RE: GP290 vs. G260
That is a very good question. One major difference between modders, sayTS vs Tom Bowlin, is that they do different mods. Once modder willincrease the timing profile of a given engine to a set of durationswhile another will increase the timing profile to a different set ofdurations.
And in addition to increasing durations, improving the flow postcross sectional areas is another area in which they canb differ. Onemight shoot for one port shape and cut the ports accordingly. Anotherwill go with a different port shape.
And now, some modders also custom make parts to bolt on these engines: Zen G230, 340, 260, 270, or whatever (even for the CYs).
Just what would the difference be beteween an ESP and a TS? Hard totell. But clearly, TS will put on alot of custom built parts like reedintake "plenum," even a custom TS lower end crank case and clutchhousing, etc.
As for what makes a TS worth $1000 and the ESP about $550? The TS doesthrow on alot of custom hardware. Both I am sure have some sort ofporting. But what those porting work entails? (Timing profile, portreshaping, etc.), I do not know. There is absolutely no way to knowunless you buy a TS Zen modded G260 and tear it down your self andmeasure up the critical dimensions yourself.