gmini
New Member
Posts: 1
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Post by gmini on Apr 30, 2021 4:44:53 GMT
Hi,
Wanted to check if I have this right. I have late 90s JDM (mpi block/spi assemly) automatic. I wanted to compare what I believe are the Manual/Auto gear ratios. Is this right? Why difference in the first gear?
SPI Gear Ratios Manual –3.647 2.185 1.425 1.000 (SPI)
MPI Gear Ratios Manual - 3.44, 2.06, 1.35, 1 (MPI)
SPI/MPI Gear Ratios Auto (mine) – 3.30, 2.07, 1.35, 1 (Late SPI/MPI)
Thanks
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Post by mra-minis on May 4, 2021 12:29:32 GMT
I can be contacted on martin@kmprecisionengineering.com
Yours is a 1998 - 2000 model
Manual transmission = apples
Automatic transmission = peaches
They are completely different, the internals of both are completely alien to each other.
The manual has a lower gear to aid starting from rest, the auto has a torque converter which allows for some slippage and can cope with the higher ratio without any issues.
So to answer your question, it is purely because the different gear sets within each different unit cannot be designed to be exactly nice round numbers of choice, there is going to be an Engineering Compromise, hence why you have 3.44 and 1.425 etc...
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