REAL crawl ratio?

[Blue85]

thus, i don't think the 2x multiplication for the torque converter has much real-world significance.

Even if you didn't believe in gravity, stuff would still hit the ground when you dropped it

A torque converter is a really neat device. You should read up on it. It's like a "variable" gear reduction. That's why you see a much greater gear spread in manuals than autos. The fact that an auto equipped car with around half of the gearing can have similar performance numbers to a manual equipped car proves that this device is more than a simple fluid coupling...

 

[6.2Blazer]

I actually agree with you Colby at idle an manual truck will idle over stuff better than an auto, given the same gearing. But if the load becomes too great for the manuals gearing to overcome it stalls the motor. With the auto it just stops. If the gearing is the same on both trucks I guarantee a small blip on the throttle with the auto will get it moving again.

Whether this really enters into your idea that the torque converter really doesn't give a 2 to 1 gearing advantage is somewhat besides the point. The auto truck will crawl easier over stuff if the objects being crawled are enough to over come the manuals gearing and stall the truck.

I agree with your explanation also, with the key point being "given the same gearing". The biggest issue I see is that most people claiming that the manual crawls better have never driven an auto trans with equivalent gearing. The most common TH350 and TH400 have pretty crappy 1st gear ratios, while the SM465 manual has a really good (low) 1st gear ratio. Most people comparing the manual to auto trans are using this example.

Lets use the NP205 t-case and 4.10 axles in figuring out the ratios. The SM465 has almost 54:1 crawl ratio. A TH400 only has a 20:1 ratio, so even adding 2x multiplication from the converter you only have 40:1 which is still significantly higher than the manual trans. You would have to put in 5.38 axle gears in the auto truck to get close (still slightly less crawl ratio). I don't think anybody will argue that going from 4.10's to 5.38's would make a pretty dramatic difference.

Take my 700r4 and NP241 combination (one of the best factory combos in regards to crawl ratio). With 4.10 axles that gives me a straight 34:1, and a 68:1 with the torque converter. It crawls good, and has decent engine braking going downhill...all with stock parts and gearing. A buddy runs a C6/205/4.10 setup (equivalent to a TH400/205/4.10) and there is a huge difference in crawling ability between the two trucks.

Another way to look at it, assuming you don't really believe in the torque converter being able to multiple torque kinda' like another gear is this:

TH400 only has a 1st gear of 2.48. 2nd gear for the SM465 (or "1" if using L,1,2,3) is stil 3.58. If there was no torque converter providing extra torque multiplication than you would never get an auto trans equipped truck moving, especially under load. Assuming a straight 2.48 ratio and 4.10s, that would be about the same as taking off in 2nd (or "1") gear in a SM465 with 2.73 gears.

 

[colbystephens]

I agree with your explanation also, with the key point being "given the same gearing". The biggest issue I see is that most people claiming that the manual crawls better have never driven an auto trans with equivalent gearing. The most common TH350 and TH400 have pretty crappy 1st gear ratios, while the SM465 manual has a really good (low) 1st gear ratio. Most people comparing the manual to auto trans are using this example.

therein lies the problem. i had a 700r4 then swapped to a 465. assuming you do the 2x calculation for the torque converter, the trucks should have been basically equal because 3.06x2 is close to the 6.1 or whatever the low gear in the manual is. not to mention that the tcase behind my 700 had a lower gear than the 205 behind my 465. so, the two drivetrains should have been basically equal with the 2x calculation. however, if i put it in gear the manual idles over things that when done with the auto required getting the rpms up.

i don't want this to become a manual vs. auto debate - but i would like to suggest that there is no real-world value to the 2x multiplier.

 

[longbedder]

i would like to suggest that there is no real-world value to the 2x multiplier

Then you should tell Detroit and Japan that they wasted zillions of dollars in millions of vehicles that had torque converters.

The difference that you are hung up on is at idle...an auto "knows" it's at idle and won't typically crawl over things at that setting because it's not designed to. It senses throttle setting (0%) and load (negligible) and thinks its job at that moment is to just sit there and let the engine spin without making heat or applying much work to the wheels. As soon as you imply part throttle, however, the pressure rise occurs, the power gets applied, and the torque gets multiplied.

A manual doesn't know the difference - either the wheels will spin or the engine will stall. There were plenty of guys stalling gasser 465's at Moab.

 

[colbystephens]

right, but my point is that I believe idle is the speed of the engine at which "crawl" works - thus my point on how it relates to crawl speed. the more your rpms go up, the less it is actually crawling.

 

[4X4HIGH]

You are confusing "crawling" with idling. Crawling has nothing to do with engine idle when it comes to an auto trans. You can crawl with an engine that is screaming at 4000rpm, gearing and torque convertor stall speed dictate what rpm the engine will be at when the vehicle is crawling.

 

[Blue85]

The guys with the really high crawl ratios will typically be above idle when crawling - otherwise the rig is barely moving.

The fact that you prefer the feel of the manual transmission does not mean that torque converters don't convert torque. So you can't take that ~2x out of the equation. This talk about moving a load or crawling over something "at idle" is interesting, but it is not crawl ratio as I know it.

 

[76zimmer]

The guys with the really high crawl ratios will typically be above idle when crawling - otherwise the rig is barely moving.

The fact that you prefer the feel of the manual transmission does not mean that torque converters don't convert torque. So you can't take that ~2x out of the equation. This talk about moving a load or crawling over something "at idle" is interesting, but it is not crawl ratio as I know it.

I interpret crawl ratio as "the lowest possible gear reduction of a particular vehicles components"
It doesn't necessarily mean idling, it just means the lowest ratio possible.
Many times while idling through an obstacle, the throttle is used out of necessity, and the vehicle is still in crawl mode.

Good discussion going on here.

 

[blazinzuk]

And the last two statements give a little credence to the fact that figured crawl ratio is less important in the real world. I essentially have a 45:1 crawl ratio and 44" tires. That should not crawl at all even with a V-8. At least conventional thinking says I shouldn't be able too. We have very technical rockcrawling around here. My truck crawls just fine. I am very happy with it. Sure I would like lower axle gears but that isn't going to make a huge difference. With 5.38s I would end up just over 52:1. Before my doubler crawling was an exercise in frustration.

I think Colby probably has the best setup around for crawling with a manual a 6.2 with a 4 speed. Tons of torque down low the engine will lug down and the great gearing of a 465. Someone who had driven that truck for a while especially with a hand throttle would be able to at least equal my trucks crawling ability.

 

[colbystephens]

ok dudes, i'll bow out on this one at this point. i still don't believe that 2x is a proper multiplier for the gearing, though. 2x is a HUGE amount - it's equivalent to a doubler! I don't think the torque converter acts as that much of a multiplier in the real world.

 

[Stephen]

This is like deja vu all over again.

Torque convertors do work, don't believe it if you like but somehow most of us have been able to go technical rock crawling with autos running mechanical gear ratios that wouldn't pull a manual trans truck out of the driveway. There's a lot of ways to consider it and most of them were presented here.

But enough of that dead horse.

Inches per revolution seems to still work for a gearing comparison. We still don't have a good way to figure engine torque into it but I haven't thought about this a whole lot in the last 6 years either. I guess one way to look at it is that it requires a certain amount of torque to climb a given hill. If you want to go a given speed, your engine has to be able to deliver the torque required at it's RPM level corresponding to that speed.

Let's assume it takes 100ft-lb from the motor. A 5.9 cummins will do it at an engine speed of 750 rpm but a 22RE can't do it till 2500 rpm. If the two trucks have the same overall gear ratio the cummins truck will crawl the hill and the 22RE is going to be out of control fast. Thus the fact that a toyota needs a way deeper overall mechanical gear ratio to do the same trail as a truck with a lot more motor torque.

One thing we've found that skews the equation yet some more is added vehicle control through low CG, stable handling and good shocks. Now with more control we can go through the obstacles faster and don't need the super low crawl ratios all the time. A leaf sprung top heavy truck with bad shocks will bounce around so much at higher travel speeds that they just can't stay on the line and thus have to go slower with a better crawl ratio.

Also, tire diameter vs rolling radius depends on a lot like the surface type. The tire doesn't always act like a track, they lose some of the circumference as they "roll" at low RPM. Basically the tire is still the big wild card but we can still come closer than not figuring it in at all.

 

[K5dreamer]

inches per engine rpm....there ya go.

ANNNDDDD we have a winner for the answer to the original posters issue. the problem with tire size can be illustrated by car gearing vs truck gearing. I was always blown away by guys saying we needed 4.56 gears for trucks. to me, those were drag race only gears. now, im realizing those are what ill want for my truck if i put 40+in tires on my truck, and im still aiming for 20+ mpg.

And just my two cents on the dead horse...... lets cook it and eat it.
yes, torque converters work, max torque is not presented at idle, and the clutch packs are not engaged because the speed of the pump is so low. when the engine speed increases, line pressure in the trans goes up, clutches engage, and the torque converters multiplication factor becomes very apparent. Its why most heavy tow rigs use auto trannies.

 

[76zimmer]

clutches in a torque convertor?
I think the clutches in a clutch pack inside a transmission are fully engaged when selected to be, by the valve body. The pressure may become higher with more rpm, but they are still engaged fully, otherwise you could burn up the clutchpak just idling.
AM I wrong thinking this way?

 

[K5dreamer]

Some quick numeric calculations for your viewing pleasure......

My truck as it sits, TH400/NP208/3.08 gears/33in tires. would work out this way......

19.86:1 crawl ratio - 1rpm:5.22inches - 0.19 RPI (Rotation Per Inch)

Modding my truck to... NV4500/Lowmax 3.0:1 NP205/4.10 gears/33in tires would give....

68.88:1 crawl ratio - 1rpm:1.50inches - 0.67 RPI

modding further with the same 68.88:1 crawl ratio would be....

33in tires = 1rpm:5.22inches - 0.67 RPI
38in tires = 1rpm:1.73inches - 0.58 RPI
44in tires = 1rpm:2.01inches - 0.50 RPI

So for both crawl ratio, and "RPI" a larger number is better. Maybe we could adopt the dual statement of a given Crawl ratio and RPI. kinda like HP and Torque, even if you have the same hp in two engines, the one with more torque is better, by the same token, for the same crawl ratio, the setup with the higher RPI would be better.

 

[K5dreamer]

clutches in a torque convertor?
I think the clutches in a clutch pack inside a transmission are fully engaged when selected to be, by the valve body. The pressure may become higher with more rpm, but they are still engaged fully, otherwise you could burn up the clutchpak just idling.
AM I wrong thinking this way?

I could be mistaken, but i know the fluid pump is on the input shaft of the transmisssion, if it aint turning..... i dunno how there is line pressure but there is a reason i paid someone else to build my tranny.

EDIT - oh and some converters do have clutches, my 700R4 has a kevlar lockup clutch. Its solenoid activated though.

 

[blazinzuk]

What Stephen said just reinforces the fact that crawl ratio is just another bench racing term. What works for one truck may not work for another. Simple as that

 

[82355]

I think the clutches in a clutch pack inside a transmission are fully engaged when selected to be, by the valve body. The pressure may become higher with more rpm, but they are still engaged fully, otherwise you could burn up the clutchpak just idling.
AM I wrong thinking this way?

No, you are not wrong.

Martin

 

[Blue85]

I could be mistaken, but i know the fluid pump is on the input shaft of the transmisssion, if it aint turning..... i dunno how there is line pressure but there is a reason i paid someone else to build my tranny.

EDIT - oh and some converters do have clutches, my 700R4 has a kevlar lockup clutch. Its solenoid activated though.

Of course the clutches engage at idle. We all know this because we feel them engage when moving the gear selector from P to D. The entire converter housing rotates with the engine and this engages with the pump directly. If the engine is running, the pump is turning. The driveline torque comes in through the turbine shaft, which is allowed to slip through the fluid coupling.

I guess I'll have to describe it. It's the transferring of fluid from the housing fins to the turbine and back through the stator that creates the torque multiplication. The output is turning more slowly than the input - which is similar to what? Gear reduction, you say? The stator can only spin in the direction opposite of the converter and it reverses the direction of the fluid. As engine speed increases, the pump and turbine get to be at a similar speed, so the stator really isn't doing much. Here the torque multiplication is reduced - similar to 1:1 gearing. Since the converter is like "variable gearing" you get the much shallower ratios in the automatic.

And no, 2:1 is not an exact figure. Different designs give different ratios (higher stall speeds give greater torque multiplication), but for standard types it is typically close to 2.

 

[6.2Blazer]

therein lies the problem. i had a 700r4 then swapped to a 465. assuming you do the 2x calculation for the torque converter, the trucks should have been basically equal because 3.06x2 is close to the 6.1 or whatever the low gear in the manual is. not to mention that the tcase behind my 700 had a lower gear than the 205 behind my 465. so, the two drivetrains should have been basically equal with the 2x calculation. however, if i put it in gear the manual idles over things that when done with the auto required getting the rpms up.

i don't want this to become a manual vs. auto debate - but i would like to suggest that there is no real-world value to the 2x multiplier.

I just remembered you have a 6.2 which likely leads to your impression in this whole topic. The 6.2 has a governor in it so you are not really at idle while under load. If you are crawling at idle (foot off the accelerator) and encounter an obstacle, the governor in the 6.2 is actually applying more fuel in proportion to the load in an attempt to maintain the set idle speed (up to a certain point). While the rpm's aren't actually rising, the engine is basically doing the equivalent of giving the truck more throttle.

Same idea as cruising down the highway. Lets say on flat ground you are turning 2,000 rpm at 30% throttle to maintain speed. You now come to a steep grade and you go to 75% throttle just to maintain 2,000 rpm.

Nobody here is trying to say that automatics are better than manuals, rather just simply explain that the torque multiplication of a torque converter is real.

Again, take my buddy with a 19:1 crawl ratio with 42" tires on a 6,000+ lb. truck that can crawl in the rocks (not that graceful, but not any big issues either). Saying there is no torque converter multiplication is the same as saying that a SM465 truck could crawl just as well in high range and 3.08 gears with 42" tires........and I think we all know how well that would work.

 

[K5dreamer]

Blue85 - thanks for that post, i just had a face-palm moment.