CABOCURT Posted March 15, 2007 Report Share Posted March 15, 2007 I'd like to change the final drive ratio from 3:73 to 3:11 in my '95 sts. Even though the 4t80e is in great shape at 80k, i'm sure a nice rebuild would'nt hurt. Does anyone know if it would be much of a problem to change the ratio's while doing this?...... Also, has anyone heard of a late model five speed auto being adapted into an early sts/etc? A six speed would even be better!!! (that way i could run a 2:73), don't ya know!! Much thanks, Cabocurt Link to comment Share on other sites More sharing options...
JasonA Posted March 15, 2007 Report Share Posted March 15, 2007 You cannot change the gear ratios. The 300 hp engine doesn't have a whole lot of low end torque. The 3.71 final drive ratio was specified to make up for that. The 3.11 in the SLS is so because the 275 hp engine has that low end torque. If your car only has 80k miles on it, it's not even broken in yet. Don't think twice about it. If you just absolutely wanted to spend money on the car, and lower the cruise RPM, you'd want to swap in an entire SLS or Eldorado powertrain (the 275 hp engine) to go along with the gear ratio change. Or...just sell your STS and buy an SLS (like mine!). Jason(2001 STS, White Diamond) "When you turn your car on...does it return the favor?" Link to comment Share on other sites More sharing options...
CABOCURT Posted March 15, 2007 Author Report Share Posted March 15, 2007 Thanks for the quick response..... But, not really what i was asking. I don't really believe i'll have a torque issue. I've deleted the ultra restrictive exhaust system and installed a high flow 3" cat and 3" exhaust system all the way to the tips. The change in hp and torque have been "incredible". Also added a k&n drop in filter. I can barely keep it on the ground. I believe the 3:73's were more for an "off the line" peformance issue. I'm not super concerned about this now... Link to comment Share on other sites More sharing options...
Ed Hall Posted March 15, 2007 Report Share Posted March 15, 2007 What is your reason for wanting to change ratios? Better fuel economy? How about just adding larger diameter tires. For fuel economy, I would go for a tires as tall and narrow tire I could fit under there. Something like a 205/75/15. Link to comment Share on other sites More sharing options...
CABOCURT Posted March 15, 2007 Author Report Share Posted March 15, 2007 YES.... FUEL ECONOMY IS A BIG ISSUE ISSUE, HOWEVER; I REALLY LIKE THE IDEA OF LESS WEAR AND TEAR ON THE ENGINE AT HIGHWAY SPEED. I'M IN CALI AND CRUISE AT 80 . I'VE INSTALLED 235-50-18'S ALL THE WAY AROUND. TALLER THAN STOCK AND LOOKS ARE SWEET TOO..... Link to comment Share on other sites More sharing options...
Ed Hall Posted March 15, 2007 Report Share Posted March 15, 2007 Your wide low profile tires aren't the best for fuel economy. For fuel economy, you want non-performance tall and skinny tires. You'll sacrifice some handling but it'll soak up those California roadway bumps a lot better. Wear and tear on the engine is not an issue with these cars due to design. The Northstar is a very long lasting engine and they've been known to last 500k miles. Link to comment Share on other sites More sharing options...
Cadillac Jim Posted March 15, 2007 Report Share Posted March 15, 2007 The differential is a separate module in the 4T80E and can be changed without ovehauling the entire transmission. It pulls out the passenger side of the transmission. There is a gear ratio check in the PCM that detects when the wrong final gear ratio is installed, and will throw code P0370 if you change the gear ratio. I have no idea what would be required to modify that check without changing the PCM. I suspect that it would require the same level of re-engineering as a performance chip, i.e. building a new PCM. You could get another PCM for a VIN Y engine that is otherwise identically equipped as your car. -- Click Here for CaddyInfo page on "How To" Read Your OBD Codes-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data -- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC Yes, I was Jims_97_ETC before I changed cars. Link to comment Share on other sites More sharing options...
Ranger Posted March 15, 2007 Report Share Posted March 15, 2007 During testing and validation, the Northstar was run at WOT for 300 hrs (12.5 days). That should eleviate any wear & tear fears. Link to comment Share on other sites More sharing options...
CABOCURT Posted March 16, 2007 Author Report Share Posted March 16, 2007 The differential is a separate module in the 4T80E and can be changed without ovehauling the entire transmission. It pulls out the passenger side of the transmission. There is a gear ratio check in the PCM that detects when the wrong final gear ratio is installed, and will throw code P0370 if you change the gear ratio. I have no idea what would be required to modify that check without changing the PCM. I suspect that it would require the same level of re-engineering as a performance chip, i.e. building a new PCM. You could get another PCM for a VIN Y engine that is otherwise identically equipped as your car. THANK YOU VERY MUCH FOR YOUR GREAT ANSWER. I REALLY APPRECIATE THE CLARITY. CABOCURT Link to comment Share on other sites More sharing options...
95SevilleSLS Posted March 16, 2007 Report Share Posted March 16, 2007 During testing and validation, the Northstar was run at WOT for 300 hrs (12.5 days). That should eleviate any wear & tear fears. Was that on the older northstars, like the 93 model? Did anything happen after that 300 hrs? That's some really cool info, where did you find that? -Dusty- - 02 Seville STS, white diamond - 93 Sixty Special, Tan with vinyl top - 79 Coupe DeVille, Tan with Tan top - 06 GMC Sierra Z71, Black - 92 Silverado C1500, black and grey - 83 Chevy K10 Silverado, Black and Grey Link to comment Share on other sites More sharing options...
CABOCURT Posted March 16, 2007 Author Report Share Posted March 16, 2007 During testing and validation, the Northstar was run at WOT for 300 hrs (12.5 days). That should eleviate any wear & tear fears. Link to comment Share on other sites More sharing options...
CABOCURT Posted March 16, 2007 Author Report Share Posted March 16, 2007 JUST GOES TO SHOW YOU HOW SPECIAL THE NORTHSTAR AND SURROUNDING ENGINEERING REALLY WAS (AND IS). THAT'S WHY I LOVE MY STS...... A CROSS BETWEEN A FERRARI AND A BENTLEY ..... BUT, HOW ABOUT THOSE HYDRAULIC MOTOR AND TRANSMISSION MOUNTS .THE NORTHSTAR LIKES TO TEAR THEM UP....AND NO I DON'T LIKE SOLID MOUNTS........ Link to comment Share on other sites More sharing options...
Ranger Posted March 17, 2007 Report Share Posted March 17, 2007 During testing and validation, the Northstar was run at WOT for 300 hrs (12.5 days). That should eleviate any wear & tear fears. Was that on the older northstars, like the 93 model? Did anything happen after that 300 hrs? That's some really cool info, where did you find that? That was in the initial testing of the Northstar. Not sure what you mean by "Did anything happen after that 300 hrs?" Learned this from our old Guru who was is a GM engineer and was involved in the design and testing of the Northstar. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.