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TR6 Moss TR6 Vacuum Advance Conversion question

bunzil

Jedi Trainee
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It's probably been discussed here before but I couldn't find the thread so kindly bear with me...

I see Moss offers the conversion from retard to advance for later model TR-6's. Can someone give me their thoughts about how well this works versus just disconnecting the retard? Is it worth the $89?

Thanks, as always!
 

Bob Claffie

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The "retard" distributor was strictly a smog tool and was detrimental to performance. I have no experience with the change over but if it was my car I would do it, Every other car benefits from an "advance" distributor why not yours ? Possiibly have to experiment with initial timing to blend in with the added advance.
 

TR3driver

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You should be able to see somewhere around 8-10% less fuel consumption on the highway with the advance. Looks like $4/gallon is here to stay, so do the math. $90 is 10% of $900, which is about 225 gallons (assuming $4/gallon). How long does it take you to burn that much fuel?

I'm surprised though, that Moss claims the advance port is there under a plug. The later carbs that I have seen do not have the advance port drilled (or tapped) at all. The location of the port opening into the carb throat is fairly critical for proper operation, so it's not a trivial thing to add. Might be worth checking before you spend your money.

But note that you aren't going to see any more power with the advance. Neither advance nor retard do anything at full throttle. You might be able to notice that the engine seems a bit more eager at part throttle (better throttle response), but even that effect is pretty subtle. Better gas mileage is really the only advantage of the vacuum advance.
 

poolboy

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Since the retard worked off Vacuum, once the rpms exceeded 1100 rpms the manifold vacuum was inadequate to fully activate the retard, so I wouldn't classify is as being "detrimental to performance"...
NOx emissions were reduced by retarding the ignition timing when the engine was idling.
All the same, mine is disabled.
 

TR3driver

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For all but TR250, the retard is actually connected to a special port that only 'sees' manifold vacuum with the throttle fully closed. So it gets deactivated as soon as you open the throttle, regardless of what manifold vacuum does.

On the TR250, there was a valve operated by the throttle linkage that did the same thing.

The retard does waste a bit of fuel and make the engine more prone to overheat (both only while idling). It also supports the feature found on later cars, where when the engine starts to get hot, the retard is disabled thereby raising the idle rpm and (hopefully) preventing a boil-over. It doesn't really affect performance otherwise. Mine (on the Stag) is only disconnected because the module is bad and replacements are not readily available. But if I ever get it running again, I do hope to do the advance conversion, for the reasons I stated above.
 

poolboy

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You're talking about the throttle linkage vacuum valve..the 69 TR6 had that set up, too.
I guess technically it should be mentioned that high vacuum during engine overrun also activated the retard, but that would be a deceleration scenario and not affecting performance in a negative way, IMO.
 
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bunzil

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Thanks everyone. I've read about the retard countless times (there's a joke in there somewhere) but never fully understood it's role mostly at idle.
 

phil56

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I converted my TR6 from vacuum retard to vacuum advance. The only issue I found is that the roll pin that holds the vacuum unit to the distributor body fell out, which resulted in the vacuum unit pushing itself out of the distributor body and severely retarding the ignition. This caused a significant loss in power. With the vacuum retard, if the roll pin falls out, the vacuum unit pulls itself into the distributor body when vacuum is applied. I have always seen vacuum units held to the distributor body with one or more screws. I installed a very small machine screw and nut in place of the roll pin.
 
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