Tee Dee RC Conversion - Is it really this simple?

I thought the major discussion about SPI in cox engines was centered on engines with mufflers because those engines would ingest their own exhaust. Obviously, for steady control of fuel air mixture across the RPM range it would be better not to have SPI at all and a twin needle carb but that's not going to happen (at least not the twin needle carb).

On a TD equipped with an RC carb but without a muffler I would not have expected any useability problems even if it's mot ideal to have SPI altering the fuel air mix at different RPMs. At a constant RPM the SPI will lean out whatever mix was set at the carb but this leaning would not normally be noticed by the engine operator because he simply adjusts the needle valve until he hears the engine perform the way he wants. I am aware that on simple air bleed carbs like this the mixture is not evenly controlled throught the RPM range and that SPI would be another variable to contend with but ...

Are we not over complicating things by worrying about SPI when I don't intend to use a muffler or is it really that much of an effect?

I guess the real impact of SPI on a RC carb - even without a muffler - is that SPI counteracts to the throttle barrel, which, when at least partially closed, is supposed to richen the mixture by creating a stronger depression/suction in the carb , and thus draw in more fuel than with a fully open throttle..

Because the SPI will open the crankcase and reduce the depression inside, the richening effect of the closed throttle will be impaired.

Therefore the throttle effect of the RC carb on a SPI engine is only marginal to that on a non-SPI engine.

(I hope my Hunglish will not unable you to understand what I mean)