Help with Coyote Rear End Gear Ratio and IRS Components

[JeepFlyer]

I'm close to finalizing my order for the parts to complete my IRS and I was wanting some feedback.

I read through some search results and FAQs on drivetrain selection and the numbers are starting to make sense now. The only problem is, all the examples and search results I'm finding are using higher HP and torque numbers than the Coyote.

So here is what I'm thinking of running:

Tremec TKO 600 (TCET5008)
Torsen T-2 Differential 3.55 Ratio
Gear ratios for the Tremec: 1st -2.87 // 2nd - 1.89 // 3rd - 1.28 // 4th - 1.00 // 5th - 0.64
and I'd be running 315/35R17 tires (if you want to plug it into a calculator online (http://bob123e.tripod.com/askbob/Gear_Ratio-MPH_Calculator.htm))

With this combo I would be sitting at 2100 RPM at 71 MPH. I'm more than happy with that number. But will I be able to afford the rear tires with the 1st and 2nd gear lengths?

So what gear ratio are all of you Coyote guys running out there? I talked to Mike Forte and he said after driving the Coyote, he thinks it has plenty of power, even at the low end.

In a perfect world this would be my setup:
Aluminum Diff Housing Case
Control Freak Reinforced Case Cover
Torsen T-2R Diff with 3.55 Ratio
Solid IRS Mounting Hardware


I'm open to suggestions, criticism, and ideas on how to spend more of my money, so what are your critiques?
Is anyone running a Torsen T-2R?
If so, is it really worth another $200?

[32J]

I'm struggling with the exact same dilemma. The roadster is so light that a 3.27 rear diff would still allow plenty of fun factor without smoking all the tires, while still keeping RPMs (and noise) down for cruising. HOWEVER, this will be my first build. I've scoured threads on multiple forums, and I particularly pay attention to posts by guys who have gone through multiple builds with various set-ups. And you know what the consensus was?...

NOTHING!

There were guys who 'swore' by the 3.27 with the TKO600 and 0.64 5th, and other who loved the 3.55. And some of them even switched from 3.73s to 3.55s, or from 3.27s to 3.55s. AHHH! I need help! My OCD is getting the best of me.

I won't be tracking, autocrossing, or dragging. Just street cruising.

32J

[Jay-rod427]

I'm struggling with the exact same dilemma. The roadster is so light that a 3.27 rear diff would still allow plenty of fun factor without smoking all the tires, while still keeping RPMs (and noise) down for cruising. HOWEVER, this will be my first build. I've scoured threads on multiple forums, and I particularly pay attention to posts by guys who have gone through multiple builds with various set-ups. And you know what the consensus was?...

NOTHING!

There were guys who 'swore' by the 3.27 with the TKO600 and 0.64 5th, and other who loved the 3.55. And some of them even switched from 3.73s to 3.55s, or from 3.27s to 3.55s. AHHH! I need help! My OCD is getting the best of me.

I won't be tracking, autocrossing, or dragging. Just street cruising.

32J

Not just trans ratios, but what engine it goes with. Revvy coyote, or torque monster plays into that selection as well. High horsepower torque build, or lower power that needs the mechanical advantage of a lower rear gear.

[Chris @ Forma]

We are on our 8th project and here are my thoughts:
First and foremost 32J you don't have serious OCD as everyone who knows me will tell you that it is CDO, like OCD except in alphabetical order as it should be.
We haven't use a TKO in any of our build but instead have opted for 6 speed Ford MT-82 gen 2 tranny. Gear ratios are very similar except add 3.66 on the low end. For rear ends we have primarily used 3.31 and below 45 mph we can pretty easily smoke the tires. Coyote has great torque throughout its useful speed range. If you opt for forced induction, you may want to increase your tire budget. We have a Coupe with 12.6 psi of boost, makes a little over 800 HP and it will smoke the tires at pretty much any speed below 120 mph in any gear 4 and below.

[Al_C]

I like the 3.55 rear end option. In fact, that's what I have. Gen II coyote and TKO 600. .64 5th gear. Right around 70 mph at 2000 rpm in 5th gear. I have the "old style" IRS with an 8.8 center section. Got it from Mike Forte. I can easily start out in 2nd gear (I don't, but could). I think I could probably start off in 3rd if I really wanted to. Reminds me of my father who at one time had a Ranchero with a 3 speed and a small 6 cylinder. He'd back out of the garage, into the turnaround, then take off. He'd be in 2nd before he left the driveway. That was a prime example of engine abuse... The coyote could handle that without blinking, but I don't have a turnaround.

[Hacksaw84]

I am still building but here is my setup:

Gen 1 Coyote with cams and a cobrajet intake manifold
TKO 600 with the .64 OD
Torsen diff out of a 16 PP car (3.73)
315/30/18 rears

I cant really tell you much about how it compares to other configurations but after doing some research a while ago that's what I decided on.

[rich grsc]

I'm struggling with the exact same dilemma. The roadster is so light that a 3.27 rear diff would still allow plenty of fun factor without smoking all the tires, while still keeping RPMs (and noise) down for cruising. HOWEVER, this will be my first build. I've scoured threads on multiple forums, and I particularly pay attention to posts by guys who have gone through multiple builds with various set-ups. And you know what the consensus was?...

NOTHING!

There were guys who 'swore' by the 3.27 with the TKO600 and 0.64 5th, and other who loved the 3.55. And some of them even switched from 3.73s to 3.55s, or from 3.27s to 3.55s. AHHH! I need help! My OCD is getting the best of me.

I won't be tracking, autocrossing, or dragging. Just street cruising.

32J
I'd use that in a minute, I think it'd be just right, NEVER a 3:73 for a cruiser, 3:55 would be perfect if autocrossing.

[BradCraig]

I have a Coyote Gen 3 with TKO (.64), 3:55 rear is perfect in my opinion. I don't see the need for the Torsen.

[RedRaider58]

I'll revive this old thread a little more...

Trying to decide between 3.15 / 3.55 / 3.73 for a Coyote with the new TKX, 17" wheels and IRS. I've built the spreadsheets to show RPM vs MPH, but need some real work experience on what works with these cars. Looking at more of a cruiser, but may dabble in Autocross to hone my skills. There are a few options for the TKX available (linked below), the major differences seem to be first and fifth, but any way I slice it the 3.15 seems to be pretty decent, covering the bulk of what one could expect in Autocross with 3rd gear and having a lower highway cruise RPM than the other gears.

Since most seem to enjoy the 3.55, what am I missing? Is it the seat of the pants acceleration, or something else? Does any one TKX look more appealing for these cars than another?

https://americanpowertrain.com/the-all-new-tremec-tkx-is-here/

[edwardb]

I'll revive this old thread a little more...

Trying to decide between 3.15 / 3.55 / 3.73 for a Coyote with the new TKX, 17" wheels and IRS. I've built the spreadsheets to show RPM vs MPH, but need some real work experience on what works with these cars. Looking at more of a cruiser, but may dabble in Autocross to hone my skills. There are a few options for the TKX available (linked below), the major differences seem to be first and fifth, but any way I slice it the 3.15 seems to be pretty decent, covering the bulk of what one could expect in Autocross with 3rd gear and having a lower highway cruise RPM than the other gears.

Since most seem to enjoy the 3.55, what am I missing? Is it the seat of the pants acceleration, or something else? Does any one TKX look more appealing for these cars than another?

https://americanpowertrain.com/the-all-new-tremec-tkx-is-here/

The TCET17765 version of the TKX is basically identical to the TCET5008 version of the TKO that is the most common for these builds. Starting with the very common 26 spline input, same 1-4 ratios, and a slightly higher .068 5th versus .064 in the TKO. That's the one I'd recommend and I suspect will be the most typical. I'd recommend the modelling you do is with that version of the TKX. I've had builds with a 3.27 and a couple with 3.55. All things being equal, I liked the 3.55 quite a bit more and there's a reason it's the most popular. I found the 3.27 a little "soft" in the lower gears. The very slightly difference it made to highway cruising RPM wasn't worth the trade-off all the rest of the time IMO. You'll get lots of opinion on this topic, and most will cite what they have. Understandable. Not everyone has extensively driven other than the one they have. I assume you also know the 3.15 version of the IRS center section can't be changed? Any of the other versions can do a gear swap-out to another ratio if you want. Due to internal differences (I don't know the details...) the 3.15 can't. Something to think about.

[CraigS]

I will start by saying any diff from 315 to 373 will work. 435hp is more than enough for a 2500# car. But which will you enjoy the most? I'd probably go w/ 355 or 327. EdwardB makes a good point in favor of the 355, more snap in 3rd and 4th. I'd go w/ the TKX w/ the 3.27 first and .72 fifth. First gear is pretty much a throw away gear w/ anything over 350hp. Unless you run drag radials you can't use full throttle in first anyway so I pick the gear that will make around town driving easier. The 3.27 let's you start from a stop w/ just a tiny bit of gas so it's just easier. The .72 fifth splits the difference between the two previously available fifths at .64 and .8 something. The .8 was a great roadrace gear because of the minimal rpm drop going 4th to 5th. While the .64 had a huge drop, it was a really nice interstate cruise gear. Probably 90% of FFRs have the .64. Oh, don't worry about a torsen. The standard Ford lim slip works just fine. BTW my experience is 15 years in my MkII. Started w/ a 400hp 351 and had 308, 327. Then a 408 of maybe 450hp w/ the 327 and then a 315 w/ the IRS upgrade. I would have preferred a 327 but the 315 was available at a real good price. BTW. If you get a salvage rear suspension be sure it includes the brakes. They work really well so you don't need to buy rear brakes (either stock or wilwood upgrade) at all.

[Railroad]

And I was sorta wishing I had gone with some 373 gears.
The engine is so smooth, I do not think the cruise rpm would bother me.
Engine seems soft up to 3k rpm.
It seems I drive in one gear lower than my other cars.

[BradCraig]

3.55 is a nice middle ground, I have no complaints at all paired with my Gen3 Coyote and TKO. My own $.02 is that the 3.73 may be a bit tall for 1st. The salvage center sections are fairly cheap so if you don't like, it's easy enough to swap out. As far as the Torsen, I don't know much about them but the Mustang guys seem to have mixed opinions on them.

[Duke]

I have the 3.55 IRS, 2nd gen Coyote w/Lund tune, and T56 mag close ratio trans. Personally, I think the car could use another 100 or so HP. Spring I'm likely going to swap the 3.55 for the 4.08 option Ford Performance offers. With the extra over drive gear it should be fine on the highway RPM, not that it matters that much since it's just a toy car.

[nuhale]

I have a gen2 coyote with 3.27. I didn't spec this as I acquired the build and previous owner made the call as intended to put in a 427. I decided to leave it alone as I could go back on it later if I wanted to swap gears. I've been pretty happy with the 3.27 but do notice a big gap between 4th and 5th on the TKO600. My intention is that this is not a "highway car" but in does ride really nice and low RPM at 80. I've read all the posts between the 3.27 and 3.55 and it's made me crazy as well but all in all I'm pretty happy with how the car performs as it sits.

[RedRaider58]

Thanks Guys,

I was kinda curious if someone would jump to the defense of the 3.15 since it can generally be had for a little cheaper than the others. This is likely due to the mentioned fact that it can't be changed over. Between the other two the general consensus seems to be the 3.55, which makes sense consider that is what FFR offers too. Will probably end up going that way, but am honestly disappointed at the lack of pull outs available on Ebay right now. I plan on keeping the brakes and last I looked there was one complete 3.15 and one complete 3.55.

When initially planning the build it seemed like there were tons of rear end pull outs available, now everyone seems to be parting them out individually... Unless someone else has a better idea I'll probably just approach a local scrap yard. Heck, maybe they will even cut me a deal on a rear-end and motor combo.

[BradCraig]

Thanks Guys,

I was kinda curious if someone would jump to the defense of the 3.15 since it can generally be had for a little cheaper than the others. This is likely due to the mentioned fact that it can't be changed over. Between the other two the general consensus seems to be the 3.55, which makes sense consider that is what FFR offers too. Will probably end up going that way, but am honestly disappointed at the lack of pull outs available on Ebay right now. I plan on keeping the brakes and last I looked there was one complete 3.15 and one complete 3.55.

When initially planning the build it seemed like there were tons of rear end pull outs available, now everyone seems to be parting them out individually... Unless someone else has a better idea I'll probably just approach a local scrap yard. Heck, maybe they will even cut me a deal on a rear-end and motor combo.

Parts Farm in GA posts rear end pallets regularly and that's where I got mine. I like the option because they are typically low mileage (Thanks Mustang drivers!) and provide the diff, brakes, ebrake cables, and spindles. Doing it this way also saves quite a bit of $$. One will come along, be patient. May want to call a few of the salvage yards and let them know you are looking so you get the first call.

[Richard Oben]

We have been doing FFR cars for over 20 years. In that time we have pulled a lot of gears out, 2.73, 3.73, 3.27, 4.10, and others I can't think of probably. NEVER pulled a 3.55 out, put a lot of them in, but never took one out. Live axle, IRS, big block, small block, big small blocks (408, 427), DOHC, Coyote didn't matter. Just stating the facts, Richard.

[CraigS]

I was fine w/ the 315 gear but I had a high torque 408 pushing it. My wife drives a 2015 MustangGT w/ manual trans and the 373 gear. I would change it to a 327 if it were mine but she doesn't care so it stays 373. Like Railroad says the Coyote is such a smooth higher rpm engine cruising at 23-2400 vs 2000 isn't a big deal. But I would not put a 373 in an FFR unless I got it for free.

[edwardb]

...But I would not put a 373 in an FFR unless I got it for free.

Have to disagree with that. It depends. I decided to try a 6-speed T-56 in my Gen 3 Coupe build. The ratios are different than the commonly used TKO. Upon further review (https://www.tremec.com/calculadora.php) found for 1st to 3rd the T-56 with 3.73 was very similar to the TKO with 3.55. 4th to 6th do give a slightly higher RPM, but it's negligible. It looked good on paper so went for it. After the first season driving, can confirm it's excellent. Drives and feels a lot like the TKO and 3.55 I had in the Roadster. But with a second overdrive and nicer shifting. For my driving, can't say I notice a huge difference with the Torsen that was part of the 3.73 diff. But nothing about it I don't like. I wish it would have been free... But again confirms that rear ratios have to take everything into account: Engine, transmission, tire size, and intended use.

[rich grsc]

I was fine w/ the 315 gear but I had a high torque 408 pushing it. My wife drives a 2015 MustangGT w/ manual trans and the 373 gear. I would change it to a 327 if it were mine but she doesn't care so it stays 373. Like Railroad says the Coyote is such a smooth higher rpm engine cruising at 23-2400 vs 2000 isn't a big deal. But I would not put a 373 in an FFR unless I got it for free.
Not true. You'd have to PAY me.

[mike223]

My theory on gearing is this:

1- Go look up your potential 1/8 and 1/4 mile times / speeds based on HP + weight.
2- Pick your rev limit.
3- Figure what gear it takes to bump the rev limiter going through the lights in 3rd gear in the 1/8th - and in 4th gear in the 1/4.


That gives you a pretty clear picture of where you want to be.