All Small Six RPM? 1966 Mustang - 200ci - 4sp - 3:20

66R08T · May 3, 2024

Hey all - I'm trying to figure out if my tach is accurate.

1966 Mustang
200ci - 4sp - 3:20g - 195/70/14tires
At 70mph the tach is reading 2350rpm
And at 2500rpm that feels to be maxed out.

Does this seem about right ?

Thank you
-Michael

frozenrabbit · May 3, 2024

Your tire size will factor in. Try a GPS speedometer app on your phone to make sure your speedo is correct. Try this online calculator.

Calculate RPM for Given Speed(MPH), Rear Gear Ratio, and Trans Gear Ratio

purperformance.com

aussie7mains · May 3, 2024

At 110km/h with that axle its is more likely to be doing around 3100. So NO the tacho is way off, check the settings.

DON · May 3, 2024

66R08T said:
Hey all - I'm trying to figure out if my tach is accurate.

1966 Mustang
200ci - 4sp - 3:20g - 195/70/14tires
At 70mph the tach is reading 2350rpm
And at 2500rpm that feels to be maxed out.

Does this seem about right ?

Thank you
-Michael

Is your question about the numbers being right or the performance at 2500rpm?
Both?

66R08T · May 3, 2024

For sure both.
I feel like the tach reading 2350 @ 70mph is too low. The engine seems to be getting close to it's max RPM - so I'm guessing the tach is off.

66R08T · May 3, 2024

Screenshot_20240503_171014_Samsung Internet.jpg

@frozenrabbit
Thanks for that Calc tool - yep - I'd say my Tach isn't calibrated properly.

Bill56 · May 3, 2024

Check the back of your tach to see if it has a switch marked 4, 6 or 8.
That could be the issue.

66R08T · May 3, 2024

Bill56 said:
Check the back of your tach to see if it has a switch marked 4, 6 or 8.
That could be the issue.

Yep - that's my next step.
Will report back once I get a chance to do that.

66R08T · May 6, 2024

Bill56 said:
Check the back of your tach to see if it has a switch marked 4, 6 or 8.
That could be the issue.

Well - indeed it was the dip switch settings.
Got it set correctly and now at 70mph it's showing a hair over 3K

Thanks to you all for the help.

All Small Six RPM? 1966 Mustang - 200ci - 4sp - 3:20

66R08T

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frozenrabbit

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Calculate RPM for Given Speed(MPH), Rear Gear Ratio, and Trans Gear Ratio

aussie7mains

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DON

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66R08T

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Bill56

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