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Though I know with enough money, anything is possible, would it be a difficult exchange to take out an 8V71 and put in a 6V92 in? Would this be a good idea? I'm thinking about buying a 1977 40 ft. MCI with an 8V71 and Allison 4 spd. that gets 5-6 mpg. Would putting a 6V92 help the mpg? Pros and cons anyone?
Thanks
Ahh the eternal question of power versus economy. You didn't indicate if the 6V92 is a turbo or not. Called a 6V92T or 6V92TA. The turbo engine will increase power and improve fuel economy. ^The rare non turbo will be worse than the 8V71. The turbo engine will not like life with a 4 sp manual gear box. The 92 series seem to want to live above 1500 rpm and loose liners and cranks below that. I have seen very few 92 series engins in busses survive to teardown as the tour drivers like to short shift and load the engines at low RPM. In an extreem case we were over hauling an 8V92TA ever 6 months due to this abuse till a driver got on it that kept his foot out at low RPM and kept his revs up. It lasted almost two years with him untill the bus was sold. There all sorts of technical chalenges doing this as a low cost swap. 1ST is matching trans, alternator and air compressor to the new engine. Secound the 6V92 is shorter. So you need to line up the rear pully to the fan drive box and re build the mounts to work. Drive shafts, shift linkage etc etc. ANd last but not least the 92 series engine puts much more heat into the coolant than the 71 series. It has to do with how they cool the intake air. Change the rads and go to the highest capacity you can fit in the holes. A fellow I helped do this swap on a MCI 5 C built his own cooling system with the masive rad out of a truck to cure this problem. Good luck.
Thanks for the input Bubba. I found another coach with a blown 8V71. Would a 671 go in without too much modification? Would the 671 be terribly underpowered for a 40 ft. coach with a 4 speed manual tranny? I'm not too concerned about pulling hills at 60 mph since I have more time than money. What about putting in a road ranger with the 671? Any thoughts? Thanks
Short answer in regards to the 8V-71 to 6V-92 swap, about the only difference you will see is the -92 series if it is turbocharged will keep climbing after the -71 series has had to downshift. Since both engines are about the same displacement and rated HP you will notice very little difference in fuel use.
The easiest swap would be to put a turbo onto the 8V-71.
I personally like the -71 series better than the -92 series, particularly in coaches. The -71 series will overheat but not as soon or as often as the -92 series engines.
If we are talking an inline 6-71, it would most probably not fit. It is too long to fit in an MCI engine compartment. Some MC-5 models came with the 6V-71 engine. It was more than just a little bit doggy. The same bus with an 8V-71 would really move out.
You can put a Road Ranger into an MCI but the shift linkage will never be very tight. A company in the Portland, OR area did put a 13-speed RR into an MC-8 with an 8V-71. That bus would blow past almost every other bus going up to the ski areas, including 8V-92 and Series 60 equipped buses.
The question you have to ask yourself is what are you trying to accomplish? Finding a coach with a good power package to start with is going to cost you a whole busload of cash less than any coach you have to swap power packages. Also, unless your significant other is never going to drive or really likes shifting, I would go with an automatic.
Hello - I have a 6V92T (277 hp) in my MC-9 (5 spd manual). I prefer it to a 8-71. The 8-71 is way too loud - it irritates me. The 6V92T is better on fuel at cruising speeds an flat terrain, in the hills they achieve the same mpg. A manual transmission helps quell some engine bay heat (just a bit, they run cooler) and improves mpg.
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