P30 Chassis
I would like to know. can you get high geared rear ends for the P30 chassis? someday I would like to get a higher geared ring and pinion to get the rpms down a little. anyone ever done that?
Forum Discussion
NO YOU CAN NOT. OK maybe you can, but there are some serious considerations, that highly limit what you can do, or what benefit you will get. I'm going to make an assumption that if you are asking this question, that you are talking about a motorhome with a TH400. If so, you have a critical problem - TC stall speed. When I first dropped the 502 in my coach, I changed the gearing, because I had gobs of low end torque. What I found was, that unless the engine was turning 2500 RPM or higher, there was enough TC slip, that it had virtually NO impact on my mileage. So cruising at 55, compared to cruising at 75 or higher resulted in the SAME mileage. It was not enough slip to heat the trans, but just enough to hurt the mileage. The only thing changing the ratio did for me was forced me to cruise at a higher speed. You can just tell, especially with an engine computer and live display what is really going on.
These vehicles are designed surprising well, in that TC slip, gear ratios, and weight are all designed to work together. If you change one thing, there is a domino effect, a whole series of other things that are no longer "in tune" with your change. The picture is bigger than just a personal preference of mileage vs drivability.
BTW: You don't just want to change your TC to a lower stall speed, because then you will never be able to get rolling with the change in gear ratio. I hate to say it, but the only viable solution is going to a 4L85E which will give the acceleration off the line, and the low engine RPM in 4th with lockup. Still not sure that a older 454 will handle it. Maybe a late version Vortec can, but probably not the original 454 from the 70s and 80s.
These vehicles are designed surprising well, in that TC slip, gear ratios, and weight are all designed to work together. If you change one thing, there is a domino effect, a whole series of other things that are no longer "in tune" with your change. The picture is bigger than just a personal preference of mileage vs drivability.
BTW: You don't just want to change your TC to a lower stall speed, because then you will never be able to get rolling with the change in gear ratio. I hate to say it, but the only viable solution is going to a 4L85E which will give the acceleration off the line, and the low engine RPM in 4th with lockup. Still not sure that a older 454 will handle it. Maybe a late version Vortec can, but probably not the original 454 from the 70s and 80s.
