Mirage775

Thinking about buying everything new, when I get ready to install the engine and trans in my NB.

At least I think this is a Z? Found this trans on Summit - Ford Performance Parts Super-Duty T-5 M-7003-Z

Summit says 300 ft lbs is all that it can hold, but in the comments, people are saying it's holding up to 400-450 ft lbs, which is more than I need?

Wanted to mate it up to this Blueprint 306, 370 hp / 350 ft. lbs Ford 306 c.i. Fuel Injected

Will the aluminum heads on the 306, work with Martin's headers?

Thanks!

mrmustang

Send your existing transmissions to
The 5&6 Speed Specialist | Hanlon Motorsports

They have built some of my old T5 transmissions for road racing, easily handle what your engine is making. No need to buy a brand new transmission that is not up to the task at hand when you can send a core down and have them build it to your specs.

Bill S.

Mirage775

Bill,

I don't have an existing transmission.... I never did the swap, but wish I had. I would prefer to buy a new engine and trans... I was just asking if that trans would hold 350ish ft lbs?

mrmustang

They have cores, and no, your choice of "new" transmission is the exact one I blew up twice behind my 351W/385hp Ford crate engine while road racing. The third time, I sent it to Hanlon and never was able to blow it up again, although, god knows, I tried .

Bill S.

Mirage775

Damnit... That's why I don't trust peoples review comments on websites... When I get ready to pull the trigger, I'll give them a call. If I don't buy new, I was thinking about buying an Exploder bottom end and Trick Flow 350hp Twisted Wedge Top-End Kit from Summit. I'd be happy with 350hp in the little Miata But I would want a trans to handle it? Also, do you know anywhere that has T-Bird 8.8 diffs readily available?

mrmustang

Join Corral.net or fordthunderbirdforum.com for the T-bird center section. A post in both of their wanted sections (here too) will generate the center section you desire.

Bill S.

tbone heller

In a Miata, you will destroy the tires before you destroy a T5Z.

engineer

Hi,

The T5z is a decent transmission and will hold up to 450hp without issue if driven with respect (i.e. no hard launches or ripping through the gears hard, flat shifting etc.). I run a T5z behind my 331 which is pushing 425hp...had it for 4 years without issue and covered 20000 miles.

However, if I had my time again I would go for a TKO box, they are stronger and will take a lot more abuse than a T5 can. It is slightly heavier and bulkier (not by much). I would have swapped it out but I have to redo the clutch, bellhousing, tailshaft setup to make it happen...and the cost of that is prohibitive...when I can just rebuild the T5 if it ever lets go.

So to answer your question. Yes you will be fine with a T5z at that 350 HP level, but a TKO would be a better option if you have plans to work the transmission hard.

Cheers

Sunshine Guy

The torque rating on the T-5Z transmission is a factory-method rating based on the expectation of 100k+ miles service life, as you'd expect in any "normal" passenger car. As others have suggested, it has proven to give satisfactory performance car life at somewhat higher torque ratings depending on 1) how it is treated (avoiding power shifts and high rpm launches with very sticky tires), and, 2) the weight of the car versus available traction. As tbone heller suggested, "normal" street tires (even down to perhaps a 200 treadwear rating that fits inside the fender wells) on the very light Miata serve as a "fuse" to dissipate some of the abuse that otherwise would be directed into the drivetrain.

When considering transmission strength ratings, notice the discussion frequently revolves around "horsepower." Horsepower is actually only a mathematical calculation based on torque multiplied by rpm. It is torque that breaks transmissions, not horsepower. For example, a stroker small block V8 cammed to peak out at 4500 rpm might make "only" around 350 horsepower, but its likely 400+ ft./lb. of torque would be testing the limits of the T-5 in a vehicle capable of hooking that torque to the ground. Conversely, a 7500 rpm motor making 400 horsepower could well be within the T-5Z torque rating. Bottom line, choose your trans based on torque, not horsepower (and available traction).

As others suggested, the T-5Z has proven to provide good service in V8 Miata conversions not subjected to full-on drag strip type of abuse. It's not unbreakable, but also not an unreasonable choice in the right application. Plus it is reasonably priced, very light, and shifts about as well at high rpm as any fully-synchronized box you can put behind a V8.

The TKO 600 is a definite step up in strength (by a lot). It is also physically bigger, about 30 lb. heavier, and not as smooth shifting at 6500+ rpm due to the difficulty of synchronizing the larger, thicker gears with more rotating inertia. There are modifications available at the top transmission shops to improve its high rpm shifting, but of course that comes at a significant cost. Properly broken in and operated correctly, it shifts just fine in normal street performance use. Interesting to note the TKO boxes are based on the Tremec 3550 which is based on a 5 speed that was custom designed a long time ago for UPS delivery trucks; an overdrive was added to the old, top loader 4 speed to create this design. So you "maximum effort" guys can thank Big Brown...

I don't know much about the new-at-this-time Tremec TKX, other than it would appear to likely be the basic TKO design in a sleeker, more streamlined and compact case that appears to come with the synchronizer improvements made popular for the TKO by the performance transmission shops. I notice gear ratios are the same as the TKO, so I'm guessing it's very similar internally except for the synchro upgrades (good things on both counts). I suspect this will be a very popular box and worth researching.

I originally planned for a TKO 600 behind the 400+ ft./lb. expected from the stroker motor in my (glacial) build. However, to get the highway cruise rpm I desired to match my cam, tire size & rear gear ratio, etc. I selected an Astro A-5 transmission gearset with an optional .75 overdrive ratio. I needed an overdrive halfway between the .82 and .68 ratios available for the TKO and this did the trick. Nearly as strong (not quite) as a TKO and much stronger than the standard T-5Z on which it is based, it provides another viable option. Not much savings over a TKO, but the light weight and good shifting advantages of the T-5 it is based on remain. Built by Stan at Pro-Force Transmissions.

We are lucky to have so many good options these days.

engineer

+1 to the Sunshine Guy for the excellent post above. I agree 100%.

The new TKX would be my choice if I could do it again. But the T5z is a a great unit that will last a long time if you treat it with a little respect.

Sunshine Guy

It is reasonable to anticipate that new users on this forum, now and in the future, will use threads like this as a primary resource for making component decisions on their builds. It can be confusing to sort through different opinions on mildly controversial subjects such as the suitability of the T-5Z transmission behind V8 engines producing significantly more torque than for which the T-5Z is rated.

I attribute that controversy at least in part to the wide variety of actual experiences different people have had, often owing to their proclivity for driving their cars with widely varying amounts of driveline shock and abuse. I also believe a significant portion of any T-5Z negativity comes from long years of experience in the Mustang/Camaro community where they have much heavier cars with larger, sticky tires, an application not directly comparable to a V8 Miata conversion.

So when considering the advice of tbone heller above, for those who don't know, he has owned his high torque, supercharged V8 Miata with a T-5Z for many years. He is speaking from experience, not theory.

I stand by everything I said previously about stronger alternatives, but I also give heavy weight to tbone's actual experience of successfully using the T-5Z in a high torque, street performance conversion (i.e., not a car subjected to frequent or dedicated drag strip use with slicks).

One final, obliquely-related thought: Clutch adjustment can be finicky on these cars; many have struggled with it. A clutch not quite fully disengaging may allow the T-5 to shift with acceptable feel in normal driving but this will greatly accelerate synchronizer wear (attempting a really quick and/or high rpm shift will likely result in a g-r-r-unch). I think many T-5's have been hurt over time by poor clutch disengagement, and then when the box ultimately has a catastrophic failure from a missed shift it is incorrectly attributed to inherent weakness rather than the actual culprit, clutch adjustment. Any box will eventually suffer damage if clutch disengagement is not complete.

Sunshine Guy

...and for those boneheads like me that frequently labor under the delusion that good enough may be suspect while too much is just right, here's a couple interesting videos on the new Tremec TKX.

Features, benefits, specs, and applications:
Actual teardown of a TKX to see the guts:
I really like what I see here; the question for most builders will be whether it's worth $800 over the price of a new T-5Z that may be perfectly adequate for most applications.

New TKX notwithstanding, I'm still very happy with my selection of the T-5Z based box with Astro A-5 internals and a custom overdrive ratio, because it gives me both the first gear and 5th gear ratios I wanted to match with my tire size, rear gear ratio, and engine power characteristics. Plus, it's lightweight, easiest to fit to tunnel and exhaust, and it's light shifting. Although only rated at 485 ft./lb. (upgradeable to 575 ft./lb. with an optional, hardened input shaft I decided I didn't need), it nevertheless cost as much as the TKX. Which is probably a reasonable indicator on the extent of my dementia...

fitz

The Fox Body mustang with the 4.9 litre v8 made between 130 and 205 HP and 233-270 ft-lbs of torque. It was pretty much gutless and the stock transmission was fragile. There are aftermarket versions of the T5 which are anything but fragile but the PN you quote is for the original production car and while it might withstand a bit over 300 ft-lbs, I doubt that any tires you can stuff under the back of a stock Miata will hold that much torque so, tires will become the clutch protecting your drivetrain from damage.

Reese04

No, some of you may have had good luck with your T5Z, I have not. My engine turns 365 rwhp and 300ftlb torque dynotuned. I hammered it hard of the starting line, then hit 3rd gear really hard, barked the tires, blew the T5Z. I now have a TKO500. Do yourself a favor. You have more horsepower, over 300, then pull it out, sell it. Buy a TKO or some other high hp high torque rated xmission. T5Z is not it.