TRX850 enging in a 3TJ

[Evilchicken0]

It's not just about torque but how and where it's deliverred. Twins tend to get grip and drive out of bends better than IL4's

[dobbslc]

I've got a TRX & a 3TJ sat in the garage mmmm revs v torque.
The TRX is a big lump for a twin though it's almost as wide as the 4 cylinder FZR engine!

[Mad Ad]

KIYOSHI you are right the blade does make more torque than the TRX but like Evil said it's ease of use, the balde's torque is 3000 rpm higher which makes it less acessable. Also I have a TRX engine already in my current race TDM I just wanted to make it handle better. If you have a copy of the article in Motorcycle Mechanics I would be very interested in reading it.

So far my initial investigation shows that it should not be too much of a truma as the rear of the engine seems to line up already but I have not made 100% accurate measurements yet and the front mount should just need a set of brackets I just need to clear some space in the garage to get started.

[KIYOSHI]

I dont have a copy but im sure if you called them they will have a back issue or 2 kicking around.

I like the idea of a twin in the chassis but imo the trx lump is miles away from the best option. 90+bhp Er650 engines in 400 chassis work very very well. A 748 lump would be awesome and a stock 100bhp!

Are you limited to capacity restrictions? or any other limitations?

The other issue id be concerned about is weight distribution. The 3tj chassis is designed for the very light 400 engine, although i will agree the 600 transplant works well having ridden a 92bhp hybrid in anger. BUT i would be a little worried about cornering grip with a heavy 850cc v twin in the chassis as the amount of drive required to obtain 40/60 weight distribution would possibly cause some stability issues. Did you not say the bike would be used for sprinting? If tyre warmers are not allowed id be a little concerned. Maybe look at making the swingarm slightly longer (similar situation to the early R1, big bhp, stacked gearbox, lots of weight on the front = very long swingarm which most racers had made longer still!)

What are the stock BHP/torque figures for a trx and at what revs? How do they comopare to say a 918 blade 748 duc, er or sv 650? Or even a tuned 400?

Anyone know the weight of a trx engine? Ill happily weigh a 400 motor if anyone is interested in comparing power to weight figures?

[KIYOSHI]

Shit, im know looking at a spare RRSP race chassis thinking about the possibilties????

Anyone got a spare 500cc 2-smoke single kicking about? Or even 2 with a custom cranck and case, that would be a challenge.

[Kayla850]

The TRX engine is heavy, probably around 70kg or so and the quoted figures are-

80 bhp @ 7500 rpm

58 ft/lb @ 6000 rpm

but that's with the standard cans and carbs. You can add at least 10bhp if you use FCRs and open pipes :)

[KIYOSHI]

Dont believe the Japs, they tell lies!

Ill put money on a stock TRX making something in the region of 70bhp, add that to the weight and a mild tuned 400, say 75bhp will leave it for dead, anywhere! Add another 10 bhp for a highly tuned 400 and there will only ever be one result. And that big heavy twin will kill the handling which is the best feature of a 400.

I really like the idea but the only way it will ever work is to go down the modern 650 twin route.

[KIYOSHI]

Just out of interest my FZRs weigh about 150kg with approx 8 to 10 litres of fuel so about 140kg with a dry tank.

Figure 0.607 bhp/kg for an 85bhp machine

If we said adding the TRX engine put 20kg on and app 75bhp you will be looking at 0.468 bhp/kg thats asuming its a race bike stripped to the bones.

[Kayla850]

Just out of interest my FZRs weigh about 150kg with approx 8 to 10 litres of fuel so about 140kg with a dry tank.

Figure 0.607 bhp/kg for an 85bhp machine

If we said adding the TRX engine put 20kg on and app 75bhp you will be looking at 0.468 bhp/kg thats asuming its a race bike stripped to the bones.

Yes, but that 75bhp is with the standard pipes and carbs. If you tune the TRX engine (like you have the 400) you can assume around 100bhp (with carbs, 878cc higher compression pistons and race cans). It'll probably cost around £1000 to get there, but it's doable.

It's interesting just because it's different, but I definitely think Yamaha are missing a trick by not making a smaller parallel twin.

[KIYOSHI]

You hit the nail on the head, A small compact inline twin is the way forward. Look at the facts, it takes a modern (light weight) 650 twin in a 400 chassis with 90bhp or more to beat a tuned 400.

Yamaha will make one sooner rather than later im sure.

Special builders have been doing it for years with Cagiva Mitos.