 8k on a stock bottom end.Breaking the HT circuit to prevent a spark is never a good idea, the resulting very high voltages can cause insulation breakdown and is very hard on the igntion amplifiers.
Mr2Mike said:
F.M said:
It`s usually a little spring on top of the rotor arm which under centerfrugal force at high rpm, breaks the contact between the rotor arm & the cap......
The centrifugal mechansim actualy fires the opposite plug which will be near the end of it's exhaust stroke. Because this plug requires a much lower voltage to ionise, the plug the rotor is pointing at does not fire. The solution is the same though, remove or jam the mechanism. That said I'm really not convinced the Sud engine is safe to 8k on a stock bottom end.Breaking the HT circuit to prevent a spark is never a good idea, the resulting very high voltages can cause insulation breakdown and is very hard on the igntion amplifiers.
Usually the spring simply shorts to earth, via the shaft of the dizzy, onto which the rotor arm mounts.
stevieturbo said:
How can it fire the opposite plug if the arm isnt pointing there, and doesnt have any electrical connection to that post ?
Because the centifugal mechanism moves another contact out in the opposite direction. This wasn't on an alfa rotor arm addmitedly, so they may short to ground.Edited by Mr2Mike on Saturday 1st September 13:11
Yep, Stevieturbo's explanation is correct: there is a little centrifugal copper weight retained by small springs, which shorts out the spark by earthing it to the distibutor shaft. The mechanism is easily visible so the OP should be able to work it out quite easily by removing the distributor cap and examining the rotor arm. 
I ran an Alfa 1500 Veloce boxer engine in a Raffo Tipo 12 kit car for a while. Rather than solder it up, I simply gobbed up the cut-out on the rotor arm with a blob of araldite - job done.
The engine would then rev smoothly to a self-imposed rev limit of 7000 rpm, but that might have had something to do with the fact that it blew head gaskets on a pretty regular basis. In the Raffo, however, the cylinder heads were pretty accessible so after a bit of practice changing a head gasket was a hour's job. As a result, I never bothered investigating more permanent sloutions like uprated gaskets or wills rings.
I ran an Alfa 1500 Veloce boxer engine in a Raffo Tipo 12 kit car for a while. Rather than solder it up, I simply gobbed up the cut-out on the rotor arm with a blob of araldite - job done.
The engine would then rev smoothly to a self-imposed rev limit of 7000 rpm, but that might have had something to do with the fact that it blew head gaskets on a pretty regular basis. In the Raffo, however, the cylinder heads were pretty accessible so after a bit of practice changing a head gasket was a hour's job. As a result, I never bothered investigating more permanent sloutions like uprated gaskets or wills rings.
Edited by Sam_68 on Sunday 2nd September 08:04
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