Crawl ratio Q's for the big low RPM torque monsters

[nickwood48]

Since a diesel makes max torque at say 1800 rpm, versus a gas which has peak torque at @ 3200...would this equate into a similiar crawl ratio reduction? Ok, further explanation...

1800/3200=56%, so diesel makes peak torque at 56% of the gasser, therefore, if an ideal crawl ratio is approx 100:1 for a gasser with a stick, could a diesel get away with say 60:1?

Or, if anybody has experience wheeling a diesel that could comment on appropriate crawl ratios. I dont want to wasty time/money with low gearing if its pointless....or break drivetrain with to much multiplied torque since the 4bt has alot of low end.

Thanks,
Nick

 

[Behemoth60]

That's one of the best first post questions I've ever read.

Indeed, a diesel makes usable torque right off idle. A diesel rig with a crawel ration of around 50-60:1 will be very comfortable along side gasser rigs running 70-80:1 of crawl ration. I did Rubicon on 50:1, and Moab on 60:1, and it was sufferable. More would have been better.

That said, in my own personal diesel rigs, TippyR sports 175:1 with a 203 doubler, and Snowflake brags 210:1 with a Marlin Toybox. Low gears are never pointless if you actually wheel your rig, especially if you are on the rocks. Lower gears will actually reduce your breakage if you use them properly. With lack of proper gearing, you're riding the clutching and giving it power, and hitting things harder than you should since you can't go slow enough. With low gears, your slow and in control, and less likely to break if that's what you choose. You can also choose to break any part you want. Low gears are a powerful tool that you can use for good or evil.

Peter Straub

 

[Tapage]

Well I can't talk much about real rock crawling .. but in my general off road experience with a good diesel engine you can drive it fine at 1000 - 1400 rpm fine ..

With aprox 70:1 and 37" ( keep in mind CR are directly related with your tire size ) I can drive fine at 1000 rpm and enought torque to crawl over " rock " ( my kind of rocks ) with no clutch.

But get reallu huge reduction is better in your control coz for example your PS funtion much more and better at more rpms you have ..

 

[roscoFJ73]

One of the thing I like about my 1HZ is when a steep climb gets steeper at the top the diesel may slow down to 800 rpm but it will not stall .
In a gasser I would be reaching for the gear stick looking for a lower gear and end up having to do a hillstart in at an unfavourable angle
It really is quite amazing sometimes.

 

[BJ-44]

Even the old 2B in mine does great offroad, it will die down in some of the hardest situations but usually doesn't die even if it think it will. It doesn't lack power offroad with 35"s and stock 4.11 gearing. A comparable small block V-8 would have to go faster and run higher rpms to make the same torque 1800 rpms or below as 2B. The gasser would have to have lower reduction to equal the same torque at the same speed but higher engine rpm. So you are definitely correct that it can act like a gear reduction. There is a point to where you can have too much gearing because a lot of times you need some foward momentum.