I was wondering if when you try to find the actual torque the vehicle has after the rear end, do you use the ratio of the torque converter or do you neglect it?
Example: say i have an engine with 300 ft-lbs of torque at the crankshaft, a transmission with a 3.00:1 first gear, and 3.50:1 rear end. Is the torque, when starting from a dead stop and neglecting drivetrain friction losses, after the rear end 3150 ft-lbs(1575 to each rear wheel)? Or do I need to consider the torque converter in calculating this? so if the torque converter has a ratio of 2:1, the torque would be 6300ft-lbs(3150 to each wheel)? Thanks for any help.

 

I would multiply including torque converter but use engine torque at converter stall speed.

 

I'm not too familiar with the concepts of stall speed. Do you mean if the converter locks up at 2000 rpms, then i should find the torque of the engine at that rpm and use that? then the torque converter would be at a 1:1 ratio and any multiplication would be gone and the converter wouldn't matter. I thought the converter multiplied the engine's torque at lower rpms until it hit the lockup speed? But again, i'm not familiar at all with how a torque converter works.

 

Due to the many different designs and variables the "Torque Multiplier" can have many different multiplication ratios. How do you know yours is a 2:1 and not a 2.5:1? At which RPM is it most efficient, and what rpm are you using for your calculation?
How confident are you with your torque figure, and again at which rpm is this figure accurate? The converter is going to slip always (unless it is "locked up" not stall speed) and has a one to one coupling with the crank and the pump. Still you will not be able to calculate the output torque when you have no idea of how much loss you recieve through the transmission, so your calculations will only be speculative at best.
Here is a link that you may find interesting, and is worth a quick read.
There is also a small write up regarding HP and Torque from Cat.
Rotational losses have to be taken into consideration, and you are assuming that the differential applies an even split of output to each wheel, which, it does not.
Your formula is also missing the rear axle ratio which will also affect the amount of torque applied to the wheels.
Temperature is also a very big factor here. Your engine is not making the full 300 FT. lbs. of torque from a dead stop since the rpm is so low, so these figures in your example are very inflated.
Rear wheel Dyno will compensate for all of the variables that make this calculation so difficult to estimate.
http://www.imagelegacies.com/HPandTorque.html
Here is some reading.

 

I guess it would be easier to explain what its all for. I'm trying to do as much research as i can into what would be the best optoin for upgrading my '79 bronco. I'm basically deciding between a diesel(cummins or powerstroke), newer 5.4 v8, or the stock 351m for an engine and a zf s5-42 5 speed, nv4500, aod, or c6 for the transmission. I'm basing the choice on seven factors that are cost, fuel effeciency, reliability, ability to cruise at highway speeds at a relatively low rpm, low end torque, overall power, and difficulty of installation. I have all the other values based on a scale and then multiplied by a percentage. But i didn't know if the automatics got the extra bonus from the torque converter. The manuals were easy as they are a direct drive from engine to tranny. The rear end ratio was in there as well, it was 3.50:1. I know a lot of factors affect the real world torque that the engine produces and that some is then lost in the drivetrain, but if i knew the different variables that went into calculating the torque, then even though the numbers would be off from the real world, they would all be off by the same percentage. This would still give me the answer i need. I don't know if the c6 torque converter is a 2:1, that was just a guess. Thanks for that link. You don't know how long i've looked for somewhere to relate the torque and horsepower like that.

 

Now you have created an even greater variable, and these are, time, money, and mechanical ability. You also have to consider local laws that may have restrictions on engine swaps.
You have also mentioned cruising at low engine rpm's. I am assuming that you are shooting for decent mileage, and need to warn you that this is not always the best thig for smaller displacement gas engines. I read all the time where guys are shooting for crazy low rpms by using extremely high rear axle gears. Depending on how the vehicle is going to be used, may not be so great. Given tirque and HP curves of different engines, you have a big decision in front of you.
I would say that the automatics do not necessarilly have any extra bonus, since they are not very efficient and draw a srious amount of power.
I think there are some other considerations for your project. Are you going to tow? This will be limited by the wheelbase, so the diesel might be overkill. I will admit that these engines would be pretty cool to install, but given the limited capacities of a bronco, might make the diesel too much work for a given application.
Using this for off-road? Mud and sand might require wheel speed instead of slow tire turning torque, so a decent gas engine might be a much better choice.
I think one of the deciding factors would be how you are going to use this vehicle. There will always be a compromise. Making the smallest compromise is key.

 

Lol! Yeah, you're right on. I've thought about this and thought about this and these looked to be the best choices. I'd really like diesel with the zf 5 speed, but after writing it down and using the percentage of importance approach, it looks like the best choice is going to be just to swap the zf 5 speed in and leave the stock 351m. The diesel would be awesome to have, but it is probably going to be too expensive and complicated to do, especially the cummins. I don't think we have any laws that apply to engine swaps, if we do they're not enforced so that wasn't a concern for me. So far, the numbers on the sheet show that the manuals all have better pulling power as they have lower first gears. Also better gas mileage as they are manuals and you can kinda choose the rpm you want. I was shooting for a cruising rpm of about 1800 rpm, which most of the transmissions will do at about 70 mph, except the c6 which hits it at 53 mph. Any lower of an rpm and i'd be afraid to ruin main bearings in the engine or tear up the overdrive(had it happen in a truck). It will mainly be used for a trip vehicle. Things like going on a camping or hiking trip, but so far its been a 4 wheeler. We do drive it on the road quite a bit though and i will also be towing a 4000-5000 lb boat on occasion. Now i guess you can see my problem a little better. I need it to do everything but i know no vehicle can do everything, so i need a really good compromise.

 

Stall speed is loosely defined to be the engine RPM when you do a power brake just before launching a drag run.

If you were I and I were You, I'd go with the wide ratio 5 speed.

I have been attempting to write a thread in the mileage forum to address the facts & myths surrounding mileage. There are many ways to increase mileage without high initial cost.

 

Stick with the set up you have now and get a Klune extreme underdrive unit!! It will give crazy low crawl ratio that you are wanting, without affecting your truck when it isn't engaged. It goes between the trans and transfer case, it will save you a lot of money and work. But diesel would be the way to go if you want torque!! If you have a heavy equipment junk yard around you that is where you want to get your motor!
That's all they have is diesels so it isn't like freaking gold like at a regular car junkyard!!
Look for a kawasaki 65 they got cummins or isuzu motors in them!! they are just pick up motors in them!! you'll have to change the manifolds unless you want a stack coming out of your hood!!

 

I wouldn't worry much about torque at the rear wheel. You got 4L, and that should give you enough that you may damage the rear end if you try it hard enough.

There are several possible engine/tranny combos, and it really depends on momey and time which one to choose.

 

Yeah, I really wanted the diesel and maybe there is a heavy equipment junkyard around here somewhere. I've never seen or heard of one though. I really wanted a better final gear so that unit that goes between the t-case and trans is not really what i'm lookin for.

 

Most everything is doable, the question is at what cost? BTW, 460's are a popular swap for 78-79 Broncos -- much cheaper and a lot easier.

 

I also thought about the 460. That would give good torque and with the 5 speed would also be ok at highway speeds. also it would be really easy to swap in and there are tons around here. The only downside that really turned me off to the 460 was the horrible gas mileage. I at least wanted 14-15 mpg, and the 460 could never do that. I think i'm going with the zf 5 speed first, and that way if i wanted a diesel later, the transmission for it would already be in place. Cost wise, well i'm in college right now so first i'm about 400 miles away from the bronco most of the time and second i dont have that much money right now. I still want to go ahead and plan for this next summer because i'll be able to work on it and i will have money then. I know i can get the zf for at most $800. Thats for a rebuilt one so i'm pretty sure i can get a decent junkyard one for half that. plus all the clutch stuff like master cylinder, slave cylinder, pedal assembly, flywheel. I think its probably the best way to go. It'll still have plenty of torque to pull or tow with. I know its not going to be a towing monster. Its a bronco. But i did want it to be able to tow that 4000-5000 lb boat and i think it could and get decent gas mileage with the 5 speed.

 

Very Interesting,
What type of equipment is a kawasaki 65?
Also, In what type of equipment does the engine usually out live the equipment?

Wouldn't an computer controlled 460 get better mileage than a carbed?

 

Yeah the fuel injected would get better gas mileage but it still wouldn't get 14-15 mpg like I wanted.