Engine tuning TDM 900
Posted: Sat Apr 04, 2020 11:03 am
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
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