GT17 or GT20 for K1100 head?
Turbo Mini Forums

It's been a while since my last post! The GT17 is good for 18psi or so, but I found anything above that it just wouldn't pull above 6.5k, I swapped mine out for the TD04 and that boosts to30psi no problem with around 500rpm more lag initially. The main issue with the GT20 is the ridiculously small wastegate, I found the TD04 only starts to creep above 20-25psi higher in the revs, so running anything lower should be fine without the need for an external wastegate.

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1/4mile in 13.2sec @ 111 terminal on 15psi

Oooh. That is encouraging info. I’m swapping to a td04 on the 5 port.

In the 13's at last!.. Just

Im hoping my disappointment with the drivability (how quickly it makes boost) of my TD04 will be dialed out with concentrating on the ignition advance in the 2500-5000rpm range. Yes, it’s great over 5000rpm, but I prefer the GT17 or GT20 as far as drivability. Both will make crazy power and deliver boost fast and from low revs.

Yeah the GT17 is like a switch, it spools really low down, 1500-1800Rpm. My TD04 is slower to build boost but I found it nicer that when the engine is properly on cam the turbo is also pulling hard. The GT17 it literally felt like you stop accelarating top end. For hill climb, twisty roads, and a lot of stop start general driving around the Gt17 is far better, the acceleration from stamping your foot down is almost instant. I'm running 9.1:1 so it always feels ok off boost, and I have lots of advance too.

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1/4mile in 13.2sec @ 111 terminal on 15psi