Well your choices show that you do not "fear the gear" as we like to say around here.
But at this level of conversation, aside from you choosing which way you want to bias the driving experience, the engine itself has an equal value in the equation. It's right up there with tire size and transmission type.
You can't change the aero all that much on a Bronco, so highway speeds are still going to be a big decider on what ratio you finally choose.
To your question about 2500 rpm, how does your engine pull now at 2000 rpm? A basic carbureted 302 almost has to be up in the mid-2000's and a little above if it's not perfectly dialed in. If you've got a really well tuned engine and have built a sweet combination you can more easily go lower in rpm.
The good news is that even the higher levels of engine speed aren't doing real harm to a 302. As we've said many times here, many of us have run 3000-3200 rpm for hours getting where we're going and have had no issue with the Broncos.
Now, you asked about "stressing yourself" while worrying about rpm. Not about the engine stressing. We can't help you with your own level of stress and worries, other than at least trying to alleviate your fear of higher rpm levels with your engine.
But the engine itself couldn't care less below 3000rpm. And not much even above that either.
There are several members here that have good running carbureted engines that pull down to near 2000 rpm at highway speeds and do very well. Only having to downshift when the roads get steeper.
But that said, I think it's safe to say that "most" of the other 302's that are not fuel-injected or deeper breathing down low are not going to appreciate anything below 2500. And if you do go lower in rpm by choosing the taller gear ratio, you are then losing some of your rock-crawling happiness. Depends on where that RV cam of yours is happy. Plan to downshift when the road starts pointing your Bronco a little more up in the front.
Once you add EFI to the equation, and add decent exhaust, or go smaller tires, all that changes. I bet I could run 2000-2100 rpm at 65 all day with my Explorer motor and smaller lift and tires and still have good acceleration and off-roadability to a point. But that would take 3.73's instead of the 4.56's I'm running and I'm not ready to go there yet. Still like to keep things easy off-road as well.
Besides, chirping tires into second on an old utility vehicle is kind of fun!
Add a 351 or deep-breathing stroker to the mix, and those lower rpms are a piece of cake with the proper tune or EFI. But again, as you've worried about, you then suffer a bit off the highway.
Sounds like you want to bias it to off-road, but not get screwed on the road. Correct?
Given 33.5" to 34" tall tires, a sufficiently lifted and rigged out heavy Bronco, you could go as tall as 4.56 for the street and keep it near 2500 @ 70mph (or 2350 @65mph) or so. Or go 4.88's and bias it towards the off-road and acceleration, but run at the higher 2700 rpm range on the road.
You'd still go better off-road with the 4.56's than with your previous setup most likely (not sure what that is now?) but if you wanted to go to the off-road side and used 4.88's you'd be at about 2700 @ 70mph. Probably puts you at about 1300-1400 rpm at 5mph in first gear, high-range. Pretty good compared to most except for the dedicated rock crawlers.
Would be more than enough gear for my type of wheeling. Not sure about yours.
Again though, all depends on how well your engine would pull your brick breaking wind called a Bronco down the road at speed.
So figure out what condition your engine will be in for the majority of your drive time and go with that. If you're going to Explorerize a 351w or stroker, you can pretty much do anything you want.
If you're going to run just the (unknown?) "RV" cam and a carb in a 302 I would have to say stick with the 4.88 since 5.13 is getting up there in the higher speeds on the street.
Not that it's going to hurt the engine to run 2800 rpm. But it starts being more of a compromise and might bother you to rev that high. At 2700 and below you're in the sweet spot. Great off-road, weaker pinion in the front, higher rpm on the road.
Whether the 5.13 is too weak for the 44 in your case, it again depends on just how you drive off-road. Heavy right foot? Leaping and bounding over hill and dale with great enthusiasm? Or poking along and taking the technical aspects of finding the right line over an obstacle?
In other words, how hard are you going to be on that 44?
I saw a pinion snap on an '06 Rubicon it's first trip out after a 4.88 swap. The previous year with 4.11's it had done just fine, but at just 20 minutes out of Moab the large tires, the smaller pinion, and an inexperienced buddy driving, that was a trouble filled 20 minutes!
Luckily most live longer lives than that, and he had 37" tires and a buddy driving, but you see where it's going.
How much are you willing to spend to make a 44 hardier?
And what level starts to stress you out? And who are you trying to keep up with off-road? And how do you drive? And how happy do you want to be on the highway?
Don't even bother figuring MPG into this conversation. All are going to be close. Can't say which was is going to give you an extra 1/2mpg, or whether that's even pertinent. Might be all the same.
All that rambling is by way of saying that while 5.13's and 35's might be perfect for some Bronco owners, I think that they will be too low for your needs. Even the 4.88 is pushing it from what it sounds like.
All you have to do though is decide which way you want the bias. Street or Trail.
Easy peasy!;D
Yeah, right...%)
Paul
I’m in the process of going 408w & 4R70. But, off-road it wheeled good. It would of been perfect with the Tera Low gears in the D20. Good luck & have fun!
