GPZ Intake and Exhaust Mods

Steve Northrop blackgpz at
Sat May 2 08:24:49 PDT 2009

     The ZRX1100 and GPZ motors are similar mechanically except for 
camshafts and compression ratio. The GPZ is 11:1, the ZRX 10:1. The ZRX 
camshafts are milder to keep cylinder pressure up with the lower compression 
ratio. The GPZ camshafts are in between the ZRX's and the ZX11's in 

     There is no K&N OEM replacement filter for the GPZ.

     Reed block-off plates are required for Stage 3 since some of the lines 
for the KLEEN air system go to the airbox and you will be ditching the 

     The reason for using an aluminum fan when replacing the stock exhaust 
system with a header is the stock exhaust header pipes are double wall pipes 
so there is not as much heat where they pass by the cooling fan. Aftermarket 
header pipes are single wall and generate much more heat in this area, 
increasing the chance of melting a plastic cooling fan. Another plus of the 
aluminum fan is it's 6 blades in stead of 4 so it moves a lot more air when 

Steve in Western NY
'96 GPZ1100
'08 KLR 650
'08 Tuono Factory
"You Can't Fix Stupid", Ron White

----- Original Message ----- 
From: "keith fraser" <fraskei at>
To: "gpz list" <gpzlist at>
Sent: Friday, May 01, 2009 8:50 PM
Subject: GPZ Intake and Exhaust Mods

I have been considering intake and exhaust options. I came across this page 
on the muzzy site, , showing the 
effects of different mods on a zrx 1100. It's my understanding the gpz and 
zrx motors are very similar.
There isn't much difference in power between the stage 1 and stage 3. I 
would like to stay with the stage 1 but would like to replace the stock air 
filter with a K&N. The air filter is tiny, only about 2/3rds the size of the 
filter in my old Ninja. K&N doesn't list an air filter for the GPZ, anyone 
know of a compatible K&N part #?
If I did decide to go to a stage 3 would I need to buy the reed block off 
plates? Is there anything else that would need to blocked off or disabled?
Unless I find a really good price on a used exhaust system I will probably 
buy the v&h supersport. It fits my budget and is the only black pipe I have 
been able to find. Does anyone know of any dyno charts for the v&h pipe? Or 
any other pipe and jetting combos?
Also I have seen a couple sites recommending changing out the plastic 
radiator fan for an aluminum aftermarket one, is it really necessary?

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