A forum for owners of Yamaha TTR250 trail and enduro bikes!

Abbas · Member

Shorty pipe

Cubber · Super Guru

Abbas it seems as if your question has been overlooked cry , have you fitted a short pipe yet?

Looking at the pictures it would seem likely that it would miss the oil cooler without a problem.

Let us know, please.

Martyn

TTRfan · Super Guru

Robin Webb runs a shorty pipe with an oil cooler in extreme desert conditions with no problems.

matteo · Veteran Member

shorty pipes

davecambo · Senior Member

i too would like one of these. anyone know where from?

TTRfan · Super Guru

Hi guys

The shorty pipes were made specifically for Totally TTRs by a local firm whose main market is making complex stainless steel exhaust systems for Maseratis etc.

I have these shorty pipes made up in batches of 5 as they are quite expensive and they sell slowly.

Up until the last batch they were absolutely fine.However, something went wrong in manufacturing the last batch and the exhaust guard nuts were welded on in the wrong place, the pipes were too short and the bend was slightly wrong making them incredibly difficult to fit disbelief

I wonder if the jig was dropped or a drunk apprentice made them on a Friday afternoon confuse

Because of these problems, I have withdrawn my advert until such times as I have a supply of shorty pipes that are up to standard.

CRD used to make a similar shorty pipe but it is very rare for these to turn up for sale.

Sorry guys cry

Brian

matteo · Veteran Member

Ahhhh...... so this picture was one of yours Brian?

TTRfan · Super Guru

matteo wrote:
Ahhhh...... so this picture was one of yours Brian?

Yep biggrin

mossproof · Super Guru

RE: Shorty pipe

sammyttr · Senior Member

only problem with having a shorty pipe is if you flood the exhaust it goes straight into engine and higher chance of hydro locking from the water.

domski1 · Senior Member

sammyttr wrote:
only problem with having a shorty pipe is if you flood the exhaust it goes straight into engine and higher chance of hydro locking from the water.

I never thought of that one, surely though if you are in water that is up to the exhaust tail pipe you would have already sucked water in through the airbox and the bike would have to have stalled?

mossproof · Super Guru

Think I could put up with that risk for a bit more ooompf! As you say domski, the margin isn't that large, 4" or so. If the water's deep enough to enter the tailpipe it'll be going into the filterbox soon enough, and if I've dropped her in the river, the u-bend won't make a difference when she's lying down!
Managed to get over the xr400 urge by going laning with my bro and mates for a day. Nothing wrong with the ole TTR apart from the purple rims, and it's hard to beat the 6 speed box for decent cruising speed, even with 14/52 sprockets. Still intend to do a bit of tweeking though - can't help myself!

Markvan · Guru

Shorty header pipe

TTRfan · Super Guru

The October 1999 edition of the US Motocross Action magazine reported that a free flowing end can add power (and significantly reduces weight over the stock item) but a larger bore header pipe did not! Shortening the existing header by 5" however produced 2bhp extra on the dyno.

CRD developed and sold a shorty pipe for the TTR250 and it must be assumed that they would have done the development and checked that it actually added power. Pity I can't find any advertising material from the time to check their claims.

CRD no longer sell the shorty pipes but they (very) occasionally come up on eBay. They don't have the exhaust guard mounting points which the Totally TTRs version does have wink

Brian

JDM_stig · Veteran Member

RE: Header pipe

petenz · Super Guru

JDM_stig wrote:
but for 2 bhp is it really worth it ?
Does it add any torque, that`s really what we need not bhp.

If you have a 100hp.. 2 more an't a lot..

But the TTR only has about 23 at the rear wheel

so 2hp is around a 10% increass....

-- Edited by petenz on Saturday 10th of August 2013 06:35:53 AM

petenz · Super Guru

JDM_stig wrote:
I understand that but what does that 2 bhp actually do ?
We want more torque which is why Im asking if there were any improvements in torque.

The short answer is.... Yes

HP & torque are are inter linked..

your max torque is up around 4000/5000 rpm maybe higher

& thats where the gain will be...

If what you are after is trials bike type torque ?

start with compression ratio / stroke length / cam profiles / fly wheel weight...

A high out put torque motor is designed to be that..

For the TTR adding mass to the fly wheel would most lightly yeild the best gain in torque..

Stroke length is the real key... longer the stroke the more leveage the piston has

on the crank...

Theres some info on this site about fly wheel weighting for torque...

http://www.woodsracer.com/portal/forums/content.php

-- Edited by petenz on Saturday 10th of August 2013 11:20:24 AM

-- Edited by petenz on Saturday 10th of August 2013 11:34:46 AM

Lin · Senior Member

We fitted the short pipes sold by Brian and picked up mid-range torque, not sure about the top end but certainly no power loss. If the pipe does add 2bhp to peak power, that's +7% from a simple bolt-on part change so I'd say it's worth it.

Markvan · Guru

I am gonig to get a shortie soon. Wonder why it wasnt done at

the factory. Thought maybe cooling had something to do with it.

Or mr yamaha thought the power was sufficent

JDM_stig · Veteran Member

I understand that but what does that 2 bhp actually do ?
We want more torque which is why Im asking if there were any improvements in torque.

JDM_stig · Veteran Member

the increase in BHP doesnt go hand in hand with an improvement in torque, a 2mm wider pipe can add 4-8 bhp at point X, but that wider pipe can alter the torque curve a lot, remember that 4 strokes still require back pressure to work correctly,

A graph from the shorty and standard pipe would yield more answers then trying to muddy the waters with BS about flywheels etc,
the flywheel isnt being replace with the exhaust, you are correct about any rotating mass being better for the torque while on the move but remember that mass has to be rotated or driven across the whole rev range so from lower down it will sap speed as the engine will take longer to reach the desired revs,

loosing 2lBft at 900rpm but claim to be 2bhp higher at X point isnt a gain,

I work in the real world of remapping and tuning so I can certainly add some mud to make myself look good,
all what I was trying to find out is does the replacement alter or add torque over the standard pipe ?
and a graph would be used to sell an exhaust in the real world as it proves or disproves the improvements claimed.

TTRfan · Super Guru

petenz wrote:
JDM_stig wrote:
For the TTR adding mass to the fly wheel would most lightly yield the best gain in torque..

Like the flywheel on the left with the weight band?

brindabella · Senior Member

it sure would be nice to get a good before and after torque curve.

I've never seen a single dyno chart for the TTR250.

Not sure I would trust exhaust manufacturers though.
But they are probably more trustworthy than big pharma's new expensive drug trial reports.

so many ways to "cheat":

1. best of several dyno runs - data that didn't look good discarded;
2. different tuning adjustments before and after;
3. different/thinner/less oil before and after;
4. different/lubricated/adjusted chain before and after;
5. runs with different external temp/pressure without proper compensation;
6. etc, etc.

a flywheel is just a temporary energy storage system.
no torque increase under throttle, but slower spin-up and more resistance to momentary stall.

I reckon most riders would want a flatter torque curve rather than more power at higher revs.
(although sometimes you can have it both ways, but rarely with a single modification)

This brings on my "pet peeve":

torque and power are NOT independent "animals".

if you have a graph of one versus rpm, you easily draw a graph of the other.
(just multiply torque by rpm and re-scale).

the maximum torque point also happens to be approximately the point of best specific fuel efficiency.

maximum power determines maximum speed, when geared exactly to achieve that speed at the max power rpm.

comparing two bikes on their maximum torque is often misleading, because often one bike will develop
its smaller max at a higher rpm, but will have different gearing, so that the red line speed in top is the same.
counter intuitively, this can mean a nominally "lower torque" bike can have better acceleration in an equivalent gear.

end of rant, bring on the dyno charts!

Lin · Senior Member

Torque is the rotating power of the crankshaft- a "twisting force" provided by cylinder pressure acting on the crankshaft through the piston and con rod. It is measured on a dynamometer and is expressed T = R . W where T is torque, R is dyno lever length and W is load registered.

Torque varies with engine rpm, piston engines have a "torque peak" where maximum torque is developed. Many factors contribute to the amount of torque produced by an internal combustion engine and where in the rpm range the torque peak sits. Valve timing, bore/stroke ratio, conrod length, efficient gas exchange from induction/combustion chamber/exhaust design all play a roll but there many many other factors.

A graph of an engines torque output is obtained by plotting different torque measurements taken throughout a selected range of rpm. This is the "torque curve".

Horse power is expressed as HP = T . N divided by a constant (K) where T is torque, N is rpm and the constant is a number provides the result in bhp, ps, kW etc depending on what units of "horsepower" are required.

A graph of an engines horsepower output is obtained by taking the different torque measurements taken throughout a selected range of rpm and using T . N/K to make a power output curve.

The engine that can produce better cylinder pressure, and more effectively convert that cylinder pressure to torque is going to make more horsepower (HP = T . N/K)

To make the engine user-friendly we want lots of T (torque) over a broad range of N (rpm) In other words, "lots of area under the torque curve". Conversely a "peaky" engine has a sharply sloped curve each side of the torque peak (and HP peak) and is not as user-friendly, requiring many gearshifts and other tricks from a skilled rider to extract maximum performance.

Heavy flywheels don't make torque, only cylinder pressure makes that. Heavy flywheels store torque as inertia, you can use it but once it's gone it's gone.

Modifications that alter gas exchange (volumetric efficiency) such as different pipes, different carbs, different cams, different air filters etc affect cylinder pressure (positively if well founded, or not if not) Depending on the modification the effect will most generally be more pronounced in a specific portion of the torque curve. Sometimes a positive gain in one area may be accompanied by a loss in another. An example: increasing valve overlap and duration will generally improve high rpm torque at the expense of low rpm torque. Mods that improve torque below (and up to) the torque peak give more apparent "grunt". Mods that raise the curve a bit after torque peak produce better "power". Exceptions are mods that reduce mechanical friction and mods that improve combustion efficiency. They generally have an effect across the entire operating range, albeit not always proportionally.

-- Edited by Lin on Wednesday 14th of August 2013 10:07:57 AM

-- Edited by Lin on Wednesday 14th of August 2013 11:38:18 AM

-- Edited by Lin on Wednesday 14th of August 2013 08:33:11 PM

TTRfan · Super Guru

Still trying to track down a copy of the October 1999 edition of the US Motocross Action magazine. Are there any American owners on here that can help please?

I am hoping it has some dyno charts showing the result of fitting a shorter header pipe.

Brian

Henry · Veteran Member

RE: Shorty header pipe