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Discussion Starter · #1 ·
I have a '71 CB350 (twin) tachometer on my '81 CX500. After some research, seems that the CB350 tachometer has a 20:3 ratio vs. the CX500's 4:1. My question is...what is the CX500's actual engine speed if the CB350 tachometer is reading 1000, 2000, 3000, etc etc RPM? I guess my math is a bit rusty.

Thanks.
 

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Discussion Starter · #2 ·
From my rough calculation, does that mean the CB350 tachometer is reading 1.6x's what the engine speed actually is?

Making the denominators the same, it would be 20:3 and 12:3.

Then 20 / 12 = 1.6666



So, if the tachometer is reading 5000 RPM, the actual engine speed is 3000 (that is, 5000 / 1.6 = 3000). Does this sound about right?
 

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I got a similar number but I hate ratios so I was wondering if the tachometer seems like it's reading high or low. That would confirm everything.
 

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10000 = 6000

9000 = 5400

8000 = 4800

7000 = 4200

6000 = 3600

5000 = 3000

4000 = 2400

3000 = 1800

2000 = 1200

1000 = 600
 

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Discussion Starter · #5 ·
10000 = 6000

9000 = 5400

8000 = 4800

7000 = 4200

6000 = 3600

5000 = 3000

4000 = 2400

3000 = 1800

2000 = 1200

1000 = 600


My ride today kinda confirms the whole thing. I took the bike to between 9000-10000 RPM (this would be 5400-6000 RPM on a stock CX tach), and was going about 60mph.
 

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Discussion Starter · #7 ·
So you're probably safe to take it up to 15000. But the tach probably doesn't go anywhere near that high.


Nope...only 12000. But I guess I can still go by my Speedo (which is now a small Sigma BC800 bicycle computer).



At least it's good to know I'm not abusing the engine if I'm reading 10000 RPM! hahaha

But WOW...my exhaust is screaming at that point.
 
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