OM602 target cruising rpms - PeachParts Mercedes-Benz Forum

PickleRick · #1 10-29-2022, 03:30 PM

Hey guys. I'm finally done with my TDI Toyota 4 runner resto mod and now starting on the little ladys om602 discovery 2 build.

I'm tossing between using the land Rover 3 speed with locking overdrive but a 6l80e would net better gearing options.

4.03, 2.36, 1.53, 1.15, . 85 and . 67

Currently has 33 inch tires and the stock 3.54 gearing. Likely ok for stock trans but in order to use the 6l80e we should go min. 4.88. I think the 0 to 60 times and daily drive manners for city traffic would be nice.

This would bring her to @3000 rpms at 90, a speed we hit frequently on our highways to hang with traffic.

I have never driven a 602. Planned mods are an upgraded injection pumps and a TD04 turbo with fmic. Also a good egt gauge as the turbo will be a trial and error situation unless someone can make suggestions. Shooting for 150 to 175 hp and 250 to 300 ft lbs of torque.

I want to keep her in comfortable cruising rpms as to not lug the motor. Please let me know if the gearing needs to allow more rpm for given speeds..

Attached is a gear calculator I hope someone can check out and make suggestions if rpms need to be higher or lower.

The following chart lists the road speed you will be going while the engine is at a given RPM. Road speed is calculated based on the transfer case and underdrive being in high range.

Road speed at given RPM in miles per hour
Gear in first column.

2000rpm 2500rpm 3000rpm
1 10 12 15
2 17 21 25
3 26 33 39
4 35 44 52
5 47 59 71
6 60 75 90
7 - - -
8 - - -

Thanks ahead of time guys.

Phillytwotank · #2 10-29-2022, 04:37 PM

In my car the turbo is making good boost at and above about 2200 so I would think that would be the same for you and you would want to be cruising around there.

PickleRick · #3 10-29-2022, 05:09 PM

Sweet thank you. If that's the case I'm pretty good as common speed limits are 35 45 60 and 70.

My TDI is a little unhappy at 45, the most common secondary hwy speeds as if I'm stuck doing the actual speed limit I'm at 3000 rpms in 3rd or 1900 in 4th. Much happier doing 50 in a 45 which is what God intended man to do(and woman)

While I'm able to do this and be happy because diesel sounds make me smile I need a factory feel for the little lady who's much more needy for smooth operation.

I'm not sure if the 6l80e locks up in every gear or not based on load/tps but the 6 gears gives much more room for target operations than what I've used on previous conversions

JHZR2 · #4 11-02-2022, 11:20 PM

Wait, 90 what? Mph? With a discovery and a 602? Besides being wasteful and unsafe, it’s just crazy.

A 602 in a w124 does beautifully with stock gearing. I’d want to match this. Smooth and quiet.

PickleRick · #5 11-04-2022, 08:05 PM

Quote:

Originally Posted by JHZR2

Wait, 90 what? Mph? With a discovery and a 602? Besides being wasteful and unsafe, it’s just crazy.

A 602 in a w124 does beautifully with stock gearing. I’d want to match this. Smooth and quiet.

Please see gear ratio chart I posted

59 mph 2500 rpms 5th gear

75mph 2500 rpms 6th gear

90 mph 3000 rpms 6th gear.

Those are close to your posted pic at @70 mph 2400 rpm are they not?

75 to 80 will me a more common cruising speed but 90 needs to be doable.

The 4.0 V8 isn't a power house.

Hanging with traffic at 90 is safer than texting and driving.

JHZR2 · #6 11-04-2022, 08:54 PM

Quote:

Originally Posted by PickleRick

Please see gear ratio chart I posted

59 mph 2500 rpms 5th gear

75mph 2500 rpms 6th gear

90 mph 3000 rpms 6th gear.

Those are close to your posted pic at @70 mph 2400 rpm are they not?

75 to 80 will me a more common cruising speed but 90 needs to be doable.

The 4.0 V8 isn't a power house.

Hanging with traffic at 90 is safer than texting and driving.

90 isn’t safe no matter how you cut it. Especially in a custom truck of unknown quality, never designed for such speeds, hanging with people with cars in various levels of disrepair doing similar speeds. It’s just plain dumb.

And doing it in a souped up 602 making more than design power while cruising at speed is even more unsafe. Good luck when you throw a rod in that truck at 90mph…

PickleRick · #7 11-04-2022, 09:59 PM

As far as rig quality it's been a daily driver for over a year now and very well maintained. You don't keep a discovery 2 on the road for 250,000 plus miles without good maintenance. It's my experience that outside nearly every major US city there are highways and on these highways people run 20 to 30 mph over the posted 60 to 70mph speed limit. Since the disco 2 was a huge suburban hit I'm betting there are plenty of these luxury SUV owners who have no issues hitting over 80mph daily with their rig. Coil spring solid axle, all time 4 wheel drive, 4 wheel disk brakes and active traction control/abs system. They were well ahead of their time.

Correct me if I'm wrong but a 602 would cruise to Cali and back at 70 mph (3000 rpms?)

The engine doesn't care if it's in a car, suv, plane or boat. It cares about egts and rpm. If egts are safe i see no reason for it to cause an issue, what am I missing here? Why exactly would it throw a rod? An engine doesn't see speed correct? Is the engine afraid of the land Rover? I fail to see your logic on this.

If you don't like the plans for this one you'd really hate my VW TDI converted first gen 4 runner that I've built for a daily driver.

Anyway,. Thank you for the pic. If you're cruising 2500 rpms at 65 ish and still have plenty of power to speed up to 70 and maintain that likely means I need to aim for my cruising rpms to be similar.

JHZR2 · #8 11-04-2022, 10:51 PM

Quote:

Originally Posted by PickleRick

As far as rig quality it's been a daily driver for over a year now and very well maintained. You don't keep a discovery 2 on the road for 250,000 plus miles without good maintenance. It's my experience that outside nearly every major US city there are highways and on these highways people run 20 to 30 mph over the posted 60 to 70mph speed limit. Since the disco 2 was a huge suburban hit I'm betting there are plenty of these luxury SUV owners who have no issues hitting over 80mph daily with their rig. Coil spring solid axle, all time 4 wheel drive, 4 wheel disk brakes and active traction control/abs system. They were well ahead of their time.

Correct me if I'm wrong but a 602 would cruise to Cali and back at 70 mph (3000 rpms?)

The engine doesn't care if it's in a car, suv, plane or boat. It cares about egts and rpm. If egts are safe i see no reason for it to cause an issue, what am I missing here? Why exactly would it throw a rod? An engine doesn't see speed correct? Is the engine afraid of the land Rover? I fail to see your logic on this.

If you don't like the plans for this one you'd really hate my VW TDI converted first gen 4 runner that I've built for a daily driver.

Anyway,. Thank you for the pic. If you're cruising 2500 rpms at 65 ish and still have plenty of power to speed up to 70 and maintain that likely means I need to aim for my cruising rpms to be similar.

It’s not the RPM, it’s the fuel and power needed.

A w124 doing 70 down the road at 3000rpm needs what? Maybe 50 hp to keep speed?

A much less aerodynamic, heavier vehicle with more drivetrain losses will need what? 100? 120?

So it is very much a fueling, egt, turbo time at temperature and pressure issue.

WRT speed, I travel a lot and drive all over. People drive faster than the limit, but not 90. Even in places where the limit is 80, while some folks push it, other vehicles like heavy trucks don’t. It doesn’t make it a good idea. Especially in a vehicle where acceleration is sluggish, handling is poor, braking isn’t great, etc.

PickleRick · #9 11-05-2022, 06:27 AM

We'll have to agree to disagree here.

Similar power and displacement, lesser quality built TDI diesel motors came in these rigs in nearly every country world wide except the USA and do not blow themselves apart at highway speeds.

Neither do the swapped smaller 1.9 TDI motors all the Cherokee guys run with similar weight/aerodynamics.

You'll know if you're pushing her too hard by the egts. Can we do 90 up a grade in the rocky mountains without issue? Likely not?

1000 ft above sea level on my local highways??? Doubt it will be an issue over most of the east coast.

Other than posting a very useful pic of speed and rpm I'm not sure why you've posted on here other than to internet argue. Again, thank you for the informative pic but your opinion otherwise is useless.

JHZR2 · #10 11-05-2022, 09:14 AM

You realize that not everyplace operates like an autobahn, right? Many vehicles in Europe are limited to 60, 70, 80 km/hr. Do the math. Kilometers, not miles.

I just drove extensively around Norway. Certainly no roads doing 90mph.

I think you grossly underestimate the power needed to make such speeds, and the sluggish performance that will come from such an engine in such a large, heavy, unaerodynamic rig. A w124 fit with a 602 did 0-60 in what? 13s? It’s not going to make a brick that weighs twice as much accelerate very well. Meanwhile whatever souping up you do will just impact longevity.

This isn’t speculation. You can tell me I’m wrong all you want. It doesn’t change physics. Including how unsafe driving that thing is going to be at 90 mph, should you ever make it to that speed.

Your life in your hands, just don’t inconvenience the rest of us.

87tdwagen · #11 11-05-2022, 05:17 PM

What's the gearing of the stock trans? 3 speed overdrive?

IMO the 4.88 with the 6l80e kinda makes first gear relatively useless, maybe a bit better if you eventually mount 35s, but that would then alter the rest of the gearing effectiveness. How wide of a gearing selection do you have available for those diffs? I can't recall the manufacturer.
Sounds like a fun project.