Is 13-1 compression to high?

A Yamaha racer who builds and races WR 400 and 426 engines suggests I go to a 13-1 piston, New cam and valves and pipe and carb mods for more power. I have done a lot of research and I am sure he knows what he is doing.. My questions is how long will a stock motor verses this setup last given the same set of riding circumstances? Am I drastically reducing the life of the engine or do most people consider this a good combination of improved power without sacrificing very much engine life. I see guys are posting 5000 miles before teardown. That makes me think it is a pretty strong motor. The bike is used for mostly woods riding, which an occasional enduro and dual sport ride. I rode a WR done exactly this way and loved the power.

[ December 25, 2001: Message edited by: levy1 ]

It will not be worth the money, in my opinion. Take a look at how many Yamaha MX team engines grenaded in the past. It is common knowledge that the WR and YZ get pretty short lived(Especially in the Crank and valve area) when heavily modded.Freshen up the motor, and leave it alone. If you want to up the compression for a little more grunt,that would be as far as I would go.

Just ask some of these guys who have had to make repairs to their motors, and I am sure you will hear the same advice.


agree with dvb

for a start you have ti valves already and so to have larger ti valves will be serious cash.

i personally don't think your mate knows this bike that well. typical paper power.

if you ride woods you need more torque and instant throttle response. there's a lot you can do to the carb but the trouble is you need to do this yourself.

what does he mean by new cam, can you explain because as i'm aware we don't have another cam available for these? stroker TALK about it but that's all it is. talk.

if you increase the valve size you will reduce the torque. bad move.

why not buy the variable camwheels and try different settings.


Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now