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RPM vs MAP/MGP or RPM vs TPS in a Link G4+

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Hi all,

Over the winter months we have put a larger turbo, gen 2 GTX3582r .82 a/r and came from a gen 1 GTX3071 .63 a/r, and I have thought about finally getting around to setting up the closed loop boost control. This is a drag car with a 2l engine and I am thinking, is this worth setting this up closed loop on this large frame of a turbo with such a small engine? If so would RPM vs TPS be the best option or would TPM vs MAP/MGP be better?

I'm also curious about if TPS is better for the load axis on a large turbo and the throttle lets say is at 50% at 20 psi will my AFR be different if the throttle is a 100% at 20psi. I think I may have figured this out as I'm typing but I'm still going to ask. (My thought was why would you tune a car to have the same pressure at the 50% and 100% if the load axis is TPS) - is that though correct?

I have never tuned something on this small of an engine with this large of a turbo charger and just trying to get some insight on this so I have an idea of what to expect.

Hi Michael,

From my experience (in a boost control perspective), the reason you would use RPM VS TPS is limiting boost down at a lower throttle %. Example at 50% TP you are targeting 180KPA instead of your 250KPA target at 100% TP. This is useful in traction limited applications etc.

Closed loop control can be good to keep dead on target, open loop is obviously just that, open. In different altitudes / ambient temperatures your boost can rise/lower as your solenoids duty cycle is set in stone.

I don't believe being a large turbo/small engine combo makes any difference to whether you should or not setup closed loop control. More so to do with application. And straying off target in a drag car is probably not something you want, especially when run repeatability is desired.

Hope that assists somewhat lol


For a drag car you are probably better doing timer or gear referenced boost (or both) rather than a throttle axis. In general if you get off the throttle your run is stuffed anyhow.

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