oubowtie06
Member
- Aug 3, 2008
- 34
- 0
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?
Wanting more power
- Thread starter oubowtie06
- Start date
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.
Ol'89r
LIFETIME SPONSOR
- Jan 27, 2000
- 6,961
- 45
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.
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.
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.
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.
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Ol'89r said:
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.
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oldguy
Always Broken
- Dec 26, 1999
- 9,419
- 0
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.
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.
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.
I think everyone agrees on the high compression piston for sure. The bike needs it for the low end burst.
Matt90GT said:
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. :rotfl:
Matt90GT said:
That's certainly your right. :cool:
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- Aug 2, 2000
- 13,510
- 19
TT builders? Those guys are fags!Matt90GT said:
helio lucas
~SPONSOR~
- Jun 20, 2007
- 1,020
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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...
:|
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...
:|
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.
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.
Matt90GT said:
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.
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