superman22x

Disclaimer: Purists, I recommend you hit that back button now, it's for your own good! You won't want to see the carnage unfolding here.

Hello fellow Rennlist members,

I've been working on a project for a month or so now, I'm going to try and keep this one documented through the process. What I started with was a 2005 tiptronic Carrera S (purchased right from a member here). It had a loud ticking sound, suspected bore scoring. Car arrived and I took it for a short drive. It ran fine, but it was clear the engine was not healthy. Rather than driving it until the rods clearanced the side of the block, I decided to drop it and sell it as it was; a rebuildable core.

I know many would say this is a waste, it's going to be more expensive, balance will be gone, etc. I have some advantages here: 1) Being in the Detroit area, LT parts are very plentiful, as is all the expertise I could ever need. 2) I have a machine shop in my garage, so any of the expensive pieces, I am making myself. I will have a lot of time invested in this project by the time I'm done. But I think I will have less cash invested than many have in a rebuilt 3.8L. The LT engine weighs similar if not less than the 3.8L, so weight balance will be maintained. And most of the weight of the engine is down low (none of those pesky cams in the heads), so no loss there either.

Here is the car, it's got 130k miles, it's in decent shape, some paint blemishes here and there. After I'm done, I would like to see what I can do to clean up the paint and headlights a bit. This car spent a good part of it's life in the California sun, the headlights, rear carpet, and rear quarter glass weatherstripping have their scars to prove it.







Now onto the plan for this car. I never intended to get a Tiptronic. They have their place, just not in my garage. So out it goes (still have it for sale!). Fast forward to today, I have a G96 in the garage and an LT1 sitting next to it. There are lots of threads out there of LS swapped 996s, and a number of LS swapped 997s. I wanted to try something a little different. I love the way the LT engines drive, I've even gotten 26mpg in an LT4 Camaro on the highway! The LT engines are easy to find, and the LT1 is identical to the L86 minus the intake, oil pan, and accessory drive. They are about the same price as an LS3 of low miles, and a bit better performance.

Here is the engine as it arrived. 5,000 mile engine from a 2016 Camaro. This engine had something dropped on it when it was in storage, cracked the intake and chunked one of the intake ports on the head. I still need to get that welded and then I will flycut it myself. I've never fixtured a head on my mill, but I'm confident it will be fine.







First step after getting the engine and transmission, was to start working on mounting them. My first attempt was going to use the Porsche flywheel with an LS4 starter. The LS4 starter mounts to the transmission bellhousing rather than the engine. The advantage being, I could use the Porsche ring gear and eliminate the need for the 14" GM flywheel. This could reduce my bellhousing thickness by 1". Unfortunately, once I got it all together, I found the LS4 starter would not work, it's length interferes with the axle outputs, and the size interferes with the body of the car. In the process of testing this, I built a 1/2" bellhousing adapter. The LT1 uses two pins to locate the crankshaft center line, and the G96 uses two dowels. I can't drill all the holes on my mill in one fixture, but I was able to bore the 4 holes needed to keep the shafts concentric in one fixturing. The bolts are only there to keep the parts clamped, never rely on bolts to hold something concentric. I bored the holes for the pins and dowels so that they would be dead on. Drill bits tend to wander and drill over their nominal size, they are good for heavy material removal but that's about it.

Together at last:


Notice, I made a mistake drilling the holes above the pins... Not sure what I did wrong there, asleep at the wheel I guess. No big deal.

Here is a shot clearancing the center for the Porsche flywheel. I had to use a trepanning tool for this. Took a little while, and made some unearthly squealing noises. The bar I used was way too small for this really, too much deflection. And I ran out of my favorite Aluminum cutting oil... WD40. I made a MUCH larger version to cut the 14" hole for the second piece of this adapter plate, that will be shown in the coming weeks. I actually made that from the 10" plug I cut out of this bellhousing plate.




That's where I'm at with the bellhousing build so far. I just ordered a 1" sheet of ATP5. This is a cast aluminum Tool & Jig plate. It's not nearly as strong as 6061, but it doesn't need to be. The bellhousing is only cast aluminum afterall. The advantage to the cast aluminum tool and jig plate is it's stability and flatness right out of the package. It's flat within 0.005" and will not move at all (no internal stresses), which is important when cutting a 14" hole out of it. Doing it again, I would use the same aluminum for the 1/2" plate. The plan is to bore the LT1 pin locations in the new plate and use an extra pair of LT1 pins I have to locate the two plates concentrically while I pin and bolt them together. permanently. This will net me a 37mm thick two piece bellhousing adapter. If I had myself a big ol HAAS CNC, I would have bought just one plate and cleared the inside out. Gotta work with what you have though.

After getting the drivetrain mated together, it was time to test fit it. I already made a set of mounting wings for the heads. Same as you have seen in other LS swaps. I only had 1/4 aluminum for the mockup pieces. Enough to hang the engine and get hole locations figured out. I have some 3/8 plate coming for a more permanent solution.

Here is the LT1 in the car. I had to clearance the rear cross member just like in the LS swaps. Some have said that is not a critical bar because it's just sheet metal. It definitely is critical, it's boxed and punch pressed for strength. I will be welding in a new cross brace when the engine is completed. I also swapped out the camaro oil pan for a wet sump corvette LT1 pan. This gives the needed ground clearance.



That's it for now. More to come on the flywheel soon. I picked up a super low miles 991.2/991 GT3 flywheel for cheap. It's a dual mass/twin disc made by LuK. Nearly identical to what is used in the LT1/LT4/LF4 cars, so I think it should be just fine. My plan is to simply make an adapter that bolts to the LT1 flex plate and has the 10 bolt porsche bolt pattern formed into it. I like factory parts, and I like the idea of maintaining an OEM dual mass flywheel. It will keep the total flywheel mass similar to that used in the LT1 from the factor ~65lbs. The GT3 flywheel assembly is ~55lbs.

superman22x

As far as the Tip to manual swap - That should be easier in my case than someone keeping the M97. I do not plan to use the Porsche ECU. Chavis Performance and Engineering has a great solution with a CAN module that translates the messages between the GM and Porsche systems. I may need to have a dealership flash my BCM, but otherwise, I'm hoping most modules are ignorant of whether the car is an auto or manual. One problem I had was without the tiptronic shifter, the car will say "Shift to Park" and lock the key in the ignition. I jumped the wire for now which works. If there is a problem here, I can always tie it into the Ebrake switch, it's a good reminder to put the Ebrake on every time then! I don't think the manual system has a different key interlock that the Tiptronic doesn't have? There will of course be some other miscellaneous wiring with the manual swap, but nothing that should be too difficult. Clutch pedal, reverse lights/lockout...

The list of parts I need/purchased for the swap (italicized I already have):

• G96/G97 (I chose G96 for the taller 6th gear)
• Shifter Assembly
• Shift Cables
• Clutch assembly
• Forward Mount and Transmission Cross member
• Upper "Horseshoe" trim around shifter
• Clutch pedal (a real pain to install!)
• Master/Slave cylinders
• Brake fluid reservoir
• Axles
• Complete clutch lines
• Clutch switch
• ECM/BCM reflash if maintaining M97 (unsure of other modules just yet)

Jumped "Shift to Park" pin.

roadie13

Amazing project! You are a fearless car surgeon.. Keep us posted!

BerlinDaniel

Good luck! Why not an LSx? Also that chipped block.... ohhhh lord no.

roadie13

Yeah, that block would worry me too. I'd try to put the most pristine engine in there I could locate..

superman22x

Not the block, just the head. Rest of the block is fine, and it's not in a structural area of the head, just a sealing surface. If it was structural at all, I wouldn't bother with welding/machining. If it was enough to damage the rest of the block, the intake threads and other things would have been damaged. It's very isolated to this spot.

superman22x

One of the complications of the swap is power steering. Most, including myself, opt for electric power steering. The 996 you can get away with manual steering from what I hear, but not on the 997. The LT engines do not come with power steering as all modern GM vehicles use electric assist now. So while waiting for more major components to arrive, I took the time to make the fittings for the steering rack. Had some rods of 1144 "stressproof" lying around, so these didn't take long to whip up. I'm aware you can buy them for $90. But I prefer to make things like this. I used some Dykem and verified with a JIC/AN fitting I had around to make sure it was getting contact all around the flare. So I should be good to go! My plan is to purchase an electric pump soon, couple different options there. Some like the MR2 units, there is a Volvo unit, and the Porsche TRW unit. Seems like they are all pretty equal.

Petza914

This is cool. I'm impressed by what you're able to fabricate and your problem solving skill-set. I'll be following along.

Steve 911

Now this is cool, will this be the first LTx swapped Porsche? These engines are capable of crazy power so it should be quite the handful once done!

superman22x

Thanks! I think this is the first LTx swapped Porsche. The LT engines are great. GM gets a lot of backlash for using, "old" technology, but I've driven a couple modern 600hp cars, nothing has power delivery like the LT engines, top end, bottom end, consistency... But I'm a bit biased, I've worked on the LT4/LT1 Camaro at GM for 5 years.

93Jaffe

This is my kind of project! Not sure where you are located but would like to see it at a meet one day. Sorry if I missed it - are you planning for a dry sump? If i'm not mistaken there is a pretty high risk of oil starvation with this conversion.

superman22x

I'm over in the greater Detroit area.

I'm planning to go with the wet sump Corvette pan for now, just for simplicity reasons. I'm not sure how that will go to be honest. The sump is at the back of the engine when mounted in a normal configuration, which of course puts it at the wrong end for a hard accel in the 911 chassis. But I have no plans to track this car, so I guess we shall see how that goes. The dry sump systems are commonly available at least since they were in a lot of LT1 corvettes and all LT4 corvettes. All LT2 Corvette engines are dry sump as well, and the tank is integrated into the accessory drive even.

93Jaffe

I believe the oil starvation mostly occurs on track with higher side g forces. With baffling on the street I would imagine it would be fine. Just thought I'd offer my .2 cents because that's about all i know on this subject sadly.

superman22x

I do think the LT engines improved a bit on that issue, the LS3 heads in particular had issues returning oil to the pan from what I have read. In that situation I should be good, the Corvette pan is well baffled.

superman22x

Nothing big to report. Been working on wiring the last few days. I am mounting the ECM in the engine bay. I am planning to reuse relays/fuses that Porsche already has used for most of the power requirements. Couple differences though. With the fuel pump control module, a 25A battery power and 10A ign power is required. The 10A can be shared with another component. I would like to add a fuse at D8 for this if I can. I need to see if I have some pins that will fit, otherwise I may just order a random used Porsche or VW fuse box and salvage some pins. For control wires, I am reusing everything I can in the car. I ordered a 25 pin connector and some blank pins so I can create a harness connector in the engine bay.

The other minor problem is ignition. The Porsche DME provides 12V to the starter solenoid relay. The GM ECM only provides a starter signal based on a CAN message. So my plan is to provide 12v ign power to the relay. Maybe I will route through the clutch switch so I don't forget that one day...

This is my fuse diagram so far. Once I finalize it, I will print a version to keep in the fuse box. It took me a long time to figure out fuses D3 and D4. No 997 fuse diagram I have found matches mine. Porsche didn't bother to put out a fuse diagram for the Tiptronic cars apparently.