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4.10 vs 4.56 - Don't want a soggy bottom end

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Redfred

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I would like to get advise from you guys since we all have similar rigs in here. Before I found this forum, I got a lot of great advise from a couple other forums by guys that are in the muscle car scene and they had a lot of knowledge on the engine component discussions but I felt like I needed the expertise from truck guys when it came to the gearing, so I appreciate any insight you guys have to offer. My 85 K10 SCLB has a 350sbc, TH350 with a 6" lift and 35" tires.

Motor: it started life as a very humble GM crate and I'm doing a Vortec head swap (modified to accept .525 lift), Eddy performer RPM intake (1500-6500rpm), Eddy performer 750cfm vacuum secondary carb, and Lunati Voodoo cam (1400-5800rpm). Cam specs are .468/.489 lift, .219/.227 duration @.050

Rear axle: Swapping out the 10 bolt with a junk yard 14 bolt FF that is being completely rebuilt from WMS to WMS. I'll be keeping the front 10 bolt for now and just doing an 8 lug conversion with a regear once I choose the gear and this is where I'm stuck. What I DO know is it will be either 4.10 or 4.56

The car guys for the most part say it will be soggy on the bottom end with anything under 4.56 since I'm not going the RV/towing cam route. The truck is primarily a toy and will be a back roads/trash truck/toy kind of rig, so I wanted to go a little more aggressive with the cam than a low lift smooth idle cam which there's nothing wrong with that, I just wanted to have a little more under the hood. I moved my RPM range up a little with that cam but I figured I could compensate with gearing. I'm not concerned with MPG or even highway RPMs BUT I don't want to be completely wound out at 60 mph at the same time.

So there lies my question. I'm leaning toward 4.56's and have been for a while and from talking to friends and researching, it seems truck guys aren't as convinced that a taller gear than 4.56s would make the truck (with my motor specs) a terd on the bottom end. Maybe it's because car guys by default have launching from the line at the drag strip programmed in their minds, I don't know.

The 14 bolt had a 3.73 geared Gov Lock so I have to buy gears AND a carrier because I want to run a Detroit locker and the Gov Lock carrier will not accept a locker. A G2 carrier compatible with a locking diff is $400ish and this creates an issue because of the 14b FF carrier break between 4.10 and 4.56 gearing. From my understanding, if you have to pick, it's more desirable to use standard gears instead of the thick ring gear. If I go 4.56 (with a 4.56 and up carrier to keep a standard thickness ring gear) and later decide I want to go back to 4.10, I would have to buy another carrier along with the 4.10 gears which will just be more cash I don't have. I know I could get a 4.10 and down carrier to begin with that will work with a thick 4.56 ring gear but I just would rather not use a thick ring gear. BUT (lol, I know.. It's my friggin OCD kicking in) if I got a 4.10 and down carrier with the thick 4.56 ring gear, I could keep the carrier and then just go shop for a standard 4.10 ring gear and pinion if I were want to take the 4.56 out and go with 4.10s.

The whole standard vs thick ring gear thing is just a secondary thought but my preference is to not even change gears once it's all built. I want the gear that will work best with my motor specs to give me a good pulling/accelerating bottom end. Eventually, I'm rebuilding the TH350 tranny and can put a higher stall converter in if needed although I don't know that it will be necessary. The RPM power band isn't that high I don't think.

Sorry for writing a novel on this but it's a lot of cash and labor to me and I'd like to avoid round 2. So anyway, 4.10 vs 4.56.... what do you guys think?
 
I don't know much about your cam, but my friend had a GM crate 350, TH400, 4.11 and 35" TSL's. It could have used more gear. I say go 4.56.
 
Simply not that much difference between 4.10 and 4.56 gears. Part of the decision is how the truck is going to be used as 4.56 with "only" 35" tires and no overdrive would make the engine sing pretty good on the freeway.

I cringe at the thought of spending big money to get new 4.10 gears and an open carrier for the 14FF since those are so common from the factory. You should seriously consider selling the current axle and getting another one with that combo as it should save you a lot of money and time in the long run. This is also my argument for 4.10 gears if you have them factory....it will probably cost more for gears than a complete axle.

Same goes for the front axle as you should be able to find an 8-lug 4.10 geared 10-bolt ready to go. Again, why spend the time and money to get gears and hubs to convert the current axle.
 
6.2Blazer said:
Simply not that much difference between 4.10 and 4.56 gears. Part of the decision is how the truck is going to be used as 4.56 with "only" 35" tires and no overdrive would make the engine sing pretty good on the freeway.

I cringe at the thought of spending big money to get new 4.10 gears and an open carrier for the 14FF since those are so common from the factory. You should seriously consider selling the current axle and getting another one with that combo as it should save you a lot of money and time in the long run. This is also my argument for 4.10 gears if you have them factory....it will probably cost more for gears than a complete axle.

Same goes for the front axle as you should be able to find an 8-lug 4.10 geared 10-bolt ready to go. Again, why spend the time and money to get gears and hubs to convert the current axle.
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This ^^^ If you find a set with 4.10's you're way ahead of the game money wise, and get to try out the 4.10's for free. If you like em, install the Detroit and call it done. If you feel the need for more gear, you haven't lost anything. Starting with a 3.73 gov locked 14 is the problem. There is no upside to having that, unless someone paid you a grand to take it off their hands.
 
Sounds like 4.56s get the most nods. The 14b was a buddies and we drug it out from the woods where he dumped it about 15 years ago. I've already got it stripped down to the bare housing and another friend sand blasted it for me.

I've kinda entered the " might as well" zone with it so I think I'll hold on to it. I know that if I found one already geared, I still couldn't keep myself from tearing it down to replace seals and bearings. Just a part of the OCD illness. The carrier and gears is definitely a significant expense but there is a cheaper carrier that summit has that I've looked at. It's a motion brand. I just figured if I go as far as I am, why cheap out on that one part when the rest will be higher end parts. I seem to fall into might as well zone all too often.

I'm shopping for some used 8 lug take off parts for the front so hopefully I'll find a set of hubs and brakes for cheap.

I know the motor largely dictates stall but what stall converters do you guys run with 35"+ tires and 4.56?
 
I run what the factory put in front of the 700r4, not sure if is 1500????
 
For what it's worth, I am running stock 5.7/700r4 with 35's. 10 years now. More ponies would be nice but it will run down the road at 65 without tearing the engine apart in 3rd With 4.56:1 R&P. Would be nice to go to 4.88:1 for the wheeling moments. I don't tow or haul, but it does weigh 7000 pounds dressed for the trail.
 
If memory serves, the stock converter is about 1200 stall on my 700. If it's the same for yours, then you will be out of your power band on takeoff. The 4.56s will rev you into your power band 10% faster than 4.10s. Or you can get a higher stall converter to takeoff in your power band. Either option will put you high in the rpm range on the highway.

Probably not what you want to hear, but it sounds like your cam isn't suited to the truck. Torque is everything with trucks as heavy as these. Your engine sounds suited to a street car or mud drag truck. Both of which would likely be running high stall converters and wouldn't be very worried about highway gearing. Maybe this lines up with your intended use, but it's not the norm.

For what it's worth, I have 35s, 4.56 1 tons with Detroit lockers, 350 with rv cam, 700r4 with stock converter. It's a very functional setup. I trail and street it (nothing hardcore) and it almost never sees over 3000 rpm.
 
rebelgregory said:
If memory serves, the stock converter is about 1200 stall on my 700. If it's the same for yours, then you will be out of your power band on takeoff. The 4.56s will rev you into your power band 10% faster than 4.10s. Or you can get a higher stall converter to takeoff in your power band. Either option will put you high in the rpm range on the highway.

Probably not what you want to hear, but it sounds like your cam isn't suited to the truck. Torque is everything with trucks as heavy as these. Your engine sounds suited to a street car or mud drag truck. Both of which would likely be running high stall converters and wouldn't be very worried about highway gearing. Maybe this lines up with your intended use, but it's not the norm.

For what it's worth, I have 35s, 4.56 1 tons with Detroit lockers, 350 with rv cam, 700r4 with stock converter. It's a very functional setup. I trail and street it (nothing hardcore) and it almost never sees over 3000 rpm.
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That's pretty much spot on. I sacrificed some torque in the idle-1400 rpm range to have a mildly higher revving motor. The gears and stall is how I planned to compensate. My power band is still what I consider low RPMs so I still feel confident that with the right stall, I can still have a strong pull with the bigger gears. I don't even know what stall is in there now. The dust cover is off so eventuall I'm going to look for some stamping on the case.

I may just get a 4.10 and down carrier with a 4.56 thick ring gear. If I feel like it's too much, I'll just be out a gear set and at that point might would shop for a used set of standard 4.10 gears on eBay.
 
If you have an engine that you know is lacking in the bottom end this shouldn't even be a consideration- go as low as you can with the gearing when you spend the money. Unless you're going to look for a complete set of axles with 4.10s like Rene suggested there is no reason to even consider them. 35s with a TH350 and 4.56s does fine on the interstate unless you plan on a lot 75+ MPH driving. That's what I had in mine and loved it at 65 MPH. If you had an o/d trans I say look at 4.88s.
 
Under gearing a truck can really be a bummer, not to mention probably one of the most common mistakes. Go 4.56, and maybe down the road build a nice little 700 to get the all around down the road if need be.
 
I just can't get past the title... :haha:


when in doubt, gear it..
 
ryoken said:
I just can't get past the title... :haha:


when in doubt, gear it..
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I didn't catch the alternate insinuation until you said that :doah: oh well.

I appreciate the advise. It seems almost unanimous that 4.56 is the way to go with my application. It will never see the freeway but just the deer woods and country back roads.

Just checked out online at Summit :waytogo:

Next task at hand is shopping for rear disc brake conversion...

Thanks guys.
 
Redfred said:
I appreciate the advise. It seems almost unanimous that 4.56 is the way to go with my application. It will never see the freeway but just the deer woods and country back roads.

Thanks guys.
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Freeway not important, then for sure 4.56.
 
35's 4.10's TH350 approx 2250 rpm @ 55 mph Comp 268H cam, Vortecs, Carbed, 2000 stall, No problem down low but for you 4.56 better.

With that cam duration and stock stall id say yes a little week down low with 4.10's. I'd be a little skeptical on that 1400 rpm claim.
 
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My 88 K5 has a new stock 350 tbi, 700r4, 4.88 gears, 35" tires. The 700r4 has a low first gear, from what I have read. The blazer gets moving pretty quick for a lazy engine. I am a bit afraid to really nail it off a stop with 10 bolt axles and a stock rear drive shaft. I don't do any serious off roading, so I opted to not change out axles. I really like the gearing around town. On the freeway, I think 65 mph is 2400 rpm. It gets the engine rpm up to where it makes some power. I can open it up and go faster, but it really buzzes the engine to stay at higher speeds, not that I should really be going that fast.

If you don't care about the freeway, then 4.56 may be a good compromise for your 3 speed trans and use.

I was thinking that the engine in my 79 pickup has a similar cam to yours, but being a 406, it will make a cam act more mild. I run a 264 comp hydraulic roller, and had a 270 comp hydraulic flat tappet. The rest of the engine is built as well and it makes awesome low end torque, but in a 350, the same size cam will push your rpm range up. My pickup has Th400, gear vendors overdrive 0.78:1 ratio, 4.10 gear, and 33" tires. At 65 mph, the rpm is around 3k without the overdrive. Acceleration is pretty good, but the engine has low end torque and can be easily pushed to 5-6k rpm. It feels like the power flattens out at 5k or so and it has a small (600 cfm carb.). More gear would be better if I was trying to race it. Your 35" tires will make that gearing seem like less than my 33" tires.

The K5 did have 3.73 gears and really sucked with 35's. Overdrive was hardly usable on the freeway.

If you had overdrive, it would be soooo much better. You could have 4.88 or even lower and still do some highway driving in OD even if it was a bit fast. I wonder how much difference the higher first gear in the th350 and 4.56 will make vs. my low first in the 700 and the 4.88. Your advantage is an engine that will make more power than my stock GM 350. My stock engine is gutless before 2k rpm and it is done making power by 4500 rpm. The pickup has aluminum heads, porting, intake, full roller, 10.2:1 CR, and all the good stuff and it starts pulling right away (low stall RV/Allison torque converter) and can be pushed to much higher rpms than the 350 tbi. It is wide awake at 2500 and pulls like a freight train from 3500-5,000 rpm.

That is a tough choice. It sounds like you really need some gearing for your truck, but it would suck to go too far and have it wound out when you don't want it to be.
 
blazer74 said:
35's 4.10's TH350 approx 2250 rpm @ 55 mph Comp 268H cam, Vortecs, Carbed, 2000 stall, No problem down low but for you 4.56 better.

With that cam duration and stock stall id say yes a little week down low with 4.10's. I'd be a little skeptical on that 1400 rpm claim.
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Yeah, I am skeptical. Lunati makes great cams and I've read that the unique grind of the Voodoo line is how they broaden the rpm range compared to older traditional grinds but with that duration, I was thinking 1700-1800 on the power kicking in. I'll run it and see. I'm waiting to do the transmission last because I'm broke right now. I should be able to get some r&d time in to decide on the converter.
 
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