130 views and no one has the answer? :dunno:

 

Different case with a much larger reed block. Much larger transfer ports in the cylinders. Interestingly enough, the exhaust ports are smaller on the HO cylinders.

 

The exhaust ports on the HO are substantially wider than the old 600. Taller too. The opening into the y pipe is reduced is size but still the same size as the y pipe mouth. The area below the boost port has also been altered to increase flow. The air flow potential of the HO far outstrips the standard 600.

 

Here are some approximate measures I took off a 600 H.O. cylinder. I don't have the specs. off the old motors with me currently. If you hold a HO cylinder next to a an older motor you can easily visually see the differences. The HO cylinders are definitely a much better design. If Polaris put a better stock pipe on the HO's I think they would own the 600 class.

Top Exh. = 30.5
Btm Exh. = 65
Exh chd width = 51
Aux Exh width = 14
Top Transfers = 50.5
Btm Rear Boost = 66.5
Other Trans btm = 64.75
Bore x stroke = 77.25 x 64
Exhaust Duration Approx. Range = 198.5 - 201

 

Thanks for the info guys. I knew it had to be new designs, shapes, etc that couldn't be obtained with the old cylinders. It looks like they left some on the table for aftermarket guys with porting and a single pipe too. HTG had a CFI at 150hp(and not ontheir dyno) with porting, single pipe and 1000' race timing and fuel setup. So, 140hp might be obtainable for trail setup.