T5 vs Toploader 4 speed???

wr3stler17

Member
May 11, 2016
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hey fellas i’m going to swap my c4 for either a t5 or a 4 speed top loader but i’m stuck between the two. I’m currently running 3.55s and as soon as i hit 65 i’m at 3k rpms so highway gas mileage goes out the window and i don’t want to be cruising at 3-4k. What i’m asking is what is more worth my while I drive on the highway a good bit to shows and whatnot and i still want what’s best performance wise too. Also engine is a mildly built 351 windsor with about 420-430 to the wheels with plans for more power so the trans needs to be able to hold up too. Also putting a 9 inch rear with 4.11s in soon but don’t worry too much about that i have more ring and pinions if needed just looking for opinions
 
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rustaddict

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Aug 23, 2014
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Agree you need the overdrive. If I wanted to run 65mph with 4.11 the toploader wouldn't be an option. Do you already have the 4.11s ?
 

garth66

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Nov 27, 2006
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I swapped out the T10 (4 speed) in my 66 for a T5z - best upgrade I could make! I have 3.55 rear end ratio too. I like to DRIVE my cars, not just to the local Cars & Coffee, but I like to take them on weekend trips with my wife. Having overdrive makes it sooooo much more enjoyable on a roadtrip of any kind. Some would say the final drive ratio of a T5z in first gear is too short with a 3.55 rear end, but I like it! I have crisp performance off the line, can "light em up" at will, and still enjoy cruising on the highway.

So the question becomes, how will YOU use your car, or what kind of driving will you do with it? If you do 99.9% of your driving on the street, stick with a street gear, like your current 3.55? With a T5, the 3.55 is probably as steep as you should go to maintain a street car feel. Others will disagree because they are willing to give up some of that street "feel" for an extra tenth or two at the track. It depends on what you want. See if you can find anyone local with similar setups to what you're considering and see if they'll take you for a ride, or even let you try it to see if you like it.

Here's a nifty RPM Calculator so you can see what your engine speed will be based on your transmission and rear end gear ratios.

As far as the T5 options go, you want the T5z. The latest version, the so-called “Z” box that was used in the ’93 Cobra, is equipped with the best of all the updated parts including hardened gears, shortened shifter throws, a bearing collar made of steel, and tapered output-shaft bearings.

Check out MDL for reference to gear ratios on any trans you're considering:

Here's a good article about overall gear ratios which you should read before committing to a 4:11 rear gear:

As for strength, the article above discusses that as well. The T5z is rated at 330 lb-ft of torque capacity, but I know of folks on another forum who have similar HP engines as yours and run the T5z on the track with no issues. The T5 should be able to handle your power level just fine. UNLESS you're merely banging gears and/or drag racing! And if showing off on the street, NEVER rev it up and side-step the clutch! That's just foolish and asking to break things.

One more thought... I'm guessing you want to go drag racing since you mentioned plans for a 9" rear end and 4.11 gears. If you're not drag racing and subjecting your car that that kind of abuse, there's no need for a 9" rear end (and all the extra weight it will add to your car). I was planning to upgrade mine from the 8" to a 9" and the good folks a Currie Entereprises (THE 9" experts!) talked me out of it. They assured me my 8" (they rebuilt the center section) was more than capable of handling 400 HP! An article here states the 8" rear end is is easily good to 300 HP, but talk to the real experts - they know their stuff!
 
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2Blue2

will be trying this sex one when I can find it
Mar 5, 2019
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I have a 9 inch 4.11 detroit locker and a T5 w/scatter shielded 289 in my 65. What a great setup, I love it. Of course not to many 'highway' miles in Hawaii.
 
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GT1966

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Sep 26, 2002
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Just a quick note regarding my experience. I replaced my T-10 4-speed with a T5 and it really is fantastic for highway trips. The 5.0 is mild with only 315HP, so the T5 can handle that. I wouldn't push 400HP through a standard T5. As for gears, I am running an Eaton TruTrac with 3.25 gears in an 8". I would highly recommend going to 3.50 gears because you need to drive 80mph to get out of the dreaded 2200 rpm FlowMaster 40 system drone. It's much quieter on the highway at 2500 rpm. My 2 cents.
 
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Stang a long

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Apr 29, 2012
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I run a T5 in a 1978 Cobra II behind a hoped up 302, If your going to run a t5 I would recommend replacing the countershaft bearing retainer plate with a solid one and replace the slider keys and a good shifter with solid stops! I made these changes to my Transmission and have 500 passes at the drags with full power shifts. Before I made these changes to my T5 I was setting 12 to 20 passes on a gear box!
 

nickyb

WAIT,you now have a pair?
Apr 3, 2009
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To get a t5 to live behind your h.p.levels it'll cost what a new tko cost.save for The new one,you will be much happier.
 

Stang a long

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Apr 29, 2012
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The problem with a TKO is they are imposable to get from gear to gear at 6500 RPM, if you have to granny shift you should run an Automatic
 

zookeeper

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Aug 25, 2001
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I hope this doesn't offend the OP, but you're building a recipe for failure. You don't have the budget for a stout trans to handle the HP you have now, but you have the budget to plan for more HP. See where I'm going with this? Lord knows I'm on a budget myself, but here's the bottom line: planning is what keeps any project out of the dumpster. Treat your project like an architect plans a house. If you're goal is to have a two story house, but your immediate budget only allows for either a second story or a strong foundation, build the foundation now and get the second story when your budget allows. If you can't get all the power you have now to the ground, why in the hell would you build more? Just some free advice and worth what it costs...
 

TT670

Founding Member
Jul 10, 2001
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Everyone's so quick to bash the T5. I've been banging on a stock 93 GT T-5 in a 400hp 65 Mustang for 19 years without even a hiccup and Lots of people successfully drag race T-5's even with slicks! I know of one guy who's got 8 years running in the 11's on slicks in a fox body mustang with the same T-5Z.

Search the fox body forums and you'll find countless people beating on T-5's and loving every minute of it
 

Stang a long

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Apr 29, 2012
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The TKO is a Granny shifter box I know from experiance that is not the way to go, and you say the T 5 is to weak tell us what to use for a transmission.
 

southcross2631

Active Member
Dec 13, 2019
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One draw back to a small block toploader is the weak input shaft . The big block toploader requires a bigger throw out fork and different clutch disc and throw out bearing. My small block top loader twisted the input shaft in 3 passes with slicks. Built 306 with 28x9 slicks. Having Liberty Gears make me an input shaft from 300M material. Supposed to be good to a thousand h.p.
DSCF3572.JPG

I would go with a T5 z or a beefed up AOD and not do the stick shift swap.
 
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SadbutTrue

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Everyone's so quick to bash the T5. I've been banging on a stock 93 GT T-5 in a 400hp 65 Mustang for 19 years without even a hiccup and Lots of people successfully drag race T-5's even with slicks! I know of one guy who's got 8 years running in the 11's on slicks in a fox body mustang with the same T-5Z.

Search the fox body forums and you'll find countless people beating on T-5's and loving every minute of it

This. I had a 360hp/400tq 351w behind a *very* used 89T5 for almost a decade. Granted not a ton of annual use by me, but other than a little whine in 2nd (which I was convinced was just miles before me, not due to the power), it did fine. I bought it for $450 and sold it for $300. And I now have a 408 with closer to 470hp/500tq behind a T5z and i have zero worries.

Traction kills transmissions. In a light 66, unless you have a slicks and a well setup rear, you aren't hooking all of that power. I don't race my car, and I do like to take it long drives. So OD is a game-changer. In fact, I just got 17.4 mpg going from San Diego to the far side of LA a month ago. Yeah, I was surprised too.

I can't independently vouch for the 11s on slicks thing, but I do know that it'll handle 450hp on a typical commute.
 

D Durden

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I'll echo some of the things the team here has said. Probably any transmission will work . . . UNTIL you start dumping the clutch and getting traction.

I'm old, and my setup is old, but, for the most part, we're both still running. :) In 1994 I updated my '65 coupe with a 351W (409 stroker), a toploader, and a 9" rear. The Windsor is a solid lifter motor and, BACK IN THE DAY, was a hot little motor . . . around 500hp on the dyno. That was in '94, BUT that toploader is still doing fine, and she's a driver. That being said I fully admit she's no drag car, and I have a 3.00:1 rear.

I understand the heavy highway use, thing. I drove her mainly in Tennessee where it was 30 minutes to a decent place to eat. I just moved to Texas, and there will be more of that. The 3.50:1 rear is going to eat into the mileage for sure, but what you might want to look at is how much extra money is it going to be for the extra gas versus the extra transmission cost to get the OD. It may be one of those things where you'll save $200 in gas every year if you dump a few grand into a transmission. Meh?

If you go with the 4.11, though, yeah, you'll need to rethink that.

Just an old dude talking, but when you start getting into the 4.11, slicks, 500 ft-lbs, and I'm driving it to the drag strip on the highway normally . . . you'll either need a serious budget or truck with a trailer. For every guy who says "I've been running this setup for 2 years, and it's NEVER broken" there are probably three guys putting their car on a trailer because they can't drive it home. When you push like that with a limited budget, eh, you break things. And it's always that night when your friend with the truck is out of town. :)