Anyone use a GT25?
03-07-2015, 02:36 PM
#16
Race Car
Join Date: Mar 2012
Location: Austin TX, drinking beer in the garage
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Well, I can only share my experience on my 3l 8V, but the GTX3576R 0.82 flows more than the GTX3076R 1.06 by the time it comes into boost, and if it reaches my desired peak boost perhaps 300rpm later the engine makes more torque in any load situation than with the GTX3076R - with a short runner intake. I wouldn't bother with a GT35-sized turbo with the stock intake. This 76mm compressor felt just wrong with the GT30 turbine, though it did not become really obvious before trying out the GTX3576R.
The GTX3576R takes a very brief longer time to spin by the time the engine is at 0 bar of boost but once the turbine begins to be "cranked" it spools much harder than the GTX3076R. It reflects in my wg duty cycle table. The higher flow is also shown by the fact I had to chop down the ignition map by several degrees anywhere above 0 bar. The engine was knocking pretty bad with the settings of the smaller turbo.
The GTX3576R takes a very brief longer time to spin by the time the engine is at 0 bar of boost but once the turbine begins to be "cranked" it spools much harder than the GTX3076R. It reflects in my wg duty cycle table. The higher flow is also shown by the fact I had to chop down the ignition map by several degrees anywhere above 0 bar. The engine was knocking pretty bad with the settings of the smaller turbo.
Also this is on a 2.5 liter (for now), so I'm not sure I'd realize the benefit of the HX40 turbine the way you did moving up to the 68mm GT35 turbine. The car sees 21-24 psi boost depending on how adventurous I feel and drinks only corn juice. Right now I get stupid fast spool wit the k27/8, if I'm over 3k rpm 1 bar is basically instant. I'd like to be able to get 1 bar by 4k with my next turbo setup (also on the 2.5 liter), but also have enough headroom to feed an in-progress 16v 2.9 liter and make 450+ rwhp at lower boost than I have to run now to get the performance I want out of the tiny k27.
oh one more question. do you think you'd gain much power without sacrificing a lot of spool if you moved up to a gtx3582?
Last edited by Dougs951S; 03-07-2015 at 03:48 PM.
03-08-2015, 08:19 AM
#17
I can't comment on the Holset as I have never tested these turbos.
To justify a GTX3582R on an 8V you would have to run lots of overlap/valve lift with a much-worked head and a short runner intake to give the room needed for this large compressor. It makes sense to me that the 1.06 turbine housing would work best with this 75 lbs/min compressor, making for a turbo laggy enough to be a chore on the street.
Some more interesting notes here comparing both turbos on a Subaru, for what it's worth. There is no mention of the cams used but I would guess they would already be pretty aggressive if it's a Time Attack car.
To justify a GTX3582R on an 8V you would have to run lots of overlap/valve lift with a much-worked head and a short runner intake to give the room needed for this large compressor. It makes sense to me that the 1.06 turbine housing would work best with this 75 lbs/min compressor, making for a turbo laggy enough to be a chore on the street.
Some more interesting notes here comparing both turbos on a Subaru, for what it's worth. There is no mention of the cams used but I would guess they would already be pretty aggressive if it's a Time Attack car.