1968 Porsche 912 - LS Swap (ultimate Frankenstein)

[wkrtsm]

TRANSAXLE UPGRADE FROM 901 to 930 (SHORT BELL HOUSING, 1976)

The Chevrolet 6.2L 376 c.i. 430 HP LS3 engine has 300 foot-pounds of torque at idle (~800 RPM) with a max torque of 424 foot-pounds. The main transaxles in early series Porsches are the 901(902), 915, and 930. (G50 and 996 are newer transaxles that are used for LS swaps, but lets stick to 901/915/930). All 4-cylinder 912s have 901 transaxles; 911s with flat 6-cylinder engines have 915 transaxles; Turbo 930s and Turbo Carreras have 930 transaxles. The 901 cannot withstand the torque from an LS3 and is at high risk of failure. The 915 could appropriately be used for small block chevy swaps, but is not recommended for LS3 (6.2L) swaps. Whereas the 930 transaxle is ideal for an LS swap.

The problem with the LS3 engine for the 901 and 915 transaxles is that the 300 ft-lbs of torque at idle greatly exceeds the 70-80 ft-lbs rating of the 901, and is right at the 270-300 ft-lbs rating of the 915. So after an LS swap with the 6.2L LS3, you could literally release the clutch pedal at idle and snap/shear/disintegrate a 901 transaxle, and either damage the 915 or greatly accelerate its wear, but not damage or accelerate wear of a 930 transaxle which can handle ~700 HP, e.g. 650-690 ft-lbs of torque. (there are stories of 901s being used in "very powerful" race cars that lasted a long time, and stories of beefing up 915s, but the conclusion typically is the 901/915 are not optimal for an LS swap). 930s come with a premium, however, which is high cost. Short bell housing 930s (models 930|30, 930|32, 930|33) from 1976-77 are ideal for 912/911 since they're about 2" shorter than the long bell housing 930 (930|34, 930|35, 930|36, 930|37) and require less or no cutting of the torsion tube.

I took delivery of a very rare 1976 short bell housing 934 transaxle (racing variant of 930 transaxle) I was able to secure about a week ago:



Here are the 3 factory stars stamped into the casing, denoting it's a real 934 transaxle. This particular transaxle was built as a spare for 934's and it's unknown what it was used in, but it was recently rebuilt and anything needing replacement was replaced:

This 934 transaxle is essentially a 930 transaxle with larger carrier bearings. Since the 930 transaxle can handle 700 HP, I would guess this would be rated for 800-900 HP. FYI - there were only 31 934s made in 1976-77.


REAR COIL OVERS AND REQUIRED CHASSIS AND SHOCK TOWER REINFORCEMENTS

For an LS swap, any Porsche needs to be converted from using struts in front and shocks in the rear to coil overs. Traditionally, all of the rear weight from the chassis, body, engine, and transaxle was absorbed by the spring plates that are attached to the torsion bars. Whenever you hit bumps or potholes with the rear tires, the force/stress was loaded on the torsion bars - which act as springs. When coil overs are used, however, the torsion bars are not used and the force/stress is relocated to the shock towers via the coil springs -- which the chassis was not designed for. Since the shock towers sit on the "crossmember" beam that connects via welds to the chassis mains, there has been a history of the stress from coil overs breaking the main welds of the crossmember (on to the chassis mains) as well as ripping shock towers loose. To overcome these new relocated forces, the original crossmember welds need to be augmented by additional (supportive) sheet steel that's welded in over the joint; and the shock towers need to be reinforced with sheet steel. The work below addresses these new needs.

Get the car up on QuickJack 5000TL's (see this link ) and place 4x4's under it just for safety's sake (a vertical 8 foot treated 4x4 can hold 6000 pounds via compression strength before it begins to buckle)

Time to pull the entire rear end and prep the cross-member and shock towers for weld-in reinforcements:



Remove undercoating & paint to check the crossmember welds -- which look very good, along with the virgin steel from the 60s:


Prep the shock towers for Elephant Racing's weld-in reinforcements:


Don't forget to prep the back side of the crossmember for reinforcements:


WATER COOLING - RADIATOR
Pull the gas tank before grinding in the engine bay, and also to make way/prep for the taller-thinner new aluminum gas tank from Renegade, which leaves the hole open for hot air to escape from the radiator:




UPGRADE TO LONG WHEELBASE (LWB)

912s and 911s manufactured in 1968 and prior were all short wheelbase (SWB). The wheelbase of SWB cars is approximately 2 inches shorter than long wheelbase (LWB) cars made in 1969 and later. LWB was one of the features implemented to improve handling and the issue related to the alleged "rear tail spin," causing Porsche designers to consider SWB to be too tail heavy. Thus, LWB was introduced, among other mods such as using lead weights in the front bumper, two batteries in the front, etc. The choice of whether or not SWBs handle better than LWBs on the street/track is really a personal preference: for each driver/racer who favors LWB, there's someone who favors SWB. I chose to upgrade to LWB for my own safety, because I am introducing a lot more weight in the rear from an LS3 engine *and* a 930 transaxle, even though the LS3 engine does weigh less than the 911 flat-6 engine.

The long trailing arms arrived today, and they're in great condition and have only a few spots with minor surface rust. It was a good purchase because they were sold with the complete brake parts, stub axles, and drive hubs (with 5 wheel studs). The studs are longer than usual, so they had to come from a car that was likely a wide-body with wheel spacers. I'll totally disassemble them, degrease & pressure wash, replace the bearing seals, pack new bearings with grease, then apply Metal Prep (from POR-15, for phosphoric acid etching) followed by coat of POR-15 glossy black.

The pic belows show the long trailing arms next to the short trailing arms:

[wkrtsm]

WELD-IN CROSSMEMBER REINFORCEMENTS

Since the shock towers were not designed to handle all the force/stress from coil overs, the crossmember, which contains the shock towers, needs to be strengthened where it meets the main chassis. I used a plasma cutter to form a piece of (weldable) 16 gauge sheet steel based on a cut-to-fit piece of paper. Each sheet metal piece for the right and left side bends down to cover the main vertical weld. I still need to drill e.g. 5/16" holes in these sheet metal pieces so that rosette (plug) welds can be used to glue each piece in addition to the edge welds. Note that the crossmember seems to be quite thin itself, almost as if its 18 or 20 gauge. Using 14 gauge or 1/8" sheet metal on the crossmember offers no advantage since it's not as malleable and flexible 16 as gauge and much harder to hammer-form when working into shape. (good luck trying to hammer-form 1/8" plate steel welded on top of 18/20 gauge, as its tack welds would probably rip out of the thinner crossmember when hammering).

Note: you have to grind off the mill coat (galvanized layer) near any edges that get welded so that a clean arc can be formed. If not, welds will be inefficient and subpar. Also, the fumes from welding over mill coat are dangerous.


Here's the raw unfinished piece (all 16 gauge) for right side:


Here's the unfinished piece for the left side:


Here's an image of the left piece after the holes for rosette welding were drilled and ground smooth:


The pic below shows the smaller piece that gets welded into the top face of the crossmember next to the chassis main:


Here's a decent looking bead run with flux-core on the vertical arm, and notice the rosette (plug) welds in the 1/4" holes I drilled into the reinforcement piece to "glue" down the center of the sheet metal


More progress below:

Since the metal is so thin on the crossmember, I had to first tack the corners with multiple spot welds, hammer and shape, and then close up with more spot welds. On occasion, I could then run a small bead over many spot welds, but the risk of burn through is high when doing that. Thus, leaving it as a patchwork of multiple spot welds is "good enough for Government work." Note that I'm not using fluxless TIG or MIG, which has no flux spatter. It's the repeated spot welding via flux=-core that result in layers and layers of flux spatter. (in other words, if you could run one bead, there would be substantially little flux spatter).

Today, I also welded the top washer on the shock towers, since they appear to be be only spot welded:


WELD-IN SPRING PLATE MOUNT REINFORCEMENTS

The spring plate mounts near the torsion tube bushings also need to be reinforced. The pic below shows this area cleaned up for welding:



The chassis metal is thin in this area, so you need to spot weld multiple times, while moving to different areas each time to minimize warping. Move around the perimeter using numerous spot welds, hopping back and forth to areas which are the coolest until the perimeter is completely covered with multiple spot welds. Thus, you can't run a bead with flux-core, rather, overlap multiple spots welds so in the end it appears to be one contiguous bead.

[Matt at Pelican Parts]

Great pictures! It's not very often we get such a detailed look at these LS swaps. The added extra factoids about SWB and LWB are appreciated too! Please keep us updated on this ongoing project,

[wkrtsm]

RENEGADE HYBRIDS BASIC LS KIT

Today I received the basic LS kit less Kennedy parts. (I ordered the adapter, pressure plate, starter ring gear, flywheel, stage 2 clutch disk, release and pilot bearings directly from Kennedy separately).

Below is the custom cradle which bolts into the LS block and the engine mounts in the rear corners of the engine bay:

The cradle "is a beast" and appears to be top quality engineering, along with its glossy powder coat.

The other parts such as hoses, coolant top off container, water pump, hoses, belt, aluminum water core mount for hoses, and bags of nuts & bolts are shown below:


Because the car is a 912, I will need to install engine mounts in the unused plate steel that's in the rear corners of the engine bay:


I don't think I'll cut off the original "donut" style 912 engine mounts (below) because I'm thinking of having some plate aluminum machined to bolt in the LS3 cylinder heads to provide additional engine support. That's because I am planning on north of 500 HP, and think it's too much for the 2-main bolts in the back of the custom cradle to support alone - but that's just me.

[wkrtsm]

Finally finished the right crossmember and shock tower welding. It works out that I didn't use the Elephant shock tower bracings because they did not come up and extend over the top of the tower -- and thus I made my own via plasma cutter. FYI - the sheet metal over the crossmember and main chassis is 16 gauge, whereas the two plates that are welded to the tower are 14 gauge. I'll clean area up with POR-15's degreaser, then metal prep, then POR-15 glossy black -- just like the entire firewall in the engine bay.

[wkrtsm]

Here's a pic after applying POR-15s Metal Prep (phosphoric acid solution) on the new sheet metal reinforcement on the shock tower and in back of crossmember. Metal prep halts any rust and molecularly etches metal and previous coatings so that the final coat of POR-15 will stick to it. Again, all the sheet metal on or near the crossmember is 16 gauge, and the vertical supports for the shock towers are 14 gauge, since they don't need hammering/shaping. 14 gauge, to me, is too thick to hammer and shape, whereas 16 gauge is just right.



After applying Metal Prep on new sheet metal in front of crossmember. Yes, I had to lay down multiple spot welds via gas-less flux-core welding, since running a smooth continuous bead is only possible if using gas-based TIG or MIG welding, which has less spatter and is more controllable/smooth. Indeed, it is "death by a thousand spot welds," but is it a tried and true method used for welding thin sheet metal. The image below shows 16 gauge sheet metal, which can be hammered/shaped.



Final coat of POR-15 on both sides of the chassis main next to the crossmember.


Final coat of POR-15 on the shock tower reinforcements (right side):


Final coat of POR-15 on the shock tower reinforcements (left side):


Final coat of POR-15 on the spring plate mount reinforcement:

[wkrtsm]

[wkrtsm]

SWB vs LWB TORSION TUBES

The pic below (from another post) shows 2 short wheelbase (SWB) torsion tubes on the bottom ('68 and earlier), and one torsion tube from a long wheelbase car ('69 and after) on the top. Do not believe any posts or parts vendor who states you can simply bolt LWB trailing arms into mounts on a SWB torsion tube - since the angle is different, and the distance from center is smaller for the LWB pivot points. SWB trailing are much shorter than LWB arms (look at my pic of both above).


CUTTING OFF TRAILING ARM PIVOT POINTS FROM MY SWB TORSION TUBE
I used a grinder cutting disc and removed the rear seats as well as the hump in the middle. Some of it was fiberglas, because about 15 years ago I gutted the interior and chased down rust in the rear seat corners, due to a leaky rear window. I repaired some of the rusted out seat areas with fiberglass, then wire brushed the floor panels, applied POR-15 everywhere, then had the car painted and had new window seals and headliner installed. The 930 transaxle will really protrude quite a bit above the torsion tube, so I didn't want to mess with aligning and measuring space needed, and instead chose to let the 930 have all the space it needs. Then I can weld the seats back in, or even fabricate my own 18 gauge sheet metal doghouse. (this is also not a family/friends car, where someone needs to sit in the back seat, so rear seat accommodations don't matter).

I can now clearly see the torsion tube and mounts for the SWB trailing arms.





PLASMA CUTTING

I use one of the better auto-darkening Lincoln welding helmets, with a large focus area, and solar charging of the battery. For welding I use shades 10-11 (on the high setting) and for plasma cutting I use shade 6 (low setting). Plasma cutting is similar to the brightness from an oxyacetyle cutter, which is about half the brightness of a welding arc (MIG, TIG, flux-core, or stick).


For plasma cutting, you need a larger 27 gallon or greater compressor with 5-6 SCFM, so I use a 6.2 SCFM @ 90 PSI which can get up to 175 PSI. For plasma cutting and sand blasting it's not so much the PSI, it's the SCFM you need, which should be greater than 5-6 which you can only attain with 30 gallon and higher compressors. Note that for high SCFM (near 5-6), it helps to have a 1.5-2 HP electric motor, cooling fan with belt, and a beast compressor assembly -- not the skimpy compressor assemblies.




You should use 220 Volts AC for a plasma cutter, so if you don't have 220 VAC in your shop/garage, then call the electrician and have them install a conduit box (plug) that runs 220 cable to your breaker box. I picked up a beast 220 VAC extension cord, so I can plasma cut in the driveway as well.



I also use the 110/220V BestArc (Generation 7) BTC500DP plasma cutter which is one of the most popular that has great ratings.

[wkrtsm]

The plasma cutter was able to cut through the top of 5/32" thick mount in about 10 seconds. I wanted to stay away from the weld so I didn't cut the tube any.





There are some welds on the side from which surrounding metal needs to be cut, and then it's just a matter of hammering down until the bottom needs to be cut.





The only thing to do now is grind off the welds. I slightly scarred the tube with the plasma cutter near the top weld on the on the left; however, I'll just patch that up with a one or two "cap passes" via welding.

[Matt at Pelican Parts]

Wow that plasma cutter is really putting in work! Really nice investment!

[wkrtsm]

Thanks. Plasma cutters are replacing oxyacetylene cutting torches. Someone stated on a welding forum that after they were charged ~$250 to have their gas bottles safety inspected, pressure tested, and then re-filled, they decided to buy a plasma cutter.

[wkrtsm]

I wire brushed the torsion tube to remove scale rust, corrosion, and dirt using a pneumatic die grinder (1/4" wire brush attachment), as well as ground off the original weld metal. Next up will be fabricating new trailing arm mounts.






I removed the original 912 engine mounts, and the blank rear mount plates in the corners, so that I can weld-in the box-like 911-style engine mounting brackets. I first used a plasma cutter for the initial cuts, then a diamond-tipped disc cutter, followed by an air-chisel to break the original spot welds. I still need to grind off the last bit of original welds to smooth out these areas. There's not much damage to the original chassis mains, only a few nicks and scrapes with the grinder.



These areas were finished up with a grinder and then smoothed out with a pneumatic die grinder. So its ready for POR-15 after I get the 911-style engine mounting brackets welded into the corners:



Something I don't like is how sparse the original welding is in the rear corner where the chassis main meets the bumper chassis, which looks like a structurally weak area. I'll weld some sheet steel into these corners to reinforce them:

[wkrtsm]

The Kennedy Engineered Products adapter, pressure plate, stage 2 clutch disc, release bearing, and pilot bushing arrived today. Engine is due tomorrow.

Here's the adapter:


Here's the pressure plate assembly with disc inside.

[wkrtsm]

Received the LS3 engine (6.2L, 430 HP) and it fits very well. It works out that I don't need to cut the torsion tube at all since the shift linkage protrudes in the linkage box well enough, and the 4-stud transaxle mount is directly below the torsion tube.

Below are some pics:

[Matt at Pelican Parts]

Looks like the engine fits in there quite nice! Keep up the good work!

[wkrtsm]

WHERE TO WELD IN LWB TRAILING ARM MOUNTS FOR CUSTOM SETUP - SOLVING A 3-VARIABLE PROBLEM

In addition to having a custom installation involving conversion from SWB to LWB, my trailing arm mounts on the torsion tube need to be more outboard because of the fat nose of the 930 transaxle. This is not OEM specs for a LWB '69-71 912 or 911 since they didn't have 930 transaxles.

Now, the main problem with different trailing arms, new 935 spring plates, and cutting off the old SWB trailing arm mounts on the torsion tube is that you not only don't know where to weld-in the newly fabricated trailing arm mounts (on the torsion tube), but you don't know what the dimension of the mounts are either.

The above dilemma translates to what is known as a 3-variable problem. The 3 variables that need to be considered to solve the problem are

1. Ride height
2. Toe
3. Camber

Variable 1 - Ride height. The first question that needs to be answered is how high should the wheel center be when there is no engine/transaxle (weight) on the rear of the car? This can be easily determined by knowing that the formal Porsche definition of ride height is based on the difference in the vertical distance (from the ground) between the center of the torsion tube and the wheel center. How can this be approximated? Well, if you haven't realized, every side photo of a 912 or early 911 reveals this distance because the center of the torsion tube is marked by the small plug near the rocker panels in front of the rear wheel. The vertical distance, gauged visually, is the distance that's apparent between the torsion tube center and the rear wheel.

For example, the pic below shows my car when it had a 912 engine it, but what's important is the ride height that I liked. Notice in the pic that the height of the torsion tube center and the wheel center are about the same. So for practical purposes, I will call this "equal" heights from the ground.



Now that the car is in the garage without an engine/transaxle, I know that wheel hub center needs to be the same height as the torsion tube center. This is actually simulating where I want the axle when rear engine/transaxle weight is on the car. It doesn't matter if I have a one million pound engine in the car -- this ride height needs to be maintained. I have just solved the first part of the problem, for which I can use hanging wires to place the wheel hub when the trailing arm is bolted into the new 935 spring plates.

Variable 2 - Camber (default is -1 degree). The second variable to be solved is camber. Once the axle center is set to (via hanging wires) the same height as the torsion tube center, I will know that when the 5-stud mounting surface of the stub axles are purely vertical, then the camber is close to zero. This problem is solved by using a bubble or digital angle leveler and ensuring the spring plates are vertical and tightened at the heim joints. However, the recommended default camber for early 911s (912s) is -1 degrees, since under acceleration, the top of the tire moves outboard -- which essentially replicates most driving, i.e, under acceleration. Thus, I'll set the axle hubs to -1 degrees inward (before welding in trailing arm mounts).

Fabricate and Weld-in Trailing Arm Mounts. Once the rear wheel hubs are in position (via a wire jig assembly and the spring plates are vertical, where ever the trailing arm ends are now located near the torsion tube is where I want them to be after fabricating and welding the new mounts to the torsion tube, and then bolting in the trailing arms.

Variable 3 - Toe. Once the engine/transaxle are installed, I can adjust toe by using the nuts on the heim end rod.

Final alignment. When the much heavier engine/transaxle are finally installed, one of the benefits of coil overs is that I can set ride height (delta between torsion tube center and wheel center) by adjusting the coil overs. As long as I know camber was set to zero when the spring plates were vertical when the height of the axle was the same as the torsion tube center, then I know camber problems will be minimized -- because I set camber to zero at this ride height. The final tweaking will occur during a professional alignment.

You must recall that the above discussion is assumed as a way to find out the dimensions and weld-in locations of the new trailing arm mounts when there is no weight on the car (no engine/transaxle). There is no way anyone could tell me where to weld in the trailing arm mounts and what the dimensions of the mounts should be if the above sequence was not followed. Another big problem is the fact that LWB trailing arm mounts can't be in the OEM locations on the torsion tube because the 930 transaxle nose is wider than the 901 and 915 transaxle. Therefore, any suggestions like buying a new LWB torsion tube center and welding that it would be wasteful.

[wkrtsm]

For the original 3-variable problem setup, the pic below shows the new ERP 935 spring plate bolted tentatively but not torqued to the steel LWB trailing arm without trailing arm mounts on the torsion tube. (fyi - the LWB trailing arm has not been cleaned, wire brushed, and coated with metal prep and POR-15 - so it looks disgusting. i laos need to replace the bearing seals, bearings, e-brake pads, etc, and clean up the wheel hubs and half shafts))

[Matt at Pelican Parts]

Great to see the progress still going strong! Loving all the details on this build

[Ryan_Cunningham]

This is awesome! I'll be following this.

I bought my ZZ4 powered 1972 Porsche 911T with the procedure already completed which also came with a SBH 930 transaxle, but it's really cool seeing what had to be done by going through your thread.

I was surprised at how easy it was to drop the engine and reinstall it, with a bit of assistance from a fellow Pelican.

Not sure how I'm going to do it yet, but I purchased a salvage 2001 911 Turbo with G96.50 a few months ago to swap the powertrain and transmission.

I'll be updating my thread in the engine swap forum once I start the process, which will likely take a couple of years due to other commitments.

But awesome progress! Any idea what brakes you are going to run and tire sizes?

[wkrtsm]

WELDING TOGETHER A JIG TO ALIGN STUB AXLES IN LWB TRAILING ARMS FOR ZERO TOE-IN - A CASE OF PURE SYMMETRY

Today and yesterday, I spent the majority of time welding up, installing, and setting a jig which bolts to each stub axle, and forces the wheel hub (with 5-studs) to be exactly parallel with the other side.

Since I am fabricating and welding in new LWB trailing arm mounts, the major question concerning where the mounts should be located on the torsion tube can only be answered if a jig is made to bolt the two opposing axle stubs together -- in parallel. If you ask yourself the question: is there an accelerated way to make both stub axles parallel at the same time? The answer is yes, make a jig whose ends are exactly 90 degrees from the supporting beam that goes from side to side. This makes the stub axles symmetric.

Next, the problem is still not solved because I am installing 935 spring plates the same time. However, if I ensure the heim rod end in both plates are screwed all the way into the housing, then the spring plates are symmetric.

With the jig now bolted into place on the stub axles, I know the toe-in is zero, since the stub axles are purely parallel with one another. I noticed that both trailing arm ends are too close to the torsion tube, so I can back out the heim rod end the same distance on each side to force them more to the rear.

Before I weld in the trailing arm mounts, I will set the camber of the half axles to -1 on both sides, since that's the default street setting for early 911/912, as the top of the rear tires rotate slightly outboard under acceleration.

Below are some pics of the jig bolted in, the LWB trailing arms, and the 935 spring plates:






Note that (pics below) I flipped the 935 spring plates so that the heim rod end housing is inboard, and the plate is outboard. This allows me to set the trailing arms about 1 more inch toward outboard, causing the mounts on the torsion tube to be more outboard. This is required to accomodate the big fat nose of the 930 transaxle next to the torsion tube:




In the pics below, you can see the trailing arms sit too close to the torsion tube when the jig is on and the heim rod ends are screwed all the way in, so I'll back out the heim rod ends to position the arm ends about 1 more inch away from the tube.