Soft limiter mod - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 12 (permalink) Old 07-18-2009, 05:48 PM Thread Starter
 
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Soft limiter mod

saw it on some RC51 website and it sounded interesting.
I pushed the pin blk/wht pin out soldered a pigtail connector (made from a Cdrom cable that i found in the trash). No cutting/stripping any of the original wire, routed the red wire through the rubber boot.





Has anyone else tried this?
i dont know if i noticed much other than it bounces off the redline (just past 10k for this bike) like any other bike i have owned.

I never went near the rev limiter prior to doing this maybe i should unplug it and see what happens around 9500rpm.

I read the soft limiter starts cutting in at ~9250? Does that mean this unlocks some top end power by allowing it to rev to the hard redline?

Last edited by jh4db536; 07-18-2009 at 05:53 PM.
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post #2 of 12 (permalink) Old 07-18-2009, 10:50 PM
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Honda america decided to restrict the RC51 after 9250rpm. So what happens is the bike stops building horsepower at 9250rpm but still revs 1000rpm more. By doing this mod you just allowed the motor to continue building horsepower to redline! Increasing it by about 5hp at the very top. You wont really notice it unless you ride in that last 1000rpm alot. Although now you can tell people your peak horsepower is higher. Not bad for a free mod!
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post #3 of 12 (permalink) Old 07-19-2009, 03:17 AM Thread Starter
 
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i see so there really is a "jumper mod" for the RC51 too.
cool, i didnt notice 5 hp though lol anyone have dyno charts showing this top end gain?

I thought the jumper mod on my zx6r's 600 & 636 made a huge difference. dynos show a ~8whp gain on those bikes. free is good though
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post #4 of 12 (permalink) Old 07-19-2009, 08:40 PM
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When I dyno'd mine recently, I noticed the bike was still gaining HP until the soft rev limiter cut in.
So it wasn't hard to estimate by extending the line on the dyno chart to 10K as it was pretty linear.
My conservative estimate would be 125 HP, my most likely result would be 128 HP, and my most optimistic estimate would be 130 HP at the rear wheel.
So 5 to 8 HP was my estimated gain.
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post #5 of 12 (permalink) Old 07-20-2009, 07:17 AM
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Does anyone know if the soft limiter is used in Aussie spec bikes??

Looking at my dyno, the power levels out at about 9300rpm!!!

Ita
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post #6 of 12 (permalink) Old 07-20-2009, 02:36 PM
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Originally Posted by Ita View Post
Does anyone know if the soft limiter is used in Aussie spec bikes??

Looking at my dyno, the power levels out at about 9300rpm!!!

Ita
Only the North American bikes had the soft limiter. Your dyno chart shows the bike revving all the way to 10.2K RPM.

However, it looks like your fuel curve is all over the place.
At around 4800 RPM the air/fuel ratio is way lean at 14:1, and then 8500 RPM it swings the opposite direction and becomes way rich at less than 11.5:1.
You've got a plateau from 7800 to 8800 RPM due to the lean condition.
I'd try to adjust your fuel mix and try to keep it at 13.2:1 which is the ideal power ratio.
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post #7 of 12 (permalink) Old 07-21-2009, 05:39 AM
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Originally Posted by SubSailor View Post
Only the North American bikes had the soft limiter. Your dyno chart shows the bike revving all the way to 10.2K RPM.

You've got a plateau from 7800 to 8800 RPM due to the lean condition.
I'd try to adjust your fuel mix and try to keep it at 13.2:1 which is the ideal power ratio.
Thanks for the reply...

The plateau from 7800 to 8800 RPM is where it's really rich... The dyno guy thinks the high volume snorkle and airbox will sort that on the track. I haven't ridden it yet, so will look at further tuning after getting a leg over it!!

Dyno guy would have had a play, but his software wouldn't talk to the PCII...

Ita
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post #8 of 12 (permalink) Old 07-21-2009, 05:58 PM
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Originally Posted by Ita View Post
Thanks for the reply...

The plateau from 7800 to 8800 RPM is where it's really rich... The dyno guy thinks the high volume snorkle and airbox will sort that on the track. I haven't ridden it yet, so will look at further tuning after getting a leg over it!!

Dyno guy would have had a play, but his software wouldn't talk to the PCII...

Ita
Yeah I meant way rich from 7800 to 8800. I got distracted by a phone call.
I'm surprised the lean condition didn't cause much HP loss down low.

When I first got my RC51, the previous owner had a fuel curve causing a real lean condition at 5600 to 5800 RPM.

You could feel the power drop off despite how much you rolled the throttle, and eventually would start misfiring at 5800. If you moved past 5800 it began running fine.

Once I remapped the PCIIIr, I no longer had any problems.
I'll have to find my old map and find the A/F ratio at that RPM.
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post #9 of 12 (permalink) Old 07-21-2009, 06:07 PM
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Well after looking at my previous two dyno charts, it appears that 14:1 is not as bad I as I thought. Mine has a range from 3000 to 3500 that's at 14:1, and the rest is from 13.0 to 13.2:1.
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post #10 of 12 (permalink) Old 07-24-2009, 10:21 AM Thread Starter
 
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so that's what it does. nice. (not my dyno btw)

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