Transmission and axle ratio selection

[VKannan]

Hi all,

Wondering if I can get some feedback on my considerations for my rear end (and possibly transmission) ratios. Here's what I have so far:

Crate engine LS3 with TKX combination, Connect & Cruise package
Power: 430 HP @ 5900 RPM, 424 ft. lbs. of torque @ 4600 RPM
Maximum GM Recommended RPM: 6600
2.87 1st, 1.89 2nd, 1.28 3rd, 1.00 4th,.82 5th, REV- 2.56

Will be using an MPS Auto Salvage rear end and I can choose between 3.55 or 3.27 gearing.

I could ask and see if I can swap out the TKX in the package with one that has a 0.68 5th, but not sure if that's possible.

With all that being said, I've run the following numbers assuming a 315/35/17 rear tire:
Screen Shot 2022-11-29 at 10.00.54 AM.pngScreen Shot 2022-11-29 at 9.59.23 AM.pngScreen Shot 2022-11-29 at 9.59.08 AM.png

The car will see almost exclusively long highway drives or local "spirited" canyon carving (I live in Arizona). It will not see the track. I need something comfortable to drive in for a long time or to have some fun on backroad twists, which I realize are at odds with each other. Right now I'm leaning towards the 0.82 5th that comes with the package and using a 3.27 rear end ratio, but wondering if others feel like that will be frustrating on long drives and if instead I should see if I can switch for the 0.68 5th gear and 3.55 rear end so that my cruising speed in 5th at 2300rpm increases from ~65 to ~73 mph.

Thoughts? Recommendations for something else?

Thank you!

[Jeff Kleiner]

Ideal would be 2.87 first and .68 fifth with a 3.55 rear end. It will render good punch in first gear without being too short and have long legs on the highway. With a 3.27 rear a 2.87 first gear will be a bit soft on takeoff and the .82 rear will still be a little low on the highway.

Jeff

[rich grsc]

With that HP and Torque, .68 and 3:27. You won't be happy with the engine at 2300 on long cruises. Better to be around 1900-2100 RPM's. That engine will be just fine with 3:27

[Hoooper]

You definitely want the 0.68 5th, especially with those first couple gears because you are going to want the lower rear gear. Where are you buying this from? I didnt realize the connect and cruise was available with anything other than a T56. I have a T56 close ratio and LS3 with 2.66 1st, 1.78 2nd, 1.30 3rd, and 0.50 6th gear, 3.55 rear. I am pretty happy with it on the highway, cruises 70 at 1650 RPM, but I am going to a 3.90 rear gear because the early gears are just much longer than they need to be. With a 3.27 rear gear and the 0.82 5th your first few gears will be way longer than necessary and the cruising RPM will be way higher than necessary. These engines dont need to be spinning 2500 on the freeway going 70, its just creating a lot of extra noise and burning a lot of extra fuel.

[FLPBFoot]

This subject will get you a bunch of different opinions, so here is mine......

I am running a TKO with a .64 OD and a 3.55 rear end. I see the TKX doesn't come with that deep a OD. For mine, the high speed cruise RPM is nice and low 75 mph @ 2,200 rpm. The only issue with this deep OD is the jump between 4th and 5th gear. Not a huge deal but cruising around 55 mph you are either higher RPM 2,550 in 4th or 1,650 in 5th which will lug the engine.

Have you thought of going with the .68 OD and the 3.27 rear end? This will give you 75 mph @ 2,150 rpm. I think you will still have plenty of power for some spirited driving. The car only weighs 2,300 lbs. As you point out there are trade offs with pretty much every selection. Sorry to not be more helpful. Good luck.

[VKannan]

Here it is a 3.27 rear and 0.68 5th at 2000 rpm for cruising, 3000 rpm for shift point, and 6000 rpm:
Current pick - 3.27 rear with 0.68 5th @ cruising.pngCurrent pick - 3.27 rear with 0.68 5th @ shift point 3k.pngCurrent pick - 3.27 rear with 0.68 5th @ redline 6k.png

Please poke holes in this proposed setup before I pull the trigger! Thanks everyone!

[VKannan]

Sorry I didn't reply to your original question. It's from Pace Performance. Their product description specifically states "connect and cruise" but I think what they've actually done is taken the motor and ECU from that package and mated it with a TKX so it's probably not an official package, but the motor is still covered by the General Motors limited 2 year / 50,000 mile parts & labor warranty so that's all I care about. It's not searchable on their site anymore, you have to call to get details. It's right around $14,900 +/-$100 and that includes delivery, tax, and swapping out the oil pan with the C6 pan for fitment. Much better value than a Coyote package when you factor in the nearly $2000 in extra parts that you add to the factory five complete kit for a coyote install that aren't needed here.

I was trying to get modern technology and reliability for the best value. My calculations showed the gap to be around $7,000 between an LS and a Coyote, both in crate engine form under warranty. That's about 1.5x difference. Dan from FF was very convincing/reassuring that this would be easier to install than a Coyote.

You definitely want the 0.68 5th, especially with those first couple gears because you are going to want the lower rear gear. Where are you buying this from? I didnt realize the connect and cruise was available with anything other than a T56. I have a T56 close ratio and LS3 with 2.66 1st, 1.78 2nd, 1.30 3rd, and 0.50 6th gear, 3.55 rear. I am pretty happy with it on the highway, cruises 70 at 1650 RPM, but I am going to a 3.90 rear gear because the early gears are just much longer than they need to be. With a 3.27 rear gear and the 0.82 5th your first few gears will be way longer than necessary and the cruising RPM will be way higher than necessary. These engines dont need to be spinning 2500 on the freeway going 70, its just creating a lot of extra noise and burning a lot of extra fuel.

[edwardb]

I've done a couple Coyote builds and one LS build. Didn't come anywhere near the $7K difference you're describing. In fact, I was surprised how close they were to the same price after also hearing from others that the LS would be cheaper. I suspect it's true if you're doing salvage and your own build. Many more LS engines out there and agree the aftermarket parts are a bit cheaper. Again likely due to volume. But apples to apples, new to new (what I've done) didn't see a big difference. Also don't quite get the $2K add to the Coyote. Yes, you have to swap out the oil pan, and the specified Moroso parts aren't cheap. But everything else (alternator, starter, bell housing, clutch, intake, fuel components, etc.) listed in the FFR instructions are required for either. Maybe some of this comes with the package you're describing, but I doubt all. My LS crate motor build required about $500 for the starter and alternator, and a front runner system (expensive) to add A/C and power steering. Plus had to change the water pump. Those pieces bolted right onto the standard Coyote. So it's maybe not quite as simple or clearcut as you describe. 1.5X difference. No. Easier to install? After doing both, they're about the same. Very similar in fact. No need to respond. Just citing my experience.

The main reason for my response though is I've done builds with the .63 5th gear and the .82 5th gear. For what you're describing (long highway drives, canyon carving) you'll be way happier with the .63. You'll get tired of the higher engine RPM's required at cruising speeds with the .82. Tremec calls it their "road racing" ratio for a reason. It's good for track use where you get the closer ratio between 4th and 5th and RPM's and absolute top speed aren't the main concern. But for a street cruiser, it's not the best in my experience. Now a T-56 has both. Have that in my Coupe. Best of both worlds. But doesn't fit every build and adds weight and cost.

[Ford & Jeep Fan]

With that HP and Torque, .68 and 3:27. You won't be happy with the engine at 2300 on long cruises. Better to be around 1900-2100 RPM's. That engine will be just fine with 3:27

I agree with rich 100% .68 or .63 and 3.27 .

[Jim1855]

I like the .6x 5th and 3.27 in 8.8 and now 3.31 in the 2015 Super 8.8 rear ends. But mid hp & torque in the 400's at the wheels has a lot to do with that.
All of your serious driving is in the first 4 gears, well actually in 2-4, first is a launch and quick change to 2nd. Use the OD 5th as a highway cruising gear.
When running road tracks, I used 3rd & 4th with only an occasional downshift to 2nd.
Your engine hp/torque needs to be considered when selecting the rear gears.
So I guess that I agree with Rich except I used to cruise at 2,200/80mph for hours on end. My engine doesn't like <2,000rpm but was never in that range for long.
Jim

[AROCK]

I like the .6x 5th and 3.27 in 8.8 and now 3.31 in the 2015 Super 8.8 rear ends. But mid hp & torque in the 400's at the wheels has a lot to do with that.
All of your serious driving is in the first 4 gears, well actually in 2-4, first is a launch and quick change to 2nd. Use the OD 5th as a highway cruising gear.
When running road tracks, I used 3rd & 4th with only an occasional downshift to 2nd.
Your engine hp/torque needs to be considered when selecting the rear gears.
So I guess that I agree with Rich except I used to cruise at 2,200/80mph for hours on end. My engine doesn't like <2,000rpm but was never in that range for long.
Jim

My combination is 427 stroker engine, .68 TKX , and 3.55 rear gears at 70 mph I am turning a little over 2000 rpms and have plenty of power when I push down on the accelerator in 5th gear. I also went through a great deal of thought before I made my decision and I am glad I did. This combination is best for all around driving and cruising.

[GoDadGo]

Because of your engine choice (430-HP LS-3) you will find that it will be very capable cruising down the interstate at 70 MPH at 1750-2000 RPM's with no bogging issues because the camshaft specs are very mild.

As an example, I'm running 3.73's out back, with my 5th gear being a .75 O.D. while my 6th is a .50 O.D. Though my 383 has a more radical cam profile with an operating range from 2500-6500, the lack of weight allows me to cruise down the interstate at 1,750 RPM's at 70 MPH in 6th.

If you do a lot of interstate driving you will need to pick your O.D. and R.E. ratios accordingly.

LS3 / 430-HP / Cam Specs
Camshaft Type (P/N 12623063): Hydraulic roller
Valve Lift (in): 0.551 intake / 0.522 exhaust
Camshaft Duration .050 in: 204° intake / 211° exhaust
Lobe Separation (degrees): Unknown

Redbone's SBC 383 / Cam Specs
Camshaft Type (P/N XR288HR-10): Hydraulic roller
Valve Lift with 1.5 Rocker Arm Ratio: 0.520 int./0.540 exh.
Camshaft Duration at 050 in: 236 intake /242 exhaust
Lobe Separation (degrees): 110

Good Luck & Happy Wrenching!