GM 8L90E 8-Speed Auto (C7 Corvette / LT1) gear ratios
The GM 8L90E 8-Speed Auto (C7 Corvette / LT1) is an eight-speed automatic.
First gear is 4.56:1 and 8th is 0.652:1. Divide one by the other and the overall spread is 6.99:1. That is a very wide spread. With eight gears to share it out, the steps in the middle can still stay civil.
8th is an overdrive at 0.652:1: the output shaft turns faster than the input shaft. Two of the eight gears are overdrives. 6th is direct drive at 1.00:1.
The biggest step is 1st to 2nd, where the ratio drops 35%. The smallest is 6th to 7th at 16%. On each upshift the revs drop by the same percentage as the ratio.
The final drive lives in a separate diff, so the speed table shows three common ratios: 3.42, 3.73 and 4.10. With a 3.73 final drive and 225/45R17 tyres, 8th at 6,000 rpm works out at 295 km/h (183 mph), and first runs out at 42 km/h (26 mph). That is how tall the gear is, not a top speed. Drag and power decide that. At 70 mph in 8th the engine turns about 2,290 rpm.
Ratios
GM 8L90E 8-Speed Auto (C7 Corvette / LT1): ratio per gear, and how far the ratio drops from the gear before.
Gear
Ratio
Step
1st
4.56:1
-
2nd
2.971:1
34.8%
3rd
2.075:1
30.2%
4th
1.688:1
18.7%
5th
1.27:1
24.8%
6th
1.00:1
21.3%
7th
0.845:1
15.5%
8th
0.652:1
22.8%
Road speed at 6,000 rpm
Road speed at 6,000 rpm on a 225/45R17 tyre (1.993 m rolling circumference), by final drive. No slip, no drivetrain losses.
Results are theoretical: stock ratio specs, your inputs, no drivetrain losses. Verify with your drivetrain supplier before spending real money.
Swapping the engine as well? StandaloneHQ counts the inputs and outputs the new engine needs and shortlists the wire-in ECUs that fit: ECU Pinout Planner.
BoxSelector crunches gear ratios, tyre sizes, and RPM figures to give you useful speed and cruise data for your build. The results are theoretical, based on stock ratio specs and your inputs, and assume perfect mechanical conditions, zero drivetrain losses, and a world without speed bumps, traction limits, or your right foot getting sweaty. Real-world results will vary. Probably a lot for automatics.
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Gear ratios may have changed, and manufacturers love to quietly update things.
We've done our best to source accurate ratio data from factory specs and reputable technical references. Some ratios (particularly on production variants with running changes) may differ from the figures listed here. Always verify critical specs against your actual unit or a current manufacturer source before committing to anything expensive.
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