Yamaha Excell heads-vs-HydroTech heads

[Way2Lean]

Year or so ago, I installed a set of HydroTech heads on a 98 150 V-max. Compression ended up right at 165 across the board. Checked it with another gauge and same numbers.
I messed with that set-up for quite awhile and it just never seemed to do what I thought it should.
So, I set that powerhead aside and put an Excell powerhead in it's place. Used all of the 98 electronics though.
After tinkering with that for awhile, I finally had a performance gain that I considered to be worthwhile.

Now considering installing those HydroTech heads on the Excell. BUT, the Excell heads have different size combustion chambers. The HydroTech heads do not.
Anybody know why the Excell heads have different size chambers, and what am I going to screw up first by installing the HydroTech heads.
Thanks in advance.

[Rusrog]

Tell me more about the different size chambers in the Excel heads. By how much? Is it a difference in the pocket width or depth? From cylinder to cylinder or from bank to bank? I have a couple of sets of 6K7 Excell heads but I didn't notice a difference. Now I'll have to go look.

Also, which Yamaha heads did you get? The modified stock heads or the billet or offset chamber heads?

Russ

[Ray Neudecker]

The Excell has different port heights on 1 and 2 and the cc's of those two chambers are also different. Obviously the Hydro Tec heads were meant for the 150-200 blocks which do run the same port height on all cylinders.

[Way2Lean]

I've not cc'd either set of heads, but, the excel heads have visibly obvious differences between cylinders. Just wanting to know the theory behind this.
Hydro tech heads must be modified stock, then again, not sure of that either. They "appear" to look / be manufactured just like a stock head.

[whatsamerc??]

whitch ones are better the excell 6k7 or the special 6g7?......benji