My 2006 Cayman S LS3 V8 conversion

Hi Guys, Late October last year i acquired a 2006 Cayman S with a seized engine, the previous owner was using it in a driving school when the trouble happen. The car was listed on online auction where i happen to browse and made a mistake of reimagining if only i can stuff an LS3 V8, next thing i know i won the auction by $100 over and walla $7600 2006 Cayman S . Well i have to plunk another $1400 bucks to transport the car from Louisiana to Washington State. After much researched and calling to find a replacement engine or rebuilding i came to a dead conclusion the cost will be $13K to $18K for a refresh refurbish engine (yah an used unknow mileage with new piston rings and gaskets). Well Plan B that is, we all know the LS3 have been done many times now and the real hesitation is the amount of fabrication to the engine firewall and lost of leg rooms. After much measurements on stock form i figured i would need to move the seat one click forward from the most rear seating for cruising around town and for more aggressive track driving i would need two clicks. The stock seat angle of the back rest on a stock form it work just fine. Also from the investigative work, the seat when set max to rear it was limited by the cross bar and not the engine firewall, in fact it has 2 inches of clearance. For reference I'm 5'11" and 240 lbs. My best estimate is that i could afford to give up 2 inches and worst case use a thinner profile seat like a carbon fiber race seat. Another goal is to use the stock transmission to keep the transaxle to stock position and simplify the conversion. So the decision was made: Engine: GM LS3 with 430HP crate engine Engine ECU : Undecided Transmission: Stock Cayman S 6 Speed, stock trans mount Trans to Engine Adapter: Kennedy Engineer Clutch: Kennedy Eng. Starter: Kennedy Eng. Axle; Stock Water Pump: Electric Generic Water Pump Remote Manifold. 417 motorsport Power Steering: TRW Brake Vacuum Pump: Bosch electric Vacuum Engine Mount and Subframe: Home/DYI Made by me Total Phase 1 Target Cost below $30K, this is cluding the car. Experience: 1st time engine swap Welding: Intermediate, home DYI, MIG, TIG and Stick Fabrication: Intermediate General LS Engine know how: None/ZERO Automotive; Decent, over 30 years of DYI (but NO engine rebuild) Electrical: Design RF Electrical Engineer for a leaving before retirement The car 2006 Cayman S with 136K Miles. Condition: grade B, the clear coat pealing, NO major accident and stock View attachment 277974

Time Completion target end of 2022, maybe up and running?

Let me know if you have any questions. I've had my LS3 Cayman running since 2015. You can just tie the brake vacuum to the LS.

Hi Joshua, Actually i have downloaded as much pictures from your build for reference. What ECU and wiring harness did you end up using? Also did you bother to hook the CANbus to run the dash nor the PSM. I'm still undecided whether to buy the kit from Rexxgxx Hyxxxxx, its $4500 but plug and play. What angle where you able to align the engine? Thanks, M_Mode

Joshua, Do you recommend to adjust the fuel pressure or are you running stock pressure (55 PSI). For my engine it require 58 PSI. Any other tips would you recommend? The car will be more street oriented but maybe a few autocross days per year.

My fuel system is completely stock. We have a dyno and I touched up the tune a little to accommodate the pressure difference. Super easy. I ran the GMPP ECU and harness for the LS3-480. It's only 5 wires to make the car run. Super easy. It's not a motorsports harness, basically just like an OEM GM harness trimmed down. It's not tied into the Porsche side of the car at all. I have a CAN based digital dash with a few analog sensors (oil temp/pressure & EGTS). The ABS still works but no other nannies. You can hook the GM crank sensor to the OEM ecu and also install the OEM water temp sensor in the LS cooling system and run the stock cluster.

Engine mock up is in place. Still contemplating how much should i keep the engine back from the original location or keep in same place. Using LS4 balancer still has very tight fit to keep the e-brake bracket. I was able to keep the engine zero deg on both plains. Having the engine about 1 inch back will give me good compromise. Another modification i anticipated is to add some clearance on the cross bar above the firewall. Base on the measurement the stock LS3 intake will have same height as the top of the bar. Easy enough to put some loop bar just above the intake and retain the section where the plastic engine compartment side cover. My goal is reuse most panel to contain engine noise and heat. So far i'm not seeing any compromise yet on leg room. Engine accessories will need custom brackets to clear the firewall, need to lower the alternator further down perpendicular to the firewall support that was cut and enclose to clear the pully and belt. Joshua, how much did you set the engine back and any issue with the axles. Did you use spacer on the axle to add length?

For reference, see the inside cabin shots with the balancer next to the hump from the firewall. Both are about the same height. On this configuration the LS3 engine is sitting pretty much level both axis on stock height trans mount but setback 1.25". I did confirm that the cross member between the engine and transmission clearance has about 0.5-.75 gap, no modification needed. Not sure how much angle would that add to the axles? Also the engine is sitting ~ 5 - 5.25" above the jack points . I used the corvette engine mounting bracket and round rubber mounts. More pics

Just completed transmission bracket modification to accommodate the 1.25" set back to relief some space between the firewall and engine. I reused the the old transmission brackets and modified to add 1/4" length. I also need to bend a little the brackets to change the angle. Another part i need to make is the cross bar loop to replace the portion of the crossbar above the engine intake. I wish a mandrel pipe bender will be nice to do this job.

Guys we have the parts comes in, Engine, wiring harness, elec. water pump. and semi solid transaxle mount. Change: I have to replace the engine mount using a 1/2" angle bar and drop it 0.5" to give some angle rake to the engine keep the oil close to the pick up tube.

Mocking the alternator mount using LS4 balancer. Need to add more clearance from the firewall, may be half inch. Still contemplating ato add the AC.

Today i made some progress on prepping the engine reversing the manifold and configuring the valley to accomodate this change. Doing so i have to removed the oil pressure sensor to accommodate the clearance needed for the throttle body in reverse configuration. Also i found that few bolts and vacuum outlet has some clearance issues in reverse form. I manage to tig weld the old oil pressure port and grind the plastic ribs from the manifold to relieved the clearance issue.

Minor change, original plan was to use the LS4 balancer due to the low profile. The difference between the LS3 stock balancer is 2 inches shorter. I'm trying to minimize additional changes to the transaxle angle and legroom. need to find a happy balance. The Ls4 balancer definitely buy you clearance, the draw back is that yo have to make your accessory bracket. which is not hard just take time. Another options is use the ICT Low mount alternator kit. This fit the LS3 crate and it has less than 13" inches width span from balancer center bolt. This is perfect for the clearance i cutted from the firewall. The ICT setup looks factory and avoid belt slippage in the future. Also using the stock LS3 balancer i can use the ICT AC low mount kit along with the LS3 AC compressor. Both kit will look factory. Also I relocate the oil pressure sensor that was taken from the valley pan and reused the bung that was welded on the oil filter side thing, not sure what's called. Since the ICT kit is what i'm going to use, i need to move back the engine 1 or 2 inch further more, on its current setup the best estimate the offset of the transaxle is around 9 to 10 degree. (after 1.3" setback), adding 1 or 2 inches may set to 18 degrees. I may need additional spacer on the transaxle to compensate on the additional extension.

Short update, I was able to mate the transaxle to the engine, in the KEF instruction you have to install the clutch then the adapter and transmission. Well doing this way will leave you one extra allen bolt. This bolt is only access from the inside of the adapter where the clutch assembly. When you have the transmission and engine bolted together you have no access to install it. So i have the adapter mated to the transmission then mated to the engine. Also test fitting the AC bracket to see how it fit. One note here is I plan to use GM Sanden 7176 AC compressor (hopefully I can integrate the POrsche AC system). Its seems that the GM AC compressor is smaller than the Porsche unit. Initially concern about the Corvette engine mount may prevent the AC assembly too fit but after looking at the AC drawing dimensions, looks like it will fit. Until i get the AC we would only know, stay tune. I made the decision to add clearance on the engine crosss member, 1/3" inch is a little to close for my liking. The exhaust from fleabay fits nicely and surprisingly build good quality. Only issue is that one of the plug wire access may require a different wire configuration, the stock straight GM plug wire will not work. Otherwise since it is a mid pipe i have more option to route the exhaust pipe. Starter that came from KEF also is installed, bolts that came with it is 1 inch too long, need shorted.

Received the Sanden AC compressor, did not waste time fitted and confirmed it fits, see pictures for clearance. The E brake mounting cable bracket relocated, but still have no full solution. how to link the cables back. The engine and transaxle need to get back in the car for final clearance inspection. Need to refab final transmission mount. Test fit the axles.

I only understand half of this thread, but I am enjoying following along anyway! Thanks for sharing. Sent from my iPhone using Tapatalk

Hi, I'm sorry for a very cryptic posting. Yah its hard to follow due to the lack explanations and purpose. My intent is really to capture the build and document the parts pictures for reference for others who may plan to follow the same path. Maybe when the build is in the state that is more relatable (like when its running} i'll make a video to capture the thinking and the mind behind build and why? I'm glad your still able to make sense and enjoying comics picture post. Thanks, M_Mode

Today i tried the new engine with all the accessories and their brackets. This is exciting to know how much clearance from the seat, if i'm going to loose leg rooms using the stock seat and If accessory brackets have been enough room to operate properly. Well i'm happy to confirm that i can still set the driver seat as far back as the stock (basically no change). Worst case i may gave up one click. That is acceptable compromise. On top of the engine the throttle body need to be relocated instead of bolted on the manifold, Overall this alignment will be the final dimension, need to refabricate the transaxle mount to set final engine location. Also the exhaust clearance is looking good have multiple options maybe even use the stock Porsche muffler to save money.

Any updates lately?

I'm in the planning stages of the same swap. Right now my m97 is fine but I cant trust it for any track use. Hows it coming along?

Its coming along fine, i got back on the project about 8 weeks ago. Between January to July i was busy moving and renovating two houses. Now family a settled in and have less yard work, i have more time dedicated to fun hobbies. Additional work i did is to add bracing to the engine compartment triangulating/boxing for rigidity. The GM wiring harness is reconfigure and inplace. Motor is oil primed, custom parts are painted, i was using random spray paint just for rust prevention (no show car here). By the way a new 718 GT4 was acquired also, It will be a good comparison later.

Another more thing, I also reconfigured the internal fuel pump inside the gas tank totally eliminating the filter module out of the system. That was simply replaced with a barb coupler reusing the original hoses. This will give me the max PSI of fuel which i would regulate to the necessary LS3 fuel requirement. My concern the pump would not have enough volume to support. a LS3 engine. Looking for suggestion

some really nice fab work on the subframe and bulkhead. Are you going to trim out the top with a glass panel or remake the cover? Whats you're plan for engine management?

erfont01 thank you for kind complement, Regarding the engine cover, i would like to address the heat and engine noise clutter. I would start with a full on cover then create a 2nd version leaning toward showing the engine. The engine management will be done by the GM factory computer and the dash electronic will utilized the original Porsche ECU to provide signal for the coolant temp, speed, AC control and RPM, i think that are the basic?

If it can be made into a documentary, many friends should like to watch it

How about oiling system upgrades? Accusump and baffled pan? Are you planning on tracking it? The subframe design is similar to Pound Design or what Inspire Automotive Garage did on youtube. Did you use those as a general plan? Sorry about so many questions. I'm trying to gather the all info I can to plan my swap for next fall/winter. Your GT4 is sick btw. I would probably be really dragging *** on the 987 project if I had that

The car will serve as a 90% street and 10% track. When i say track (non competition) just fun laps to our local Pacific Northwest tracks, may be Autocross? Another discipline i need to watch my self is not to go overboard, in the end this is a hack car, the value is purely for individual satisfaction. I wish i have the patient to documents and take time to note each work so that others can benefit, i get it. This is why i still take time to upload and write some cryptic notes. Just be patient to me if you have question i will try to answer them. The subframe design was just my own, practically replacing the original aluminum flat bar and aluminum skid plate and making a single unit out of steel. For the engine mount, I utilized the jack pads because it was the closest in alignment with the engine and independent of any subframe. Meaning i can pull the transmission without needing to bring down the engine. What amazed me is how easy (yes easy) to bring down the entire assembly (Trans and engine) all together, if can utilize quick connections for fuel, cooling and others in one hour time frame you can have sitting in a table jack. The 718 GT4 is a wonder car specially you like driving manual, being one with the car. The power is not high strung at all and very predictable and if you think you made a mistake just lift the foot from gas pedal and it will track back it self.