I recently swapped in a 2.73 gear in my Roadmistress as one of my steps toward getting a lot better fuel economy all the while keeping the car civilized. Another step was replacing the 225/75/15 tires with 235/75/15 tires. Other upcoming mods are…. replace the clutch fan an electric fan, K&Nfilter, add a tranny cooler and gut the converter. This past weekend I had a chance to do a long trip highway gas mileage run. The phone rang Friday night and it was a friend needing a casket (new & empty) taken to St. Louis from Kansas City, Mo. The trip was 525.8 miles total and the fuel used was 20.5 gallons. Overall economy was 25.64mpg. While on the road I tried to maintain 73-80 mph on the way there and 68ish-73 on the way back. Since I was going for the best fuel economy, I let gravity help me speed up going down hills and then backing off slightly on the throttle the more I climbed back up hills to work the engine less (like driving with a vacuum gauge). The cruise of course was never used. I have considered building an engine using a 305 block and a 400 crak. I think it would run ok on the TBI setup and give even better bottom end yet maintain similar economy to the 350. the increased low end would make pulling out into traffic easier. It might even let me swap in a 2.56 gear. These old TBI motors are so easy to work on. Carry a few ignition parts/tools and an extra serp belt and it’s hard to get stranded motor wise. I may omit the factory oil cooler eliminate the chance of one of the lines failing and leaving me stranded.
I've always heard, but never experimented to find out for myself, that the use of cruise control can add a mile or two per gallon.
Unless your converter (I am assuming you were referring to the catalytic converter since I can't think of too many positive things resulting from gutting your torque converter) is plugged up I don't think you will see any gain whatsoever from gutting it. In fact I think it would be way more hassle than anything. I would just leave it as is and work on increasing the overall efficiency of your engine.
^^^ This, I've heard the exact same thing. In fact whenever I use it, I always eye the fuel economy gauge and its always doing much better than when I drive it.
cruise will let off the gas to maintain speed and kill momentum going down a grade and then open the throttle up as much as it takes to keep the correct speed going up the grade. also when it accelerates harshly to go up the grade it will frequently unlock the torque converter compounding less efficiency. all are poor things to do when going for gas milage. if you were on a perfectly flat road. cruise would be a good option. grades make it an enemy when compared to good driving vigilance when trying to get optimum mpg. gutting the cat will let the exhaust flow a little better. my cat currently rattles alot. the stuff is starting to get loose. i dont want it shooting into my muffler and causing problems. saying cruise added mpg was a sales tactic for selling cruise. mpg is more about how you are working the engine than maintaining constant speed regaurdless of cost. peak highway mpg is usually the lowest maintainable rpm in your highest gear. its pretty logical. it has no statement of an actual speed. i think my 60ish mph test will have even better numbers. the motor turns about 1250 rpm @ 60 mph on pretty level ground and the motor seems to not mind it. i prefer driving around 60 anyway.
25-26 mpg is really great. Wish I could muster out that much. How difficult was it to swap out gears? And by that- are you talking about the rear diff gears? What if any were the cons to swapping to the 2.73?
things you really need for a 92-92 (and maybe 91) roadmaster are... ring and pinion set that has the reluctor ring for the antilock brakes to work correctly. the ring comes with the gm set along with w new crush sleeve and a couple new pinion shims and ring bolts. i bought new bearings/races for the pinion jst to make it easier and decrease the chance of having to re-do it all from a marginal old bearing crapping out in the near future. some GL5 rated grease. i had 2 quarts on hand. posi additive if you have a posi. new pinion seal. mine took the one without the flange. some require a flanged seal. if you havent looked closley at yours to know whick one yours is, have one of each on hand. the are not interchangable. new cover gasket, mine was a c-clip rear so the axles dont bolt in which was kinda good since i didnt have to remove the wheels.mof course if your brake shoes hang up on the drum, you will have to also deal with that. anyway. pulled the nut from the pinion after removing the driveshaft and plugging the rear of the tranny to keep the fluid safe. pulled the diff cover catching the old grease for disposal. removed bolt holding the pin that secures the axles. pushed each axle in and removed the it's c-clip. pulled axles out about a foot. unbolted diff unit and pulled/pried it out making sure i noted which shims went to which side. unbolted the ring bolted the new one on(the bolts are left hand threads). bolted new ring to dff. cleaned the diff bearings after making sure the races showed no signs of bearing/races needing replaced. removed old pinion and bearings and races. my friend dave did most of the labor since he is a meticulous machinist mechanic of 30 years. he has done so many of these that he can do them by feel and then show how good his 'feel" was when you see the numbers. he installed the pinion with the new crush sleeve, bearings and shims. as he reinstalled the diff, he stated that it felt like it was goind to be too tight. he was right. we ended up swapping the shims from side to side when it was all said and done. he said about 95 percent of gm r&p replacements he has done on 1985ish and up car never need reshimmed. then we put it all back together and cleaned the housing out real good one last time, recovered, added lube and additive. once you start reinstalling the diff into the housing you may have to shim differently more than once to get the gear pattern to be right. if you tighten the pinion too tight or need to reshim it, you will need a new crush sleeve each time. so having someone doing that part will help eminsley i the long run. poorly installed gears are noisy and dont last long. mine are dead quiet. i can NEVER hear them, even when driving in under ground parking structures. i can say that about my old gears. they made a little noise from the time i bought the car. dave is pret sure its from one of the old pinion races having a slight wear to it. he said the 3.23 r and p looked great and i should throw it on ebay....maybed. since i had a 3.23, that meant that the lowest numbered gear set that gm made for it was a 2.72 that is why i went with that number. when you got a 2.56 gear (usually in sedans) they used a 7.5 inch r&p. the same as a camaro or s10 except the roady had the pinion machined for the reluctor ring. oh yeah... you also have to change the transmission reluctor ring (still available through gm)so your speedo will be right. .. done at a later date. here is the process.... remove driiveshaft and rear transmission speedometer housing. note precisly where the ring is one the shaft. your new one needs to be installed exactly in the same place. use a 4 inch grinder with a good (metabo comes to mind) cutting wheel. it helps clearence a bit if the cutting wheel is worn to a smaller diameter. use the wheel to carefully cut through the old tranny reluctor ring trying not to scar the shaft. once you get the ring off, make sure there are no scuffs or debris on the shaft that will keep the new ring from sliding on. now comes the fun part. use a torch to get the new ring almost red hot. once heated, slide it onto the shaft to where it needs to be. it will cool within seconds grabbing the shaft. you cant use heat to remove the old ring because the heat can damage the transmission. reassemble and start going further with less fuel. it took us 2.5 hours and that includes driving to daves(press) 15 miles away to press the pinion bearing on. i figured it up, and for the mula it took, it will pay for itself in well less than 20 tanks of gas. its hard to put a price on driving 75, getting 25+mpg AND being this comforable all at the same time.
if you wanna call it the con side.... i used to be able to lay black marks at will when taking off. not any more can hardly spin a tire. thats where the 94-96 LT1 power would still be able to shine. my holeshot has diminished by what i would call 35 percent. once the car is at 10 mph, it seems like most cars. there are a few instances where when driving through areas of towns that are 45mph zones. the car will now stay in 3rd gear with the converter unlocked where before i could lug it in OD locked up. given the gearing difference, i dont know if it is really a neg side effect. might just be an situation where its is a little better for the motor since it aint being lugged. if i were driving most of my driving at 45-55mph, sucess might be marginal.
20mpg per tank if the highway driving included 65-70 at times. 22.7 and 23 driving only 50-55 and only highway. other than that once in a while a tank might yeild almost 21mpg but mostly 20 if i drove sane. if i was crazy some+, then i might get 17 or 18 per tank. always use cheapest gas from Quik Trip.
