Cams vs Big Bore

[cbc76am]

Don't disagree with byeatts on the airflow, I have rp on my bikes. I mod the stock yz airbox to open it rather the 300 dollar velocity stack, but Im sure it's better. I really like the grunt off the 500, it helps jump up on the snow from a stop, it gets you out of messes. If every day was a blower pow track speed day I'd say just get the 450 flowing, but spring snow, techy climbs, ditches and creeks... I'm all for a 500 with the breathing mods as the combo.

 

[GKR]

Just in the process of building a 590 Built Racing kit on a 2016 KTM500 with DCR cam, 44mm TB and RP exhaust. Field Vortex tune by C3 in the fall and hopefully it rips, expecting good things.

 

[M5-]

So, all the parts ordered, decided to veto the BB and stick with the stock bore. I do at least 100 hours a season hence the 2 bikes, something always breaks, I don't feel like seeing how long the 500 actually lasts it needs to go the 100 hours no questions asked. I know the stock bore will get me through. I'm going with cams of some sort, a port job, a pipe and a Velocity Stack, tune it and forget it. I bought every bearing, a new crank, piston, timing chain, water pump and a 2020 transmission (new pinion gear design) with 3.5 hrs on it, my 2018 basically has no 2nd gear, and finally the GYTR oiler. Lastly, I ordered the parts to install an FX 5th gear which will give me close ratio 1-4 and 14% overdrive for the trail as compared to a YZ 5th. I'm going to roll the dice on the starter motor. Coupled with my 2022 Yeti it'll be good enough for me for a season then roll it into "B" ride status. You've got to love how cheap blue bikes are to rebuild it's just not worth selling it for nothing with no 2nd gear and buying new, the last thing I need are more new wheels, tires, swingarms etc. sitting in the shop.

So when I started this thread Cams vs BB my decision is cams.

M5

 

[gpr]

Big bore all the way. I have built and tested it all. A big bore with more compression will make more power everywhere. Essentially like taking your existing power curve and moving the entire thing up.

On my dyno a yz450f with the Athena 500cc 102mm cylinder, 14:1 cp piston make +7hp.

You will never make that kind of power with a set of cams. Also bigger cams in a stock engine WILL loose bottom end power. bottom end power, and mid range is what you want with a snow bike.

Also depends on where you ride. I run 14:1 big bore pistons on 91 pump gas for hundreds of hours with no detonation on several YZ450f motors. However I live at 5000ft, and snowbike at 9000ft and higher.

 

[byeatts]

Big bore all the way. I have built and tested it all. A big bore with more compression will make more power everywhere. Essentially like taking your existing power curve and moving the entire thing up.

On my dyno a yz450f with the Athena 500cc 102mm cylinder, 14:1 cp piston make +7hp.

You will never make that kind of power with a set of cams. Also bigger cams in a stock engine WILL loose bottom end power. bottom end power, and mid range is what you want with a snow bike.

Also depends on where you ride. I run 14:1 big bore pistons on 91 pump gas for hundreds of hours with no detonation on several YZ450f motors. However I live at 5000ft, and snowbike at 9000ft and higher.

BB do make HP, They do not increase RPM as a high rev cam does, We have both and the stock piston has much more reliability and longevity and pulls higher RPM with the cam , intake and RP exhaust. The BB makes more grunt however the rpm is what creates track speed.

 

[cbc76am]

Not sure I agree completely. The big bores are reliable when properly installed and setup. And they don't hurt rpm at all. Cam, pipe, intake, map or tuning with afr all are important too... But I see no down side to doing the 102mm setup other than more hp everywhere. They Rev just as fast as a 450, at least to what a butt dyno can pickup