426F cyl. head

Boit

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#1
After doing a ton of research and reading, I've decided that I would like to concentrate my energy and focus on maximizing the cylinder head on my '00 YZ426 instead of doing any displacement increases. I've emailed and talked to a few specialty shops about this and am leaning toward one in particular. What concerns me at this point is the possibility of losing the crisp throttle response that I've spent so much time and energy to attain. I have an incredibly powerful low-end snappy response that I don't want to lose or diminish one iota. Is it possible to retain this attribute. . . . and/or even enhance it while still adding to the mid and mid-top? I'm an engine-sensitive rider who avoids the rev limiter by about 1200 RPM so I'm not looking for a high revver. If I could keep or add to the off-idle power response plus adding in the mid, I would be in a higher Heaven. I use C-12 fuel and enjoy doing the jetting for maximum return. Any advice, ideas, opinions, experience...etc. would be appreciated.
 
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#2
Boit - What were you planning on doing to the cylinder head?
 

Boit

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Rich; First, I had in mind to have the head flow benched and ported. I was hoping for some advice and guidance on other areas such as cam options and is this worth pursuing? Are slightly larger valves and anti-reversion cuts worth consideration? To get better flow numbers, do I have to sacrifice my marvelous low-end burst for a stronger mid? That sort of thing.
There is a fellow racer who is 6'9" and about 320 pounds who holeshots regularly on his 426. He's very secretive about his engine work but whatever it is, it works! If he has upped his displacemnt, more power to him(pun intended), but I'm not interested in going that route. I want to concentrate on the head area. I'm not expecting a huge horsepower gain, but a modest improvement with what is already there. Is this attainable?
 
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#4
The cylinder head can be made a little better but nothing earth shattering. The guys who are charging $700 plus for headwork are to put it bluntly, jerking people over.
I believe there is a lot to be had by using adjustable cam sprockets like the Falicon pieces and different base cam timing. I have some ideas on what should be done but so far I haven't seen anyone that is producing a cam that fits my needs. Even with a different grind, without a lot of dyno time you are rolling the dice. This engine responds incredibly well to an increase in displacement, an increase in compression, tightening the squish clearance, and retarding the intake cam timing. I'm afraid if you go the porting route alone you'll be disappointed.
 

Boit

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#5
Thanks. Your info and opinion gave me something to plan around. The Falicon adaptors are something I am going to when I decide on a definitive plan. I'm not fast enough, or brave enough, to take advantage of an increase in displacement.
 
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#6
The mods I outlined above are generally part of a properly done big bore. The changes tend to clip the high end (above 10K) power a bit in favor of a much more broad torque curve. The peak torque increase isn't as important as the increase in the breadth of the torque curve. The low-mid rpm torque trough is pretty much eliminated especially when using oversized headpipes. All things considered it's the best mod I can think of for the average rider/racer. Flat trackers are about the only group that notice the difference in overrev power.

If you aren't comfortable with a displacement increase then by all means save your money and pass on the headwork. I've spent a lot of time with this cylinder head on the flow bench and dollar for dollar high priced headwork is a bad deal in this case.

A good interim approach would be to use an oxygenated race fuel like Phillips B35 or one of the VP MR series fuels. Lots of response and good top end power is just waiting. Probably the best bang for the buck for guys like you who are comfortable with jetting the FCR.

Let us know what approach you decide on.
 

Boit

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#7
The advice on the fuels is my next step. I'm sure I can get the MR2 but not so sure about the Phillips. Am I correct to expect to go richer on the MR2 when I switch from C-12? It will be fun and beneficial to my learning experience to compare the differences. I'm all giddy now.:)
 
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#8
Originally posted by Boit
Am I correct to expect to go richer on the MR2 when I switch from C-12?
Yeah you'll definitely have to go richer, but given the heat and humidity you are probably experiencing this time of year it may just even out :)
 

sfc crash

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#9
hey rich,wouldn't performance mods for a four stroke yzf motor be the same as a car, ie, port matching the heads to intake/exhaust manifolds, pollish the exhaust port(some in the auto world argue that leaving intake "rough" helps to atomize the fuel mix) increase vavle dia with a three angle valve seat, increase vavle duration( either with a cam and or rocker ratio) ,run richer on the carb, advance the spark timing in conjunction with higher octane fuel, and low flow air filter and exhaust? i fear i might have just shown my total ignorance of the subject, but i'm picking up my wr426 this weekend and had planned on those mods.
:think
 
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#10
If you aren't satisfied with the stock performance of the WR (pretty unlikely) there is very little that you need to do.
Everyone starts by cutting the throttle stop to YZF specs so the throttle opens all the way.
If you are still looking for more you can retard the exhaust cam 1 tooth on the cam gear to set your WR to YZF cam timing, uncork the exhaust by using a Vortip exhaust insert or something similar, get the jetting sorted to your liking, fill it with good gas and leave it alone. The rest of the stuff you've described is essentially a waste of money and time on this engine for the vast majority of riders.

The specifics:

- Polishing the exhaust is just BS eye candy on ANY engine
- The ports, manifold junctions and valves/seats in WR/YZF cylinder head are remarkably good stock so unless you are taking it apart for some other reason don't bother.
- The cam acts directly on the valve bucket so there is no rocker. The lift is more than adequate stock, and the profile is VERY GOOD.
- The ignition timing is fixed unless you pop for a $400+ programmable ignition, and unless you have a lot of experience testing curves it's pretty hard to improve on the OEM setup.
-The stock air filter flows the same as a TwinAir on my flowbench but doesn't seem to be as rugged so the TwinAir IS a worthwhile investment from a durability standpoint
- Once you change to a less restrictive exhaust insert the OEM pipe and silencer is hard to beat.

Be happy, you bought an incredibly powerful well engineered motorcycle that is difficult to improve on with ancient hot rod techniques :)

One last thing. Make sure you lock the doors of your truck when you park at Chicago Cycle. You never know what kind of creepy freaks might be wandering around in that neighborhood :eek:
 
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#11
Here Here Rich!
Sfc, congrads on your decision to go with the big WR, you Will NOt be sorry unless your less than 5' 8 and can not bench press your own weight!
As far as old school hop ups, Yamaha knows all about all that apparently, they did all that good stuff before even tooling the production line! Dude, 5 Titanium valves, 12.5 :1 compression on (good) pumped gas, The only real mods you need are the throttle stop, exhaust insert and DONT FORGET THE GRAY WIRE! This is a High performance racing bike that is cheaper brand new than cheapest car you can get in the states! (dont quote me on that)
Sarge, strap this bike on once you get it unwrapped and jetted and see if you still think it needs anything. It is a great tribute to the design of a bike when the most popular aftermarket purchase for a bike is stickers and seat covers :)
 
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#12
They sell a TON of pipes for these bikes but I fear the majority are bought by complete boobs who hurt the performance more than they help it. The good part is if you have a large enough surplus of power (these tend to) you can screw the bike up with stupid mods and still have a great bike. This phenomena is often described as the Z1 factor :)
 

sfc crash

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#13
ancient hot rod mods! wtf! listen, i'm working on something right now that'll revoullutionize the motorsports industry, it's a tire with, get this, steel belts!ha! i kinda figured i was showing my donkey on the last one.but hey. anyway, as far as the stock bike being fast enough, i'm not good enough to ride a rt100 let alone a wr426, but being all grown up i get too 'cause my paper route money has built up!:D . oh yeh, i always lock up in chi, i used to live on chicago and wollcot. thank god i'm a country boy,now!
 

Boit

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#14
I was hoping to spark some discussion about this cylinder head. Thanks. Also, to drift off topic a little and to respond to the exhaust issue, I would like to add my opinion based on my experience. The first thing I noticed on my 426 was that it seemed to be very soft on the low-end compared to my Stroker KLX 338. Yes, it had a fairly sudden burst of power once it reached the low-mid, but I expected more on the low from a 426cc machine. After installing a certain aftermarket headpipe/silencer combo, the off-idle power came alive like an angry wasp and tamed the transition into the mid range. As a side note, to make the most of this engine, I DID begin using C-12 fuel and jetted crisp to attain the throttle response that I demand. The stock exhaust allows the engine to rev very well, but not all riders want to hit the rev limiter corner to corner. I prefer to shift when my seat-of-the-pants dyno says that power is beginning to wan. The low-end burst that I now have allows me to feel confident that I can drive hard from the inside line and accelerate enough to clear a double that the 2-strokes need a better run at. This is my strength but at the sacrifice of another weakness. Doug Dubach is notorious for hitting the rev limiter. Well, he's light years faster than I will ever be. I race/ride for the sheer pleasure and fun of it. I've been riding since I was 12 and am now 48 and it's more fun than ever. It's fun to not only ride, but to piddle with my machine. I don't drink, smoke, gamble, do drugs, chase women..etc. I live for dirt bikes and I make no apologies for that.

Oh, I DO wear a size 11 Aunt Marilyn style butt-hat.