Engine tuning TDM 900

[howardsmed]

Hi Folks
And here I am back again, I have had three TDM but always use this site as the people on it tune their bikes and the TDM crowd tend to buy hard luggage instead. this time I have purchased a TDM 900 a really late model 2011 one of the last made. As I did when I tuned my last 850 ( with Marks oversize valves, and Kent cams) I dyno my bikes before and after every stage of tuning work, I have a friend who owns a dyno and I kid you not I have dozens of dyno sheets here on every bike I have owned.

The stock TDM 900 engine is very softly tuned, much softer than the 850. the cams are very mild and the static compression too at 10.4:1, however this aspect is not all it seems as the inlet cam closes sooner so the dynamic compression is in fact quite a bit higher. I believe Yamaha knew exactly what they were trying too accomplish, give the model range a bit of a update without adding too much in the way of outright power. I conducted three runs on a absolutely bone stock TDM 900 and all were within 1 hp of each other at just under 76hp rear wheel @7000rpm.

The milder cams in the 900 have lowered the rpm at which maximum power is produced, it should do the inlet cam which controls the engine speed at max power is produced closes nearly 10 degrees earlier. the Wide Open Throttle ( WOT) torque is also increased from the 850, BUT far more importantly Yamaha engineers got a vastly better part throttle torque increase, lets face it most people do not ride their bikes at WOT everywhere, using some degree of part throttle is more usual even if you are thrashing it (race track use precluded)

The much higher dynamic compression ratio ( 9.20:1) of the 900 engine will only assist in part throttle torque. Fuel injection helps in this higher ratio, with its excellent fuel dispersion properties.
The TDM and TRX engines have a dynamic compression of 8.7:1 due to the slightly longer cam timing.

I have had the ECU re-flashed, and fitted a set of Scorpion ovals. Previously I had cut the stock mufflers open removed the CATS and welded the whole lot back together, the power increase was only 1hp, BUT the torque was better and the response time ( the time from 2500-7000 rpm on the dyno at WOT was a full 3 seconds better.

The plan for this winter is to keep the engine in a softer state of tune than that done by others which included fairly hot cams, ruining to some degree the fantastic part throttle torque and lower rpm full throttle this engine has .

The plan is to fit a TDM 850 inlet cam, this is a direct fit, ( good old Yamaha) the 900 exhaust cam will need regrinding too TDM 850 spec. Set the squish at 0.030'' ( as I have done on nearly 500 engines of all types over a 35 year period) and cut the valve seats really well (I use a firm who have a Newan Contour BB head-shop machine, these things are £85K and cut valve seats to an accuracy of under 0.001'') I use 5, 6,7 angle cuts for the race prepped XS650 engines I build
And maybe bore the throttle bodies a mm or so. the usual problem of finding larger throttle plates I thought could be sorted out by taking some from a different throttle set maybe an R1 as they are 40/41/45mm from various years. set the dynamic compression at 9.5:1 which should see the compression pressure right up near the maximum Yamaha claim it will tolerate at 239lbs/in. ( FYI this is an enormous compression pressure, and will alone give fantastic response and torque) this pressure is only made possible by fuel injection and high velocity ports.

I thought my current and future findings might be of interest to the TDM 900 engined TRX owners. I fought the notion of FI for a while, ( actually early fuel injection pre about 1995 was fairly bad) but once you have it, the ability to tune it, and what it "brings to the party" far outweigh carburettors.

The plan is to have more of the same without ruining any aspect of the current performance. I don't really need more than 80hp, I have data logged throttle position and rpm on a bike and gone out for a wild thrash around Surrey, it is astounding even when you think you are going mad how little WOT you use. most bikes pick up rpm so quick the response you want is often achieved without max rpm and WOT

Oh just while we are here, the Kent 09 cams have a very long seat to seat cam timing figure, obviously no compression can occur until the valves are completly shut, so the compression increase required just to get back to STOCK dynamic compression figures using these cams is high, very high !
low dynamic compression will affect lower rpm and part throttle torque a lot, with the Kent 09 cams, you need somewhere near 12.6:1, this is not an assassination of these cams, but many have tested then back to back with stock cams and the increases are not huge. they are worth maybe 5 hp at the very top end, but this comes with a price attached.

More to follow. if you want to see the dyno sheets in various iterations just email me


Howard

[cobbadiggabuddyblooo]

Love this sort of info.
Sounds like it’s just another walk in the park for you.
I learnt all this over the 4 yrs of building my trx thanks to a couple of good mentors.

I had a set of yam-9 cams when I first rebuilt the trx with 12.5:1 pistons.
Great midrange but felt like someone turned of the tap from 7000rpm.
Didn’t stay on the bike for long and fitted some assymetric cams from a friend racing TRX’s in Germany.
They have an extra 0.5mm lift and 3* less duration than the Over/ V2 cams and just about all the Arias 12:1 pistons I sold now use this cam set up. Sits around 8.7 d/comp too.
I questioned the 300 seat to seat duration on the yam-9 cams and I’d check this with the timing wheel and dial gauge at the time. Can’t remember the number now but it wasn’t 300.

I’ve just shifted the cam timing once again after having the valves/ seat (3 angle ) reground and another new set of valve springs fitted. Kept the inlet at 2.3mm/TDC but shifted the exhaust to shut a little earlier from 3.2 to 2.2mm at TDC to find a little more drive out of corners.
Haven’t dynoed since this last change but I can feel the drop off of power now at 8500 instead of the limiter at 9500 previously.

One mod I’ve been using for a while now is removing the centre shim from the std MLS head gasket to find improvements.
Even on my Arias motor, I’ve re-used the MLS head gasket 5 times with no issues.
Just clean them up and re coat with Hylomar blue.

Even the YEC trx cams I had where only 283 from seat to seat with 1 mm extra lift and 253 duration at 1 mm

[tigcrafttdm]

Just for comparison when I was delving into the tdm/trx850 tuning.

trx850 std engine 77hp with fcr carbs (iirc) and 2-1 race exhaust I had made locally.

As above with 878 JE piston kit and fcr's. 91hp.

All std ignition/ports.

All on same dynojet dyno.

[coxylaad]

following this.

I have a tdm900 with a tuned engine including:

cams
compression raised
carillo rods
ported head
Ignijet ecu
performance headers

as a road bike its just an amazing bit of kit.

Interesting what you say about the cams, I used to own a stock tdm900 engined trx, and the tdms power delivery in the low to mid range definitely feels a little softer off the throttle at low rpm.

[skelly]

I'm following this as I will soon be building my TRX race engine.
Have any of you ever looked into removing the rotor and running total loss ? My old racebikes had this set up and span up a treat.
Any thoughts on removing the balance shaft ?

Cheers,
Skelly.

[jpe70]

I'm following this as I will soon be building my TRX race engine.
Have any of you ever looked into removing the rotor and running total loss ? My old racebikes had this set up and span up a treat.
Any thoughts on removing the balance shaft ?

Cheers,
Skelly.

Run total loss if you want, there's not much needing power anyway. But removing the balance shaft is not recommended. If I remember correct it's been tried and let's just say it's there for a reason.

[howardsmed]

Just for comparison when I was delving into the tdm/trx850 tuning.

trx850 std engine 77hp with fcr carbs (iirc) and 2-1 race exhaust I had made locally.

As above with 878 JE piston kit and fcr's. 91hp.

All std ignition/ports.

All on same dynojet dyno.

Last Tuesday I visited Newman cams in Kent, they have an Andrews Products ( USA cam manufacturer) cam reading machine. I wanted to check the TRX850 cams I have, as the inlet 850 inlet cam fits the TDM 900. it is a straight bolt in
The information gained was interesting to say the least. the stock TDM/TRX 850 cams are

238 degrees at 1mm lift with no tappet clearance. both inlet and exhaust are identical and have 8.00mm lift. 298 degrees seat to seat timing.

A few years ago I did the same with a set of Kent YAM 09 cams. these have 240 degrees of duration at 1mm lift with no tappet clearance, seat to seat is 300 degrees. lift is 8.25mm on both in and ex cams

the accelerations and velocities are to all and intents and purposes identical, ( they would have to be otherwise the stock springs would need changing) so what you get with a set of YAM 09 cams is essentially a bit more lift. This might account for why some members on this forum, say that the Kent cam change is not very noticeable when done alone. ( most change compression, etc at the same time)

I will do the same cam measuring process on my TDM 900 cams, when the engine is in pieces later this year, I am told the inlet is 10 degrees milder and 0.25mm less lift, and the exhaust ( which is not interchangeable with an 850) is 16 degrees less duration.... we will see !!

A slightly later inlet closing figure on the 850 cam will allow for more dynamic compression, the TDM 900 is quoted at 10.4:1 but in reality is actually 10:1. I plan to run a dynamic compression of 9.4:1 which will equate to around 11.5:1 static. part throttle performance will increase, Yamaha say that the engine/combustion chamber will tolerate 243 lbs ( 1680Kpa) maximum cylinder pressure, so this is what I am aiming for. Make no mistake, 243 lbs genuine compression pressure is huge.

Howard

[cobbadiggabuddyblooo]

Figures I had been given there was about 10* more duration on the exhaust cam than the inlet on the trx 229/238 rings a bell from memory.
The TRX YEC cams I recently sold where 253 both inlet and exhaust at 1 mm and 283* seat to seat with 8.95mm lift..