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I thought I'd test the wastegate on my GT2560R after work yesterday. I wanted to see if it would make boost with the internal wastegate flapper door wide open. So I disconnected the actuator and let it flop. It seemed to rev a little freer off idle, and it was more willing to take off from low revs. Not a big difference, but I noticed it. On the road, it was a real dog until about 3.5k, where it started to pick up. By 4k, it was making boost. By 5k, its really starting to haul ass. Thats with the wastegate wide open.

With that in mind, as well as the last dyno run making peak HP at only 5k RPM, I think its time for a bigger turbo. Like a GT2871R, with a .86 A/R turbine and 76 trim wheel. The compressor is a little larger than I'd like, but the turbine side should be able to keep up and allow the engine to follow a more natural VE curve. New dyno charts coming soon. I'm shooting for 280 WHP at 13 psi...

Shoot me a PM if you decide to upgrade. The GT2560R is pretty well suited to my little 1991cc m20.

why not a gt3071/76r?

At my altitude, a smaller compressor is better suited to this motor than it would be at sea level. I need a higher pressure ratio to push the same amount of air. A 3071/6 would be too much compressor for me up here. I'd be off of the efficient part of the compression map and possibly into the surge. At sea level it would be ideal. Much like the GT2560R would be ideal for a 2 liter m20 at sea level, but too small for my 2.7. I like the GT2871R because its not much larger on the compressor side, but it can be had with a much larger turbine wheel and housing. It'll do just fine...

Swapped em out today. It didn't take long at all. Thats one plus about the td manifold. Its all easy to get at. The .86 turbine housing was much larger inside, not suprisingly. The 53.8mm, 76 trim wheel wasn't huge, but it did look much more flow oriented. The turbine gas flow charts show the difference better than a photograph. The old .64 tops out at about 14 lbs/min and the new .86 achieves about 22 lbs/min. What does this mean?

Where it used to make full boost at 2k, it now makes full bost between 3 and 3.5. Once its up there, lag is just as insignificant as it used to be with the undersized turbine. It rips through 4-5k and holds on like it should on the top end. No more falling off past 5k. I rather like it, and it will be back to the dyno as soon as I can afford it.