Yamaha TRX850 Enthusiasts Forum

You're welcome to come and grab mine, as I don't have verniers to measure them. I'm at Burpengary, text me if want. I'm also wanting to know the measurements of them so I know which ones are inlet & exhaust.

The oversize valves I supplied are :

27mm inlet.
29mm exhaust.

I actually quite fancy trying 28mm inlets

Mark

thanks Mark

Hi, I removed some material from the piston to solve the problem , the radial clearance should be 0.05" or 1,3 mm minimum according to the JE data.
checked it with some clay and its save now , the face clearance is (was) enough .
It would have gone wrong with no modification

My piston are done now too.

So, everyone has taken up the valve pockets in the piston crown?
How much?

Killerwhale wrote:So, everyone has taken up the valve pockets in the piston crown?
How much?

You need to, but only if you're using high compression pistons.

My results:


For further info see my rebuild topic viewtopic.php?f=6&t=9765

It would have been interesting to know the contribution from each modification separately, but that would cost one a fortune on dyno time and a lot of putting the engine apart and back together again.

Hi Robert,

That really is a great result, the bikeshop that reworked your head did a very good job indeed .

I'm glad that your winter works came good in the end. That is one of the very best Trx curves I've seen. Your big valve cylinder head really is making an awful lot of power and torque for you. Congratulations

It must be lot of fun to ride with more than 85Nm (62 lb-ft ) of torque spanning 2500 revs ( 5700 - 8200rpm ). My home ported head,running 868 Yamaha pistons with the same +1mm oversize valves, but only std exhausts (not Akras) can only muster +85Nm for 1700 revs ( 5200 - 6900rpm ). I'm hoping an Akra and a little ignition work this summer will help me close the gap on yours in the torque stakes. I will always be a little behind you for power, as my torque peaks some 600 revs earlier than yours (6270 ish versus 6850 ish). As power is basically torque x revs divided by a constant, my outright peak power will be little less but I will aim to match your peak torque of 91Nm and it's spread

Thanks for posting your results of your efforts for all to see. I for one am mightily impressed.

Perhaps we will have to arrange a track day in the Nederlands. A sort of Anglo Dutch ( or indeed European ) Trx Track Festival.
Actually the more I think about it the more I think it could be possible. Perhaps for next summer with a little prior planning.....and some Trx fettling over the winter

Mark.

Ps.
Edited to say I have just checked my dyno sheets and have found that my peak torque of 64.8 lb- ft equals 87.8 Nm so I'm lagging you by 3.2 Nm or 3.6%

Thanks Mark. Yes it rides like a dream. I just came back from a bike weekend. I found myself alone on the Autobahn with no luggage or anything ... 234 km/u on the GPS nav.

Oh and a Dutch trackday would be great of course. Assen is expensive though, being a GP track and a lot of amateur racers would like to train and practice there.
We also have Zandvoort which isn't too bad, although it is a typical car track, with boarding close to the track.
I would really like to meet up with the UK riders from this forum, but I don't think I can make it in August on Cadwell ( it was Cadwell right?).

sanddune51 wrote: Edited to say I have just checked my dyno sheets and have found that my peak torque of 64.8 lb- ft equals 87.8 Nm so I'm lagging you by 3.2 Nm or 3.6%

Crap Aussie fuel?
Gordo-

234km/hr ! Thats 145mph which is very impressive for a Trx... Glad you're enjoying it to the full .


Mark.

Here are some photos of some of the new +2mm inlet valves.

Like a "Dipstick" I've managed to post all this in the wrong thread.... Apologies. It should of course have been posted in the 2mm oversize inlet valves available thread.



A new inlet valve at 28mm


An original Trx inlet valve at 26mm


A few shots for comparison of the new 28mm inlet against the original 26mm









If you are interested in a set, ping me pm.

I find myself extraordinarily busy at the moment so won't be able to participate in discussions on the merits of bigger valves . Do use the search button though to find answers to your questions. There is a stack of great information on the forum .

Mark.

cobbadiggabuddyblooo wrote:

Killerwhale wrote:

sanddune51 wrote:Thats interesting....

82Nm of torque = 60.5 ft-lbs which is very very good for 4400 rpm .Mine is only 51 ft-lbs at 4400 as standard,so you're over 18% up.Before you all shout at me,yes,I know we comparing different dynos,but heck,18% is way beyond the realms of plus or minus 2 or 3 per cent dyno disparity.

75Nm of torque = 55.3 ft-lbs. This shows that the mathematics behind the 5225rpm therem holds up.
You've around 55.3 ft-lbs torque and 55.3 bhp at 5225 rpm.

Thanks for posting your numbers.I hope you're able to fill in your torque depression at those revs.

Maybe I'm being way optimistic for my home built motor.


Mark.

If you have not seen it my latest dynochart is under my bike in the member bike department
Guess we will have a lot of comparison charts soon, i have to wait until my mech done all race bikes for 2013 season though...

4400 rpm 58.5 ft-lbs
5500 rpm 60.5 ft-lbs
6200 rpm 62.16 ft-lbs / 72Hp
with the best run showing an 86.71hp
http://i393.photobucket.com/albums/pp14 ... rspeed.jpg
http://i393.photobucket.com/albums/pp14 ... torque.jpg
http://i393.photobucket.com/albums/pp14 ... irFuel.jpg
got that same dip around the same area as you too Killer, and the spike in the air/fuel at 5000 may be as you said before about the accel. pump.
Thats my starting point with the FCr's and old 2 into 1 system...
Next step
I'd be keen to see how it comes up just with the Akra system and kent cams as a comparision before any other work internally..


You can see by the dyno sheet the red line is with the small teastrainer bung in the end of the pipe and the blue line was with the open 58mm can (needle jet dropped and how the bike finished off).. and the green as std factory FCR settings and jets... it's still running the std 150 mainjet with bellmouths and Ramair twinsock

Nutted out why the dip in torque curve most of us have experienced at similar RPM with FCR's and mild tuning...
Overlap and reversion.
If running the std air box change you'll need to tune the intake horn to suit and if running no box at all then you'll have to live with that as with such an open area, you'll never get a neutral or slight pressure against the intake charge to keep it at bay.

I am surprised that no one has looked closely at the YZ450 and its variants as a source of parts. Yamaha 5 valve motors are built to a loose template based on the original research engine (a story in itself). The YZ 5 valve series was probably the most intensely developed 5 valve ever for the huge offroad market. If I was building a serious TRX engine I would be looking closely at a late model yz450 combustion chamber and porting. The yz came in a few bore/stroke ratios and I,m sure amongst all those titanium and steel valves, 12k conrods and maybe pistons suitable for a killer big bore at a fraction of the price of bespoke items and probably better. Then there is the huge aftermarket for YZ,s. What the TRX community needs is someone with access to the range of YZ and its variants parts

Been there Lenny and looked at a few bits n pieces, hence the 220mm rear disc set up I now use.
YZ Rod length is way too short for a TRX too, valves won't work either.