CNC head porting

Great site! Wasn't aware of the gearbox failures. I was wondering if any 426 owners have had the CNC head porting offered by Works Racing? They claim a 15% increase in head flow right in the middle of the meat of the powerband. That translates to a nearly 5 horsepower increase in that RPM range. I have emailed Greg Bates at Works to get more information and to ask a few questions such as if there are any carburetion problems that might arise after installing the recommended #175 main jet? (#162 is stock). Greg assured me that the engine will carburate cleanly. Anyone with experience with this?

They claim 5hp.. make sure that you get it in writing and dyno before and after at your local dyno.. and have them up about it! :)

Yamahas heads are good and i doubt very much that 15% extra flow is going to give you 5hp... we'll see i suppose! :D

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**Ride it like you Stole it!**

Matt Porritt

99 YZ400F

Vist the Rubber Chicken Racing Online Shop

Discounts for ThumperTalk members.

i agree with matt, are they claiming 15% more flow & you've equated it to BHP?

the 15% is probably the full head job. just the valve seats & ON IT'S OWN i bet it's 1-2 only. it's definately a no-loss mod & comes under blue printing not tuning (in my humble opinion!).

if you get a before & after dyno chart off them then there's no bull-& if you do could you let me know. depending where this power gain is, tells us where the big valve heads would make their power.

I checked into this also. Unless I am mistaken, they claim the HP increase WITH an aftermarket pipe installed along with the porting...(?)

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99 WZ, all YZ mods, de-octopused, OEM YZ tank and IMS seat, jetting by Clark/James, got forked by Pro Action, DSP airbox, PB Header, Stroker SX-1 SA, Thumper Rad Guards, Acerbis Hand Guards. Moab, HERE I COME!!

Originally posted by Taffy:

i agree with matt, are they claiming 15% more flow & you've equated it to BHP?

the 15% is probably the full head job. just the valve seats & ON IT'S OWN i bet it's 1-2 only. it's definately a no-loss mod & comes under blue printing not tuning (in my humble opinion!).

if you get a before & after dyno chart off them then there's no bull-& if you do could you let me know. depending where this power gain is, tells us where the big valve heads would make their power.

Thanks for your replies and opinions. Yes, I arrived at a 5HP increase based on nothing more than the 15% flow increase. Obviously, that would not be real-world results. The web site URL is worksracing.com. if you would like to check it out yourselves. The brochure does not have a dyno chart to back up their claims, it just has a chart the compares their porting of air flow against valve lift to the stock head. I plan to have this porting done and utilize the Vortex airbox in conjunction to further take advantage of the increase in flow. I have already installed the White Bros. hi-boy titanium head pipe and carbon fiber silencer and have noticed a subtantial boost right off idle. It lost a little on top but the gain down low and in the middle more than offsets that for me. I'm one of those guys who MUST tinker all the time. That's the best way to learn(along with listening to others), in my opion.

Yes, Works Racing used an Up Tite exhaust system on their 426. I'm trying to get dyno figures from Greg Bates at works now. I will post that when it's available.

Just wrote Greg a note asking about dyno results, also checked my old emails from him. I found one where he claims a 1.4 HP increase with the CNC porting and using the Up-Tite exhaust. He admits that the stock pipe makes 1 ft.lb. more torque. Still, that's enough of a power increase that it would definitely be noticeable.

I want to thank you guys for your input in other areas of the 426. I just got a Hinson basket in and the info concerning the screw heads rubbing against the gear will be invaluable. Also, someone posted a site where the micro fiche is online. That is so important to me as well.

Differnt bikes respond differently to the same mods also.

White bros claim 5-7hp for the E-Series Pro-Meg.. I know for a fact that you're looking at less than that.. I'd say 3-5 'real life' hp.. not these fairy ones most mfg's measure in! :)

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**Ride it like you Stole it!**

Matt Porritt

99 YZ400F

Vist the Rubber Chicken Racing Online Shop

Discounts for ThumperTalk members.

boit,

any chance of finding out where in the rev range this 1.4bhp increase came? also it's vital that you find out whether it was the 400 or the 426 head.

it's going to make a bigger difference to the 426 & will make a difference lower in the rev range.

to me the engine doesn't sound exactly strangled. does anyone else have an opinion. i've never done much dyno work but i just spent a week on holiday with a man who does & i can ask him.

Taffy

Taffy, I'm waiting on a reply concerning what the dyno shows with this porting vs stock. I'm very curious as well.

If I remember correctly from what I've read, the cylinder head for the 400 and 426 are exactly the same. The carb for the 426 is what makes them different since the 400 had the FCR from the street bike whereas the 426 has an FCR specifcally designed for it. I agree the the engine isn't necessarily starved for air/fuel but the CNC porting should allow it to breathe better since each porting job will be within less than a hair's thickness of the next whereas you would get different port shapes with someone doing it by hand.

I've always loved the way 4 stroke engines sound and feel and have been waiting patiently for the YZF to come along. I bought a KLX 250 in '94 and had Larry Roseler and Doug Johns of Stroker build the engine and suspension. I also convinced a local shop here in New Orleans to do some head work. This shop specializes in drag bikes and I begged them for help. They liked the potential of the KLX engine and did the porting along with flow benching. The Stroker kit at that time had the option of a 13.5 to 1 compression ratio Wiseco piston which I opted for since I wanted maximum output. With the Mikuni pumper carb and Big Gun exhaust, the bike is very quick and is still running strong.I gusseted the frame around the swingarm pivot myself and had it powder coated lime green instead of that purple crap. This bike is a ton of fun to ride and the Stroker suspension is much better than the stock 426 suspension. Larry does excellent work.

Boit

B***** hell! i'm used to talking to aussies this time of (your) night but not Yanks-god dam!

you sound like you've been around the block & know your stuff.

did you know that the 426 will need the CNC job more than the 400? thats what i meant.

taken to it's extreme if you put a 250 cylinder head on a 500 ANY kind of porting job will have extremely good results!!!

i've looked at your posts & you make it clear that it's a 426 so no problem.

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