Hi,
I have a 1985 E150 van conversion (to a passenger van). Recently slightly larger tires (28.9" dia vs 27.1") were put on (due to an excessive number of blowouts) and this seems to have thrown the final drive ratio off by quite a bit. Even taking into account the change in the speedometer and odometer, my mileage has gone down to 11-12 from 14-15 mpg.
Currently, when crusing on the freeway at 60-65, I'm pulling about 10" of vacuum which drops down below 3 when going up even the slightest incline. Going 70 on the flat is 7" and on any incline goes to 0.
In gear and at a standstill its 18" and 21" at idle and in neutral. High rpms in neutral will still pull 20-21" so i dont think i have a major exhaust restriction, and im not running lean so i dont think there are any major vacuum leaks.
This leads me to believe that the new ratio (equivalent to putting a
3.25 gearset in) is a bit too tall for the larger diameter tires and weak motor. As it is, the engine (5L V8, 2bbl 2150 feedback carb) and tranny (AOD, not AODE) are stock. The current gearset is a 9" 3.5. Am I on the right track here? Or should I be looking for something with the motor/tranny?I believe that in order to return the final drive ratio to the way it was before putting on larger tires, i'll need a 3.72 gearset (actually
3.75, but those are hard to find!). Ive also considered a 3.89 or 4.11If changing the gearset is reccomended, what ratio? I'd like a bit more acceleration and torque than the original stock set up (with the smaller tires and 3.5) but I also want to keep the gas mileage reasonable.
Would using a 3.89 or 4.11 make a big difference? (The van is a conversion, so its several hundred lbs heaver than the empty cargo van it was, but i don't tow and i do spend a lot of time on the freeway)
Oh yeah... what sorts of odd tools are needed for this operation should i try and do it? Aside from a heavy duty socket set / torque wrench and a dial gauge, that is. I've seen some people use a press (which i really dont have), but is that really necessary?
I know, its a lot of questions, but it helps to keep everything together.
thanks in advance!