Quote:
Originally Posted by Samurai ...Obviously, that has to be changed to 4.88 at least... |
Quote:
Originally Posted by ex670c Hi Guys,
Dirty_Dan is running a MDI3200TC with NGT520+T18 and has changed his Differential Ratio to 4.88:1.
He is using the vehicle up in the Himalayas, Dharamsala.
I hope he shares his overall experience with this upgrade on the MDI3200TC+NGT520 combo.
Regards,
Arka |
Newer vehicles equipped with the MDI3200tc motor also come with 3.73 crown gears. So does the Thar MDi. This ratio was forced upon M&M by government
emission/fuel average standards.
I bought an Invader, with MDi3200tc, October 2009 when prospects for the launch of Thar looked bleak and I wanted a new car going into winter up here in the snow and cold. Straight away I was very disappointed with the Invader's power at low speeds, from a standing start, and its poor performance climbing the steep slopes here at the front range of the Himalayas. One fine day I was trying to go down a mountain. I had to go around a sharp, steep, narrow curve. I had to go uphill in reverse to crab around this curve and almost dumped the whole works down into a gorge because the motor fizzled out on me, it didn't have the juice to go up in reverse. This dangerous "last straw" convinced me to make a change. Quick. After exchanging emails with Arka and Brutus (Brutus designs his own differentials.) I resolved to change the crown gears from the factory 3.73 to
4.88. I knew this was likely to be a bit complex and/or in need of skilled experienced hands so I went to a flagship M&M dealership in the Punjab to see what could be done. The head mechanic said that the crown gears could be changed but that it was not a simple bolt in proposition. The 4.88 crown gear fits in the "pumpkin", the differential housing, okay height-wise but was a bit thicker than the 3.73 crown gear and hence would not fit width-wise.
His solution was to carefully grind down the bearing housings (see below), fit in some shims, precision washers, around the bearings to guarantee a smooth friction surface and add new matching input spindles to fit the 4.88 crown gears. The input spindles attach to the propeller (driveshaft) on one end and fit into the crown gears on the other end. He also put in a new speedometer gear from an army jeep that matched the speedometer to the new gear ratios. He might have altered some other parts slightly but if so whatever else he did was inconsequential and was lost in the lanuage barrier between us.
The results were better than expected. My Invader with the 4.88s has roughly 15%-20% more low end power. I now have a great second gear that charges up hills. First gear, low range,
is very much a creeping gear. In 2wd I can keep up with Scorpios and Innovas up to 30kph and a lot of times around here that's as fast as you get to go before the next switchback curve.
on very steep hills and I can out accellerate Taveras. On the flat, up to about 30kph I can out accellerate Scorpios provided they are old and belching a little blue smoke.
With the 4.88 crown my fuel average around town is 12.1-12.3, highly acceptable. Out on the road at higher speeds...I dunno. I never checked. We don't have real roads here, only old goat paths that they paint black the week before the road inspector visits the area. We don't see speeds over 60kph here much. On trips into the Punjab where they actually have roads worthy of the name, I can only say that the engine did not seem to be laboring excessively at speeds around 100kph.
The work took 2 days to complete.
Upside: you get a vehicle with a lot more low end power. The difference is amazing. This ratio seems to take advantage of the MDI motor's low end grunt.
Downside: It is risky. Its a mod that is only as good as the mechanic who does it, and it is expensive if he messes up.
Cost: I will let those who are interested figure this out. It could go anywhere from between 16,000 to 25,000 ruppees, my guess, depending who does it. Much of the cost
is labor since it was a repeated process of grinding and fitting. I am sure I paid a premium price since it was a M&M dealer who did the work.
The head mechanic said that he expects the differential with mod will last as long as a normal differential. He said when its life cycle is thru that I could just replace the whole
differential with a normal complete 4.88 unit. I have had my differentials inspected twice locally since the modification 16000K ago and
there is no appreciable wear.
I don't know if this is the right diff but here is the idea.