| PROJECT: Impala SS "Fast Forward" LS4 6T70 conversion |
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| TBM Impala SS Project Fast Forward |
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Hey guys/gals. This is the little slice of TBMSport.com that we carved out to share the progress of putting the 6 speed automative 6T70/75/80 into our latest project vehicle, a 2008 Impala SS.
There has been a lot of internet chatter on it all over the place, but a lot of it has been scattered and partially correct...with a healthy sprinkling of internet trolls pissing on the idea from the clueless sanctity of their couch and keyboard. So, we'll start off with giving you the bulk of the accurate information and facts that has been gathered and confirmed.
If you've followed TBM over the years, you've seen us go from simply offering 04-06 Pontiac GTO SAP grilles, custom tail lights and front bumper repair kits, to Trailblazer SS dual exhaust valances and exhaust systems, to our latest system of products: GM 6 speed automatic conversion systems.
After being the first to perform two successful 6 speed swaps in our Trailblazers and proving that you don't have to give up cruise control, ABS, 4WD, the time came to examine and explore other GM engine's adaptation of a 6XXX transmission; from old Pontiac V8's and Buick turbo V6's to Ecotec's, LT-1's...in every conceivable GM platform. Having provided tech support/parts/programming for a whole bunch of crazy one off LSX 6L80/90 project vehicles (wrapping up first Hummer H3 Alpha conversion), it was time to officially spread the love with the transverse mounted and non LS-V8 groups.
You may have noticed that our Project Blue Flame page is down (4200 I6 Trailblazer turbo 6L80 project) Sadly, there were some engine failures and garage space reshuffling involved and our '08 Trailblazer is no longer with us. So proudly stepping up to fill the shoes of "what's new" is our latest project acquisition, 2008 Impala SS.
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We have learned what we need to in order to convert an LS4 W-body to a 6speed auto using the 6T70 transmission. And with that, the Imp SS has moved on to a new home, replaced by the 1994 Corvette project vehicle.
NOTES for DIY enthusiasts:
We have determined that the only sensible way to approach this is to make a new 6TXX case have that can accommodate the Northstar and GM Metric engine bolt pattern (3.8, 3800, 3.1, 3.4, 3400, LS4, etc.). We worked it all out and found a source to make that happen for a reasonable project price of under $1k. BUT there are several other issues. Due to the taller and wider transmission case that LS4 motors will require the following:
-a change in inside exhaust manifold (possible custom)
-custom cross over pipe
-custom mini starter
-change in K-member and axle shaft (2012+ Impala)
Critical key parts list (this will be updated as new information surfaces):
TBMSport T42 (4speed) -T43 (6speed) interface module and harness. This allows you to keep 99% of your harness as it left the factory.
GM OEM drivetrain parts. As GM saw fit to add the 6T70 to the Impala (with the 3.6 DOHC DI V6) in 2012, most of the drivetrain goodies are there straight from your local GM dealership or junkyard. Unfortunately, the transmission itself will not bolt up as the high feature V6 doesn't use the LS4 bolt pattern. Prior to that model year the only 6TXX transmissions that had our bolt pattern were weak Ecotec 6T45/50 transmissions. That would have meant buying two different transmissions to make one fit ours. But never fear!! There is a perfect fit. 2013-present Buick Regal (GS) and Malibu turbo Ecotec M7W-6T70 transmissions have the LS4 bolt pattern and higher torque capacity. Best part...as of now the transmissions are dirt cheap used! This makes the oil pan starter solution a win!!
GM used (at least) 3 different engine cradles for this generation W-body Impala/Lacrosse/GP. One for the pushrod V6's, one for our LS4, and another for the new 2012-14 Impala DI V6 for. As luck would have it, the mods that were made to accommodate our LS4 are different on the 2012-14 (passenger side). And the mods that allow the 6 speed transmission to fit are dramatically different from the 4T6X (driver's side). Current thought for a solution is to offer a bolt-in /weld replacement subframe component. The part of course would allow either transmission to fit, so that it doesn't become a one way mod. But until two subframes are side by side to measure and consider transmission contact/interference, we cannot definitely say.
Of course after that physical fitment is addressed you're then looking at a TCM control module and harness situation that is going to run about $1300 and some calibration time for the specific engine (assuming you don't have an E67 LS4 vehicle). It is assumed that the GM metric V6's and N* engines will need to have all the same issues address to reroute exhaust around a different shaped transmission.
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| 5.3L LS4 |
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| TBM T42-T43 Interface Module & Custom Programmed ECM |
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Ok...let's get to the important 6T70/75 conversion details:
1-The easiest conversions will be '07-09 because they use the 58X ECM system which is critical for the 6 speed transmission to network with. Hopefully we can develop a cost effective solution for you '05-06 guys, but quite honestly, the cheaper way is to just swap the ECM, harness and engine to a newer model. Yes, there is a stand-alone system out there. No, it is not cost effective or readily/universally available because it requires custom and specific programming to YOUR car, transmission, driving style, engine components..PLUS the additional hassle of rewiring your existing harness so that your ECM and BCM don't freak out. So, we stick to GM systems and everyone plays nice-nice on your car's network. Plus, your vehicle is easily serviceable. Keep your ABS? CHECK! Factory Onstar and remote star still working? CHECK! TapUpTapDown (including ImpSS)....Optimistically HOPEFUL! Will I have to hack my harness and make a lot of one way mods to my car that exceed the value of the car? NOPE! That's not how TBM does things.
2- Fiero.NL has been a remarkable resource for helping establish some parameters on what can/can't be done for swapping into our cars. If you haven't check out his webpage, do yourself a favor and do so. However, unfortunately, because a Fiero is ancient technology compared to the LS4 W-body, there are a LOT of creative licenses that can be exercised when putting an LS4 in a Fiero compared. Beyond the similar engine layout arrangement, almost nothing else is transferrable or comparable. What works easily for those applications requires modifications to our application.
3- The main issue of starter relocation is well documented. Two solutions (oil pan starter vs. custom case adapter) have been determined. Parts production and release scheduled within 3 months.
4- Critical key parts list (this will be updated as new information surfaces and is confirmed):
TBMSport T42 (4speed) -T43 (6speed) interface module and harness. This allows you to keep 99% of your harness as it left the factory and keep your original vehicle features and functions.
Miscellaneous OEM GM drivetrain parts! As GM saw fit to add the 6T70 to the Impala (with the 3.6 DOHC DI V6) in 2012, most of the drivetrain goodies are there straight from your local GM dealership or junkyard. Transmission mount, axles, cooling lines, etc.
The 6T7X transmission: Unfortunately, the more widely known 6TXX transmissions themselves will not directly bolt up to the LS4 because the High Feature DI V6 doesn't use the LS4 hellhousing bolt pattern. Prior to 2013 model year the only 6TXX transmissions that had this bolt pattern were weak Ecotec 6T45/50 transmissions. That would have meant buying two different transmissions to make one fit the LS4. Plus you'd have a weak and small torque converter. Additionally, the 6TXX transmissions came in torque ratings and case size configurations. That makes the initial hunt for the right one that fits our application quite a chore, not to mention the wave plate failure issues. If that weren't frustrating enough there are different TCM modules which will require specific reprogramming. More on this later in time.
But never fear!! We've found your perfect fit. 2013-present Buick Regal (GS) and Malibu turbo Ecotec (M7W) 6T70 transmissions have our bolt pattern and higher torque capacity. Best part...as of now the transmissions are dirt cheap used! This makes the oil pan-starter solution a WIN!!
You're welcome! 
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The engine cradle/frame. Sadly, it was discovered that GM used (at least) 3 different engine cradles for this generation W-body Impala/Lacrosse/GP. One for the pushrod V6's, one for our LS4, and another for the new 2012-14 Impala DI V6 for. As luck would have it, the mods that were made to accomodate our LS4 are different on the 2012-14 (passenger side). And the mods that allow the 6 speed transmission to fit are dramatically different from the 4T6X (driver's side). Current thought for a solution is to offer a bolt-in /weld replacement subframe component. The part, of course, would allow either transmission to fit, so that it doesn't become a one way mod. But until we have the two subframes side by side to measure and consider transmission contact/interference, we cannot definitely confirm a simple engine cradle solution.
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| 2008_LS4_Transmission_Mount_part |
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| 2008 W-Body V6 Engine Cradle |
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| 2012-14 Impala Engine Cradle |
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Cross over pipe. The front cylinder banks will no longer have a convenient hump between the transmission and throttle body to funnel exhaust fumes. There is approximately 2" of space between the throttle body and top of the 6T7X transmission case. An oval replacement crossover pipe solution is pending.
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