4.10 OR 3.73

[depark]

Originally Posted by Shaggy

Any updates on this thread????? I'm running 3.73 w/33's 5.4 V8 and its not doing the job pulling a 6000# rv.

Hi Shaggy
I have a 5.4 with 4.10's a 33" tires and tow about 5500#. I live in the mountains and definitely would opt for 4.56's next time. I find that the 4.10's just aren't enough to tow in the mountains with the 5.4 IMO. I added a SCT Livewire TS+ tuner recently but haven't had a chance to do any towing so can't comment on that yet. So 4.56 is the way to go.
Cheers
Darryl

[Shaggy]

Depark thanks for the word. What's the RPM'S like without the trailer at hwy speeds? Say 65 MPH? I'm worried that 4.56 will suck without the trailer?????

[Glider]

I look at this as partially a question of on-the-road experience, and partially a question of straightforward math.

This graph below is from Ford; it shows maximum torque at 2500 RPM, and rapidly increasing power all the way up to 4500 RPM. In my experience with my 2006 5.4 (8,500 lbs, no trailer) anything above 2,000 RPM is great. Below 2,000 RPM, I can loaf along, but I better get it above 2,000 if I want to do anything more than that.

That motor is fine loafing, but if I want performance, it is really happy between 2,000 and 3,000. If I want to make it roar, I put down the pedal and wind it right on out to 4,500 or 5,000. I haven't pulled a trailer, but I suspect that if I were doing so, I'd want to keep it above 2,000 or 2,200.

I don't have precise data on this yet, but it appears to me that if I'm slightly lugging the motor vs spinning it up a bit, I am not significantly adversely affecting the fuel mileage. It looks to me like keeping the motor in the sweet spot when power is needed--for my current load, that is in the 2,000 to 2,400 range--uses no more gas than trying to get by at a slower spin.




With that in mind, the table below is something that I put together. It shows engine RPM for my 5.4 with different axle ratios and tire sizes, at different speeds and in both 3rd gear and OD.

You can see pretty quickly that if you start with a stock truck--3.73 axle and 245/75R16 (30") tires--and then switch to 285/75R17 (33")tires, you will get very close to the original RPMs if you go to 4.11 gearing. Doing this basically gives you a straight swap.

You can see, however, that this straight swap might not be ideal if you expect to do a lot of towing. At 65 mph in OD, you are at 1,922 RPM--still not in the plus-2000 sweet spot.

If you go to 4.56 gearing, you are up to 2,132 RPM at 65 mph in OD, and if you bump it up to 4.88 gearing, you get to 2,282.

Based on your usage and the math, it looks to me like 4.56 or 4.88 gearing would be better for you than 4.11.




In some of my final conversations with Ramsey, he told me about his experiments with lower ratio gearing. The van he was building at the time of his passing was going to be a 4.88--and I'm virtually certain that he was going with 33" tires for that one. Ramsey really liked how the 5.4 motors run when they spin up. I think he was on to something.

When I did my conversion, I opted for 4.11 axles and 285/70R17 tires. I'm happy with that combination, although if I had unlimited time and money, I'd experiment by swapping back and forth between 4.11 and 4.56 just to see what the differences would be in power and gas mileage.

So--that's the math, and, perhaps, a bit of wisdom from Ramsey. Past that, I think it is a matter of feel and experience, and I think a number of folks have offered some good advice here.

I will be very interested to learn what you decide to do, and how you like it once it is done. Please post back with an update.

[boywonder]

Originally Posted by Glider

When I did my conversion, I opted for 4.11 axles and 285/70R17 tires. I'm happy with that combination, although if I had unlimited time and money, I'd experiment by swapping back and forth between 4.11 and 4.56 just to see what the differences would be in power and gas mileage.

Glider: What are you getting for gas mileage with the setup above?

[Glider]

Originally Posted by boywonder

Glider: What are you getting for gas mileage with the setup above?

Around 13 at present, combination of stop-and-go and highway travel. What do you get with yours?

[reelchef67]

I have 5.4 with 3.73 and I live north shore vancouver. i drive up and down all the time.
I'm only running 245's and i'm wanting to go 4.10. I cant maintain speed on hills without pushing it. MY van is heavyish but cruises really nice does seem to hit a good range until im doing 65 or so. With the bigger tires you're looking at I would do 4.10 in a heartbeat.

[Shaggy]

Thanks Glider for some killer info! I have a couple of weeks to make my decision. I pull our trailer several times a year but mostly in flat Texas, I do want the ability to go the mountains so I'm leaning to 4.56, I just hope that's not too low for just the van at freeway speeds.

[Glider]

Originally Posted by Shaggy

Thanks Glider for some killer info! I have a couple of weeks to make my decision. I pull our trailer several times a year but mostly in flat Texas, I do want the ability to go the mountains so I'm leaning to 4.56, I just hope that's not too low for just the van at freeway speeds.

Shaggy, with a 4.56 at freeway speeds, you'll be spinning 2,000 - 2,400, depending on how much of a lead foot you are. I spin my motor up to that all the time, and it is really happy in that range. Next week, I'll make a point of dropping out of OD on the freeway and doing some miles in that RPM range. I'll let you know how it feels.

[arctictraveller]

Originally Posted by Shaggy

Thanks Glider for some killer info! I have a couple of weeks to make my decision. I pull our trailer several times a year but mostly in flat Texas, I do want the ability to go the mountains so I'm leaning to 4.56, I just hope that's not too low for just the van at freeway speeds.

I agree, good info. I just finished up about 4000 miles with a 5.4, 4.10's 32" tires at about 9000lbs GVW and no trailer. Roads were freeways, single lane mountain passes, and low range crawling. The 5.4 certainly likes to rev, and if pushed hard it will pull the passes (averages were about 7K feet with one at 9800 or so) without holding up (much) trafic. I prefer not to run it that hard if I don't have to, but I suspect that with even deeper gears, it would have adequate power without reving it as much. If I were towing a trailer or running taller tires, I don't think 4.10's would be enough for me.

The fact that Ramsey was planning on running 4.88's makes me wonder if he wasn't building a bit of a performance truck rather than one for long distances, but I'm sure it would have been great fun in Baja. Speaking of Ramsey and Baja, don't forget were having a memorial a few days prior to the 1000.

[reelchef67]

Originally Posted by arctictraveller

I agree, good info. I just finished up about 4000 miles with a 5.4, 4.10's 32" tires at about 9000lbs GVW and no trailer. Roads were freeways, single lane mountain passes, and low range crawling. The 5.4 certainly likes to rev, and if pushed hard it will pull the passes (averages were about 7K feet with one at 9800 or so) without holding up (much) trafic. I prefer not to run it that hard if I don't have to, but I suspect that with even deeper gears, it would have adequate power without reving it as much. If I were towing a trailer or running taller tires, I don't think 4.10's would be enough for me.

The fact that Ramsey was planning on running 4.88's makes me wonder if he wasn't building a bit of a performance truck rather than one for long distances, but I'm sure it would have been great fun in Baja. Speaking of Ramsey and Baja, don't forget were having a memorial a few days prior to the 1000.

That's good Info. I regularly drive the coquihalla highway to Kelowna from Vancouver.
I'm on 245's with 3.73 and live on the north always driving up the cut.
I can't tell if just getting a tuner to change the shift points or putting a 4.10 would be better.
If I could find an LSD it would worth it.

I was thinking of going to 235/70/16 winter tires next year.