After a lot of research and trying to keep the auto trans in my BB coupe I've decided that the best way for my build combination is to swap out my TH 400 for a TKO 600 5 speed manual.
I'm going to order the complete kit through SST and have the choice of either the close ratio .82 or the wide ratio .64 final gear.
In your experience what is working best for street and highway use.
I'll be running an estimated 600 hp/tq 496 with possible 3.36 rear end gears.
Are there any upgrades or options you would suggest getting with the complete kit?

 

What's the bottom end torque curve of that engine look like? I am running 3.70 gears with the 0.64 OD behind a 450 hp 400ci small block. The engine didn't much like anything below freeway speeds with my Q-Jet. With TB-EFI it's stretched the bottom side of the powerband a bit, so I can cruise at 45-50 in 5th as long as I'm mindful of not really loading the motor up.

That said, the 3.36s will stretch the usability of 4th out in your case a decent amount. Could be OK. If you do LOTs of highway driving, the 0.64 would be better. 0.82 if you're mostly doing <60mph.

Better yet, the T56 options will give you an extra gear right in the middle. If I could do it all over again, I'd heavily consider a 6-spd.

 

I really like the .82 in mine with the 3.36. Keeps 5th as a very useful country road gear, rather than highway/freeway only, and makes it a usable gear on high speed circuits. Having said that, a 600hp 496 will probably have more than enough torque down low to turn the 0.64. If I were putting a tko in my old f250 (and I plan to sooner or later) then I will go with the 0.64 for low rpm highway running. Mostly depends what you want from the car.

 

My 6t8 has the .64 overdrive with a 3.73 , that being said the .82 would have been a better choice for me. The .64 is useless on the track and with my engine set-up any acceleration in 5th under 55mph it just chugs and backfires, AT 70 it's fine. T

 

With the 3.36 rear, get the .82 OD. I have had a .62 OD Tremec 3550 with 3.36 gears and 5th was only usable at 65+ mph on the highway. The drop between 4th and 5th was too large.

Which, is why I swapped to a T-56 Magnum close ratio for my 496 BBC swap. Gear ratios:
2.66 1.78 1.30 1.00 .80 .63
5th is great for two lane roads and 6th for the highway. 2000 rpm in 6th will give me ~68 mph.

Think about your engine as well. Will it be happy at 2000 rpm (assuming carbed vice EFI)? A 600hp 496 may be happier at 2500-3000 rpm cruise.

Gear calculator:
https://americanpowertrain.com/p-160...alculator.html

Another calculator:
https://www.hurst-drivelines.com/hdc-rpm-calculator-2/

With 3.36 rear, .64 OD, at 65 mph you will be turning 1737 rpm. Probably too low for your engine.

 

You definitely have a decision to make. There is no wrong one. You just have to decide what makes the most sense to you. It has everything to do with how you will use the car. My car is strictly street. I wanted the overdrive for highway cruising. It's not fun to go screaming down the highway at 3000 rpm. I went with the .64 and its perfect. Most of my driving I treat it like a 4-speed. On the highway I drop it into fifth and loaf along at about 1900 rpm. ( I have 3.55 rear gears. )

 

I have 3.70 rear and .64 5th and right on the edge. I wont hit 5th until well over 60 in most cases. HP 383 450+ with a fairly flat torque curve. With 3.36 I would go with the.82 for sure.

 

I could not agree more! I see 3 scenarios for going with the .82 OD:

1. A rear 3.08 gear or less in the rear end with the current 4 speed, maybe
2. You race on a track where the 5th gear is really not an OD to reduce revs or save gas
3. A cam in the engine that does not operate well below 2,000 RPM which could cause drive ability issues on the highway if the revs were below 2,000 RPM.

Personally, for most people who are looking for an OD on the street, the goal is to reduce revs for highway cruising which is the real intent of an OD gear, not to be used as another gear for acceleration. Just about any V8 can accommodate low revs with zero issues. Any V8 will make sufficient torque to operate with a steep OD gear. The OD gear issue is really limited to low power 4/6 cylinder engines and even just about any 6 cylinder can handle a steep overdrive gear. My stock L-82 with 3.70 gears could easily pull revs from 1,500 RPM and up and would cruise all day at 1,700-1,800 RPM in 4 th 1:1 and this from a 290-300 Gross HP with a cam not known for low end torque.

I have to chuckle when folks have a BB 502+ engine and ask if the .64 OD will be compatible with the 600 ft/lb motor...the freaking motor could pull a freight train from a dead stop without sweating and they are worried about a .64 OD....NOoooo

My 10 C6Z06 with tons of HP and torque cruises in 6th OD .50 at 1,750 RPM @80 MPH all day long...when I want to accelerate I drop it down to 4th 1:1 just like any car and effortless pulls away......FAST. And no it is not because of the fuel injection system...my carbed OEM L-82 would do the same with no stumbling at all


When I get a 5 speed for the L-82 355 with AFR 180 heads, 10.2:1 compression, and Howard's roller cam (219/225 duration, Lift .525/,525, LSA110, operating range 1,500-5,600 RPM) with 425+ Gross HP and tons of mid range torque which it was built to provide as you can see from the specs, there is no question that the only OD I would select and want is .64OD, hand down, zero dilemma. If I need to accelerate, drop it down to 4th 1:1 and off you go just like today with the OEM 4 speed.

 

I agree too - and you raise some points that I'd like to emphasize some of my own thoughts on.

I've seen this argument a lot and I really wonder how often this is true. With a 3.36 gear and 27" tires, 6000 RPM would take you to 143 mph in 4th gear. I wonder how many people are driving C3s and seeing 145+ regularly on race tracks...

I don't have much experience w/ engines beyond my tiny 400ci, so I don't want to cement my feelings here as truth, but I tend to agree with you. There's a LOT of motor there.

On this I have to disagree a little - my engine is similar to yours and a bit more CI. The carb didn't stumble but it definitely didn't feel right. Carbs can't be as well-metered as an EFI throughout the powerband, as the signals they use for metering aren't perfectly efficient everywhere and there's going to be somewhere between 2, maybe 5 max variations of passages that determine fuel metering. You can't be optimum everywhere - EFI spreads the control much further across the powerband.

Like you said, probably not a huge deal with a big-block, but with my small-block there was a marked difference in engine behavior between running carbed and TB EFI in this particular scenario (50mph in 5th). I could, of course, live with downshifting to 4th and that's what I found myself doing quite a bit more often before switching to EFI. But that said, too, the places I did ~50mph on required paying quite a bit more attention to adjusting traffic speeds. I'm in a traffic zone. If I was cruising at 50 in the carbed variant and could gingerly adjust my speed up after negotiating a white-knuckler, maybe my opinion would be different.

(I'm trying not to get too angry thinking about the drivers in my area. )

 

I have no doubt you are correct with the EFI being better for fuel metering...no question. My experience with the OEM L-82 motor was that at just about any revs above 1,000 RPM, my stock L-82 had no issues at all cruising at 1,500-1,800 RPM with no surging, stumbling, hesitation...None. I have no reason to believe that the current 355 L-82 described above could do the same easily with the AFR heads and Howard's Roller cam easily based on the cruise characteristics now. Would it be better with EFI? Of course, but the carb system currently on the car should operate flawlessly based on the same cruise behavior now with the 4 speed....same as the OEM L-82....no stumbles, hesitation, surging etc...it pulls with no issues from 1,000 rpm in 4th 1:1 effortlessly....

I have spoken to a few carbed C3 owners at car shows with OEM motors and built engines with .64 OD 5 speeds and every one reports no issues with low revs on the highway. I do know some C3 motors with cams that don't like low revs with the 4 speed and 3.70 gears and they cannot get their cars to pull smoothly from 2,000 rpms...those guys would have issues with a .64OD however....more a function of the cam then the OD....

 

I think that regardless of motor you will find that the spread between the 1.0 4th gear and the .64 5th gear is just to darn big. Why do I think this? After a lot of research I bought a .64 TKO 600 which sounded great with my 4.11 rear gears. Real world was miserable, I finally bit the bullet and put in a .82 5th gear which is a pleasure to drive. Downside of the swap is that not only do you need a new 5th gear but also a new mainshaft. The mainshaft was very difficult to find in the U.S. Total cost was $500 for the gear and mainshaft plus the hassle of pulling the trans. If you really want something like a .64 start looking for a 6-speed which other than physical size would be ideal.

 

With my setup, <55-60mph meant going down to 4th unless you were really easy on the throttle.

Going to the EFI got it so I could do as low as 45... I think if I was really cruising and not trying to accelerate hard, I feel like I could even hold a steady 35-40 (though I never would). That would have been impossible with my 09 Z06!

In my area, the highway is typically 55+. My commute is usually on expressways, which are 45-55 and put me right in the zone where it sucked with the carb. On those roads in the Z06, I would be in 5th (0.75).

Anyways, I really like expounding on this subject and hope it's helpful to the OP.

 

My 383 535 HP engine is cammed 236/242 @.050. I have a 4.11, Close ratio T56. It likes to cruise over 2200 RPM. The combination is what matters. I'm happy with mine. Over 20 MPG @ 80 MPH on the interstate. I don't really see a need for a .64 with a 3.36 rear. It is pretty cool I helped 3 of the posters on here with design criteria on their builds!

 

I am one of those mako!!! You were spot on with the cam for my motor and what I wanted...thank you again....

I actually like the .75/.50 in the 10Z06

 

I have a 350+ , carb, roller motor 400 hp and 400 tq. (in my 71)

I have the .64 overdrive and a 3:55 rear. I feel this is the best of both worlds. I don't race, but do have fun.

I cruse all day long with no issues and love the gas mileage.

I shift into 5the gear at 50 to 55 mph. When I go upstate and cruse at 70 the engine is very happy - When I'm on the Island and cruse at 60 the engine is ok with it but acceleration is a little sluggish.
I can drop down to 4th and run as normal if I need a fast pass.

At 60 with the 3:36 in 5th I would guess around 1440 rpm. I'm at 1500 and have no issues.

It only takes approximately 20hp to push the car at 60, so I think you should be ok unless the engine is radical.

 

Not a vette, but i run the .64 OD behind my 496 in my 67 c10. 3.73 gears with 29” tall tires.

I’m glad I don’t have the .82. Big block torque means if i hit an open back winding road I can chug along in OD. Most times I run up to 4th on all the back roads and leave 5th for the 4 lanes. If you only ran at 60-65 you might want the .82 but let’s be honest every drives 70-75.

Honestly it’s the best mod I ever did to the truck

 

My 5 speed has a .67 5th gear. I haven't installed it yet, but in looking at projected rpm at various speeds I think a .75 5th gear or thereabouts would be ideal. I don't recall seeing any five speeds with a .75 5th gear which seams weird to me.

 

Earlier this year I installed a TKO600 from SST with the 0.64 OD. My car has a stock 3.70 rear and plain vanilla Goodwrench 350. Terrific combo. 5th gear comes into play around 50 mph or so. Car runs great all they way thru the RPM range.

I liked the SST kit and have a post on here with my thoughts and tips for install.

And I'll echo some previous comments from other posts - "best money I've spent on an upgrade".

 

This ^^^^^^pretty much describes what i would expect from my 355 and 3.70 gears and a 5 speed with .64 OD....on the street. This also mimics what GM did with the F body cars with a WCT-5 in the 80's and early 90's. The V8 cars got the .63 OD since V8's even back then have more than enough torque and the V6 cars with less torque came with the .75 OD as one who understands OD's would expect.

 

GM F body V6 cars with the WCT-5 speeds came with the .75 OD again due to the lower torque of the V6 engine. V8's came with .63OD which to me is the ideal street V8 OD.