15/20 vs 15/21

[zx809]

hey my ski is hitting the limiter now with a 15/20 wondering how much difference running a 15/21 will make?

[Rxtxruss]

Going from a 15/20 to a 15/21 it should drop 100 rpm or so

[ncdoo]

More like 300 rpms.

[zx809]

or am i better to leave the 15/20 in try and turn the limiter up to 8500? im running a stock valve train

[Ken62465]

tweak the trailing edge of your 15/20

http://www.greenhulk.net/forums/show...ll=1#post30039

[hkss]

you will never know before testing. Boost and RPM´s going Hand-in-Hand. Lower RPM lower boost.
In the range of 8100-8500 I would not change to the next step of Impeller it is too much.
When you reaching 8650 and more (8900) then it will be a consider worth - or a pump cone.
This is my personal mind. I am not a professional. Most member here know it better.
But I am testing some Impellers at the moment - and this is the rough result from testing 5 Impellers.
When I am finish testing, I will present the results here in the GH.