Yamaha TRX850 Enthusiasts Forum

Kenny, Matias, Phil and Adrien,
PM sent ..

Yeah still in, but as said before, making sure its the best option for me running 900 top end over sized valves and fcrs, eeeek more money!!!!!!

Just waiting on some more info, but I thought I would just share with you all something nostalgic about the trx in Australia, and what made me contact Andrew. I bought this magazine couple years back at a bike show, (Dated 1998) and was reminded about the yellow bike biz bike at my last racing round by a guy who raced in the ninties, and was at a practice day when bike biz told him "have a go on this" and he said it was one of the best things he rode at the time, apart from something with sheer speed like the new r1, or a well sorted ducati.
The engine specs are as follows if you cant read the text, some discontinued items.
Brooks Vee Two cams
Stock valves and porting.
fcr carbs.
over racing ignition box.
12.0:1 870cc over racing big bore kit
carrillo rods.
full staintune exhaust.
Six speed gear cluster.
All resulting in 71kw / 96 hp. Without a hole in the power curve anywhere.
Remember this is a magazine and sometimes gets things wrong. And its 17 years old.

I'm not for a minute disputing the claims of the cams performance but just how much more would they give over a properly dialed in Kent reprofile at half the price?

I'm going to put in as well, thinking that if the standard pump has around 82 standard, then with a set of fcrs and an over bore exhaust and a programmed ignition...surely we are now to 92 hp ...depending on the type of dyno that was used on the origional test too.
I'd be running the race engine had a bit more than suggested....with the cams and all.

Most TRX's std only develop 70-72Hp and with a little tuning you'll find 76-78 as an average on a std TRX and free flowing cans.
FCR's and a tuned exhaust will give you that extra 10-12 HP and get you in the 86-90Hp region depending on the flow characteristics of the exhaust.

Next ask yourself what YOU want out of your TRX motor and how you want to tailor it to meet your expectations.

Now once you've set your boundaries , research on what will compliment each other to help you achieve your goal.

I'll use my motor rebuild as an example,
Akra exhaust.. Tuned more so for midrange power and slight increase in top end,
The kent cams compliment this to some respect as due to the nature of the reground profile and this boosts the lower midrange characteristics due to the physical restrictions of the regrind.

Everything has boundaries so with the Kent cams by robbing Peter to pay Paul to get the extra 0.4mm lift, material is taken from the base circle on the cam lobe.
What this does then is dictates the nature of the ramp angles which effects the amount of lift of the valve over the whole 300 degrees of duration of actual lift from fully closed -open-fully closed.

Have a look at the flow results on my rebuild thread and you will see close to potential flow within the first half of the lift. but tapers off in the second half due to the duration.
Why, because duration to lift ratio though that early lift period relative to the std cam profile allows just a little more flow due to the ramp on the lobe and how this has been physically achieved by the boundaries placed upon it due to the fact it's been reground from a cam set to work on a different parameter.

The difference with the V2 cam is they have had the research and development and have been designed to meet the parameters worked out from trail and error and testing not only on the racetrack but to perform on the street too.
The only limitation placed upon them is where they would like to see the performance gains in flow(relative to lift/duration) and not like with a Kent regrind which is limited by the physical characteristics to start.

One reason the kent cams are listed as a YAM-9 TDM850 is because they really compliment the characteristics of what you would expect from a sports tourer.

The V2 starts off as a billet blank and the world is their oyster, something the Kent regrind doesn't have. Choice....
This allows the V2 cams to hold the duration of the lift at any specific height to get the best spread of power across a preferred rev range for a sports performance motor like a TRX. (so your gaining in the mid/high rev range)

Perfect example of this is....
This is one reason why you find the lobe centre angles is 1 degree different than the std TRX and Kent option because this would allow just a slightly shelved peak and just that little more duration while the valve is fully open.
The V2 has been developed to optimise ramp angles and lift duration throughout the whole 8.4mm of lift something the Kent cams can't achieve because of the base circle and physical limitation placed upon it.
Cam timing can easily alter the the performance of your motor so 1 degree may not sound like much but there is a method to all this madness and it's specification has a reason.
Another good reason to take a little time to dial in your cams to get the full potentual from your investment.

Don't get me wrong, the Kent cams still have their place.
Remember the boundaries and parameters it has to work with to get the best performance from the modified lobes, hence the nature of the performance they offer..

Don't just look at a final figure on a stated dyno result.
That means $%ck all apart from being a good penis extension.
Look at the dyno result over the whole rev range is what you need and hopefully Andrew may share that soon with us to give you more of a view of the gains over the the complete rev range.


How lucky are we if this all goes ahead, as Andrew is doing this as a love job so guys just take a little time to think (but not to long ) before putting up your hand out of respect for the effort he is willing to do for the benefit of those here on the forum.
A little though on what you want from your motor and how to formulate things to compliment each other..

Bloody boffin!

And for the aspiring boffin who still hasn't learnt to read yet..



Here it is in laymen's terms.
The black line being a perception of the std TRX cam profile.. (not to scale)
The green area showing how you have gained that little more lift through the first 1/3 period of duration with the Kent cams.
And the pink being the potential extra lift on offer with the V2 cams and the scope to profile lift/duration for the desired output.

we have just been schooled, excellent explaination.

Thank you.

Potential interest here too. Some more information and results from the original development engine would certainly help me decide.

I've only got a standard motor at the moment but with a 2-1 Akra system and I've recently bought the ignition module, although that isn't yet fitted.

Basically, this TRX is my 'bike for life' so I'm taking a very long-term view on its development. I'm already running it in hillclimbs and on trackdays and may even consider Thunderbikes too in the future. FCRs and an 878cc kit are also being considered.

Five Oaks 24 hr lawnmower racer Andy? I live in Horsham.

AndyAshworth wrote:Potential interest here too. Some more information and results from the original development engine would certainly help me decide.

I've only got a standard motor at the moment but with a 2-1 Akra system and I've recently bought the ignition module, although that isn't yet fitted.

Basically, this TRX is my 'bike for life' so I'm taking a very long-term view on its development. I'm already running it in hillclimbs and on trackdays and may even consider Thunderbikes too in the future. FCRs and an 878cc kit are also being considered.

Wot he said ^ .... I'm in too with an eye to the future when I'll get as far as engine improvements on the project bike.
No one tell the wife please ...

Mincehead wrote:Five Oaks 24 hr lawnmower racer Andy? I live in Horsham.

Ha ha, that pics a few years old now but yes, I used to race lawnmowers and was there at Five Oaks a few weeks back. I'm still involved actually but only from an organisational point of view these days. I get my competition kicks on bikes now.

You should get along to watch a mower race if you're local. Quite good entertainment and usually free!

It's the World Champs at Coneyhurst in a couple of weeks time.

I'm in for a set.

Should go nicely with the 878 JE big bore kit, 1mm oversize valves, FCR's and Ignitech ignition. I was originally going to go locally through Ivan Tighe for a set of billet cams, but happy to go Vee Two. I never went with the Kent ones as Tighe advised slow speed and idling could damage built up ones.

Cobba I'm still trying to convince the cheese & kisses about those 2mm valves you have.