| Author |
Message |
Buddy (63.52.4.112)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 16, 2001 - 8:31 pm: | |
Anyone have any ideas on pros and cons of swapping the 6-71 from a 4104 to an 8V-71?
I think I may have to rebuild my 6 and am wondering if it may be wise to swap it for an 8.
Thanks
Buddy |
Kirby (12.94.6.171)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 16, 2001 - 10:14 pm: | |
If you could find a good Flx or Grumman 870 at auction, cheap, with a good motor and transmission, you would have all the parts you need for the conversion. One advantage is that you'd increase your hp from 210 to 304 hp. It's nicer to drive with the automatic. The down side is you can only get a 3 speed automatic, so if you live in the hills or do a lot of hill climbing, it's not so good. Gas mileage depends on how fast you go, but you can definitely burn more with the V8 and automatic. |
Frank Allen (152.163.197.187)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 17, 2001 - 9:59 am: | |
dont forget the rearend, not the same
Frank |
RJ Long (24.130.101.25)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 17, 2001 - 10:45 am: | |
Buddy -
Anything you do to change the original powertrain will have a ripple effect, which needs consideration.
The simple answer is that the 8V71 will fit, physically.
A couple of the problems associated with this swap include inadequate cooling and bevel gear failure.
Look at the difference in size between a 4104 and 4016 radiator to get an idea of how much increase you'll need.
On your 4104, the angle drive bevel gears are after the transmission. Starting with the 4106, GM put the gears before the transmission, after experiencing bevel gear failures during development testing of the 8V powerplant. Memory's fading a little, but it had to do with torque multiplcation - torque's constant on the gears before the transmission, but multiplied tremendously on them when they're after the gearbox. The 4104's design couldn't handle the greater torque of the V-8 engine.
This redesign also required a change to the rear axle, as the ring and pinion are offset differently on the 4106 and later coaches. Using the original axle with the later powertrain will cause driveline vibration and early u-joint failure.
The rear axle has to be exchanged when installing an automatic transmission for the same reason.
But all of this can be overcome, mostly it's based on the size of your wallet.
Another alternative, if you have to overhaul your 6-71, is to rebuild it as a 6-71T (or buy a LH Reliablt 6-71T unit from DDA). The turbocharged 6-71T pumps out 275 hp, the same as a stock 8V71 that's "B" timed with N-60 injectors, the most common configuration. Other than fabricating different intake and exhaust plumbing to accomodate the turbo, it is a much simpler HP increase than a powertrain swap.
Hope this helps,
RJ
PD4106-2784 |
Kirby (12.94.3.154)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 17, 2001 - 10:00 pm: | |
Buddy, RJ is right, if you put an 8V71, or 692 or even 892 in your 4104.... it's going to run a little bit hotter. But I believe a radiator out of a 4905 might just fit, and I'm about to do that. After I put the 8V71 in my 4104, I did have an overheating problem, but only if it was really hot out (we are in South Florida) and if I was driving at higher speeds (over 70 mph). Slower speeds kept the problem under control. Rain helped occasionally LOL. But I do want a bigger radiator.
He is also correct about the differential... but, if you remove the differential entirely and remove the mounts and perches from the differential housing, turn the housing upside down, refit said perches and mounts, install a 4106 center section, you might solve the vibration problem. I have in stock a 4106 center section, just waiting for some free time to jack up the bus and apply this solution. It's supposed to work, I am told. |
jdexsquid (130.207.68.60)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 19, 2001 - 8:15 am: | |
Maybe this will help: I have a good friend that owns a 4104. He swapped out the 6-71 and stick for an 8-v71 and auto. It has been running fine for years. He didn't change out the rearend, but may have changed gear ratios. To help with the cooling he fabricated a scoop. The 8v71 is larger than the 6-71, so the engine stuck out the back of the bus when he was done! He is a stainless steel welder/fabricator, so he built a new engine cover to fix the problem. Email me if you'd like to talk with him. I'm sure he'd be more than willing to help. |
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