Messages

1

General Two Stroke Talk / Re: 125cc gp vs 125cc mx?

« on: October 08, 2011, 09:34:08 PM »

The KTM mx engine is about as good as it gets power wise, and it's actually too peaky for many mx riders out of the box.  It's about a 36hp motor.

KTM certainly knows how to build more power than that - their gp efforts I'd put in the high 40's or very low 50's...but they never made it work for an mx bike...



The yz motor is around the 32-33 mark on that scale - and has an awesome character - rolls on at various throttle openings very low in the rpm range.  makes them easy to ride - and easy to corner very fast....which turns good lap times because the rider can get on the throttle early and smoothly while cranked over.


Im told an honest 39-40hp is the absolute limit gp ktm 125 saw that would hold up during a race.  Between huge RPM fluctuations and the riders over revving them in the air, the dirt, and poor cooling compared to a road race bike..and whatever other elements...it does not seem over 40 is possible for an mx 125. 

Im told husky had 40 hp motors that wouldnt make it one race, 38hp motors that were 50/50, and 36 horse motors that would make every race to the finish line...

In any event - the pipe designs are certainly much more aggressive for the gp bikes than the mx bike...and I thikn that plays a role.  I've always wanted to build a "GP" style engine and try it on the moto track - but experience tells me it will suck..as with common modifications that currently add power - some rideability almost always goes out the window!

Even 4 strokes experience this - as many dirt track engines are just too hard to ride fast on an mx track, and although they crank out lots of hp - they go slower...even with a dyno chart that looks brilliant compared to any two stroke (of half displacement)

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General Two Stroke Talk / Re: HGT Fuel Injection kit on our YZ 144 Project.

« on: October 08, 2011, 09:23:24 PM »

I'm all for EFI on 2 strokes as the volumetric efficiency does change alot more through out the rpm range than 4 strokes, something you cant tune out with a carb.

While people don't seem to give them much credit - modern carburation systems are highly advanced.

To top that off - they do something by fundamental design that many efi systems do not; meter what happens inside the engine upstream.
Now - MASS air flow style efi systems DO measure this, at a cost - flow hindrance and complexity of system.

On high performance two strokes, we also depend on the inlet system for a resonance to help boost output.  This can be hindered via a mass sensor.  On top of that, depending where the sensor is located, two strokes experience a serious flow reversal problem in some instances.
This is also hard to account for.

EFI has been tried at the highest levels of two stroke racing by various teams, and thus far has not truly suceeded.  My "sources" tell me it came down to a few highly dynamic, and difficult reasons to overcome.  One being the bulk pipe temperatures.  This means that if an engine were loaded on a long up hill in a situation where the rpm stays basically constant, the longer it is run - the hotter the average pipe temps get.

The change in pipe temperature influence the scavenging pulses of the pipe, and changes power output.  It's hard to adjust an FI system for this without a mass air flow sensor..but a carb adjusts automatically on demand (via metered velocity).

Also, when a two stroke is coming on and off the pipe, the fuel delivery requirements are all over the place!  It's hard, again, for fi to keep up with this.  Carb's just do it..

For the road racers, it came down to this scenario - when your leaned over doing 120mph around a fast corner, at max lean angle, and you are in a controlled slide - it's important that when you need that right hand connected to that rear wheel DIRECTLY and INSTANTLY with complete predictability you have that connection.  A hair too much throttle and your highsided up on your ass - crying for mommy.

With the FI systems tried - they never got to the point where rider input was perfectly matched with what the bike did.  This made it hard to ride.

For about 90 percent of motocrossers - who dont jet their bike well anyways - this is is non issue, and I'm sure the FI system will work great.

I know a few individuals who have done FI systems to their street RZ's in various states of tunes.  From what i gather, they have been fairly sucessful - but getting the perfect fuel map is REALLY hard and extremely time consuming.  This is true of any FI project.

Making it all work seemless on a dirtbike will be tough without a battery system - but that's a simple hurdle.

o2 sensors are almost worthless on a two stroke...egt monitoring and a good tuner (person/human) is much more effective...

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Technical / Re: 2001 cr 125 goodie list

« on: August 31, 2010, 08:33:38 PM »

I am HP.

That bike stock is just sad - never ever quite ran right.

IF and that's and IF you can sell it for 2300...by all means DO so.

Pick up a newer bike - these days good yz125's can be had cheap.

Even the 05 honda was quite good stock (finally made revisions to motor that paid off)

But if you cant - and you even want to have fun - that motor needs help!  First thing you need to do is jet it a little more aggressively now - but this requires some expertise and patience.  Plus fuel choice factors in. 
I ALWAYS agree lessons will pay bigger dividends in lap times than ANY amount of motor work for non pro rider.

Somtimes when you find a couple horses - but find out how little dividends it pays off in a drag race in actual distance you can be discouraged.  I actually wanted to quit this business one day when I found the real difference in acceleration between a bike with 5 more horses than another - but I finally came to terms with the fact that I would much rather be the guy that gap ahead than behind after the start of straight!

That said - that motor is NO fun IMHO stock.  But run stock pipe for a while and see what you think of that - save you some dough - and it's quite decent in breadth.  Honda made good pipes stock!

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Technical / Re: 144cc stroker

« on: August 12, 2010, 01:41:05 PM »

The ktm 150 IS purpose built, and yes its pipe is different.

The athena 144 kit is horrible as delivered.  It's merely their 125 offering bored out.

A quick glance reveals that the ports are untouched after boring, the boost port is very easy to spot this even if you dont know much about porting.

There is a lot that goes into what stroke should be run...etc.  But at the end of the day, a well built purely bored 144 can run awesome.

The athena kit, modified, can eclipse the 40hp mark fairly easily.

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General Two Stroke Talk / Re: How do they do it?

« on: July 28, 2010, 01:41:21 PM »

First:

200hp out a 1000 GSXR  (or any other 1000) at the wheels is only a myth for almost anyone.

Really good mod 1000's are putting out about 180-185 at the wheel.

Next:

A stock moto 250f is 35ish at the wheel.
X4 that's about 140 at the wheel.  Definately well below a street bike.

A good mod 250f these days is in the range of 43 rear wheel hp.
X4 works out to 172...much more respectable.

The limits in power on the dirtbike, while not fully explored, are typically due to a couple major reasons.  One being the intake tract length.  It's much too long for high rpm inertia/resonance tuning.

The other is head shape.  Because the intake tract goes back towards the air box on the typical bike, the intake port has a fairly large turn in it. Air velocity can not be maximized as would be desired because the air must turn...

The new yami 450 is not limited as much in this respect with its down draft style head.

And lastly cam design and valve train longevity.  High end sport bikes ARE revving higher.  Their peak torque numbers, or BMEP is NOT higher than a good moto engine...but they just spin it higher for more power.  This is not proving feasable on a production motocross bike for reliability concerns.

Now:  A stock 250 two stroke is as stated, about 45 wheel hp.  That's a far cry from what it can make..
a stock 125 easily produces 30 wheel hp...usually 33.  Times that by 8 and you would get 240 plus wheel hp.  

Now THAT is impressive.  The high end motogp engines at 800 cc are rumoured to make approx that type of power at an impressive 18000 RPM.  Technology, materials, and ingenuity at its finest to make that happen.

The worlds best 2 stroke 125s are over 50 hp...still competive at CC per CC at a 100th the cost...

But range of power on the two stroke will sadly NEVER compete at half displacement..and at absolute highest level it would seem even at same displacement to a truly trick 4 stroke..that avg joe will never be able to afford.

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General Two Stroke Talk / Re: Anyone know of any cool exhaust for yz other than PC or FMF?

« on: July 07, 2010, 04:17:07 PM »

I personally love the PC.

BUT...that's on a mod bike.

The GYTR is a bills pipe for the 250.  It's so so IMHO.

The FMF is very much like stock delivery...just a tad better.

DEP...is sort of like stock..but much better mid and top.

Have not tested the SST personally, but I have not heard good things.

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General Two Stroke Talk / Re: Anyone know of any cool exhaust for yz other than PC or FMF?

« on: July 07, 2010, 02:01:55 PM »

this is on TT


This is a DEP vs stock, however includes ignition as well.

That said the ignition was not worth too much (I can't find that chart...)

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General Two Stroke Talk / Re: Some pro riders are at my local motocross track this week

« on: July 07, 2010, 10:25:28 AM »

Sipes probably hasn't rode a 2t in 6 years or so..

And shorty rides for Honda...the one company determined to rid the 2t of existence.

BUT...shorty IS into vintage bikes...AND at one point owned a full works 250 to play on...so odds are he like it.

BUt you certainly cant ask...do you think 4t's should be allowed the handicap (using word "handicap" is just asking for trouble)

Instead ask if they like 2t's because for you...and a lot of your buddies...it's the only bike you guys can afford to race....

Or if they were given the option to race either a 250f or a 250 two stroke in a 250 open class...what would they choose...if it were for a championship...

Also ask if they think their salaries would go up if bike sales were double...and ask what it will take to get bike sales up...

Plus ask if they think a normal kid with an average family can even try to go pro...and even try to race any amateur stuff competitively...at current prices, or if they think the sport is headed a different direction than it used to be...

All fair questions...but try not to show huge prejudice towards the 2t...as they make their money riding a 4t.

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General Two Stroke Talk / Re: Anyone know of any cool exhaust for yz other than PC or FMF?

« on: July 06, 2010, 10:26:06 PM »

DEP is awefully good on this bike

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Technical / Re: Airflow question from a great 2 stroke moto-x aritcle

« on: June 17, 2010, 09:34:46 AM »

the boot is from the airbox to the carb.

The bigger stop holds the powervalve at a slightly higher height on this bike.  Quite honestly you could skip this mod if you didn't want to spend the time getting it right.

The 01 actuates like most other 125's did, with a ball and ramp system.  Holding the powervalve slightly open (it's a rotary style on this bike), or higher in the port gives the engine what is called more blowdown.  Blow down is the time when the exhaust port opens to when the transfers open...and is the most critical period IMHO in a two stroke.

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General Two Stroke Talk / Re: Go Juice

« on: May 25, 2010, 11:35:41 PM »

I agree whole heartedly that avgas, when used correctly, is an excellent two stroke fuel.

If the compression, pipe arrangement, and jetting is correct, my personal findings are avgas will produce better power than pump.

Furthermore, it's strictly regulated (well...much more so than pump gas), extremely consistent, highly resistant to detonation, and relatively cheap.

It also stores well.

Are there fuels out there that produce more power? Yes.
How much more?
If both set ups are optimized for that fuel correctly...usually not more than 3-4 percent improvement best case.

Disclaimer...some fuels produced by elf, which I have not tested, show an oxygen content that's huge....and in turn may produce much, much more power (at huge prices)