Which Tremec 6 Speed Ratios?

[jpndave]

My project is a 1973 240Z I’ve owned for 30 years, my high school car. I just brought this old girl in to give her a full makeover. The plan is a Pro-Touring/G-machine type build with LS3, Tremec T56 Magnum 6 speed and possibly a Ford 8.8 in the rear. I will be doing full upgrades of chassis, suspension, paint, the works. She needs to be comfortable so power windows and locks and a replacement HVAC including A/C that actually works.

 

The company I am with is a conversion manufacturer for Jeeps mostly, Novak. My Jeep JK is linked below. We have all the tooling to do the swap components including manufacturing shafts, splining, etc. I may do a run of parts for the driveline if need be. Let me know if any of you have interests. Not sure where the best place to post all that up would be. I’d like to start a build thread and would appreciate input.

 

My current question centers on the transmission selection. I have an LS3 for mock up but need to buy the transmission. I have line on a new T56 Magnum but am unsure of which ratio and model for sure. Is the shifter location in the standard T56 Magnum in the correct location (26.6” from the rear face of the block) or is the XL a better choice (34.9” seems way too long)? Which ratios are recommended? This won’t be a full time track car. I would like to be able to do some track days and maybe autocross events but primarily a driver. Rear end ratio can be whatever is best. Highway mileage and a nice cruise rpm would be a huge plus. The three ratio choices are:

1. 2.66/1.78/1.30/1.00/.80/.63

2. 2.97/2.10/1.46/1.00/.74/.50

3. 2.66/1.78/1.30/1.00/.74/.50

5^th and 6^th can be swapped independently if necessary and don’t have to be together, option 3 is showing that change to the taller first gear set.

 

Thanks for any input you can offer.

Edited December 20, 2014 by Dave O

[Meatwad]

Going Naturally apsirated or forced induction?

[jpndave]

Going Naturally apsirated or forced induction?

Normally aspirated at this point.

[Phantom]

Assuming you're running an NA motor I would opt for option 2 with the .50:1 OD.  A couple reasons:

1) The car, with a 3.69/3.70:1 R230/R200 and stock OD tires will cruise all day at 60 MPH and 1500 RPM.

2) That set-up will allow you to pretty much just run 2nd gear doing AutoX work.

Before you buy the Tremec also decide if you are going to go with all new gauges or stick with the stock gauges.  If all new get the Tremec in it's standard configuration with an electronic speedo output.  If stock gauges option it with a mechanical output.

Have you determined your desired tire sizes yet?  That will be affected by the brakes you choose, the suspension you choose and whether or not you plan on tubbing the rear or going with some kind of flare or wide body kit.

I've been running my LS1 with an option 2 T-56 for 11 years now through a 3.70:1 R200 and 225/50-16 tires. I kept the standard electronic output and stock gauges so had to install CableX box to translate for the speedo.

My son has a '73 with a 2000 LS1 with head and cam work putting 380 HP to the rear wheels running through an R230 LSD and 17" wheels & tires.  He's putting a Reaction Research wide body kit on it to be able to handle 305's in the rear. He's running 245's in the front. Car is light and scary quick - but not done yet.

Edited December 15, 2014 by Phantom

[socorob]

I think I have 2. A 2004 gto T56. I have an R200 with 3.54. I'll tell you 1st gear lasts about a second and it's time to shift. I would go with 1 and swap 6th for idling down the interstate.

[jpndave]

Thanks for the reply Phantom. I like the steep overdrive idea a lot. My Jeep JK cruises 1500RPM/60MPH and 2000RPM/80MPH quite nicely. The lightweight Z would be no problem at all. I am more concerned with the rest of the box as the overdrive can be changed out if needed. It will be on 17" or 18" wheels, thinking 245 up front and 295 or 305 out back. Thinking Subtle Z front and YZ rear. I'll probably go with the standard GM speedo signal and change the gauges. I'm more concerned with the 1st through 4th ratios as these are more fixed and would be extremely impractical to change.

[jpndave]

I think I have 2. A 2004 gto T56. I have an R200 with 3.54. I'll tell you 1st gear lasts about a second and it's time to shift. I would go with 1 and swap 6th for idling down the interstate.

That's what I'm worried about, well that and the spacing 1st-4th or so.

[Phantom]

Dave,

The Subtle Z/YZ combo is what my son has.  He also has the Option 2 T56.

Here's my experience with the Option 2 T56 & 3.70:1 R200 LSD.

1st gear is my start gear for hills, around town, etc. I then shift to 3rd or 4th unless I'm in a real hurry and then I go through them all.  I enjoy shifting so that's most of the time. 1st is good to 25-30 MPH.

If I'm drag racing I have to feather 1st to keep it hooked up.  Even though my 280 weighs 3,000 lbs I'm running 225's so the drivetrain overpowers them.  Unless you be sure to get some REALLY sticky tires you will have a similar issue even with the 305's.  My son is running 275 BFG all-weather radials and he smokes them at the drop of a hat. They aren't very sticky.

My car holds in second gear at full throttle so I expect yours would too.  Obviously the rest of the gears hold.

Any kind of road racing pretty much never gets down to 1st so it's 2nd-4th that count.  My ratios work well for my set-up.  I've done hill climbs, autoX and even run the combined infield and oval at the Texas Motor Speedway Nascar track. No complaints.

My car was designed to be primarily a daily driver - thus it's heavier than other cars because of dynamite, a heavy house carpet, all leather interior, a 500 watt, 7 speaker sound system and AC. Any excuse I get to drive the car it's on the road unless we've had our winter snowfall then I put him up to avoid the caustic deicer they use up here on the roads.

 

Have you thought about what you are going to do for lighting? New gauges will eliminate the dark dash syndrome of the early Z's.  I'm installing new, higher wattage lights in my stock gauges this winter.

I also have an HID light kit to upgrade my headlights which sorta glow at night. I think there might be LED options for that out there now. Check around.

I'm also planning to get the LED conversions for my taillights, turn signals and marker lights.  I want the car BRIGHT at night and I really want my brake lights to show.

[jpndave]

Another possibility would be to go lower numerically on the rear end, say 3.08 or 3.31. If that engine can pull my 5500lb Jeep on 37" mud tires at 1500 RPM, the Z should be cake even at 1200 RPM. Then the launch would be good with the lower first and even better on mileage. The two things I would be concerned about is first that the cam wasn't wild enough to cause problems cruising that low an engine speed. Second that the gear spacing would work for performance.

[jpndave]

I updated the ratio list to show the third mixed option.

 

I am leaning towards Autometer gauges for several reasons. The two main are a preference for the electronic speedometer and I want to lose the Amp gauge for sure. I know you can put the later 280 volt gauge in there but may just opt for a full set.

 

I plan on keeping the car around 2300 lbs. with some lightweight pieces, such as the front clip, bumpers and hatch. The new power windows are lighter than what is in there now. The heater and aftermarket air I just removed were heavy. One piece units with the small compressor won't add more than maybe 20lbs. I have a compressor here on my desk we are designing brackets for that is very light ~12lbs if I remember correctly. I want a sound system in there too but have speakers with composite cones and neodymium magnets that don't weigh much and sound great. Same for the sub. Cruise weighs ounces with a drive by wire throttle. Lizard Skin insulation/sound proofing is very light. You can have both I think if planned correctly. Some will cost a bit more.

[RebekahsZ]

I vote for option #1.  Go with a 3.54-ish diff ratio.  I have option #2 in my car.  I wish 1st was taller and I wish 6th was lower (so I could use it).  Also, with option 2, I am out of both 1st and 2nd gears so fast that I really have to concentrate to keep from hitting the rev-limiter.

[Phantom]

Guess it all depends on how well the tires stick and the drivetrain holds up.  If you're talking basically a stock LS3 I don't think you'll have any cam "loping" issues at low rpm cruising speeds. If I'd had the option for #3, in retrospect, I would probably have opted for it. Any of those ratios, though, will have you in 4th gear in the quarter.  One point with my car is that I get no wheel spin with the 225's at full throttle in the 2nd gear with the 2.10 ratio. Thats with 325 HP at the rear wheels and about 1,740 lbs on the rear wheels with my weight included. You'll have more HP and less weight but, hopefully, wider very sticky tires.

I know a lot can be done to lightweight a Z but I don't think 2,300 lbs is going to be attainable if you really want the car to be a daily driver. When I first did my LS1/T56 conversion it added 30 lbs to the car. The interior, sound deadening, and sound system added another 170 lbs.  If you're really careful your net gain going with quality stuff might be held to 130 lbs. Then you have to figure if the wide-body items are really going to reduce the overall weight of the car by much.  Go to a truck stop and get the actual weight of the car now and then start asking weight questions and do the math.  I'm thinking you'll end up more in the 2500-2600 lb range.

[socorob]

You must be running some crazy sticky slicks! I can burn my 200 treadwear tires at will in 1 & 2, and into 3rd if I'm getting onto it. I'm only running 245's though, so my tires aren't very wide.

[jpndave]

Getting a starting weight is out of the question now. I well underway doing the disassembly. Final weight will be no problem. I have access to a four pad race scale set. I hope the 2300lb. range is doable. I be trimming weight anywhere it's even semi reasonable keeping in mind the final goal.

 

This will be a cammed LS3 minimum. Should be 500, maybe even 600hp. They respond so well to a cam and some port cleaning. My Jeep engine runs very strong with similar mods. It is slightly noticeable at an idle and really comes on strong. I won't use the VVT on this project so I'm sure the idle will be quite a bit more noticeable with a similar profile. I want a faster response than the VVT/Auto will allow. Again, I'll be lightening up the rotating assembly as much as can be done semi reasonably.

 

I'm still torn on the gearing configuration and don't want to get it wrong. The steep 6th sounds like a good choice for mileage, not sure on the rest. Does anyone know if the 26.6" back from the block face is correct for the shifter spacing?

 

Thanks for the input,

 

Dave

[jpndave]

Maybe a better question would be what speeds do I want to make shifts at? ON a road course? In a drag race? Autocross speeds? Road Driving? Maybe 1st to 50mph, 2nd to 70mph, 3rd to 100mph, 4th to 140? 5th and 6th for cruising at lower rpm?

[RebekahsZ]

Depends on the tire diameter. I built my car with a 2006 GTO LS2 and MN12 version T56. I started with 26" slicks and a 3.90 diff. I needed to shift to 4th before 600' (needed 4th to finish the 1/8-mile). But it was great for 1/4-mile (right on the 6000rpm shift light in 4th at finish line). But I don't get a chance to run 1/4-mile very often. So I went to 3.54. That moved my 1/8-mile rpm limit in 3rd from less than 600' out to about 640' and for a year I just rode the rev limiter thru the timers. Went to 28" slicks and after 6 passes, I'm not sure what rpm I am at when I cross the beams in the 660' but it's less than 6000. With 3.54 and 26" slicks at 6200 rpm in 3rd I'm at 100mph. In 4th with 28" slicks and a 3.54, at 6000 I'm at 148. With 26" tires and 3.90 at 6000 in 4th, I'm at 126. I have found the gear-to-rpm modeling programs on-line to be pretty accurate.

[jpndave]

I'm thinking 295/35-18 so 26" with maybe 3.73 gears but that can change as needed. Shift points would be a little higher than that with the cam I am looking at. I'll check out the rpm modeling and see what that yields. Thanks for the input.

[RebekahsZ]

When looking at the gear calculator programs, i found the 3.70 gears fell in between any of my useable ranges. Same with 3.36. It pretty much came down to either 3.90 or 3.54. While talking about cams: I hate the cam that's in my LQ4-swapped truck. While at WOT the cam makes about 60hp more than stock, it makes lots of fumes at idle and really surges at parking lot speeds making it really hard to drive smoothly. I rarely drive the truck at WOT; it's a daily driver and a tow vehicle. Conversely, my LS2 Z makes more horsepower than the truck even with a factory cam and is smooth as silk from idle to WOT. My Z spends a lot of time at WOT. I may at some point put a stock cam back in my truck. I don't know the specs on the cams. I REALLY like how driveable my Z is. I may never want to trade its driveability for the cheap power a cam can provide-will likely add nitrous instead. The truck sure as hell sounds better at idle, but few people in my daily life would even know what that wicked idle means. And on a road course, I'm not a good enough driver to use all the power that she currently makes (400hp).

Edited December 19, 2014 by RebekahsZ

[260DET]

Five speed Tremec is what you need, lighter and a much nicer shift.

[jpndave]

Five speed Tremec is what you need, lighter and a much nicer shift.

The five speed would be lighter ~ 100lbs as apposed to 135lbs for the T56 Magnum. Strength and shift quality not so much. The T56 Magnum is a basically TR6060 in the T56 case. The shift quality comparison would probably be valid compared to the earlier T56. Thanks for the input. At this point I just really want to find the best solution.