Benjamin Posted August 16, 2014 Report Share Posted August 16, 2014 (edited) Has anyone ever determined which torque converter ratio is best for each engine/transmission combo? Example 1: Allison AT545 transmission with TC290 (1.72:1) torque converter behind Cummins B5.9 190 hp (475 lb/ft) engine Example 2: Allison MT643 transmission with TC360 (2.86:1) torque converter behind Cummins B5.9 210 hp (485 lb/ft) engine Example 3: Allison MT644 transmission with TC494 (1.92:1) torque converter behind Detroit Diesel 6V92TA 253 hp (766 lb/ft) engine Axle torque ratings: calculated input torque to axle, determined by: T = maximum gross engine torque (lb/ft) N1 = lowest transmission forward gear ratio N2 = torque converter stall ratio (2.5 or specific value for automatics, or 1 for manuals) Say you have a Detroit Diesel 6V92TA MUI (mechanical unit injection) engine mated to an Allison MT644 automatic transmission, being used in an Orion I transit bus. Allison recommends the transmission not exceed more than 740 lb/ft of input torque from the engine for transit bus applications. Only two TC (torque converter) ratios were produced for the MT644: 1.92 (TC494) and 2.21 (TC495). As the 6V92TA 253 hp engine has 766 lb/ft of torque, the 1.92 TC ratio would be best suited to the transmission. Otherwise, the Allison HT747 transmission (for engines up to 345 hp/1100 lb/ft) is recommended. 766 x 3.58 x 1.92 = 5,265 lb/ft input torque to axle. If anyone knows what the recommended input torque to axle rating is for a Rockwell R143 series rear axle with 4.63 and 4.11 ratios, please try to answer. ~Ben Edited September 20, 2014 by Benjamin Link to comment Share on other sites More sharing options...
Jack 47 Posted August 16, 2014 Report Share Posted August 16, 2014 I can help you with this question, But first, what kind of vehicle performance are you trying to achieve? Maximum acceleration, maximum fuel economy/speed or a balance? What is the curb weight of the Orion I? Does the Detroit Diesel you are talking about have DDEC II electronic controls? For the torque converter question, higher torque converter ratios (2.86) mean more slippage and more multiplication. It is less fuel efficient but will allow your engine to reach its power band quickly. In this situation, it would be ideal for less powerful lower torque engines. Lower torque converter ratios (1.72) mean less slippage, smoother, even acceleration, ideal for taming more powerful engines. Naturally, in all cases, you will get less torque multiplication if you don't floor the pedal. Taller axle ratios (4.11) will result better cruising fuel economy and higher road speed, but will dull your first gear acceleration. Shorter axle ratios (4.63) will bring your cruising speed down, but will increase your overall acceleration. Rockwell R143 axles can tolerate lots of torque, so I would not worry about their input rating. Unless you have the latest generation of Allison 6 speed transmissions with LBSS, Allison transmissions have lockups that typically engage in the middle of SECOND gear. In any case, if you want plenty of acceleration, go for the Detroit Diesel 6V92TA with 1.92 torque converter ratio with a transmission that has the most gears possible. In a bid to answer transmission torque input limits, engines can have their torque and horsepower ratings de-rated by swapping out the injectors. De-rate for a 277 hp detroit 6V-92TA can go to 253hp and 220hp. A 220 hp de-rate by swapping out injectors would also bring the torque down to about 720 ft/ibs. Link to comment Share on other sites More sharing options...
Benjamin Posted August 16, 2014 Author Report Share Posted August 16, 2014 (edited) I can help you with this question, But first, what kind of vehicle performance are you trying to achieve? Maximum acceleration, maximum fuel economy/speed or a balance? What is the curb weight of the Orion I? Does the Detroit Diesel you are talking about have DDEC II electronic controls? For the torque converter question, higher torque converter ratios (2.86) mean more slippage and more multiplication. It is less fuel efficient but will allow your engine to reach its power band quickly. In this situation, it would be ideal for less powerful lower torque engines. Lower torque converter ratios (1.72) mean less slippage, smoother, even acceleration, ideal for taming more powerful engines. Naturally, in all cases, you will get less torque multiplication if you don't floor the pedal. Taller axle ratios (4.11) will result better cruising fuel economy and higher road speed, but will dull your first gear acceleration. Shorter axle ratios (4.63) will bring your cruising speed down, but will increase your overall acceleration. Rockwell R143 axles can tolerate lots of torque, so I would not worry about their input rating. Unless you have the latest generation of Allison 6 speed transmissions with LBSS, Allison transmissions have lockups that typically engage in the middle of SECOND gear. In any case, if you want plenty of acceleration, go for the Detroit Diesel 6V92TA with 1.92 torque converter ratio with a transmission that has the most gears possible. In a bid to answer transmission torque input limits, engines can have their torque and horsepower ratings de-rated by swapping out the injectors. De-rate for a 277 hp detroit 6V-92TA can go to 253hp and 220hp. A 220 hp de-rate by swapping out injectors would also bring the torque down to about 720 ft/ibs. The curb weight of the Orion I is 24,100 lbs. GVW. The 6V92TA is MUI (mechanical unit injection). ~Ben Edited August 16, 2014 by Benjamin Link to comment Share on other sites More sharing options...
Jack 47 Posted August 17, 2014 Report Share Posted August 17, 2014 The curb weight of the Orion I is 24,100 lbs. GVW. The 6V92TA is MUI (mechanical unit injection). ~Ben No electronics makes things less complicated with the 6V-92TA. Here is my suggestion for your situation: At 24,100 Ibs., anything over 220 hp is enough power for city use, but an Allison HT (740/747, etc.) transmission with a lower ratio torque converter (1.92) would be a better bet for durability and reliability than the MT medium-truck automatic transmissions. At 220 hp to 253 hp, you would get a very fast bus in the city that pulls from stops quickly (standing passengers may find it hard to hold on), and with a four speed transmission and a 4.63 axle ratio, do well merging on the highways, with top speed of 59 mph. The four speed transmission should provide wide ratio coverage for the taller axle ratio. A 4.11 axle ratio would get you to 65 mph and save you a bit of fuel. In comparison, I drove a Novabus Classic transit bus for the past two months, with a 6V-92TA derated to 253 hp (factory label shows 277 hp). The bus was 24,230 Ibs empty. The transmission was a three-speed Allison ATEC VR731 with torque converter ratio of 2.79 (TC-490). The axle ratio was 5.13, first gear ratio is 1.77. For city use, it was a fast bus, it has plenty of power for climbing slopes, it takes off from stops smoothly but speed builds up pretty quickly, it was easy keep up with car traffic. It takes 10.6 seconds to get to 25 mph. For highway use, the overdrive (3rd) gear kicks in at 38 mph and it was barely adequate for merging, and was governed for 60 mph. Putting more gears on it would make acceleration on the highway easier. Link to comment Share on other sites More sharing options...
Benjamin Posted September 5, 2014 Author Report Share Posted September 5, 2014 (edited) "K factor" is another thing to consider in regards to choosing the correct torque converter. It is arrived at when you divide the governed engine RPM by the square root of the peak torque of the engine. The 6V92TA MUI engine with 7G65 injectors that I mentioned before (253 hp / 766 lb/ft), has a K factor of 75.88. The 6V71TA with N60 injectors (220 hp / 671 lb/ft): K factor at 2100 RPM is 81.07. The 6V71N with 7E60 injectors (200 hp / 583 lb/ft): K factor at 2100 RPM is 86.97. My Cummins examples I mentioned have these K factors: B5.9-190 (190 hp / 475 lb/ft): K factor at 2500 RPM is 114.71. B5.9-210 (210 hp / 485 lb/ft): K factor at 2500 RPM is 113.52. ~Ben Edited September 5, 2014 by Benjamin Link to comment Share on other sites More sharing options...
Detroit Diesel 6V92TA Posted September 5, 2014 Report Share Posted September 5, 2014 Is the Allison VS1 a 2 speed transmission like the VH9? If so, what are the main differences? Link to comment Share on other sites More sharing options...
Benjamin Posted September 5, 2014 Author Report Share Posted September 5, 2014 Is the Allison VS1 a 2 speed transmission like the VH9? If so, what are the main differences? Both are single-speed plus torque converter. The VH9 was used behind the 6V71 while the VS1 graced the 8V71. ~Ben Link to comment Share on other sites More sharing options...
Detroit Diesel 6V92TA Posted September 5, 2014 Report Share Posted September 5, 2014 Both are single-speed plus torque converter. The VH9 was used behind the 6V71 while the VS1 graced the 8V71. ~Ben Okay. Link to comment Share on other sites More sharing options...
Express691 Posted September 6, 2014 Report Share Posted September 6, 2014 All I can say here is that my Crush's name is AllYson and I think about her when I ride buses with Allison Transmissions. Link to comment Share on other sites More sharing options...
Detroit Diesel 6V92TA Posted September 7, 2014 Report Share Posted September 7, 2014 Do you know of any buses or US operators that used the HT-750, HT-754, or HT-755 series transmissions? Link to comment Share on other sites More sharing options...
bradfordbrian Posted September 13, 2014 Report Share Posted September 13, 2014 Salem, OR had 35ft Orions with a 5 speed ht Link to comment Share on other sites More sharing options...
Detroit Diesel 6V92TA Posted September 14, 2014 Report Share Posted September 14, 2014 Salem, OR had 35ft Orions with a 5 speed ht Do you know which one? (It would be good info for the wiki). Also, were they with 6V92TA's? Link to comment Share on other sites More sharing options...
Benjamin Posted September 14, 2014 Author Report Share Posted September 14, 2014 Do you know which one? (It would be good info for the wiki). Also, were they with 6V92TA's? Yes, they had the 6V92TA engine. ~Ben Link to comment Share on other sites More sharing options...
Detroit Diesel 6V92TA Posted September 14, 2014 Report Share Posted September 14, 2014 Yes, they had the 6V92TA engine. ~Ben Okay thanks. Do you know if it was an HT-750, 754 or 755? Link to comment Share on other sites More sharing options...
Benjamin Posted September 14, 2014 Author Report Share Posted September 14, 2014 Okay thanks. Do you know if it was an HT-750, 754 or 755? I wish I knew. . . but the common automatic was the HT748 for buses of that year (1992). I wish I knew what the actual model was. . . ~Ben Link to comment Share on other sites More sharing options...
Detroit Diesel 6V92TA Posted September 14, 2014 Report Share Posted September 14, 2014 I wish I knew. . . but the common automatic was the HT748 for buses of that year (1992). I wish I knew what the actual model was. . . ~Ben Oh okay. Do you know of any other agencies that used the 5 speed HT series or were they the only ones? Link to comment Share on other sites More sharing options...
Benjamin Posted September 14, 2014 Author Report Share Posted September 14, 2014 (edited) Oh okay. Do you know of any other agencies that used the 5 speed HT series or were they the only ones? What more can I say? 5-speed automatics weren't really common in transit buses. Highway coaches, maybe. Unless you're talking about the torque converter lock-up effect, I wish I could explain further. ~Ben Edited September 14, 2014 by Benjamin Link to comment Share on other sites More sharing options...
Detroit Diesel 6V92TA Posted September 14, 2014 Report Share Posted September 14, 2014 What more can I say? 5-speed automatics weren't really common in transit buses. Highway coaches, maybe. Unless you're talking about the torque converter lock-up effect, I wish I could explain further. ~Ben Okay, thanks for the info though. Link to comment Share on other sites More sharing options...
Benjamin Posted September 14, 2014 Author Report Share Posted September 14, 2014 Okay, thanks for the info though. You're welcome. ~Ben Link to comment Share on other sites More sharing options...
Benjamin Posted September 19, 2014 Author Report Share Posted September 19, 2014 (edited) Jack 47, Getting back to the 1983 Orion I 01.506 powered by the Detroit Diesel 6V92TA (253 hp) engine and Allison MT644 transmission, now that I know that the MT644 was rated for engines making 235 hp and 740 lb/ft of torque when used in transit buses, I still think the TC494 torque converter (1.92:1 stall ratio) would've been acceptable as this 6V92TA (with the 7G65 injectors) was still past those limits. ~Ben Edited September 27, 2014 by Benjamin Link to comment Share on other sites More sharing options...
Detroit Diesel 6V92TA Posted October 21, 2014 Report Share Posted October 21, 2014 I remember you said the HT-747 came out around 1982 or 1983. However, was the HTB-748 ATEC around in 1984 and 1985? I am trying to confirm whether the 1984-1985 Neoplan AN440's on this page: http://www.cptdb.ca/wiki/index.php?title=Southeastern_Pennsylvania_Transportation_Authority really had HT-748's or HT-747's. Link to comment Share on other sites More sharing options...
Benjamin Posted October 21, 2014 Author Report Share Posted October 21, 2014 I remember you said the HT-747 came out around 1982 or 1983. However, was the HTB-748 ATEC around in 1984 and 1985? I am trying to confirm whether the 1984-1985 Neoplan AN440's on this page: http://www.cptdb.ca/wiki/index.php?title=Southeastern_Pennsylvania_Transportation_Authority really had HT-748's or HT-747's. As far as I know, yes, the HTB748 followed in late 1983. ~Ben Link to comment Share on other sites More sharing options...
Detroit Diesel 6V92TA Posted January 24, 2015 Report Share Posted January 24, 2015 Do you know when the Allison VS2-6 and VS2-8 became available for GMC and Flxible New Looks? Also, the VH9 and VS1-8? Link to comment Share on other sites More sharing options...
Benjamin Posted January 24, 2015 Author Report Share Posted January 24, 2015 (edited) Do you know when the Allison VS2-6 and VS2-8 became available for GMC and Flxible New Looks? Also, the VH9 and VS1-8? Flxible first used these two in 1967 when they built their first V-drive buses (Erie Metro Transit being the first taker); GMC around 1966. The VH9 was an evolution of the VH2/4/5/7 which was used in the GMC New Looks between 1960-1966. The "Super V" VS1-8, VS2-6 and VS2-8 showed up around 1966-67. ~Ben Edited August 5, 2015 by Benjamin Link to comment Share on other sites More sharing options...
Detroit Diesel 6V92TA Posted February 2, 2015 Report Share Posted February 2, 2015 Do you know much about the HT-746? I've only seen a video of a Phantom school bus and someone said it had an HT-746 and it shifted like a Voith. Link to comment Share on other sites More sharing options...
Recommended Posts
Please sign in to comment
You will be able to leave a comment after signing in
Sign In Now