MAICOFRED

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Dec 1, 2000
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I HEARD FROM A RELIABLE ENGINE BUILDER THAT IF YOU MODIFY THE SILENCER ON A YZF 250 YOU CAN GET 5 HP. WHAT DO YOU TAKE OUT OR MODIFY? NEED SOME INFO. THANKS
 

Rich Rohrich

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I think you need to start by modifying your sense of reason. Should be a piece of cake from there. :)



Fred - In all seriousness, the OEM Yamaha YZF muffler is a really good design, are you sure he wasn't referring to the WR250F muffler with the restrictive insert?
 

jimt_yz400

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Dec 25, 2000
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I've had good success with installing a DSP SX header pipe and a shortened 426 muffler. The 426 muffler will slid over the o/p of the DSP header (using the gasket though). The 250f is a little choked and with this mid the bike will
hit hard down low and pull stronger in the midrange and rev out fairly well (not quite as well as the stoker). I've even installed an adapter (a friend builds the adapter for me) that accept the white bros disks which works well for off-road (lots of low end but doesn't pull quite as long on top as w/o the
disks). A little cheaper than a full blown exhaust system and a little quieter than the stock DSP muffler which is REALLY loud ( 105db?).
 

TexKDX

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Aug 8, 1999
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You're such a pessimist, Rich. There IS such a mod. You have just missed it.

If you take the muffler apart and remove about 30% of the packing then re-assemblle, the bike will make .001 more HP in the RPM spread from 5,000 to 10,000 RPM. Add it all up, and that is 5 more HP.
 

JasonJ

Member
Jun 15, 2001
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Yeah and I herd that if you take out the baffel and stick a solid rocket booster in the hole and light it, it goes a bit faster too! Oh and looping a tie strap to the header gains about 10 Hp if you hook the other end of it to a YZ 426, :) Sorry. :p
 

BadgerMan

Mi. Trail Riders
Jan 1, 2001
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Originally posted by MAICOFRED
I HEARD FROM A RELIABLE ENGINE BUILDER THAT IF YOU MODIFY THE SILENCER ON A YZF 250 YOU CAN GET 5 HP. WHAT DO YOU TAKE OUT OR MODIFY? NEED SOME INFO. THANKS

I discovered a very simple and inexpensive modification while watching a re-run of the movie Beverly Hills Cop. This mod also significantly lowers the sound output from the stock exhaust! I just stick a plain old banana in the outlet of the stock muffler and I get exactly five HP from my YZ250F!
 

jimt_yz400

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Dec 25, 2000
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So, I gather that by the responses there really is no reason to hope for more
performance out of the 250F since the stock exhaust performs well enough.
Well, it sure seems that the bike runs stronger with the full DSP S exhaust, but maybe not. Maybe it's just louder. But I don't think so. I can actually
pull a gear higher in most situations whereas with the stock exhaust I couldn't.
Banana? Sure sounds good and it might even provide a little more lube!!
 

Rich Rohrich

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Originally posted by jimt_yz400
So, I gather that by the responses there really is no reason to hope for more performance out of the 250F since the stock exhaust performs well enough.

That's not the case at all. You just aren't going to find 5 horsepower by modifying the stock YZF silencer.
 

jimt_yz400

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Dec 25, 2000
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Yes, of course you won't!! I'm *really* sure if you'll ever get 5hp out of an
exhaust anyways, but I'm sure you could get a couple.
 

TexKDX

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Aug 8, 1999
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Originally posted by jimt_yz400
Yes, of course you won't!! I'm *really* sure if you'll ever get 5hp out of an
exhaust anyways, but I'm sure you could get a couple.

Sorry to be a stickler, Jim, but I can't agree with this statement either. There are some high buck systems on the market that actually REMOVE a few HP along the way and at peak. Dirt Rider did a YZ426F pipe shootout in March I believe. They were as nice as they could politically be to these companies without losing credibility with the readership, but some pipes flat were a waste of money. Unfortunately this applies to two stroke pipes as well. For instance on my KTM, the FMF M-20 pipe is fine, but the M-28 pipe totally screws up the power per the testing Alan Randt did for Mike Lafferty's bikes.

In the words of Billy Crystal, "it is better to LOOK marvelous than to BE marvelous".
 

MXP1MP

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Nov 14, 2000
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When I was at the Washougal race this past weekend, Larry Ward said the only mod you need to make to the 250F is change the pipe. Other then that the bike is awesome. He said with that change the bike is just as good as some highly modified 125s.

A guy from another team asked him how he liked his Yoshimura modified motor and Larry said its better but not any faster, then laughed. So engine mods will not add that much to this already awesome motor.
 

srv

Member
Nov 5, 2001
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The magazine you guys need to get is the May 2001 issue of Dirt Bike as it has a 10 pipe shootout for the YZ 250F. Get a back issue just to see the dyno graphs.

Unlike the 426F, the 250F does benefit from an after market exhaust system. Dirt Bike says, "Trust us, the YZ 250F can get even better".

According to their dyno runs, the baseline 250F put out 34.1 horsepower. Dirt Bike ranked the pipes with report card grades: A, B-, C, etc.

Pipes that brought home an "A":

Dr. D @ 36.1 HP
Pro Circuit T-4 @ 36.3 HP


Pipes that brought home a "B":

DSP SX @ 36 HP
FMF Power Core IV MX @ 36.1 HP
FMF Power Core IV SX @ 36.1 HP
White Brothers E-Series @ 36.9 HP
Yoshimura Pro Titanium @ 36.1 HP (..got a B+)


Bringin' up the rear with a "C":

Big Gun Race Series @ 34.5 HP
DSP MX @ 36.1 HP
White Brothers R-Series @ 37 HP


Obviously the HP numbers don't tell the whole story otherwise the White Bro's R-Series would win hands down.

Over at Thumpertalk.com, the 250F forum raves over the Dr. D pipe. Not only that, Gina of Dr. D Racing will give a 10% discount if you mention TT.com.

To sum up, it looks like an after market pipe will gvie you between 2 to 3 HP.

Another mod they rave about is the Vortex ignition; it's pricey though...
 

hoosierf

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May 6, 2001
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Take it from a guy who's dumped good money after bad trying to make his YZ250F run like a YZ250. Just ride it and have fun. After all the screwing around, I found the most usable power came from an uncorked WR pipe that I traded my YZ pipe 4. More bottom and you can run it quiet with a vortip.
 

srv

Member
Nov 5, 2001
7
0
Hey Boozer,

DB was perplexed too regarding the W Bros R-Series since it had the best looking dyno chart of all of the pipes. However their reason is,

"It had decent throttle response and built revs well without getting into the rev limiter. But it was lackkuster in throttle response and "willingess" to rev."

On another note...

Man, I guarantee you guys if you spent your money on a motocross school instead of a pipe, you'd be roostin' all over your pals since you'll have a better idea of how to use what your bike already has to offer. Technology-wise for our sport, we have the equivelant of high-tech Indy cars. All we have to do is learn how to use it and roost all over our buds!
 

Rich Rohrich

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The R-4 that Okie has on his 250F is so frickin load that I aim for it in the turns so I can crush it and force him to put the stocker back on.

It looks nice but it's a really poor design.
 

Boozer

Member
Oct 5, 2001
351
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i totally agree with the comment about spending money on riding education rather than on pipes and other go fast bits. If you must spend money, then go to a professional suspension tuner and have your bike set up for you, not the 'average' rider the manufacturer set it for.
i originally had a FMF Powercore IV on my 250F and liked it alot. After a big accident, it was a total write-off. So i went and bought a R4 because the muffler is held onto the pipe with two springs so in the event of another big crash (flip it over at 90+km/h), the pipe should seperate from the muffler if needed.
I fitted the R4 without the sprak arrestor (like my dealer told me. Why do i listen to my dealer??) and it ran awful compared to the FMF. So i went home and re-installed the spark arrestor and throttle response was better, and after some jetting tweaks, it ran not bad. But the FMF was heaps, heaps better, especially in throttle response and, funny you should mention it, the way it built revs. It sounded better too, as it had a tight, two stroke sound, whereas the R4 is a real RRROOORRRTTT, which sounds crap.
If there is a Whitebros rep reading this, i would like to conclude that i am a very sad customer, and i miss my FMF very much! and before you ask, no, i can't afford to buy another FMF so ill have to wait until i buy a new bike, in a long, long time.:ugg: feeling all sad now
 
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