Gore/Rohrich bigbore Breathes FIRE

SFO · Sep 28, 2001

until I receive the b03

I will just run b32

SFO · Sep 28, 2001

stock pipe 9lbs 7oz (WR426)
arrow pipe 7lbs 12oz
just weighed them,
Have to put the stock pipe back on because I didn't make a spark arrestor yet.:(

Rich Rohrich · Sep 29, 2001

Originally posted by SFO
Have to put the stock pipe back on because I didn't make a spark arrestor yet.:(

Bill - If you get the chance to run the Arrow and OEM back to back let us know what you think about the differences. With the big motor I'm sure the Arrow will have a substantial advantage, but it will be interesting to hear what you think.

SFO · Sep 29, 2001

I rode Hollister with the stock pipe today.
After the Arrow, the stock pipe is louder and subdues the power delivery.
I remember opening the throttle 100% once.
Once today I was able to open the throttle all the way.
It reminds me of the old yz 490 I had.
Short shift at least one aditional gear and don't breathe on the throttle unless you mean business.
I let my 520 friends (2) ride it and they loved the power, suspension, and the fact that it turns...

holeshot · Sep 30, 2001

Rocket Boosters

Originally posted by EricGorr
I suggest starting with a 426 rod kit and cylinder.

I already have a 426.

I've ridden my 426 and someone's 400 back-to-back, and found that the 426 romps a bit harder down low, but nothing to write home about. This is an increase of 27cc (399 to 426) and I didn't go nuts about the difference in power.

Now we have an increase of a mere 18cc (426 to 444) and suddenly we have an "oh my god, everything else is a moped, can't even open it up or it'll loop, rippin' my arms off, where's my mommy?" motorcycle.

I was wondering what differences (other than displacement) were required to create such a rocket. If you have to shoot me 'cuz you told me, got ahead and shoot.:eek:

Jim D. · Sep 30, 2001

what would the price be on having that mod done to a 2000 426??could you run pump gas in it?

Rich Rohrich · Sep 30, 2001

Differences from a box stock 426:
- 444cc displacement hits a sweet spot in terms of intake velocity with the OEM port shape and size. 98mm would actually be better but there are too many trade offs at this point.
- Compression ratio
- Squish clearance
- Piston crown shape and swirl/tumble changes
- Cyl head changes
- Cam timing due to deck height changes
- Jetting
- Running the CORRECT fuel
and last but not least assembly by an engine builder versus a factory line worker :)

A properly setup 417cc engine with 13.5 compression might have some advantage down low compared to a well tuned stock 426 but nothing earth shattering. Compared to a sloppy 426 the difference is much more noticeable.
Treating engines as systems rather than a random collection of parts can pay big dividends. These engines are a prime example of that. They respond very poorly to generic bolt on solutions because Yamaha did their homework.

Rich Rohrich · Sep 30, 2001

Originally posted by Jim D.
what would the price be on having that mod done to a 2000 426??could you run pump gas in it?

If you go to the 97mm (444cc) with 12.5:1 compression and the squish clearance is set correctly then yes you can still run pump gas. As for price you can contact Eric Gorr and he can help you with that. Prices should be on his website.

OldassKDX · Sep 30, 2001

Trade offs? Can you be more specific Rich?

Shaw520 · Oct 1, 2001

Re: Gorr/Rohrich bigbore Breathes FIRE

Originally posted by SFO

My buddies new 520 feels like a trail 70 in comparison.

SFO continues to compare his hoped-up 426 to bone stock 520's.
Guess us 520 guys should take that as a compliment!
You would'nt want to compare that to Dowdy's 520,....would you? :D

Actually SFO,I dont want to burst your bubble, I'm sure the 97mm kit made great power improvements. (I was never very impressed by the power the stock yz/wr made either). I'm glad to hear you found good results with your mods. My point is that one is only limited by his resources to proper modifications. :)

SFO · Oct 1, 2001

97mm vs 520

I should back up and say that I was motivated to change my 426 because my friend came around me so fast on his 520.
I think I will end up building a 520 as well in the future.
The 520 is the benchmark these days.
BTW, my new buddy with his 02 520 still comes around me, after riding his bike, I can't figure it out.
Maybe all those oil filters make it faster?
(maybe he is just a faster rider)

Shaw520 · Oct 1, 2001

97mm vs 520

Faster rider,....... maybe........but, the Yamis I've ridden, seem to 'sign off' a little sooner than the 520's.

But then again,... I've never ridden a 'Gorr/Rohrich' 97mm! :)

theMotoMan · Oct 1, 2001

Isn't the AMA going to limit the displacement of thumpers in the 250 class to 450cc :eek: ? Seems like a 444cc mod to the 426 seems about right! But open class is another story...:p

Rich Rohrich · Oct 2, 2001

Re: 97mm vs 520

Originally posted by Shaw520
Faster rider,....... maybe........but, the Yamis I've ridden, seem to 'sign off' a little sooner than the 520's.

And the 444 will be no different. The 520 has a distinct advantage in terms of absolute valve area to piston area ratio over the 444, but area under the curve is where the fun is :)

SFO · Oct 2, 2001

Dale just called...

I am going to run the 97mm on the dyno tommorrow.
The b03 has not shown up yet, although the receipt came in the mail.
Rich, what do you want me to do for the fuel set up, w/o bo3?
I have the b32 and the b37.
I am not going to get a lot of dyno time so it is down to running one set up.:scream:
Mounting the street tire tonight.
les' see what she'll do...:D

Rich Rohrich · Oct 2, 2001

Re: Dale just called...

Originally posted by SFO
fuel set up, w/o bo3?
I have the b32 and the b37.
I am not going to get a lot of dyno time so it is down to running one set up.:scream:

On the dyno you don't have to be concerned with throttle response and you'll generate a lot of heat anyway so run the B37.

Tony Williams · Oct 2, 2001

Fun With Numbers

I like this formula for displacement of the cylinder(s):

(bore squared times .7854 times stroke times number of cylinders)

Of course, you have to use the same values throughout the formula.

9.7 * 9.7 * .7854 * 6.01 = 444.12869886 cc

Since the motorscooter linear measurements are typically in millimeters with displacements in cubic centimeters, you'll need to either divide the end result by 1000, as Rich has done below, or enter the linear measurements in centimeters.

Tony

Originally posted by Rich Rohrich
It's 444cc :)

For those of you playing along at home it's easy.

Pi * ( (Bore /2) ^ 2) * Stroke / 1000

3.141592654 * ( (97/2) ^ 2 ) * 60.1 /1000
3.141592654 * 2352.25 * 60.1 /1000
444127.6603 / 1000
444.12 cc

For the record, Bill is a bad-ass machinist and does more math in a day than I do in a month :)

SFO · Oct 3, 2001

I would love to have you ride this bike.
Everyone who has ridden it is impressed.
I am very excited about how my biuke runs, forgive me.
It is not my intention to sell anyone, anything.
I think I am going to baja for xmas.
Maybe we could hook up, holeshot?
Rich can explain the thermal aspects of blah, blah, blah...
The bike runs good and is a veru different creature.
Actually, it is more of what you love about a yz-f. Rippin'!:eek:

holeshot · Oct 3, 2001

rippin' 444

.
SFO:

I'm sure the 444 rips, but questions have to be asked.:confused:
I can barely hang on to the 426 for more than a lap right now, but that's
probably just me. Maybe I need the 444 setup to get that roost'n feeling again.:)

I haven't been to Baja, but it sounds like a plan. Maybe you can get a group
together for the first DRN Baja ride? December is a bit far off (for me anyway), but when the time approaches, it could be posted again.:cool:

SFO · Oct 5, 2001

x-mas new years ride

How about the west coast drn faithfull make the pilgramage to Mikes Sky Ranch for the holidays?
It is never too early to start planning.
We are also going to camp at StoneyFord for turkey day.
Let me know if anyone is interested...

SFO · Oct 8, 2001

Dale just called...

The 97mm motor makes 52 dynojet rwhp.
The pipe will be measured for sound tommorow, when he runs the nutec through it.
He said the bike is very impressive on the dyno.
It made the best power with pump gas.
He said the motor runs out of air at 8 grand and flattens out.
He likes the way it runs and coming from a guy who builds national championship bikes this is high praise.
He also had praise for the pipe, which coming from a pipe designer is interesting...
He said that normaly he would not use a stepped header but there appears to be no trade off on the dyno. He said also that he wouldn't change anything, except that he found the bike hard to start.
He says that the engine noise is louder than the sound coming out of the tailpipe.

theMotoMan · Oct 8, 2001

Re: Dale just called...

Originally posted by SFO
It made the best power with pump gas.
He said the motor runs out of air at 8 grand and flattens out.

Best power on pump gas? How does that work? :think

By running out of air at 8 grand do you mean literally, as in it needs to breathe more on the intake side? :confused:

It would be nice to see a dyno chart or a list of RPM/HP figures so we can get a feel for the powerband.

Rich Rohrich · Oct 8, 2001

Re: Re: Dale just called...

Originally posted by theMotoMan
Best power on pump gas? How does that work? :think

By combining high port velocities and proper chamber and squish setup you can make these engines very tolerant of fuel.
My guess is that the pressure rise of the high lead content oxy fuel is too fast for the stock ignition curve. Less ignition advance will likely show more power across the board with the oxy fuel. If I can coordinate it quickly enough I'm going to send Dale a Vortex programmable ignition to test with so we can optimize the ignition curve to take full advantage of the fuel. Then we should see even more power especially in the upper rpm range.
This is the really fun part of engine and fuel development, taking a good combination and optimizing it for serious gains :)

Vic · Oct 9, 2001

Very cool.:cool:

Tony Williams · Oct 9, 2001

Re: x-mas new years ride

Originally posted by SFO
How about the west coast drn faithfull make the pilgramage to Mikes Sky Ranch for the holidays?

You probably want to start a new thread, but I'd be interested in a Baja ride.:)

Gore/Rohrich bigbore Breathes FIRE

SFO

SFO

Rich Rohrich

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SFO

holeshot

Crazy Russian

Jim D.

Rich Rohrich

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Rich Rohrich

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OldassKDX

Shaw520

SFO

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theMotoMan

Rich Rohrich

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SFO

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Tony Williams

SFO

holeshot

Crazy Russian

SFO

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theMotoMan

Rich Rohrich

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Vic

***** freak.

Tony Williams

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