Fredmahan

I love my recently acquired 93 SC300 manual. But the transmission ratios stump me. It seems more like a close ratio gearbox than a highway cruiser gearbox. It feels like 4th should be between where 4th and 5th are now, and 5th should be quite a bit taller than it is now. Are there any known reasons why Toyota did it that way? Are other upper gear ratios available when gearbox rebuild time comes?

Thanks, Fred

KahnBB6

iTrader: (5)

Hello Fred,

The W58 5-speed manual transmission is technically not considered a close ratio gearbox but the pairing of it with a 4.083:1 final drive in the 1992-1997 SC300 series and 4.272:1 in the 1993-1996 Toyota Supra MKIV Non-Turbo 5-speeds (Supra NA's all got 4.083 ratios for 1997-1998) does make it *feel* like a close ratio gearbox by effectively shortening each gear.

Several years ago I actually swapped from my 1993 SC300 5-speed manual's original 4.083:1 ratio to a custom rebuilt 4.272:1 ratio (with an LSD). This was with an un-modified stock non-turbo 2JZ-GE engine. I actually preferred the 4.272:1's even shorter gearing for maximum performance with a non-turbo engine. Highway cruising was optimized at 70-75mph or 80mph at highest with that ratio but it was tremendously helpful on mountain roads with varying elevations out west since each gear had even higher RPMs to work with.

However Lexus USA decided on 4.083 as the stock SC300 5-speed manual ratio to make the car's identical drivetrain slightly less racy than the same version of it that came in the Supra non-turbo of the same era. Considering the average age of Lexus coupe buyers at the time (early 1990's) this was a logical move for them.

There was also another factor influencing this: in Japan the same car in right hand drive was called the Soarer and there were different engine options, one of which was a 2.5L straight six (1JZ-GTE) parallel twin turbo that could be had with an R154 5-speed manual transmission. And a factory LSD. These RHD 2.5L turbo 5-speed manual variants ALL came with 4.083:1 final drive ratios.

Since those engines have less displacement and tend to be more "revvy" than a 3.0L 2JZ and since they were mostly driven in cities, country or mountain roads in Japan that factory final drive ratio made more sense. Although they were also well known for their prowess on high speed expressways. Even some police departments in Japan at the time had Soarer 2.5L turbo manual vehicles as high speed pursuit cars (in addition to Skyline turbo pursuit cars).

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Back to the USA SC300 models it made more sense to share production cost and satisfy the design spec of a milder non-turbo left hand drive American variant of this chassis (SC300) in manual form with the 4.083 ratio since it was not intended exactly as a sportscar from the factory but more as a sporty Lexus performance GT.

(Although as an aside the lack of any option for Lexus SC300 5-speed M/T customers to specify a Torsen limited slip differential as was a rare option available on the Supra Non-Turbo cars of the same era still baffles me as it totally suits the manual SC's.)

Further, years later when the 2002-2005 Lexus IS300 models were sold with W55 5-speed manual options the final drive ratio for those cars (which had nearly identical to SC300 spec 215hp 2JZ-GE VVT-i engines) was a 3.7x:1. Granted the W55's 1-3 ratios were a little more aggressive than the W58's but the differences in gearing are not that huge.

For the slightly lighter weight 1st gen IS300 Toyota/Lexus deemed a 3.7x:1 ratio sufficient to meet various design criteria including fuel economy. For the larger and slightly heavier SC300 5-speed manual the lowest ratio was still the particularly "short" 4.083:1.

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Once an SC300 gets turbocharger boosted power in any form (NA-T build, 2JZ-GTE swap, 1JZ-GTE swap) then I think 4.083 is mostly suited for the 2.5L 1JZ-GTE engines up to a certain power level. Certainly 4.272 is far too short with a turbo system. With 3.0L 2JZ turbo engines we generally recommend 3.916:1 (aka 3.92) from a 1992-1997 SC400 or 3.769 (aka 3.76) from an MKIV Supra TT Automatic or from a JDM Toyota Aristo (Japan's version of the GS300).

There is also 3.266:1 in 200mm size and as you also mentioned over PM a super rare Euro-market-only 3.5x:1 ratio (definitely available in 220mm size but *maybe* also in 200mm size also) but the 3.266 200mm ratio is generally for extremely powerful single turbo R154 cars with quick spool valves and VVT-i cylinder heads... or for Nissan CD009 or V160/161 transmission swaps.

Highway cruising is definitely better with a 3.92 ratio or 3.76 ratio but with a factory non-turbo 2JZ-GE engine it will take away the drivetrain's ability to give the car sufficient sporty power in each gear. I know that I did not want either of those ratios when I had my SC300 5-speed out west in mountain road country. In Florida flatland at mostly sea level elevations it's less of a concern but the character of the car would still be made slightly doggish and sluggish with those ratios... and no turbocharger.

For a non-turbo SC300 with any of the 5-speed W58, R154 or AR5 transmissions I still feel that 4.083 or 4.272 are still the ideal final drive ratios despite the high cruising RPMs on the highway.

With a turbocharged 2JZ or 1JZ engine I feel the options for taller ratios (3.92, 3.76) make more sense. Even 3.26 can make sense for *some* high powered configurations or certain transmission swaps but generally for *most* turbo SC's a 3.26 ratio is considered far too low.

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FWIW I took my SC300 5-speed with an R154 and 4.272 final drive ratio on cross country trips four times and while the cruising RPMs at 70-80mph are certainly not low they were quite livable at a cruise. I also appreciated the improved passing power with the 4.272 ratio but the stock 4.083 was also decent. If I recall it was 2800rpm @ 70mph with the 4.083 ratio and about 3000-3100rpm @ 70mph with the 4.272 ratio.

I only ever felt the 4.272 was too aggressive for decent fuel economy on the highway for sustained speed once I crossed, held or exceeded 90mph. For the most part I would cruise at 75mph on average, 65-70mph when it was necessary and never more than about 80mph sustained to achieve a good balance between long haul speed and fuel economy (with the 4.272).

With a turbocharged 2JZ engine and a 3.92 or 3.76 ratio is a much more ideal combination both on the street and highway with most common turbo-friendly manual or automatic transmissions(R154 5-speed, AR5 5-speed, A341E 4-speed automatic).

A 2.5L 1JZ-GTE engine may still be fine with a 4.083 but people also use 3.92 or 3.76 with those engines.

I haven't done any highway driving yet with the 3.76 ratio rear end that I have installed now but all around it is a good match for both street and highway use.... in a turbocharged 2JZ engine with an R154 or AR5 transmission. But 3.92 is fine also with only slightly higher revs.

Hope this helps.