454 SM465 4.10 vs 3.73 vs 3.54

[KnockingDiesel]

I'd go 4.10 and drive it. We had a 74 Crew years back with that gearing and it didn't matter if we had 100 gallons of fuel plus all the equipment as well as the trailer loaded, it was 8mpg empty or loaded.

Strickland

This is why fuel economy doesn’t bother me. My 7.3 gets 10.3 unloaded or 9.8 loaded over. @ $4.50 a gallon my K30 gets the same fuel economy while burning $3.19 per gallon fuel. And I get to cruise around my dads old truck. I’m only concerned with longevity mostly and “comfort” to some degree.

 

[Strick]

This is why fuel economy doesn’t bother me. My 7.3 gets 10.3 unloaded or 9.8 loaded over. @ $4.50 a gallon my K30 gets the same fuel economy while burning $3.19 per gallon fuel. And I get to cruise around my dads old truck. I’m only concerned with longevity mostly and “comfort” to some degree.

Dad bought the 74 CCLB used in 1990. It was used for logging until he sold it in 2002. It used a bunch of gas while doing a bunch of work. It was fearless & being loaded didn't phase it. He put 400K miles on the one that's in my avatar pic. It's 3.73/SM465/350.

 

[Bextreme04]

The donor for my engine swap was a 97 K2500 Suburban that had a 454/4L80/NP241. It had 288,000 miles on it and the still pulled fine. It had a 14BFF with 4.10's and cruised like a dream on the highway with no issues. With a 4L80, it has a 2.48:1 first gear and a .75:1 OD. It cruised at 2000rpm at 60 and 2500rpm at 75mph, which is right in the powerband you want it at without compromising fuel mileage or longevity too much. The equivalent first gear ratio of a 2.48:1 first gear and 4.10 axle is 10.16:1.

With a 465, you have a 6.55:1 first gear! So the equivalent first gear starting ratio would allow you to have a 1.55:1 axle ratio! That's insane! No one in the world would say that a 454/4L80 doesn't have enough grunt towing with 4.10 gears. In order to get the equivalent OD ratio as a 4l80, you would need to go down to 3.05 gears. With 3.05:1 rear gears on the 465 you would get a 29.90:1 final ratio(DOUBLE the overall gear ratio of a 4l80 in 1st), a 10.9:1 ratio in 2nd(still more than a 4l80 in 1st) and then the 3.05 ratio in 4th. That would put you at the same 2000rpm at 60 in 4th and 2500rpm at 75mph. That would be the mathematical equivalent(pretty close) of having 3.90 gear and the gear vendors activated. All of these RPM numbers are with 31" tires, so bigger tires would also adjust this RPM down. So say a 35" tire with 3.42's would give you the same final RPMS.

So, if your main concern is being able to tow 10k lbs and still keep reasonable highway mileage without having to change too much... you could gear very low and take advantage of the super deep gears on the 465. A high rear gear with the gear vendors will give you the same final ratio in OD, but you will basically never use 1st gear, because it is just stupid low. With 4.10s, a 31" tire, and assuming the 454 is all done by about 4500rpm.. you are shifting out of 1st at 15mph.

With the 3.05 gears, you would get 1st gear to run out to 20mph, 2nd would then run out to 38mph, 3rd revs out at 80mph, and 4th becomes the cruising/highway gear.

 

[Bextreme04]

This is why fuel economy doesn’t bother me. My 7.3 gets 10.3 unloaded or 9.8 loaded over. @ $4.50 a gallon my K30 gets the same fuel economy while burning $3.19 per gallon fuel. And I get to cruise around my dads old truck. I’m only concerned with longevity mostly and “comfort” to some degree.

That's crazy. I had a 2004 F250 CCLB with a 6.0 and it would get 20+mpg on the highway unloaded or with a few thousand pounds in the bed. I had a neighbor with a 2000 with a 7.3 and it was a dog power wise in comparison but he got pretty darn good highway mileage too and would use it to pull his 15k lb 5th wheel to Lake Powell pretty often. I think loaded he was getting in the 10mpg range.

 

[KnockingDiesel]

That's crazy. I had a 2004 F250 CCLB with a 6.0 and it would get 20+mpg on the highway unloaded or with a few thousand pounds in the bed. I had a neighbor with a 2000 with a 7.3 and it was a dog power wise in comparison but he got pretty darn good highway mileage too and would use it to pull his 15k lb 5th wheel to Lake Powell pretty often. I think loaded he was getting in the 10mpg range.

My truck is geared real low. If I keep 60-65 it’ll get 14-16, I drive 75 or so. I don’t mind the fuel I factor it in the job when I’m working and it pretty much only moves for money. That load was around 16k I pulled it just fine at 65 mph (speed limit to where I was going).

Thats why I want to build this K30, at 10 mpg it’s still 40% cheaper to operate (fuel/oil change cost/maintenance) and I’m keeping my dads truck on the road and using it for the same purpose he did.

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[KnockingDiesel]

The donor for my engine swap was a 97 K2500 Suburban that had a 454/4L80/NP241. It had 288,000 miles on it and the still pulled fine. It had a 14BFF with 4.10's and cruised like a dream on the highway with no issues. With a 4L80, it has a 2.48:1 first gear and a .75:1 OD. It cruised at 2000rpm at 60 and 2500rpm at 75mph, which is right in the powerband you want it at without compromising fuel mileage or longevity too much. The equivalent first gear ratio of a 2.48:1 first gear and 4.10 axle is 10.16:1.

With a 465, you have a 6.55:1 first gear! So the equivalent first gear starting ratio would allow you to have a 1.55:1 axle ratio! That's insane! No one in the world would say that a 454/4L80 doesn't have enough grunt towing with 4.10 gears. In order to get the equivalent OD ratio as a 4l80, you would need to go down to 3.05 gears. With 3.05:1 rear gears on the 465 you would get a 29.90:1 final ratio(DOUBLE the overall gear ratio of a 4l80 in 1st), a 10.9:1 ratio in 2nd(still more than a 4l80 in 1st) and then the 3.05 ratio in 4th. That would put you at the same 2000rpm at 60 in 4th and 2500rpm at 75mph. That would be the mathematical equivalent(pretty close) of having 3.90 gear and the gear vendors activated. All of these RPM numbers are with 31" tires, so bigger tires would also adjust this RPM down. So say a 35" tire with 3.42's would give you the same final RPMS.

So, if your main concern is being able to tow 10k lbs and still keep reasonable highway mileage without having to change too much... you could gear very low and take advantage of the super deep gears on the 465. A high rear gear with the gear vendors will give you the same final ratio in OD, but you will basically never use 1st gear, because it is just stupid low. With 4.10s, a 31" tire, and assuming the 454 is all done by about 4500rpm.. you are shifting out of 1st at 15mph.

With the 3.05 gears, you would get 1st gear to run out to 20mph, 2nd would then run out to 38mph, 3rd revs out at 80mph, and 4th becomes the cruising/highway gear.

I think there is some torque multiplying factor in the torque converter, if I’m not mistaken I’m not familiar enough with autos to do the math but I remember something along those lines. Like I said I could be mistaken.

 

[Bextreme04]

I think there is some torque multiplying factor in the torque converter, if I’m not mistaken I’m not familiar enough with autos to do the math but I remember something along those lines. Like I said I could be mistaken.

The torque multiplication is a result of stall. Basically power is equivalent between torque converter input vs output minus any loss due to heat generation. Power is a function of force(torque) times velocity(RPM). Since the input reving up to several thousand RPM before hitting the stall and the output is much less going into the transmission, the torque can be multiplied by 2-2.5 times. This difference in torque goes quickly to zero as the vehicle is moving at any real speed. At highway speeds in 3rd or 4th gear the converter is locked and there is zero torque multiplication.

Even with a high stall converter the torque multiplication would only be equivalent to the worst case gearing scenario I gave you in my post above where your 1st gear would have twice the gear ratio as the automatic.

 

[KnockingDiesel]

The torque multiplication is a result of stall. Basically power is equivalent between torque converter input vs output minus any loss due to heat generation. Power is a function of force(torque) times velocity(RPM). Since the input reving up to several thousand RPM before hitting the stall and the output is much less going into the transmission, the torque can be multiplied by 2-2.5 times. This difference in torque goes quickly to zero as the vehicle is moving at any real speed. At highway speeds in 3rd or 4th gear the converter is locked and there is zero torque multiplication.

Even with a high stall converter the torque multiplication would only be equivalent to the worst case gearing scenario I gave you in my post above where your 1st gear would have twice the gear ratio as the automatic.

I see so the torque multiplication comes from the difference in speed between the crankshaft and input shaft and as the speed equalizes the multiplication comes down to zero, thanks for the info.

As for the K30 I’ll be running 235/85 R16 (on steel wheels so I can rotate them) so they calculate to 31.72”

Which is what the speed @ rpm in my first post is calculated at.

What I might try to do is get a couple sets of tires relative to the difference in gear ratios and tow around with it.

Since 3.73 are 9% higher and 3.54 is 14% higher, then a 34.5” and 36.5” tire should produce a similar result as re gearing, right? Or am I missing something?

I can keep speed on my gps and I wouldn’t have to go far there’s a huge hill up the road from house to serve as a testing platform.

I like the idea of an overdrive but the re gear was my initial thinking since I’m having them rebuilt anyway I thought I’d try to kill two birds with one stone. 3.54 was the highest I could go without changing both carriers.

 

[Bextreme04]

I see so the torque multiplication comes from the difference in speed between the crankshaft and input shaft and as the speed equalizes the multiplication comes down to zero, thanks for the info.

As for the K30 I’ll be running 235/85 R16 (on steel wheels so I can rotate them) so they calculate to 31.72”

Which is what the speed @ rpm in my first post is calculated at.

What I might try to do is get a couple sets of tires relative to the difference in gear ratios and tow around with it.

Since 3.73 are 9% higher and 3.54 is 14% higher, then a 34.5” and 36.5” tire should produce a similar result as re gearing, right? Or am I missing something?

I can keep speed on my gps and I wouldn’t have to go far there’s a huge hill up the road from house to serve as a testing platform.

I like the idea of an overdrive but the re gear was my initial thinking since I’m having them rebuilt anyway I thought I’d try to kill two birds with one stone. 3.54 was the highest I could go without changing both carriers.

That would be a good way to try them out for sure. Engine RPM at a given speed is always a combination of all of the ratios. So trans gear ratio, transfer case ratio(if you have one), axle gear ratio, and tire size. The engine will be producing a certain amount of power no matter what the rear tires are doing. The higher the engine RPM is compared to the tire RPM, the higher the torque multiplication that is happening, but that might not always be what you are wanting.

All of that to say, it doesn't really matter where you are doing the ratio changing. You are really just concerned with the overall ratio, and the spread in ratio change between gears will really affect how it drives as well. In this case you have a fixed transmission ratio and spread. So it doesn't really matter whether you are adjusting the ratio with the tire, the axle, or a gear vendor unit.

 

[82BBC20]

I’m currently running the gear vendors OD set up on my 82 C20, has factory 454 & turbo 400 trans with 4:10 rear gear & 33” tall rear tires. Cruising 70 mph @ 2500rpm no problem, gear vendors basically replaced original tail shaft housing on trans with trans mount in stock location. Changed drive shaft to a custom built one piece unit & cut off carrier bearing mount, no other mods required. Controls for the gear vendors consist of a small under dash switch & floor mounted dimmer switch & a small control box i mounted behind my dash cluster.

 

[Craig Nedrow]

My K20 has 4.10 gearing, with a turbo 350. With 33" tires my tach is right at 3000 rpm, I don't particularly like that. I am going to a 4l80e. Using a transdap on the tail shaft of the 4l80e, and have to bore out the 205 as the new bearing is larger. I will do all the mods to learn, and also I'm frugal, different then cheap. For those that want to know, the TH350 output is smaller then the TH400 or 4l80e, which is very similar to the TH400. The kit supplies the transfer case gears and bearings that the 4l80e slides into, and the adapter hooks it all together. US shift controls everything in the trans.

 

[KnockingDiesel]

I play with tire sizes and the sm465 gears are too far apart if I do any towing. The nv4500 is too expensive since I have not been able to find one used. Been doing the calculations and even with gear vendors the spread is too far apart if I’m towing. Th400 and gear vendors are well spaced very well for towing but with 4.10 rpm is 2600 and average of 3%-5% tc slip and up 10% (2700-2860) in some case is still to high rpm for me to pay over $3k for. Not to mention I’d have to rebuild the turbo 400.

So my options are 4l80E which is where I’m leaning since OD is .75 and it locks up. They are readily available and lots of info on the swap out there. I should be able to get a rebuilt trans for 1500-1800 stand alone tcm is 400-600, tps kit is 200-400. So with all new/rebuilt parts I’d be at 3k or so. This is a lot lees than my initial cost projection.

Or the slightly more expensive option is Allison 1000. Been seeing them used in the 1500 range and stand alone tcm is $1k or so. But that is a used trans price, new almost triples that cost.


Since I started this post I bought a 1985 3+3 C30 454/th400 Silverado. This truck will take priority over the regular cab.

 

[SquareRoot]

It's easy to go down the rabbit hole overthinking these things. Fact is, we tend to obsess over minutia on paper searching for the "perfect" combination that doesn't exist. Reality is, we build to a specific goal and then spend very little time using it as intended. The quest for max power, better mpg, show quality aesthetics, all succumb to the same logic. 90% of the time the factory had it correct for the masses. Regarding the gear spread you mention; You do realize a GV turns a 3 speed into a 6 speed? A hi & lo for each gear? Don't know how you could beat that if the goal is for towing? If I recall, they are also reversible for underdrive if you have lousy highway gears.

 

[KnockingDiesel]

@Square root I have stayed up a few nights chasing this rabbit and the “best” gear spread was th400 and GV but with tq slip and anticipated highway driving the revs are still a bit high for the cost.

While highway driving/towing the revs with 4l80 and 4.10 look pretty good and seems the best balance of ease/cost/availability.

Good cruise rpm and I think the 454/4.10 would hold 4th most of the time.

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I would think while pulling a load of 3k-5k I’d be able to hold od in the flats and and down shift to third in slight/moderate inclines.

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Under heavy load/steep incline it Gould go down to 2nd and still maintain some highway speed.

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So I think given my situation the 4L80E is my best option, I’d prefer a manual but I really like the numbers here.

 

[Bextreme04]

I play with tire sizes and the sm465 gears are too far apart if I do any towing. The nv4500 is too expensive since I have not been able to find one used. Been doing the calculations and even with gear vendors the spread is too far apart if I’m towing. Th400 and gear vendors are well spaced very well for towing but with 4.10 rpm is 2600 and average of 3%-5% tc slip and up 10% (2700-2860) in some case is still to high rpm for me to pay over $3k for. Not to mention I’d have to rebuild the turbo 400.

So my options are 4l80E which is where I’m leaning since OD is .75 and it locks up. They are readily available and lots of info on the swap out there. I should be able to get a rebuilt trans for 1500-1800 stand alone tcm is 400-600, tps kit is 200-400. So with all new/rebuilt parts I’d be at 3k or so. This is a lot lees than my initial cost projection.

Or the slightly more expensive option is Allison 1000. Been seeing them used in the 1500 range and stand alone tcm is $1k or so. But that is a used trans price, new almost triples that cost.


Since I started this post I bought a 1985 3+3 C30 454/th400 Silverado. This truck will take priority over the regular cab.

The nice thing with this is that its almost a direct swap from a TH400 to a 4L80. I'm doing this swap on my K25, it is actually easier on a 2wd. They use the same output spline, so the driveshaft and everything should go right over. You will need a TPS, but otherwise just go to a junkyard and pull an 0411 ECU and pigtails from a 2000-2003 GM vehicle. You can get a custom harness made by plenty of places. You would just need ignition and battery power to the ECU, Tach input from the HEI, and tps from the carb kit. Then the ECU would run to the ISS, VSS, and main connector on the trans. If you are really lucky, you can probably get a decent condition 4l80 from the yard with the harness and ECU all from the same vehicle and be done for dirt cheap. I got my engine/trans combo with the whole vehicle for $500. I rebuilt(with upgrades) the 4l80 for about $1000.