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I don't have Jim's skillset, but I have been researching blowthrough systems for a while now. I am certainly no expert, but a lot of BMW guys who add aftermarket turbos to their cars use blowthrough. The Ford slot style sensor is sort of the gold standard. The advantages of blowthrough are that you can run a large variety of intake and piping setups, without adjusting electronic metering or recirculation valves. The intake elbows are one example. You could also run a (proper) front mount intercooler setup with a crossflow design like the TDM, and run the intakes under the headlights.* You don't have the issue of air turbulence like with an N62 setup. There is also no limit on the size or location of the filter or turbo inlet piping. You could run a 6” intake filter, directly mounted to 4” inlet piping, no problem. You have no restriction on the size or layout of the turbo inlet pipes. Also, you don't have to mess with recirculating the BOV, because the air is metered downstream of the recirc valves. You can use a proper vent-to-atmosphere BOV and have zero compressor surge. The OEM recirculation valves are ingenious, but they’re more restrictive than just venting the charge to atmosphere. Finally, blowthrough is potentially a more accurate method of metering intake air. Since OEM MAF measures the mass of air at the beginning of the intake tract, anything that happens downstream from the MAF will throw off the A/F ratio. Namely, boost leaks. A properly set up car should not have boost leaks to begin with, but there are other advantages. Lots of people use meth/water injection to allow them to increase boost pressure. This lets users to run more boost on a given fuel. But water/meth injection also changes the density of the air intake charge (you're increasing the density by adding meth). You're also changing the temperature of the intake charge when the meth changes states from a liquid to a vapor. A traditional OEM MAF couldn't account for the extra air mass (because it was upstream, at the beginning of the intake tract). But as long as you inject the meth prior to the blowthrough MAF, the MAF can account for the change in density. It is also measuring the air mass after the intercooler, which leads to more accurate mass air readings.
Blowthrough MAFs are also more accurate than MAP (so is the OEM MAF). MAP is an estimation of how much air mass is entering the engine using air temperature and pressure. MAF isn’t estimating anything. It’s measuring the exact amount of air mass.
Finally, blowthrough setups just seem to work better. I know several people that set up their intake and intercooler piping how they want it, dial in the fuel ratios for the blowthrough MAF, and then are able to change tons of other components (including turbos) without constantly having to go in for a retune. Hope this helps. *Note: Selin’s upcoming blowthrough design is not set up for a front mount intercooler. It mounts just after each side mount intercooler in the intercooler piping. You would need to weld a slot-style MAF bung on to your particular intercooler piping, and then have it tuned. I was just using an example of the options blowthrough provides.
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