Yamaha TRX850 Enthusiasts Forum

I have a TRX850 with short carbon Scorpion cans, I bought a ported and polished head, if I fit it with stage 1 or 2 dynojet what sort of power increase can I expect?

Fit the worked head, but don't fall for Dynojet crap (at least for this bike). Rejet with Mikuni parts in a bench and you might see 5 extra. Fit some aftermarket oversize downpipes and you get 3-5 more. Slipon is mostly for noice...

Get som flatslide carbs and you add another 5-10 hp and with hi comp pistons to round off the package you'll get close to 100.

Better usable power will be the main gain from the flowed head alone.

Ahhh, crap. I don't know, this is guesstimates.

As it is, you probably won't notice anything except noise and maybe a horrible dead spot around 4k rpm.
Replacing the stock ignition unit with a Ignitech gets rid of the dead spot and allows for custom mapping, well worth the money.
As already stated, most carb kits for TRX's are crap as they come from the USA which never had the TRX, so what you get is a TDM kit.
CV carbs can be set up to work very well, but you need a good needle profile and the right sized main jet, which is harder than it sounds to get right.
The stock Yamaha needle is quite good, the standard mains are usually too big.
With otherwise stock carbs and headers, the flowed head has the same inlet and outlet restrictions, so you won't see any appreciable gains.
With bigger exhaust headers and bigger flatslide carbs (FCR/TMR) you start to get something you can feel, but flatslides are even harder to set up correctly than CV's.
Performance Bikes built a hot TRX way back in 1999 and they got 92hp at the rear wheel. 1mm oversize pistons, 13:1 compression (up from 10.5), FCR41's, ported and volume matched head. Quite a lot of work.
Not much has changed since then, just harder to get parts.

Why go to all that just to get a little bit more power, why not just enjoy the TRX for what it is and buy some thing with the power you want. Leave well enough alone and just enjoy the hell out of a great bike. My thoughts. Kenbev.

I've nothing against anyone who wants to work over the TRX and get every last bit of performance out of it.
Cobba has kept us all amused for years with his epic endeavour to build an Over Racing spec bike, and he bloody well did it!
Quantime did a similar amount of work many years earlier, as did Honkdawillydahonk and he got his bike written up in PB!
What should be quite clear, and it was never a secret to begin with, is that making the bike stop better, turn better, and weigh less, is equally important as getting more power if you want to go faster.
Blue spot brakes, cartridge, emulator or USD forks, and lighter wheels make more difference than 10hp, and probably costs less too.

Hi Kenbev,The trouble for me was that I liked every aspect of the TRX apart from its power output.I went looking for higher hp bikes but found nothing that I liked better than the TRX’s design and how it rode.Decided to go down the “ EXTERNAL” engine mods and “ INTERNAL” suspension mods path to wake up the motor and improve the bikes composure,Flatslides,Free flowing cans and Programmable ignition certainly woke up the motor with instant throttle response from 3000 rpm in any gear and the 9000 rev ceiling let you hold a gear between corners better.Cost more than half of the bikes value but it is why I still own it. Cheers.

One way to get more performance out of your TRX (or any other bike for that matter) is to reduce the visit to McDonalds and KFC.
… or upgrade the brakes. (Most overtaking gets done on the brakes going into corners than powering past on the straight bits )