[Robert]

Originally Posted by wdodge45

Robert,
Well decisions decisions.... What is ur take on the GT_K 550's, u previously said they would outflow the the 62-1's. My biggest concern with any change is spool time, I don't want to lose what I have but at the same time realize I have some options. I do like the headroom on the 650's but concerns on being able to spool them like the 60-1's without making any cam changes and such. We went to the 1.30 AR housing to bleed off some boost but wanted to remove as much back pressure as possible. If the decision to go bigger I think the AR will change drastically to a much smaller AR. Your professional opinion is greatly needed and I don't want to be irrational or hasty about the turbo's I end up going with.
So here's ur chance to hook a brother up......LOL

Thanks,
Bill

Bill,
I completely understand. To be honest I was under the impression you were running T3 turbines on your current units. With that big of an A/R It just seemed like you were. If you were in fact running P trim turbines the F1-65 (P trim F1 turbine wheel equivalent) should actually flow more and spool faster even with the exact same A/R housing on there. You might actually be able to go a little smaller on A/R as the new F1 wheels physically flow more (less backpressure) than the P trim wheels they replaced. You could probably go to .96 A/R housings if you wanted to with the new wheels or you could stick with the 1.30 A/R as you know it well. Believe it or not your spool up shouldn't be too much slower. The larger compressor wheel will obviously spool up slower than the 62-1 or 60-1 but that is straight physics. The larger wheel is heavier. The thing that negates a lot of that is the new F1 wheel. It's taller tip height alone would have made your current turbos spool up even faster than they do now so that benefit will help reduce any additional lag you might find with the HP66. I say that with a grain of salt as we aren't talking 1000 RPM difference in spool up here. Maybe 100-200 RPM difference with the F1 wheel and the larger compressor. The GTK61 compressor wheel (compressor wheel used on the GT-K 550) does flow more than the original 60 series. It will be close to the 62-1 in terms of flow potential though. It should outflow it by just a few lb/min. If you were using P trim turbines before you'd have to do something custom though as there are no GT-K turbos with a GTK61 compressor and F1-65 turbine wheel.

Phew, let me take a step back from the nitty gritty tech stuff. Bottom line, if what you had before was a 60-1 compressor and a T4 P Trim turbine wheel with a 1.30 A/R you will NOT be disappointed with the GT-K 650. The 650 will give you the power you want today, the head room you may want tomorrow (or next year, etc) and a lot of great features like increased power at the bottom end and a wider more efficient compressor map. Your boost curve is going to change. There's nothing that can be done for that. Even if you went with the GT-K 550s it would change. The GTK61 compressor is different than the 60-1 or 62-1. Like I previously posted the 60 series compressors had a very unique type of boost response and compressor map. Any other compressor wheel is going to be different no matter how you slice it. But the bottom line is the HP66 is not a bad option here. In fact its a VERY POPULAR option for twin turbo LS applications trying to make this kind of power. While the boost curve is going to be different you may find you like it even more. The HP66 can flow more and flow to higher pressure ratios within the compressor efficiency island. The F1 turbines should keep the spool up VERY similar. With the amount of displacement you have and the design of the F1 wheels your boost curve may change but it won't be something incredibly dramatic. You will see it on a chart but whether or not you feel it on the butt dyno I can't say. Honestly, if new turbos are the final answer for your car the GT-K 650s is the way I would go.