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Discussion Starter · #1 ·
Trying to decide between 373 gears and 342. I have a 500-600 hp/torque engine that I’m putting in an s10 with a Tremec TKO 600. Since I’m building it for street I’m joy sure what gears to have in the rear end. 373 sound nice. But for that power and how light the truck is, shouldn’t I just use 342?
 

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With a .6x overdrive ratio why are you not considering 4.11?

3.42 ratio with 20% overdrive is often overkill that has you downshifting to pass. Your talking 30 to 40% with a 600.

Your not dropping into direct because the thing does not have power or is heavy. Your dropping into direct to get higher into the rpm range closer to peak power.

You can run a 3.42 ratio but if that means your cruising at lets say 1800 rpm where your only making 250 hp. Running a higher ratio places you around 2300 and lets say 280hp may be more beneficial. Being able to drop into direct you end up going up to lets say 3600 instead of 3200 and are at peak torque at 3500 while still building horsepower.

Torque is what moves you. Horsepower is a number based on torque. If your dang near lugging the engine cruising down the highway in overdrive it is going to take you longer to accelerate from 70 to 90 then if you were to drop into direct then accelerate.


I have no need for overdrive with a 3.42 ratio.

Those rides that have had a 3.42 ratio and overtime I catch myself running 90 mph way to much. Almost always using direct to pass or holding direct into 5000rpm.

With 4.11 I can control my speed better with overdrive. If the thing has enough torque then 3.73 is used. But I often switch from 3.73 to 4.11 because the diffrence in driving is noticable while the actual engine rpm and mileage are not as noticeable.
 

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Discussion Starter · #3 ·
With a .6x overdrive ratio why are you not considering 4.11?

3.42 ratio with 20% overdrive is often overkill that has you downshifting to pass. Your talking 30 to 40% with a 600.

Your not dropping into direct because the thing does not have power or is heavy. Your dropping into direct to get higher into the rpm range closer to peak power.

You can run a 3.42 ratio but if that means your cruising at lets say 1800 rpm where your only making 250 hp. Running a higher ratio places you around 2300 and lets say 280hp may be more beneficial. Being able to drop into direct you end up going up to lets say 3600 instead of 3200 and are at peak torque at 3500 while still building horsepower.

Torque is what moves you. Horsepower is a number based on torque. If your dang near lugging the engine cruising down the highway in overdrive it is going to take you longer to accelerate from 70 to 90 then if you were to drop into direct then accelerate.


I have no need for overdrive with a 3.42 ratio.

Those rides that have had a 3.42 ratio and overtime I catch myself running 90 mph way to much. Almost always using direct to pass or holding direct into 5000rpm.

With 4.11 I can control my speed better with overdrive. If the thing has enough torque then 3.73 is used. But I often switch from 3.73 to 4.11 because the diffrence in driving is noticable while the actual engine rpm and mileage are not as noticeable.
Can you explain to me what dropping into “direct” means? And what the benefits of 4.11 are instead of 373 or 342? I was thinking of 342 mainly because of what power I would have to the weight the truck would weigh. I honestly thought 373 or 411 would be way too much and may be best possibly for heavier applications. I would like to cruise with some Type of decent MPG but I certainly want my power that my engine is creating.
 

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Can you explain to me what dropping into “direct” means? And what the benefits of 4.11 are instead of 373 or 342? I was thinking of 342 mainly because of what power I would have to the weight the truck would weigh. I honestly thought 373 or 411 would be way too much and may be best possibly for heavier applications. I would like to cruise with some Type of decent MPG but I certainly want my power that my engine is creating.
Direct is the 1.0/1 ratio.

Have you done the math to see where your engine is going to be with "this" rear axle ratio in "this" gear with "this" tire size?

Here is grim jeepers gear ratio calculator it allows for easy comparing of gear ratios and tire size changes. It has a large list of saved transmission ratios or you can enter your own.


I don't know your tire size so just picked 205/75R15 which is going to be on the small side.
I entered 2.87, 1.90, 1.34, 1.0(direct), and .68 as your tko 600 ratios.

At 70mph with 205/75R15 the engine will be turning the 2425 rpm with 4.11 and 2018 with a 3.42 ratio.

At 225/75r15 the 4.11 will be 2324 and the 3.42 being 1933 at 70.

235/75R15 the 4.11 will be 2276 and the 3.42 will be 1894 at 70.

Your butt will feel the diffrence between 3.42 and 4.11. Or you could simply plug in the numbers of what less overdrive diffrent tires sizes may end up being.

If your running a 235 tire size with a 3.42 ratio then thats almost lugging the engine at 1894 at 70. You would drop into direct and the rpm increases to 2785 and back closer to peak torque to allow for faster passing.
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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Here's something to consider, if you already hadn't. By the numbers a 2.73:1 ratio in 1st, 2nd, 3rd and 4th gear would translate the same as a 4.10:1 ratio in 2nd, 3rd, 4th and 5th gear. I think on either end you wind up making one gear "unusable" for the street. A naturally aspirated engine making that kind of power wouldn't like highway speeds in 5th gear with the 2.73:1 ratio, but you could cruise in direct (4th). The kind of power you're talking about would make 1st gear with the 4.10:1 ratio too steep to use aggressively, but you could probably do well taking off in 2nd gear. (In a prepped track/drag tire situation you could probably leave hard in 1st). Are you more likely to hit the highway or the track? I know you said street, but we all know that "street car" is an ambiguous phrase to say the least.
 

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1949 Ford Coupe RESURRECTION
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I'm with Malibu. Are you building a "wild ass" street car, or a "highway cruiser" street car? Do you care about gas mileage at all? Is it going to be a daily driver or a weekend "rip some butt" car? Do you like the sound of your electric cutouts when the engine lugs down a little or do you like to hear your engine screaming? Just thinking out loud.
 

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This is the "problem" with modern overdrive ratios. If you go with 3.73s, your 1st gear take off is either 10.70:1. 3.42s net you a 9.81. These both dont take into account the height and weight of your rear wheel/tire combo. At the same time, you have to balance the OD ratio against the rear gear ratio. Do you have a tall, heavy rear wheel/tire combo (29x15 on a 15" rim for example)? Do you have a high strung, tempermental engine that will want a higher cruising RPM? And exactly which OD ratio do you have? If you have a short tire, and a .80 OD (20%), the 3.42 is best. If you have the .64OD, then you need to A. figure out where your engine wants to cruise RPM-wise, and B. figure out what rear gear gets you there given your tire height.

You should slow down and approach this issue as a systemic one, not simply a collecton of parts.
 

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cruising RPM is what dictates the rear gear here. does the engine need to turn 2200 to clean up or is it happy to turn 1600?
 

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I wanna now more about the engine but I'm kinda leaning too the 4+ range but 1st gear is gonna be real short if it's needed at all
 

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Real short. Like ten feet at redline.
Light vehicles with mondo up & torque will spin tire easily
I'd go with 3.73
 

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Just my 2 cents, my Model A has a blown 406/700R4 combo with a 2200 stall big tire car with a 3:50 rear gear. Very enjoyable to drive and when you push on the gas it's by by time. In 4th with the converter locked, the engine is just lugging along fat dumb and happy, and it will pull pretty well before it drops a gear, then it's on. You can't go wrong with either gear unless racing is your thing.

Keith
 

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Discussion Starter · #13 ·
So for Those asking about the engine. It’s a 383 with Edelbrock top end kit 2096 on it. The trans is a Tremec tko 600 5 speed manual. I’ll post a picture of its gear ratios. This is going in an s10 with gm12 bolt from moser engineering. It’ll make roughly 500 hp/torque.
Basically I want to be able to cut up and have fun. But also would like to be able to cruise as well.

I think my power band range is 2000 to 60000….ish.
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