GoHybrid

Something I've been thinking about as I go on to turbocharge my car: is there any way to completely bypass the turbo for emissions purposes? Ideally, I'd like to be able to use a dual map - one set up for boost, the other set up with just the injector size offset, so I could run essentially stock. I'm sure you could do this by pinning the wastegate open, but i know know if it could still build boost at high throttle or if that debilitates it enough that it doesn't significantly affect the stock tune.

4drEF

If you mean smog check by 'emissions purposes' then I don't think you should be see high enough throttle to build boost that the WG can't handle.

GoHybrid

that's exactly what I mean. i understand wastegates have a spring that determines their actuation pressure, and that operation can be delayed by referencing it to a pressure lower than that actual boost pressure with a boost controller.

I guess what I'm looking to do is the exact opposite - force the wastegate to open immediately, as opposed to waiting until a certain boost pressure has been reached.

I don't think the lower IATs from leaving the intercooler and intake plumbing connected would cause a smog failure either.

what are your thoughts?

TurboIntegra

It sounds like you don't own a turbo car or have never driven one. You aren't boosting all the time just because you are accelerating. Depending on the size of your turbo, you will have to have load on the engine to make boost.

If you had a very very small turbo and were still worried about it you could pull the wastegate spring out (on an external wastegate) or wire it open on an internal wastegate.

GoHybrid

Well, you would be correct about me not owning a turbo car. I'm in the process of changing that. However, you are incorrect about never having driven one. I am quite familiar with how the various types of forced induction, including turbocharging work. I think perhaps I just misstated my purpose, which was to gather any empirical evidence people here might be able to provide as to whether a turbocharger could be selectively bypassed without requiring a lot of wrench time.

The reason for that, of course, would be to be able to submit the car to an emissions test and ensure that the output characteristics of the engine do not deviate substantially from those of a completely stock motor.

What i DON'T want to be doing is disconnecting pipes and hoses and uninstalling and reinstalling things just for the purpose of skating by emissions. I'm thinking one way to handle it relatively simply, is to make a restrictor plate at the throttle body, sized so that the airflow rate at the default boost pressure doesn't exceed the airflow rate of the N/A motor. It would effectively choke the turbocharger. What i don't know, and maybe you can tell me, is if there are any ill effects to choking a turbo. The BOV system would still be installed and operational, so compressor surge would not be an issue. I also don't know what the acceleration profile is for an emissions test. I just want to be sure that when the technician is doing it, the engine doesn't suddenly need to hit 12.5:1 AFRs because of a boost condition when the test is expecting 14.7:1.

So depending on whether the restrictor is installed or not i could run different fuel and ignition maps. What about that?

Tony the Tiger

The only way to bypass the turbo is to have a wastegate that recirculates back into the downpipe, and then force the wastegate fully open all the time.

This will get close to the charasteristics of an NA engine in terms of emissions.

The turbo acts as a heatsink, and a big reason why a lot of turbo cars fail the E-test is the lack of exhaust heat and energy after the turbo. The turbo has soaked up all the exhaust heat and energy, hence, leaving little energy to properly heat up the catalytic and sometimes the O2 sensor as well.

GoHybrid

So it seems like part of the equation is insulating the heck out of the exhaust pipes and turbo all the way up to the cat by way of heatwrap blankets and ceramic coatings so the heat is less likely to leave the system before heating the cat. Maybe then compensate for the higher EGTs on boost with a little more fuel?