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shreddr's Avatar
Join Date: Jun 2006
Location: New Jersey
Posts: 8,343
4 stroke engine hop-up

back in my MX days i became friends with Eyvind Boyesen of Boyesen Vented Reeds fame, and he ended up tuning some hot motors for me, but they always had sensible power rather than 10 more horses between 9500 and 10,000 rpm, at the sacrifice of all low end. my younger brother still races and i asked him what Eyvind was doing for the hot new 4 strokers? boring out the throttle bodies, hogging out the ports? the answer? filling the intake ports with epoxy and then hogging them out at smaller diameters to deliver higher fuel charge velocity and therefore more midrange. i think i need to pay a visit to my old friend and get my R11 "adjusted". between the cam sprockets i should be receiving soon, and some "sensible" tuning, power wheelies may be in my future after all!

2017 R1200GSW Rallye Shreddr Signature Model

Last edited by shreddr; 06-24-2007 at 06:30 PM..
Old 06-24-2007, 06:28 PM
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Moybin's Avatar
Join Date: Mar 2004
Location: Camanche, Iowa
Posts: 3,703
Please keep the group informed. This sounds very interesting.
'99 Black SA "OBSSSN" - gone but not forgotten.
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Old 06-24-2007, 07:40 PM
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motoyoyo's Avatar
Join Date: Aug 2002
Location: Camarillo, CA
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That has been the trend since around '05 in the offroad bikes. I believe it started with the CRF's at the factory level and the tuners started to notice the benefits. We went that route with my son's CRF270X when we replaced the valves. A whole cylinder head with valve seats from Honda was under $200 and they fit all bikes from '04 on. As a result it's the norm to just buy the latest head when replacing valves. That's when people starting taking notice of the different intake tract shape. Everyone was saying wtf this can't be right. The size was very noticably smaller on the newer heads.

Apparently someone applied some good testing and/or engineering to come up with those results. Not sure how it will translate to different engines but it definitely puts a damper on just opening everything up and smoothing it out.

'98 R1100S - Triple Clamps, 10mm Shortened Telelever
2007 Ducati S2R1000, 2008 KTM 990SDR
Old 06-24-2007, 09:06 PM
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lennie's Avatar
Join Date: Jan 2001
Location: Far south.
Posts: 2,048

Back when I lived in San Francisco from 1988 to 1992, I started to build a rigid framed Shovelhead Harley from parts purchased at swap meets etc.

When it came to the motor I took the heads and barrels to Ross Hannan at Hannan Machine in the east bay.

I discussed the desire to build a strong street motor with a as flat a torque curve as possible.

His solution was to weld up the intake ports to reduce the cross sectional area and build up the bottom of the exhaust ports for a more D shape.

On the intake side the reducing of the port area was to increase the airflow velocity at low valve lift. This in turn started the filling of the cylinder with more air early in the intake cycle resulting in a good cyclinder fill. We ran slightly larger valves to improve flow through the valve seat.

The bike ended up with 65 rwhp and 72 ft lbs of torque with a very flat torque curve. This work was matched to a Leinwebber by cam by a guy by the name of Bianchi in SF who setup the bottom end. Not bad for an engine rated at 45 hp from the factory.

After cold priming it was a one kick effort and always one kick cold.

Let us know how you go and try and before and after airflow readings on a flow bench if you can.

It is something that I have given thought to at some point during the ownership of my BMW. I had it ported early on and it helped a lot.

1998 R1100S Yellow is the best (now departed from my life)
Old 06-25-2007, 12:08 AM
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throttlemeister's Avatar
Join Date: Dec 2006
Location: Netherlands
Posts: 3,453
Motoman ( has been shouting this for more than 10 years. He also has a DIY guide on modifying your own heads. Doesn't seem to be too complicated, but reality is probably a little different. Still very interesting. Personally, I wouldn't do it unless I had a set of spare heads to experiment on. Too chicken I guess.
BMW R1100S 'Bumble Bee' | HyperPro 3D F&R | motoyoyo clamps | Staintune | some other bits
BMW K1200S 'tri-color ICBM' | WP ESA rebuild to specifications | lots of other bits |
Old 06-25-2007, 12:22 AM
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In a related vein, I Teflon-coated the entire interior of my induct and snorkel to increase air flow. Not as effective as the steps listed above, but helpful. It's the same stuff that aerobatic airplane builders use on their surfaces to reduce air drag. So slick it feels like there's oil on it. The stuff is $200 per gallon, but a friend at the airport gave me a pint of it, enough to do the job.
Old 06-25-2007, 05:12 AM
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JonyRR's Avatar
Join Date: Dec 2003
Location: Tacoma, WA, USA
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this is why a flow bench is so important when doing 4 stroke stuff. just hogging ports until they 'look' correct is a (thanks brad) sure way to 'tune yourself to a standstill'.

BTW, is C.R. Axtell still doing magic oout there?

Better a has-been than a wanna-be

'I am John Andrew Moffett of the Clan Moffat and by god I live, love, seek, fail, grieve and die as I so choose and I call no man master save me'.
Old 06-25-2007, 12:17 PM
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