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Wanting more power
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Posted by: oubowtie06---------------------

Hey guys i have a 2005 yz250f and i want to get some more power out of the bike preferrably top end have any suggestions?

Posted by: _JOE_---------------------

Cams, porting and exhaust will help your top end.

Posted by: oldguy---------------------

How long has it been since a complete topend? If the answer is I am not sure or more then a season that would bring a lot of 'new' power

Posted by: jb_dallas---------------------

Yeah...sell your 250 and buy a 450. You are going to spend alot of money modifying that bike. I have a hard time understanding folks that modify the hell out of 250s trying to squeeze out a few more hp. Now, I can understand that some people have so much sunk into the bike that they are committed to keeping it...and if it needs a rebuild anyway, you may as well go all out. Remember the old saying "there is no replacement for displacement"...usually true with 4 strokes.

Posted by: Matt90GT---------------------

porting will be your best bet for top end. I always liked a 13.5:1 piston in the bike also.

Posted by: stx---------------------

What are you planning on doing with the bike? Racing I presume. If not with that displacement your gonna kill the best part of the ride. Let me know whats up and I will try and help.

Posted by: Ol'89r---------------------

First, make sure your top end (rings, piston, valves) are in good condition like oldguy suggested.

A 13.5 to 1 piston and a good cam will give you the desired extra power. IMO, a port job is a waste of time and money. These bikes have very good ports to start with. Most only need a slight clean-up on the ports and a good valve job.

The cams can be ground to give you topend, midrange or bottom end power.

Posted by: Matt90GT---------------------

I totally disagree. The porting is way better than off the shelf cams like the Hotcams or wiseco. I tried it all in my 06.

The piston is #1. helps the low end a lot. 13.5:1 is what you want. Just be sure to use premium on the hotest days you will need a 1/4 race gas in there to keep the predetonation out of the motor.

#2 is a pipe. Get a good pipe. MRD would be top of my list, then something likea PC or FMF. Drd will not help your power on the bike.

#3 porting. Hands down. The heads may be decent, but WOW can then be improved. Mid to top has a lot of potential that porting can help. I had mine done by Barton Built:

They know what they are doing on the YZF heads. It pulled way hard in mid to upper. I actually swapped the head over to a friends bike when I sold it and he only had a 13.5:1 piston in there and the head, and it pulled hard. Stock pipe and cams on that bike. It really needed a pipe.

If I were to get some cams, it would be like a crower or other custom ground unit. You will have to get matching valves and springs for the grind of the cam if you go radical.

Sorry to disagree with you 89, but I had that bike and that motor built. So speaking from experience.

Posted by: Ol'89r---------------------

Quote:

Originally Posted by Matt90GT

I totally disagree.

Sorry to disagree with you 89, but I had that bike and that motor built. So speaking from experience.

No problem. You are entitled to your opinion. Speaking from experience, so am I.

Posted by: Rich Rohrich---------------------

Quote:

Originally Posted by Ol'89r

No problem. You are entitled to your opinion. Speaking from experience, so am I.

I'll second your opinion 89r. Porting on the Yamaha 250f heads is a huge waste of money for the vast majority of riders. I've spent countless hours on the flow bench and the porting bench with these heads over the last seven years and never found gains that could justify the outrageous prices people charge for porting these heads. I've seen more than my share of "ported" cylinder heads that flow LESS air than a stocker, and end up with huge port area increases that make the engines lazy under acceleration and tougher to jet.

A careful blending of the port throat into a properly cut multi-angle seat shows the biggest gains, but that is just the normal work that comes with a good professional valve job. Fidddling with the port upstream of the port throat is total nonsense for 99% of the applications that these engines will be used in.

Changing the cam, but most importantnly the intake cam phasing will have the biggest impact on shifting the power to a higher rpm range. The Hot Cam Stage 2 intake is a good choice. It has the right spec to run with a 13.5:1 piston and the cam sprocket is adjustable so you can retard the intake LCA and further fine tune the power to a higher rpm.

Posted by: oldguy---------------------

First off JB this might be a bike he is racing in a displacememnt class so a 450 is useless to him- it would be nice if everyone could just go big.

As far as head mods when Eric Gorr built the YZ250F motor for my son to race he did not do any porting just cleaned up what was there. He was far more concerned with valves and cams.
Granted my son is not the fastest racer in the A class but that bike is. It has been ridden by a couple of the guys that are the fastest and each one has always said they loved the power delivery a couple even liked it more than their bikes.

Posted by: jb_dallas---------------------

I didnt see any mention of racing in the original question.

Posted by: Matt90GT---------------------

funny was I was on TT this morning and a similar post came up. builders were saying 3hp just on porting alone with this bike. That is a good amount of power hiding in the head and I believe it.

I think everyone agrees on the high compression piston for sure. The bike needs it for the low end burst.

Posted by: Rich Rohrich---------------------

Quote:

Originally Posted by Matt90GT

funny was I was on TT this morning and a similar post came up. builders were saying 3hp just on porting alone with this bike.

Only if the easter bunny is doing the dyno pull.

I can't figure out who is more full of ****, politicians or guys making nonsense horsepower claims in an effort to convince people to spend money with them. Both are just lying scum looking to take your money with no noticeable return on the investment.

Quote:

Originally Posted by Matt90GT

I believe it.

That's certainly your right.

Posted by: jb_dallas---------------------

This is easy enough to resolve....

OU

Are you racing that bike?

Posted by: Chili---------------------

Quote:

Originally Posted by Matt90GT

builders were saying 3hp just on porting alone with this bike. That is a good amount of power hiding in the head and I believe it.

I wouldn't use builders plural it was one builder who was trying to sell his porting service. It also happens to be the only builder who has ever seen a performance advantage by putting dimples in valves....

Posted by: _JOE_---------------------

I vividly remember a few pictures of those dimpled valves. And a dimpled piston......

Posted by: XRpredator---------------------

Quote:

Originally Posted by Matt90GT

. . . I was on TT this morning and a similar post came up. builders were saying 3hp just on porting alone with this bike. That is a good amount of power hiding in the head and I believe it.

TT builders? Those guys are fags!
http://sinaphile.files.wordpress.co...urf-no-dice.jpg

Posted by: jb_dallas---------------------

XR....that was hilarious

There has been no mention of racing by the starter of this thread. I will stand by my original comment, sell the 250 and buy a 450...rather than dropping 2 grand+ on a motor.

Posted by: oldguy---------------------

Quote:

Originally Posted by _JOE_

I vividly remember a few pictures of those dimpled valves. And a dimpled piston......

Yeah dimples are a great thing
http://i62.photobucket.com/albums/h...0f/IMG_5198.jpg
At least on cute girls and golfballs

Posted by: oldguy---------------------

Quote:

Originally Posted by Matt90GT

funny was I was on TT this morning and a similar post came up. builders were saying 3hp just on porting alone with this bike. That is a good amount of power hiding in the head and I believe it.

I think everyone agrees on the high compression piston for sure. The bike needs it for the low end burst.

Matt I don't hit TT but if you are basing your opinion on the posts of the guy doing the dimples I have some oceanside land for you cheap

Posted by: helio lucas---------------------

not sure if want to post.
that said, i don´t know if there´s 3 hp hidden on porting or not. i really don´t care.

BUT, it is very hard to make a better engine than stock other than keep the engine in shape and correct some flaws, either by production or by costs...
now if to get those 3 hp on the very peak one have to loose 10% peak torque, or torque area, what the hell is the point for a motocrosser?
a engine that have a smooth delivery, flat torque, easy to jet, wide band, reliability, matched to gearbox, etc, etc... and is competitive in almost all forms of racing, why would someone change that besides R&D or the fun factor?

damn, a 250 can compete in top mx with a 450 with +20 hp. this happens every weak in the portuguese mx nationals. the lap times are the same.
there are so much torque available on both bikes that the limiting factor is tire grip, not power or torque!

i´ve seen people put expensive exhaust systems on bikes that make more noise from piston slap than from the new pipe. or port for top end and then put a heavier flywheel? this one i really don´t understand!!!
if you want harder pull for the fun factor, get or machine for a lighter flywheel. now it´s fun enough...

Posted by: Matt90GT---------------------

no I am basing my facts on my 2006 YZ250F that I built up. The post on TT with dyno numbers helps reinforce the fact that there is power to be made by porting the head.

What are you basing your opinion on OT? How many YZFs have you ported out is what I am asking? If you say none, which I expect, your opinion is without facts.

Posted by: Rich Rohrich---------------------

Quote:

Originally Posted by Matt90GT

How many YZFs have you ported out is what I am asking?

I've done about a 45-50 YZ250Fs cylinder heads and have spent more hours looking at the 5 valve Yamaha heads on the flow bench than I can count. The work that was done to Oldguy's various 250Fs was a direct result of that work. So even though he might not have had the porting tool in his hand, he is more aware than most about the specific work that was performed on his engines, as well as the real world results that were acheived.

Given the above stated experience I can confirm that you won't find 3 horsepower in that head without cutting the intake along the centerline reangling the port, raising the floor and welding it all back together. Unless of course there is a gerbil living in the port, then maybe the extraction of said vermin might net 3 HP.

While it's certainly your right to believe otherwise, but attempting to prop up your argument by quoting the BS lies from a known nudnik masquerading as an "engine builder" just makes it hard to take your personal experiences seriously.

If you feel you got value for your money then you should be be pleased. That's a good day in anyone's book.

Posted by: jb_dallas---------------------

Rich

Are you a motorcycle mechanic by trade? I have a 99 YZ 400F and it seems you have plenty of experience with that particular configuration. Do you build engines for the general public as a business or is it just a hobby?

Posted by: oldguy---------------------

Quote:

Originally Posted by Matt90GT

no I am basing my facts on my 2006 YZ250F that I built up. The post on TT with dyno numbers helps reinforce the fact that there is power to be made by porting the head.

What are you basing your opinion on OT? How many YZFs have you ported out is what I am asking? If you say none, which I expect, your opinion is without facts.

As Rich said I am not a mechanic and trust our engines to only Eric Gorr and Rich for the work. My opinions are just thAt- but based on the seat of the pants experience of my son racing them (his qualifications while not a national pro rider he is in the upper 20% of our district A class. He is quick and tends to ring every bit of power he can from a bike). We do not rush a new bike in for mods as soon as we get it but instead he practices and races it for several hours (usually until the first valve replacement is due) and then we have Eric or Rich do their magic to it. Every time we get a bike back there is a line of other A riders waiting to test it out and compare to their own bikes- some stock and some highly modded and the usual opinion is that the bike is faster and stronger then their own.
So if I have to hold the tools and mess up my engine you are correct I don't have any facts. But if common sense and seat of the pants testing by several riders is of any value in the real world I am qualified to sp[eak on the results.
BTW I have seen many people gets hands on with snowblowers and chop off fingers- does that make them experts in the design of the augers? You above statement would support that statement. Anybody can pretend (especially on the internet) to be an expert but real world shows the differance. I rely and trust in my 2 chosen mechanics I would like to see some of your qualifications as an engine builder besides opinions backed up by the dimpler's assertions. Remember you called me out first and I have been honest on my lack of hands on

Posted by: oldguy---------------------

Quote:

Originally Posted by jb_dallas

Rich

Are you a motorcycle mechanic by trade? I have a 99 YZ 400F and it seems you have plenty of experience with that particular configuration. Do you build engines for the general public as a business or is it just a hobby?

JB rich is the kind of guy that finds the challenge of making something better by tearing it apart and studying it entertainment. Here is a thread that if you read through the fun stuff details just how Rich and Eric Gorr attained their standing in the Moto world
http://www.dirtrider.net/forums3/sh...ht=rich+rohrich

Posted by: jb_dallas---------------------

Thanks oldguy

I read alot of the thread....very interesting.

Posted by: Rich Rohrich---------------------

Quote:

Originally Posted by jb_dallas

My day job isn't in the motorcycle business (the pay is way too low) but I've kept my hand firmly in it.

About 6-7 years ago when Eric Gorr decided to get seriously into the four-stroke performance market I worked with him nights and weekends doing cylinder heads (flow bench R&D, porting, valve jobs etc.) and complete engine builds. I worked with him to develop some of the processes and specs he uses. We also worked a lot on engine forensics to get a handle on the cause of catastrophic failure in late model MX engines and what could be done to prevent them. Eric has a wealth of data and experience in this area on all types of engines.

I did that for a few years until Eric relocated to Madison, Wi. At that point I wasn't able to work with him any longer in the same capacity.

These days my involvement is more as a curious observer who plays at home on the flow bench whenever a new model cylinder head crosses my path, and the occasional sounding board for Eric's new ideas and concepts.

I hope that answers your question.

Posted by: whenfoxforks-ruled---------------------

Thanks for being you Rich! Old guy, I couldn't have said it better, really! Matt, sit back and reflect, this sure sounds like "quad information", doesn't it? You were not around when the dimple guy got ran through the ringer? Vintage Bob

Posted by: jb_dallas---------------------

Thanks Rich, you answered my question. I guess I need to contact Eric Gorr when I need work done. If I was smart, I would sell the YZ before it needs a rebuild and buy a WR or 450X, but Im already knee deep in it now.

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