VFR Discussion Group -> Bigger is not always Better...

"Larry" the caller said over phone. "did you know your RC45 air box is restricted?"

Who is this???

No prankster... it was my friend Stephen calling long distance from England and he just installed a $900.00 HRC air box on his RC45 and now claims 120HP on the dyno... mmmmm... could the stock box be modified???
(IMG:http://www.vfrdiscussion.com/forum/uploads/1113861108/gallery_3131_51_178065.jpg)



Stephen was right... stock RC45 throttle bodies are 46mm but the air box was indeed restricted to 40mm... no problem... I'll bore the air box out to 47mm on the milling machine...
(IMG:http://www.vfrdiscussion.com/forum/uploads/1113861108/gallery_3131_51_12643.jpg)



I drew up plans for 47mm bell mouth based on the stock 40mm bell mouths and purchased a block of black Delrin...
(IMG:http://www.vfrdiscussion.com/forum/uploads/1113861108/gallery_3131_51_61101.jpg)



I hates repetitious work but I labored long hours to machine 4 each bell mouths with my best accuracy...
(IMG:http://www.vfrdiscussion.com/forum/uploads/1113861108/gallery_3131_51_60103.jpg)



I love it when a plan comes together especially if it turns out perfect...
(IMG:http://www.vfrdiscussion.com/forum/uploads/1113861108/gallery_3131_51_73307.jpg)



Now I had an unrestricted air box with my own 47mm bell mouths... it was my best effort to replicate HRC $900.00 wonder air box... not to mention I get to keep my home made K&N filter whereas HRC employs a thin sheet of oiled foam and a grill...
(IMG:http://www.vfrdiscussion.com/forum/uploads/1113861108/gallery_3131_51_44329.jpg)



Time to revisit my friend Dave at Chandelle Motorsports and run my mod against my base line on the dyno... Dave wears ear defenders not to block Mr.RC45's glorious growl but to block my endless V4 yammering...
(IMG:http://www.vfrdiscussion.com/forum/uploads/1113861108/gallery_3131_51_181600.jpg)



Mercy!!! no joy... I lost 1.8HP... bigger is not better... a weeks worth of work shot down in flames... it seems Honda got the intake velocity right for a stock pipe after all...
(IMG:http://www.vfrdiscussion.com/forum/uploads/1113861108/gallery_3131_51_35549.jpg)



Oh well... calling Italy... hello Mr. Termigoni??? you love V4s and I need to open up the back door to take advantage of my front door mod... do you still make racing 4 into 1 exhaust systems with a carbon can for the RC45???
Termignoni Site

Good work as usual Larry, maybe other mods are needed to gain that potential extra power ?
You can put your new 47mm bells on Ebay advertising "the same size as the $900 HRC " pieces and bling, bling ! :idea3:
:beer:

You might need to find an HRC racing "black box" to squeeze out most of the potential HP the RC45 engine has in it, on top of modding your exhaust and induction systems.
Honda Spent jillions of dollars to get the "little" 750 to win over the Ducatis in the 90's, and I'm sure a lot of that development money went into the engine management system.
Learning to ride like John Kocinsky is a different story though! :blink:

Beck
95 VFR

Great Termi site BLS thanks!!

Now will the pipes from a RC30 fit a std 1994FS VFR?

(IMG:http://www.termignoni.it/catalog/images/immagini_tecniche/H020-1024.jpg)

also fit?

or this?

(IMG:http://www.termignoni.it/catalog/images/immagini_tecniche/H033-1024.jpg)

or even better

(IMG:http://www.termignoni.it/catalog/images/immagini_tecniche/H032-1024.jpg)



HHmmmmmmmm

At last I have met an honest man, if this had been a H.D. shop I wonder what stories would have been told. :thumbsup:

Having a closer look at the dyno chart.

The larger bell mouths are still producing hp in the last few hundred revs (as you'd expect) where as the stock ones are flattening off. For memory the race bike had a 14000 rev limit? Just to get the last few HP out of the engine?

The A/F ratio looks ok, in fact looks smoother down low which is funny? Sorry I can't remember if you have a power comander or similar fitted?

More head work and as you've suggested a better exhaust.

BUT

Then of course you'd loose some tractability.

BTW here is a chart of my bog stock 1994 VFR as a loose comparison

(IMG:http://www.ozvfr.net/albums/wombat39/aak.sized.jpg)

Interestingly my bike puts out more Hp @ approx 9800 ???

(of course you can't use these as direct comparisons... :D )

vfrgreg, Apr 20 2005, 06:15 PM 
For memory the race bike had a 14000 rev limit? Just to get the last few HP out of the engine? 
 
Sorry I can't remember if you have a power comander or similar fitted? 
 
BTW here is a chart of my bog stock 1994 VFR as a loose comparison 
 
Interestingly my bike puts out more Hp @ approx 9800  ??? 
  (of course you can't use these as direct comparisons...  :D ) 
 

I think Honda's race bike had 14,500 rev limiter...

You know Honda never stopped developing RC45 engine... last figure I've gleaned from HRC is 191HP at 14,500 RPM...

Power Commanders were never offered for the RC45... however one member of the RC45 Club is working to persuade Power Commander to ante up one for us non NL5 owners...

No you can't use these dyno charts as direct comparisions... the U.S. uses SAE HP whereas Europe uses DIN HP...

One SAE horse is the ability to lift 33,000 lbs one foot in one minute...

One DIN horse is the ability to lift 450000 kg one cm in one minute...

For the same power the SAE measurement is thus 98.629% of the metric DIN measurement...

vfrgreg, Apr 20 2005, 04:00 PM 
Great Termi site BLS thanks!! 
 
Now will the pipes from a RC30 fit a std 1994FS VFR? 
 
HHmmmmmmmm 
 

You're welcome...

The pipe may physically fit but ask Mr. Tremignoni about the difference between a 360 degree crank and 180 degree crank has on power pulse phasing... you might fail to fully fill the cylinders during valve over lap...

Mr.Tremignoni still has his personal RC30 on display at his factory...

Thanks Larry :)

The power difference is most likely due to reduced mixing rather than a volume flow difference because the speeds are still in the incompressible region. Its just not fast enough air flow to get choked (restricted by shock wave). Going from 40mm to 47mm reduces your velocity by up to 28%. With the butterfly fully open the degree of turbulence (for mixing) you get is proportional to the Reynolds number, which is proportional to velocity. Mixing fuel and air in 3D turbulence is difficult to simulate though, so who knows...all the engine companies struggle with these kinds of design point issues. Some things still have a degree of trial and error. Perhaps if you tried making slightly smaller versions in 1mm increments...but that's a lot more work to get that one point whatever horsepower increase :D

Of course you all realize by now that BLS can make just about anything in his garage though...