Let me start by saying I’m sure there’s a thread somewhere about it, and I’m sure I’m going to get flamed for it, but so be it. I also know nothing at all about gear ratios. The project I’m working on is probably also a stupid endeavor, but one I am undertaking anyway out of pure boneheaded-ness. I’m looking to manual swap my 02 Extended cab 1500. Looking to build it as a “tribute” if you would call it that to stock cars and the pure American bad-assery they represent. I know to stay true to this, I should use a 4 speed with straight cut gears. My only problem with that is that I want my truck to be somewhat decently well mannered. I don’t mind the feeling and noise of straight cut gears, but is there a gear ratio combination that could be somewhat well behaved around town, but also be ***** to the walls when called upon? Would like to see speeds of 160 or better. If this is impossible out of a 4 speed, I guess I would need to step up to a 6? Thank you for your patience in advance.

 

I would find a heavy car that has a transmission you are interested in and then drive it to see if it has the balance and qualities you are looking for.

IMO, if you want to accelerate aggressively, then you'll need a performance clutch and master cylinder. These parts will make "well mannered" driving in town challenging. (Until you build up new muscles in your leg that you didn't know you had.)

The 5th and 6th speed on a 6 speed are overdrive gears for gas mileage, so you'll see them come into play at higher speeds, giving you better mileage and lower RPM on the highway. Other than that, they aren't going to deliver anything for you on the lower end.

 

Neither. TKX.

 

https://www.tremec.com/calculadora.php

You can play around with various transmission ratios and see where your top speeds will be. With the prices people want for 4 speeds these days, I'd rather just go for a TKX or, since your project is a truck, a 6 speed out of a Frontier.

 

When you say "4 speed", which transmission are you actually referring to?

A T56 6-speed is like a 4-speed in terms of useful power gears. 5th and 6th are just overdrive for cruising. So maybe the real choice here is do you want overdrive or not?

 

Turn off the 98mph governor on the truck and see if you can even take it to 130mph safely. All your illusions of doing 160mph in that truck will quickly disappear. Between the **** aero, soft suspension, and the driveshaft turning into a hula hoop, I am betting your ***** shrink quick above 120mph. Now that we have significantly narrowed your operating parameters, you can more realistically decide on gearing.

 

I've never been happy with a 6 speed. It's one too many. A 5 speed hits that comfortable zone for me, especially on the highway, but I'd be just as happy with a 4 speed and the higher rpms. I'm talking cars and not trucks in this instance so maybe it does not apply, but I have a feeling my thoughts would not be different. I don't worry about gas mileage.
I don't own any manuals anymore due to health issues so when you look at the big picture, just be happy you can use a clutch. I miss mine.

 

The aero is garbage, I’ll give you that. But keep in mind this isn’t going to be a stock truck. Coils up front, custom 3 point in the rear, putting an ls7 with hopefully a 12:1 cr in it for the power plant. This is going to be the nastiest NA Silverado around. I want to push the envelope, not worry about what’s realistic.

 

was thinking about a Jerico or a Richmond Super T-10. This is a truck I would like to occasionally take on a 2.5 hour drive on the interstate to visit friends and family a few times/year. Going to play with the gear ratio calculator a bit more before I make any decisions.

 

really liking what I’m seeing on the TKX.

 

In that case a multi-piece driveshaft will be a necessity. Even carbon fiber in the length you would need for a 1 piece will have a critical speed too low for any real safety margin. BTW, my comments were based on actual driving of an extended cab 2002 Silverado with the governor removed and enough power to go fast enough that the whole truck felt like a paint shaker. I am not even sure the clips that hold on the lower airdam or inner fenderwells will hold up to 160mph. Your results will be interesting.

 

You absolutely need overdrive with the goals you mentioned.

4 speeds have a 1:1 4rth gear and that is no good for high speeds. If you gear the rear to suit that, it will be a dog off the start.

T56 is what you need.

 

I put a T56 in a 02 4.8l RCSB that had a Supercharger on it, 4.56 Gear in the back. It was actually quite fun. With that full size truck if you go T56 you'll want at minumum 4.10 Gears in it.

When you run close to 4.XX Gears in the back, yea that 6th gear is used and is needed. 1st is about useless at that point haha. My C5Z06 has the MN12 ratios in it so the 3.42 Gear is a good combination, then again 3085lb car.

 

tremec 6 speed is a good choice

 

Gearing wise 160 would be possible with a 4 speed or anything with a 1:1 gear ratio, it's done all the time with a variety of drag cars and the same stock cars you're looking to emulate. It comes down to tire diameter, gear ratio, and engine speed. For example 160 mph equates to 6686 RPM with a 27.5" tall tire and 3.42 gear ratio. It's more a question of if you'd have the power to do it at a given RPM and gear ratio.

As far as gearing you'd want a deeper first gear to compensate for the taller rear gear and as a result you'd tend to have a wider ratio spread within the transmission. Wider ratios mean more RPM drop between gears which is something to consider. For reference a 2.66 1st (available in T56s and similar in various 4 speeds) with a 4.10 rear axle will have a 10.9:1 effective take off ratio. If you do a 2.9 1st (another readily available 1st gear option common between T56s and Jerico/T101As) with a 3.42 rear axle you end up with 10.26:1. Both result in the 10:1 to 11:1 first gear final drive range which is an okay general starting range. If you go much taller (less than 10:1) then taking off will not be as easy/smooth and conversely going much deeper (more than 11:1) makes for a very short 1st gear.

If you wanted a straight cut 4 speed another option would be a T101A/GF4A. It's based on the T10 (similar to how a Jerico is based on a Ford toploader) and generally it's a bit stronger than the Jerico tends to be. They also have a ton of gearing options including going down to around 3:1 for first gear.

If you really wanted to get creative you could adapt a gear vendors unit to make a straight cut gear dog box with overdrive. Jericos are relatively simple since GV has a housing for them. However they do not make a T101A adapter and in my conversations with them they never will. I just finished modifying a GV T10 adapter to work with the T101A I'm putting in one of my cars. It's quite a bit of machining to make work since you have to contend with 4/7 holes shifting in the mounting pattern, a much taller reverse idler gear stack than a ST10, the reverse shift lever needs modification, and other random assorted bits of clearancing. This will not be the cheapest option by far unless you fall into a string of random craigslist and ebay deals like I did. I'm in this transmission for less than a TKX not counting the labor in machining the adapter or the other things I did like rebuilding the transmission since that was me doing it for fun.

The T56 isn't a bad option it's definitely going to be the more typical transmission used in a performance LS application. I've had multiple T56 cars and have an S1 shifted T56 magnum for a different project, they're awesome transmissions and would be more civilized than the options above for around town use.
The Frontier 6 speed or Z car CD009 variants are also pretty strong with kits readily available to adapt to an LS motor. I had a 6 speed Frontier for a few years and loved that transmission.

At the end of the day you could make any of the above options work in some form. The main thing you really need to consider is what it will be used for the majority of the time, your budget, and how much effort you really want to put in it.