How to increase the top speed of my MM540 4WD with MDI engine

Just as you wouldn't take a Ferrari offroading, similarly, don't drive your old Jeep at high speeds.

BHPian sijuko recently shared this with other enthusiasts.

Hi experts,

I have an MM540 4WD with an MDI engine and also changed the crown and pinion ratio to 4.27. I still wanted to have some more top speed, Please, let me know what is the best way to achieve it?

When I had the original xdp 4.90 with crown pinion 4.27, I felt much better, but when I moved to the MDI engine it was not doing that good in terms of speed.

Here's what GTO had to say on the matter:

I own a '97 Classic that at one time had a 4.2 final drive. The top speed increased, but I soon realised that the engine was capable of delivering a speed that the rest of the vehicle couldn't keep up with. The handling is downright scary, the steering slow as a snail, the brakes poor (by current standards) and the vehicle has no real safety to speak of. These are cars that were designed without even 1% crash safety in mind. Not to mention, the engine would be screaming so loud at 100 kmph that I'd go deaf in 10 minutes.

Make your peace with it. Just as you wouldn't take a Ferrari offroading, similarly, don't drive your old Jeep at high speeds. My recommendation = drive it at a max speed of 60 - 80, enjoy the scenery on your calm drive and be happy. Your MM540 will be very old today and many parts of it would have worn out. My '97 Classic is still on its original steering column, who knows when it will give up.

If you want a faster Jeep, buy a Thar. Although, even in the stock Thar, I don't recommend cruising above 100 - 120 kmph.

Here's what BHPian anjan_c2007 had to say on the matter:

The first option will be to go back in time, try for a good 4.90XDP engine and feel at home with your 540DP. You may still get these in the Mayapuri scrap market in Delhi. And the other option is the MSTC-listed contractors who buy written-off jeeps at govt auctions, en masse.

Coming to the International Harvester MD 2350 engine, I am yet to come across a tougher workhorse. Having used the MD 2350, 4.90 XDP and the XD3P, if ruggedness, endurance and withstanding abuse are all considered, nothing comes closer to the MD. Not even the older petrol Hurricane engines.

But the MD2350 is crude, very rudimentary, archaic etc with any other synonym you may have to describe it. The engine is fully mechanical and runs without a battery which is no mean feat.

It has its limitations and that is why in the present-day scenario it is disliked. Its NVH is the highest among all Indian-made light motor vehicles (LMV) ever manufactured. The body rattles with the rock'n roll it does & doesn't allow passengers to be seated in peace while travelling. Talks with a co-passenger are not normally audible amid the noisy diesel engine clatter. A 500-plus kms journey may require the driver to rest for 12 hours.

Since this is an ancient engine, it's best to leave it that way, rather than expecting miracles which would be like administering steroids and boosters to a senior citizen to become more nimble, run around and play football with 15 to 20-year-olds.

Yes, a case in point here is that Hindustan Motors fitted an intercooler turbocharger in 2013 to its similarly archaic and crude BMC OHV1489 cc/Stride/39 bhp diesel engine to make it BS-IV compatible. They named it Stride Plus and boosted the output to 45 bhp as they claimed. But the TC overheated this age-old engine in the long term. As a result, taxis with the TC in Kolkata have in a majority of cases removed the TC and are again happy with the 39 bhp.

Here's what BHPian dhanushs had to say on the matter:

The reason being, the MDi revs ~30% lesser than the Pequot. Also, the max performance of the MDi would be at lower rpm, unlike the Peguot.

If you really want more speed go for 3.73 which will make the vehicle drive similar to a Thar Di. However, I personally think a 540 4.27 is the best. It will give you good driveability and decent speed which the vehicle with front drum brakes and decades-old steering and chassis can handle. (Note: Thar Di has an entirely different Chassis, Suspension, Steering and Brakes)

Yes, 3,73 will require you to change the diff casing along with the spider gears.

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