what are the effects of a CAT back and 52mm TB on BLM's?
did anyone do a before and after data log of BLM's with the above mods?

I'm just curious to see how much the BLM's are affected by small changes in intake and exhaust.

 

Both of those mods would tend to allow the engine to breath a little better. In part throttle, the ECM will compensate adequately. The tuning issue will be for WOT.

On a MAF car, the MAF would detect the extra air flow and should compensate for it, provided you don't have other extensive modifications that result in maxing the MAF.

However, an SD car will not be able to detect the extra air flow in WOT and will require some modification in the eprom to add extra fuel tocompensate for the extra air flow.

On an unmodified eprom, the BLM/INTs will show an increase when running in closed-loop in value for both a MAF & SD car pretty much across the entire rpm range. The magnitude will depend on other factors and tend to be the greatest near peak TQ (which usually is max VE).