Triumphrat

Shorty · 06-12-2006, 06:48 AM

Finally got a Dyno Run in this weekend, and even though the overall readings are good I still have the "5200 RPM Dip". My scanner's not working so I can't post the graph but overall power at the rear wheel was 57.3 HP with a decent torque of 46.6 ft-lbs. Surprisingly the Air Fuel Ratio was a straight lined 13.7 all the way across (he seemed to think that I should make it a bit richer).
Present setup is 125 mains, 42 Pilots, thrux needle with (1) shim, Uni filter with restrictor plate and snorkel removed, belmouth and freeflowing Sprint pipes. My question is , should I decrease or increase the number of shims to eliminate the dip somewhat?
The Technician who ran the bike was surprised at the dip also because his "butt dyno" could not tell until he saw the printout. This was his first new Bonnie (he's a Honda / Suzuki Tech) but was very complementary stating that he knew of no Japanese Twin with our displacement size engine that came close to these results. He didn't think that the jets would need any changing because the front and end of the graph showed increases in power and torque until the rev limiter kicked in..
Any feedeback would be appreciated.

PS. I probably should add that HP started dropping at about 4000 RPM while torque was increasing...torque leveled out as HP dipped at 5250 RPM and then both increase at 5500 RPM to max out at 57.3 HP and 46.6 ft-lbs to 7400 RPM. Sorry for such a long post, I know a pic would be better.

Shorty

[ This message was edited by: Shorty on 2006-06-13 08:04 ]

SCCTrim · 06-12-2006, 07:29 AM

After reading your post I read the jenk's bolts tuning guide twice looking for a answer that satisfied me...( I have a standard blk bonnie and recently added free flow exhaust with no other mods...yes I am "lean" )...from everything I have read your setup seem's right on par with their guide.

Your ratio seem's on par with what they recommend. I am sure someone with more experience could and will properly advise you, if this was my bike I think I would add a shim...( based on not seeing a graph )....adding a shim from my understanding should help the bike pull harder @ top end unless I am misunderstanding what I am reading.

I'll keep a eye on this thread for replys.

SC

Shorty · 06-12-2006, 07:42 AM

SC...thanks for the reply. According to the Technician who ran the Dyno, he seemed to think that it was pulling well at the bottom and top end but in the middle is where it dropped off.
Like you, I've read the Jenks tuning info numerous times in order to find out what I'm missing. If you noticed, the Jenks info also has that drop as do many others whose dyno graphs I've seen on this site (mine just seems to be a bit more pronounced). I believe someone once stated that at about 5200 RPM the HP and Torque curves seem to converge. I'm almost convinced it's a needle and shims issue. Maybe I can try to take a digital pic of the dyno results and then post those.
Can anybody else post their graphs so that I can compare? I've seen FattRat's in the photo album whose setup is similar to mine.

Shorty

[ This message was edited by: Shorty on 2006-06-12 05:45 ]

kballowe · 06-12-2006, 07:52 AM

Unless you're a perfectionist, or you really just link to tinker... my humble opinion is that you are close enough. Very good tune and very even powerband. What else could a fella ask for?

There are many that work, and work, and work at it, and never get their engine into that good of a tune state.

Those are good numbers - especially considering that a 750 Honda is in the 45 HP range..... :wink:

Shorty · 06-12-2006, 08:00 AM

Thanks for the encouragement kb, it probably wouldn't bother me that much if the drop in HP wasn't that large...a gradual decrease from 46HP at 3500 RPM to 34 HP at 5300 RPM and then right back up again to 46 HP at 6000 RPM with a nice response all the way up to the rev limit.

Shorty

Pete_Twizz · 06-12-2006, 08:08 AM

With regard to the '5200 rpm dip':

Horsepower is a product of torque and rpm, so I am not sure how HP can drop off while torque increases as described at and above 4000 rpm.
The 'butt dyno' (Arse dyno in the UK) only measures torque. I believe it's Torque that counts rather than HP. If the dyno shows mixture to be good through the whole range, and torque increases steadily up to peak, then your engine is good.

ivar · 06-12-2006, 08:17 AM

As Pete says,
the HP and Tq curves ALWAYS cross at 5252rpms (as long as HP and ft/lbs are used as units)
http://en.wikipedia.org/wiki/Dynamometer

Shorty · 06-12-2006, 08:19 AM

Pete...I agree. Torque steadily increased and leveled while the HP started it's downward swing. Then it dropped about 3 ft-lbs at the lowest dip of the HP curve to where they both met on the graph, at which point they both started to climb back up (torque finding its niche nicely in the mid 40's and HP increasing steadily to 57.3).

Shorty

FattRat · 06-12-2006, 09:16 AM

It's early in the morning, my first cup of coffee is before me,
and might regret posting this
- but -
of my past four bikes, it was only the three cylinder Sprint RS
that didn't show a conspicuous dip at mid-range.

My two cylinder Sporty 1200, two cylinder Beemer 1150,
and two cylinder Bonnie 800 seem all to have had that "dip"
between 5200 & 5500 rpm. Could it be a two cylinder thang?

I'm now running what shorty is running, but with the
addition of a shim (two shims), bellmouth intake, K&N air filter,
and really free-flowing cans. I had a different set-up when
my dyno reading was taken as posted in my album.

I've learned after messing with my intake & exhaust
systems on different bikes, that the most linear power
curve is as they come from the factory. To mess with your
bike creates trade-offs, compromises, more power but
with it's share of peaks & valleys.

All this rambling, and I'd LOVE to get my bike Dyno'ed again.
My last couple of runs were taken on machines with
clogged filters and messed up electronics......
and with my home made baffle inside some D&D's,
my bike is running pretty good (but not nearly as well
as my Predators going on my 'project bike' soon).

Yeah, I'd say try an additional shim. The only reason I
added a second one was because my bike was stumbling
all over itself between throttle on & throttle off.....
I've often wondered what a third shim would do because
MY midrange lacks also (though I think it's my home made
pipes). I think I've been told to try to avoid any more than
two shims.... don't know why though.

The below Dyno results was taken when I was running:
42 pilots
130 mains
D&D's
snorkle & restrictor plate removed
about 5,000 miles on the bike.......

[ This message was edited by: FattRat on 2006-06-12 18:19 ]

dazco · 06-12-2006, 09:52 AM

The only thing that jumps out at me, tho i'm certainly no expert on this by any stretch, is the thruxton needles with one shim. Thruxtons are very rich even with none. If it were me i'd remove the shims and see what happenes. Of course the problem here is that since your seat of the pants can't detect the dip, you may not be able to tell even if it does help it. My bike's airbox is about as open as i can make it ans thruxtons with NO shims were too rich for it.