Tachometer Question.......
Freshman User
Joined: Feb 2008
Posts: 34
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Fitch~
I have an autometer tach as well and I have it set on the V8 setting and I have always thought that it worked fine. How did you know any different? I have a 360CI under the hood and it seems to do just fine in my '66. Let me know!
KILLER
P.S. What is the redline on your truck? The highest I have gone is 3800RPMs
I have an autometer tach as well and I have it set on the V8 setting and I have always thought that it worked fine. How did you know any different? I have a 360CI under the hood and it seems to do just fine in my '66. Let me know!
KILLER
P.S. What is the redline on your truck? The highest I have gone is 3800RPMs
Thread Starter
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Senior User
Joined: Feb 2008
Posts: 316
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On the 8cyl. setting, it was showing a much lower RPM than the actual. I used another new tach that is built into my timing light to compare. On the 6cyl. setting, it is excatly the same as my other tach. i have not pushed the truck to the redline. It is old like me so, I baby it.
Freshman User
Joined: Feb 2008
Posts: 34
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Hey, thanks for the info! Maybe I have been running mine at a higher rpm than I know, but I have set the idle at 500rpm according to my tach and it seems to be pretty low, but not sputtering or anything like that. I guess I run mine a bit hard becuase I am young and my truck is young at heart like myself! I just raced my buddy on his GS650 and beat him in about a half mile strip...I am purely stock though. I LOVE how durable they make the old boys! Thanks again
KILLER
P.S. Don't worry, I baby my old boy most of the time. He gets lots of rest and is never driven cold. I would hate to be accused of truck abuse..haha!
KILLER
P.S. Don't worry, I baby my old boy most of the time. He gets lots of rest and is never driven cold. I would hate to be accused of truck abuse..haha!
Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
Tachs usually run pretty close. IMHO Your speedo, rear ratio, and things like that can throw off what the perceived rpm is.
There are spreadsheet programs that will help get those answers. This is one source * * Automotive Programs by Bowling & Grippo * *
I think my system is pretty close, I run 235-75-15 tires, through 3.00 gears behind a FE powered C6. At 55 mph, my truck tachs 2050 rpms.
Speedo drive gears, and rear end ratios are often not correctly known and give false readings.
When you have been around these ol trucks as long as I have and a fellow comes in here saying his FE powered truck is getting 18 mpgs everyday, you know something is not right. I believe our trucks are getting better mpgs now than ever, with electronic ign. better carbs, etc.
Keep digging Cliff, I'll bet you will figgure it out.
John
There are spreadsheet programs that will help get those answers. This is one source * * Automotive Programs by Bowling & Grippo * *
I think my system is pretty close, I run 235-75-15 tires, through 3.00 gears behind a FE powered C6. At 55 mph, my truck tachs 2050 rpms.
Speedo drive gears, and rear end ratios are often not correctly known and give false readings.
When you have been around these ol trucks as long as I have and a fellow comes in here saying his FE powered truck is getting 18 mpgs everyday, you know something is not right. I believe our trucks are getting better mpgs now than ever, with electronic ign. better carbs, etc.
Keep digging Cliff, I'll bet you will figgure it out.
John
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 787
From: Simi Valley, CA
Tire sizes in the 1960's for F100's were: 7:10-15 / 7:60-15 / 8:00-15 / 8:20-15.
Today they're all P Metric Sizes.
The change to P Metrics means the speedometer can be off between 7 and 14 MPH, or more.
To correct the speedometer, one needs to know what the P Metric sized tire on the vehicle converts to inre 1960's sizes.
Once that's known, the speedometer's driven gear can be matched to the P Metric tire size, installed in the trans, replacing the original = the speedo should read correctly.
To arrive at the correct speedo driven gear (end of cable) depends on two factors: rear end ratio, tire size.
Today they're all P Metric Sizes.
The change to P Metrics means the speedometer can be off between 7 and 14 MPH, or more.
To correct the speedometer, one needs to know what the P Metric sized tire on the vehicle converts to inre 1960's sizes.
Once that's known, the speedometer's driven gear can be matched to the P Metric tire size, installed in the trans, replacing the original = the speedo should read correctly.
To arrive at the correct speedo driven gear (end of cable) depends on two factors: rear end ratio, tire size.
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