Speedometer KPH to MPH
Thread Starter
Intermediate
Joined: Apr 2018
Posts: 32
Likes: 0
Speedometer KPH to MPH
Hi everyone,
I'm getting ready to purchase an 81 C3. It's a Canadian car and has a KPH speedometer. What's the easiest way to convert it to MPH? Would the vinyl decal overlays work for this situation? Thanks!
I'm getting ready to purchase an 81 C3. It's a Canadian car and has a KPH speedometer. What's the easiest way to convert it to MPH? Would the vinyl decal overlays work for this situation? Thanks!
Thread Starter
Intermediate
Joined: Apr 2018
Posts: 32
Likes: 0
Speedometer KPH to MPH
Hi everyone,
I'm getting ready to purchase an 81 C3. It's a Canadian car and has a KPH speedometer. What's the easiest way to convert it to MPH? Would the vinyl decal overlays work for this situation? Thanks!
I'm getting ready to purchase an 81 C3. It's a Canadian car and has a KPH speedometer. What's the easiest way to convert it to MPH? Would the vinyl decal overlays work for this situation? Thanks!
Intermediate
Joined: May 2015
Posts: 39
Likes: 9
From: London Ontario
The speedo output on the side of the transmission has interchangeable gears inside to allow for different gear ratios. There are also aftermarket inline speedo cable gear reducers that accomplish the same thing. A combination of the two could get your metric dash to read MPH. IF you have a 3.07 rear gear ratio (my 80 did originally), then then 3.07 x 1.609 (kilometers to miles conversion) would require the equivalent speedo gears as a car with a 4.94 rear gear. An old school transmission mechanic should be able to help you out.
Melting Slicks
Joined: Oct 2010
Posts: 2,275
Likes: 337
From: "ɹǝpunuʍop", Adelaide, South Australia
if distances traveled are correct, correct tyres etc, try one of these
https://transmissioncenter.net/shop/...ratio-adapter/
i used the same style unit, but went from to MPH to KPH..
https://transmissioncenter.net/shop/...ratio-adapter/
i used the same style unit, but went from to MPH to KPH..
Intermediate
Joined: May 2015
Posts: 39
Likes: 9
From: London Ontario
if distances traveled are correct, correct tyres etc, try one of these
https://transmissioncenter.net/shop/...ratio-adapter/
i used the same style unit, but went from to MPH to KPH..
https://transmissioncenter.net/shop/...ratio-adapter/
i used the same style unit, but went from to MPH to KPH..
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
Safety Car
Joined: Apr 2006
Posts: 4,057
Likes: 421
From: BC
Nothing is calibrated or made differently except the markings on the Canadian kph speedo head but the odometer is. Find a US mph speedo head and that will do it. The gears, cable, and everything else are the same. I have done this a number of times on C3's in reverse (see my name) and you don't have to worry about gearing or anything else as there is no compensation for that in the head. Just get a US head. There isn't a big market for C3 speedometers so the cost won't be much and the work involved will be less than trying to remove one, take it apart and use a sticker. The reason to change the unit instead of the face plate or using a sticker is that the odometer will also be changed from KPH to MPH. Might as well do it right for no extra cost.
Last edited by CanadaGrant; Apr 20, 2018 at 12:26 AM.
Drifting
Joined: Dec 2017
Posts: 1,302
Likes: 226
From: PA
If you go this route you should use the offset style reducer (see pic). There is very little space between the speedo gear housing in the the tranny and the driver side "bucket" of the floorboard. The reducer mounts between the speedo gear housing and the speedo cable. If you try to put the straight through reducer style in that small space I guarantee that the bend it will force in the speedo cable will snap it in about 1000 miles. I know of what I speak.
The offset style reducer will hopefully drop the speedo cable attach point low enough to either get past the bottom of the floorboard or reduce the necessary angle to something tolerable. But I never tested that.
Last edited by vince vette 2; Apr 20, 2018 at 11:53 AM.
Melting Slicks
Joined: Dec 2009
Posts: 3,220
Likes: 651
From: Thunder Bay
I suspect you could just replace the speedometer. Not sure what's available. If you contact Corvette Clocks by Roger, they can probably help you out with a replacement speedo, or rebuild yours as an MPH unit.
Drifting
Joined: Dec 2017
Posts: 1,302
Likes: 226
From: PA
Safety Car
Joined: Jan 2008
Posts: 3,791
Likes: 428
From: Aarhus, Denmark
Drifting
Joined: Dec 2017
Posts: 1,302
Likes: 226
From: PA
I'll say this, the conversion in the US was never avoided because it was too hard. The military did it. And businesses overwhelmingly support it. The only people it is too hard for is the spineless politicians who have abdicated their intended role elected LEADERS in favor of continuous reelection through the role of elected FOLLOWERS. And thus, as has been said, people get the government they deserve.
Last edited by vince vette 2; Apr 20, 2018 at 01:02 PM.
Race Director
Joined: Mar 2017
Posts: 11,885
Likes: 4,468
From: Virginia
I'll second the 80 as being a weird mix of metric and SAE.
What is the top speed of the kph speedo? 135 or 140 kph? That should be a direct swap for the 85 mph speedo. Just buy a speedo, or complete dash, off ebay. Easy! Wilcox has instructions for the swap.
What is the top speed of the kph speedo? 135 or 140 kph? That should be a direct swap for the 85 mph speedo. Just buy a speedo, or complete dash, off ebay. Easy! Wilcox has instructions for the swap.