RPM's

rab3rd

New member
Ok. please forgive a newbie for asking what may be a stupid question.

Let me preface by saying that I run in a club class that mostly follows the AKRA BS rules, the exception being that I have to run the steel billet flywheel and a blue restrictor plate on the carb. The engine is setup with the BSP-2 cam and 10.8 pound springs. The carb main jet is a #39. The preferred gearing is 15/56. The flywheel and keyway are in the stock position. i.e. no advancement in timing.

Clutch is a Mongrel that slips at 3000 and locks at 3100

According to the engine builder that setup should be running about 12-12.3 peak HP occurring in the range of 5700-5900 RPM's (at the drive shaft) and a peak torque of about 13-13.6 Ft/LBS occurring in the range of 4200-4500 RPM's (at the drive shaft). The builder also said that I should be able to turn this setup to 6100-6200 RPM's no problem

On the longest straight of my track (about 700 feet) I see a max of a little over 5500 RPM's so I am losing top end speed. I know others at my track are getting near the 6k RPM with this setup.

So my question is (I know finally), how do I get my RPM's up?
 

rab3rd

New member
Well that really depends on the track conditions, but in the last race where I turned my fastest lap time of 50.8 I was running (cold pressures) 14 lbs in the rear and 15.5 lbs in the front. This is a sprint track (right and left turns by the way)
 

rab3rd

New member
Asking me why its stock timing as if Im some sort of idiot for having it set that way doesnt seem like a very productive response. If you have to know in order to offer any advice, its that way because that is how it came to me from the builder. I am new to racing and have been spending my time learning to drive and not worrying about the power, well now I am running consistant lap times and now ready to start tweaking the power plant to get faster.
 

rab3rd

New member
I intend on advancing the timing, I ordered an 8 degree key but thats just going to get me more power, not more RPM's. Correct?
 

Kart43

Member
Your response has now limited the # of people willing to help.

Correct response(s)
Track mandated
Builder supplied
Builder recommended
I'm a **** don't ask questions just solve my problems

Take your pick see which works for you.
 

rab3rd

New member
I see, so because I state that I felt the question was insulting in nature, IM the bad guy. No problem. Thanks for the help.
 
More power should equal more rpm, unless the kart don't handle it. My weenie pipe engines turn 6000 to 6200, and unrestricted 6400 to 6600 every week. My S/A engines turn 8000+... Just some advice, you come on here with a bad attitude, your in for a rough ride. I am done with this thread, but good luck. (I really do mean that).
 

rab3rd

New member
well, the 15 is a rule. The 56 has been determined by the fastest guys to be the gear that runs the best.
 

rab3rd

New member
More power should equal more rpm, unless the kart don't handle it. My weenie pipe engines turn 6000 to 6200, and unrestricted 6400 to 6600 every week. My S/A engines turn 8000+... Just some advice, you come on here with a bad attitude, your in for a rough ride. I am done with this thread, but good luck. (I really do mean that).

I understand, and I apologize to you and anyone else offended by my response.
 

Kart43

Member
15/56 3.73:1 may work for a perfected racer at that track. You must remember 1 mistake in a corner on an asphalt track, sets the kart flat, and bogs the engine. A newbie needs a more forgiving ratio, I would go 15/58--59 get the RPM up. As you get smoother you work toward the hotshoes ratio. I would not recommend a new driver use the same ratio as us we know they need to learn the track. You do need to advance your ignition timing the engine is operating at almost twice it's designed RPM and it was optimized for longevity and emissions not racing.
 

rab3rd

New member
15/56 3.73:1 may work for a perfected racer at that track. You must remember 1 mistake in a corner on an asphalt track, sets the kart flat, and bogs the engine. A newbie needs a more forgiving ratio, I would go 15/58--59 get the RPM up. As you get smoother you work toward the hotshoes ratio. I would not recommend a new driver use the same ratio as us we know they need to learn the track. You do need to advance your ignition timing the engine is operating at almost twice it's designed RPM and it was optimized for longevity and emissions not racing.


That all makes sense, especially the timing. I find it a bit of a conundrum when I start thinking about the whole setup. The track I race is a 7/10 mile track with ten turns. Most of the track is short runs between turns with one long straight of 780 feet. My assumption has been that it would be more favorable to be quicker on the short runs between turns than faster on the longest straight. Dont take this as me saying you are wrong, Im honest in my question. If I gear to a 58 or a 59 I gain top speed but I lose low end torque, correct? If I make a mistake in a turn and set the kart flat, am I not better to get back up to speed quicker as opposed to slower acceleration and a higher top speed?
 
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