So I'm a little stumped here and looking for ideas/suggestions on this long post. I bought the car about 6 weeks ago or so and found the window sticker for it, showing 3.73 gears as an added option. On the 700 mile journey home, I felt the RPM were a little low for the shorter gears (2100-2200), but just chalked it up to possibly a taller 5th gear in the transmission. I got a tune from Lito to fix the bogging/dead spot in the 2100-2500 RPM range and told him I had 3.73's in it, assuming that was the case.
Fast forward to this past weekend on another 600 mile drive with the car and I feel like I'm just ripping past cars on I-70 despite cruise being set at 80 in a 75. After about 100 miles or so of this, I download a GPS speedometer app and it shows I'm doing 87-88mph. Thinking the app was crap, I downloaded a second to find the same thing. Ooops. Good thing there weren't any cops hiding in the dark. Once I get to my destination, I reach out and let Lito know what's going on. He sends a new tune out, still with the 3.73's just to see if there's any difference. Take it for a drive, same thing. So we send a few emails back and forth and I find a calculator showing the RPM I'm roughly spinning at 80mph (based off the original drive home when I purchased it before the tune) and it shows I have 3.31 gears. I shoot that back to Lito and tell him I'll verify it when I get home from my trip and within minutes (literally like 15), I have a new tune with 3.31's on it. I get that loaded and head home the next day.
On the way home Wednesday, I use the GPS speedometers again and I'm now off by a couple of MPH in the opposite direction, showing faster on the speedo than what I'm actually doing. We get the car jacked up today and mark the tire and differential, manually checking it. Looks pretty close to 3.31 vs 3.55 and definitely not 3.73.
Stock tires were 245/45/19 and I swapped the rears for 275/40/19 just so I didn't have to worry about the speedometer correction. My question now is, with both sets of tires being 27.7" diameter and 728 revolutions per mile, if I truly have 3.31's in there despite the window sticker, why would the speedometer still be off by a few mph? I don't know if a previous owner blew up the rear and had a new one installed, if they didn't like the 3.73's and wasted the money to go down to the 3.31's or is there something between 3.31 and 3.55 that I might have? Could they be the rare 3.27's and causing the higher speed reading with it tuned for 3.31's? Just kinda stumped and I don't want to keep bugging Lito for another tune until I can figure this out and get those few MPH accounted for.
Thanks!
Fast forward to this past weekend on another 600 mile drive with the car and I feel like I'm just ripping past cars on I-70 despite cruise being set at 80 in a 75. After about 100 miles or so of this, I download a GPS speedometer app and it shows I'm doing 87-88mph. Thinking the app was crap, I downloaded a second to find the same thing. Ooops. Good thing there weren't any cops hiding in the dark. Once I get to my destination, I reach out and let Lito know what's going on. He sends a new tune out, still with the 3.73's just to see if there's any difference. Take it for a drive, same thing. So we send a few emails back and forth and I find a calculator showing the RPM I'm roughly spinning at 80mph (based off the original drive home when I purchased it before the tune) and it shows I have 3.31 gears. I shoot that back to Lito and tell him I'll verify it when I get home from my trip and within minutes (literally like 15), I have a new tune with 3.31's on it. I get that loaded and head home the next day.
On the way home Wednesday, I use the GPS speedometers again and I'm now off by a couple of MPH in the opposite direction, showing faster on the speedo than what I'm actually doing. We get the car jacked up today and mark the tire and differential, manually checking it. Looks pretty close to 3.31 vs 3.55 and definitely not 3.73.
Stock tires were 245/45/19 and I swapped the rears for 275/40/19 just so I didn't have to worry about the speedometer correction. My question now is, with both sets of tires being 27.7" diameter and 728 revolutions per mile, if I truly have 3.31's in there despite the window sticker, why would the speedometer still be off by a few mph? I don't know if a previous owner blew up the rear and had a new one installed, if they didn't like the 3.73's and wasted the money to go down to the 3.31's or is there something between 3.31 and 3.55 that I might have? Could they be the rare 3.27's and causing the higher speed reading with it tuned for 3.31's? Just kinda stumped and I don't want to keep bugging Lito for another tune until I can figure this out and get those few MPH accounted for.
Thanks!
