Yamaha TRX850 Enthusiasts Forum

Firstly note engine is not in a bike but in a buggy, been a work in progress for far too long now but anyway.....

Motor is behind seat at rear of chassis, collector and exhaust length in total will be about 60cm max before silencer. Was just going to go a custom 2 into 1 for ease.

However chasing maximum torque and hp, should I get another silencer and make it 2 into 2? There is no room for a balance pipe or to tune length of a 2 into 1.

Without getting technical about pulses and scavenging etc, what will work best?

Message BobTRX, I`m sure it`s Bob who has a real short system and still finds the bike goes well.

A symmetrical (equal length headers) 2-1 can work very well on an even fire motor, but is the worst possible choice for an odd fire engine like the TRX. You said you don't want to get into theory but it should be obvious to anyone with even a basic knowledge of how an exhaust interacts with an engine why this is so. They can be made to work well with a few tricks like unequal length stepped headers but unless you're willing to become familiar with an engine sim program your only guessing. This also applies to 2-1-2 by extension. A separate tuned length pipe for each cylinder will give more power and torque and allows more flexibility in where you run the headers in a tight installation. I cant believe people would fit FCR''s etc and then display total ignorance by fitting a symmetrical 2-1.

Fair enough, good call out. Another Arrow GP2 then it is after I've convinced the cheese and kisses it's needed!

Ditto..
That's why an Akrapovic is the only real choice when it comes to 2-1 exhaust system.
The other 2-1 out there are just guesswork systems with no research and development behind them.
I have all plans, outlines and demensions for Over, Akra and Nojima systems.
Tuned length for headers themselves on the std, Over and system have a common length to the link pipe or collector point( on the Nojima it's an x system)
But the Akrapovic 2-1 , the headers are longer being tuned for midrange and collect further back by the relay suspension arm. They also incorperate tapered headers and small link between the header pipes but not at the common point like the std system. That's why the 5.8hp gain at 4000rpm and 2.5hp at 7500rpm from Akrapovic.
Do a bit of a search there is a good reference with dyno results from an Akra system against a std with cans, showing exactly this to back up Akrapovic's own claimed figures.
Pop by if you want Johnno and you can jot down a few measurements and collection outlines and overall lengths to give to who ever manufactures your system.
Hopefully you can tailor a good 2-1-2 exhaust to compliment all the work you've put into the rebuild.

I have a big-bore 2-1 system of projection components on my 900 TDM block with 39mm flat slides. Poor choice and a waste of my money??

baverhae wrote:I have a big-bore 2-1 system of projection components on my 900 TDM block with 39mm flat slides. Poor choice and a waste of my money??

I typed this response 4 times before posting this

The 39MM flat slides are a great choice and will give better metering of fuel and more HP/Torque, IF tuned for the motor correctly. The exhaust….

I have a projection components 2-1 with a QUILL muffler and 41mm flatsides and the bike runs superbly with no flat spots. If I am down a few HP I'll never be a good enough rider to notice. However I do have a full AKRA system, a ported head and a set of + 1mm valves and a fully rebuilt 878 overbored block to throw in the old girl when I get the time to strip her down and rebuild ............Just enjoy it.

baverhae wrote:I have a big-bore 2-1 system of projection components on my 900 TDM block with 39mm flat slides. Poor choice and a waste of my money??

Hi baverhae,
Likewise, I have the projection two into one with a good set of frc41s...I've also got the yzf750 sp front end with a carbon fibre fender which complements the vfr800 single sided swing arm.
The whole set up is most likely highly improper in weight bias and engineering matching and would be open to all sorts of mumbled comments from the back row.,..
However when I'm on one of my regular rides,..the engine sound from the exhaust and the induction from the carb stacks coupled with the wind blasting by...you know THATS where the best place is to be.
Sure I've modded my bike, but it's modded to be ridden .

If you are looking to sell your two into one and the TDMs.....put them up and see what response you get.
Safe riding

cobbadiggabuddyblooo wrote:

lenny wrote:A symmetrical (equal length headers) 2-1 can work very well on an even fire motor, but is the worst possible choice for an odd fire engine like the TRX. You said you don't want to get into theory but it should be obvious to anyone with even a basic knowledge of how an exhaust interacts with an engine why this is so. They can be made to work well with a few tricks like unequal length stepped headers but unless you're willing to become familiar with an engine sim program your only guessing. This also applies to 2-1-2 by extension. A separate tuned length pipe for each cylinder will give more power and torque and allows more flexibility in where you run the headers in a tight installation. I cant believe people would fit FCR''s etc and then display total ignorance by fitting a symmetrical 2-1.

Love the facts, man, just love the facts