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4.11 vs. 4.56 frustration

4x4blaze

4x4blaze

That's not going to work
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Well guys, I'm at a crossroads.. And I'm afraid to pull the trigger...o_0

This upcoming summer, I plan to lift my Blazer 2" along with 33's... Nothing crazy.. But currently, it's powered by a gutless 305 backed by a 700r4 and 3.08 gears... And needless to say, it's a pig...

Now, I've got plenty of plans for this truck.. I'm currently building a 400 horse small block, built tranny, etc with a 14bsf 6 lug that's 3.73.. But unfortunately, I probably won't be able to swap it in for another year or two due to other responsibilities.

So right now I'm going to swap gears in my current 10 bolt... But what I'm wondering is if I should run 4.11's or 4.56's.. Most all of my driving is around town but I do occasionally take it on road trips during the summer. I don't want to be turning 3 grand at 70, but this 305 needs all the help she can get....:surepal: So I would really like to hear some of your guys opinions.. And I know this has been asked 1000 times before, but I could never find an answer I was satisfied with.. Thanks a lot guys!
 
If I've got the calculators right, 33's, .70OD, and 4.11 at 2000RPM will be going 68MPH. 4.56's, all else the same, will be going 61MPH. (2250RPM with 4.56's will get you 70MPH)

If you are out of overdrive (say in town) you'd be under 2000RPM at 40MPH with 4.56's.

FWIW, with my setup (SM465/3.42/33's) I'm turning 2450RPM at 70MPH. I normally just set cruise at 65MPH and call it good. Not that 2500RPM is ridiculous with the small block. Some of the trucks came with 4.56 and no OD from the factory, they turn 2600RPM just to go 55MPH.

http://spicerparts.com/calculators/transmission-ratio-rpm-calculator

I'm assuming you will convert the 14SF over to whatever ratio you pick now? Maybe run 4.56's in the 10 bolts, and if you absolutely hate them for some reason, you'd "only" have to regear the front. The rear 10 bolt is a wasted expense anyway, since you know you will swap it out. I think with OD you are going to be hard pressed to find a reason to dislike 4.56's. I'm sure there are plenty out there that actually run them however, and experience trumps the theoretical.
 
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4.56's and you'll be fine. 2275 rpm at 70 mph is ideal and it'll have some get up and go around town...
 
dyeager535 said:
I'm assuming you will convert the 14SF over to whatever ratio you pick now? Maybe run 4.56's in the 10 bolts, and if you absolutely hate them for some reason, you'd "only" have to regear the fronts. The rear 10 bolt is a wasted expense anyway, since you know you will swap it out. I think with OD you are going to be hard pressed to find a reason to dislike 4.56's. I'm sure there are plenty out there that actually run them however, and experience trumps the theoretical.
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Yes, the current plan is to regear my 10 bolt even though it will be temporary.. Gears are relatively cheap and I'll be doing the work myself, so I won't be losing much on it. I'll probably do the rear first, drive it around for a bit as a 2wd and see if I like it, and If I do, I'll swap the front as well.. and then eventually my 14bsf whenever it goes in to match the front..
 
@dyeager535 @tRustyK5

& I just wanted to let you guys know that your help is highly appreciated! Not sure what I would do without CK5 as a resource! Thanks a lot brothers!:saweet:
 
4x4blaze said:
Yes, the current plan is to regear my 10 bolt even though it will be temporary.. Gears are relatively cheap and I'll be doing the work myself, so I won't be losing much on it. I'll probably do the rear first, drive it around for a bit as a 2wd and see if I like it, and If I do, I'll swap the front as well.. and then eventually my 14bsf whenever it goes in to match the front..
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If you can get by only doing the rear to test, then I'd agree, that plan makes the most sense. I suspect you'll like 4.56's. What tires are on it now? 31's or smaller will skew your perception a bit, if you plan to go with 33x10.5R15's you can run them painlessly without a lift (IE now), to get a better idea what it will really be like running 4.56's and 33's. Just a thought. Those two inches should change the freeway RPM's by 200RPM.

In my old K5, I had the same 305/700/3.08 combo, but I was running 31's. It wasn't a speed demon off the line, but if I manually shifted it and held it in gear, once the RPM's started climbing, merging onto the freeway wasn't nearly as bad.
 
I have 4:56 in my '70 with A big block. I liked it with the 33's, and I could tell a difference when I put the 35's on.

I put 4:10s with a SF14 6 lug in my '90 K5 last year. I don't regret it with 33's. I didn't buy any gears for either end , so I didn't go 4:56.

But you know that I would find a way to install the SF14 rather than take time to mess with a 10B, but..
 
6872xtc said:
But you know that I would find a way to install the SF14 rather than take time to mess with a 10B, but..
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That's a very valid point. What is the price difference between the 8.5 and 9.5 gears? If the price isn't that far off, why not gamble on the 4.56's into the 14SF, and do the axle swap you plan on doing anyway? Opens up to a host of other parts to that project (brake lines, lug studs, driveline) but it's all got to be done anyway, and none of those are a gamble...they're going to be needed regardless of what gears you end up with.

Could certainly save yourself some time and money to do the 14SF initially, and could potentially make the swap quicker than a regear with the 8.5 in the truck.
 
The reason I'm swapping the 10 right now is because the 14 is going to need quite a bit of work and unfortunately, money.. I want to repaint it, swap the huge drums for disc, put a nice limited slip in it, and of course swap gears.. So probably 800-900.. And being a young gun, I don't really have tons of extra cash to dump into it right now..

I can get a set of gears for 200 and then with the experienced help of my old man, install it myself.. & the reason I got the 14 is to hold up to my full roller forged everything small block I'm slowly building..:whistle2: My foot may occasionally slip and I'm not sure the 10 bolt would like that...:burnout:

But right now with my 305, I think I'll be alright!
 
4x4blaze said:
The reason I'm swapping the 10 right now is because the 14 is going to need quite a bit of work and unfortunately, money.. I want to repaint it, swap the huge drums for disc, put a nice limited slip in it, and of course swap gears.. So probably 800-900.. And being a young gun, I don't really have tons of extra cash to dump into it right now..

I can get a set of gears for 200 and then with the experienced help of my old man, install it myself.. & the reason I got the 14 is to hold up to my full roller forged everything small block I'm slowly building..:whistle2: My foot may occasionally slip and I'm not sure the 10 bolt would like that...:burnout:

But right now with my 305, I think I'll be alright!
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Let me know what you are looking at for gears and I can get you a price if you want. PM me.
 
4x4blaze said:
The reason I'm swapping the 10 right now is because the 14 is going to need quite a bit of work and unfortunately, money.. I want to repaint it, swap the huge drums for disc, put a nice limited slip in it, and of course swap gears.. So probably 800-900.. And being a young gun, I don't really have tons of extra cash to dump into it right now..
Click to expand...

I won't belabor the topic, but painting is no big deal unless you want to get crazy with it. Pressure wash, rattle can, done.

No reason you can't swap it in as-is for the most part though. Will need to do the brake line halves from the tee at the axle to the wheel cylinders, driveline will most likely need shortened, perches moved, but other than that, drop in. Disks could be done later, since the 10B e-brake cables will bolt up to the 14SF drums.

If this is anything other than a mall crawler, I'd avoid an LS diff. Any chance yours already has the gov-lock? If not, need to be looking at something more stout than an LS, and even the TrueTrac is questionable IMO.
 
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I agree... just get the 14b in... gotta be done and from your list to do didnt say seals or lugs... get it that much closer...
 
I didn't have to do any driveline mods on mine. I used the 10B yoke and just opened up the dust shield to clear the pinion seal.
I have a zero rate, plus the spring perches and axle tube diameter gave it a little lift. I used some 1/2" wheel studs in mine so that the tapered seat of the lug nuts fit the wheels better than the 14mm lugs did.
Just food for thought.
 
Take your gear money and put it into the 9.5" axle. Do the disc brake swap later as funds allow. You may be able to find used drums to get you by if the ones on it are shot (IIRC, the drums cost as much as a disc brake conversion). You can even paint it later while it's under the truck. Even if it slows you down a few months, why flush hundreds of dollars into a rear 10-bolt that's only worth $25 when you're done with it?
 
Blue85 said:
Take your gear money and put it into the 9.5" axle. Do the disc brake swap later as funds allow. You may be able to find used drums to get you by if the ones on it are shot (IIRC, the drums cost as much as a disc brake conversion). You can even paint it later while it's under the truck. Even if it slows you down a few months, why flush hundreds of dollars into a rear 10-bolt that's only worth $25 when you're done with it?
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This^^^^^ a regear on an axle that is out of the truck is also much easier. Regear the 14 bolt and get it ready to install. Upgrade the brakes and locker later. You'll have a little more experience then too...
 
Fellas, the regear isn't really costing me a whole lot.. Ended up finding a brand new set of 4.56 motive gears that I scored for $75.. So $75 + my own labor doesnt sound like a bad deal.. I also have a lift that I will be using to make things easier.. But I do appreciate the opinions! & don't worry, the 14 bolt will end up under the truck eventually..

& This may be a stupid question, or a clever idea.. But are 10 bolt ring and pinion gears interchangeable between back to front? I believe they are, but I know some axles arent.. But anyways, I could run these gears in the back for now and then swap them into my front end at a later date when the 14 gets swapped in.. (Yes, my K5 is gonna be 2wd this summer... I'll be sporting a Bluetooth driveshaft....:whistle:)

Thanks guys!
 
Yes, you can swap the gears to the front. So you already have the shim kit, marking compound, fluid and gasket maker? Make sure you check out all the bearings and seals when you have it apart. I suppose if you're not going to run it long term you can tear down to inspect and then order parts instead of the normal "master install" approach. Don't forget the new crush sleeve and pinion nut.
 
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