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22 Posts
Discussion Starter · #1 ·
My long-term project mk3.5 Cabrio is finally getting a VR6. I've known I wanted to do this swap for ages and have been researching/planning how to do it for at least 4 or 5 years. I had the absolutely perfect donor car come along, a very lightly crashed 2 owner 1997 Jetta GLX 5 speed in astoundingly good mechanical condition with just 78k miles. So I decided to make the leap.

I figured this thread would be a good place to kinda narrate the build and show what I'm doing to anyone who's interested. I have the build pretty well roadmapped but definitely would welcome any insight you guys have about what I'm doing. And I know I'm gonna have some questions on technicals and best practices. This will be the biggest wrenching endeavor I've ever taken on.

Let's start at the VR6 roadmap. It's staying naturally aspirated. For now :devilish:. While the engine's out of the bay I'll do some regular maintenance items. I'll most likely do mkiv head gasket, replace valve cover gasket, new oil pan, timing chains, engine mounts. Previous owner clearly did very recent sparkplugs, rear main seal, and a new clutch so that's a win. I'll probably do replacement coolant lines too. In terms of performance upgrade stuff on engine- looking at doing 268 cams, techtonics/magnaflow catback and leaning towards techtonics on chip since they seem to have a bunch of tunes that seem to mirror my build plan. But I'm still researching.

Possibly the most striking part of this build is that I'm going very minimalist. On the Cabrio 2.0 ABA I had previously done an AC and power steering delete, those items will stay deleted with the VR6. The plan is also to nuke all of the EVAP/SAI/PCV stuff. A) The simpler this build is the better, from both a mechanical and electrical perspective. And I love a clean bay. B) This is legal in my state and C) from an ethical perspective- the Cabrio is not a daily driver, it'll see MAYBE a couple hundred miles per year tops and so I'm not amazingly worried about my carbon footprint.

Next post will be days 1 and 2 of wrenching but in the meantime- let's take a look at the donor and patient ready for action:
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22 Posts
Discussion Starter · #2 ·
Day 1 and 2 of wrenching/disassembly went well. Had a fun moment where I had everything prepped in the garage and I was like "Ok. So something has to be the first bolt to start off." 馃槀 Made the most sense to me to start with disassembling the ABA out of the Cabrio, mostly because if I screwed something up the stakes were lower and I figured that with the architecture being so similar to the VR6 it'd be a good practice round. Grille and bumper cover off first. Drained coolant. Headlights out. Pulled front clip off modularly, as such-

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For me, the gameplan is to reuse the VR6 radiator in the Cabrio's radiator support since the donor Jetta's radiator support was collision damaged and ABA/AAA radiators are different in terms of inlet/outlet. Not sure exactly if the VR6 fans are reusable or damaged, or if the ABA fans are the same part; that'll be solved another day when I can compare em side by side. Next was pulling off the ABA air intake and associated electrical, disconnecting the throttle cable, pulling electrical from starter and alternator and disconnecting any other visible electrical connectors. Pretty cool how the design works; most of the wiring harness is concentrated to the drivers side fender and anything that goes elsewhere in the bay from there is pretty obvious.
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After that, disconnected shifter linkage, the weight with the cotter pins and the actual shift linkage with the ball/socket joints. Clutch cable disconnected after that, which I would have ideally had 3 hands for. Pulled off fuel lines, disconnected the downpipe from the exhaust. Coolant lines off the heater core and the ball, distributor wire off the ignition coil, all electrical off the transmission. Next was disconnecting the stuff that's getting deleted; the EVAP, PCV, SAI stuff. Basically, I separated all of those components from the engine and pulled off their electrical connectors, and then went about gutting the actual components out. My biggest question-mark honestly is the EVAP stuff; I'm left with two white hard plastic lines under a heat shield which I'm not sure I should plug or vent to atmosphere. I'll be hitting the search function, but feel free to chime in if you have insight. And obviously, I disconnected the axles.

Overall, I was able to get to the point were I could verify the ONLY connections between the Cabrio chassis and ABA/020 trans was literally just the mounts. If you're ever thinking about doing this, that's the point in disassembly you want to get to, and exactly the point I'll get to again when it comes to separating the VR6 from the donor Jetta. These two pictures don't totally do it justice, but this the state of the ABA/020 only being connected by mounts-
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I'll have further updates tomorrow.

22 Posts
Discussion Starter · #4 ·
What happened since October 16?
That鈥檚 a very good question. I鈥檝e done a garbage job updating the build thread. I鈥檓 working on this project in my spare time usually at night and often the last thing I wanna do when I get home late is write.

But a lot has happened. Both engines are out. Engine wiring harness from donor VR6 is fully disconnected from fuse/relay box and pulled through firewall. All the SAI, PS, AC, EVAP stuff is out of the Cabrio chassis and removed from the VR6. 020 shift linkage is fully dropped from Cabrio. VR6 is on its engine stand and mid disassembly for internal upgrades and component replacement. I broke the VR6 crackpipe so had a Velt Sport replacement delivered from Urotuning. New oil pan/gasket, water pump, catback exhaust, and front cross member bushings and engine mounts have also been delivered.

Most currently, I鈥榲e got several issues I鈥檓 working through. First, I鈥檓 deciding what to do with the 02A shift linkage. Part of me wants to keep it real simple and just port over the donor linkage. But it is a little worn at 25 years old and the mkiv linkage is known to be better. But that requires obtaining the parts and probably refurbishing if used and tracking down the rare Polo mount to install without fabrication. Any insight鈥檚 appreciated.

Next, there鈥檚 very much some electrical I鈥檓 trying to wrap my head around. Most of what I鈥檝e read previously has recommended swapping the donor fuse/relay panel in, but the more I look at stuff, the more I鈥檓 leaning towards using the ABA panel connected to the VR6 engine harness since there鈥檚 stuff the Cabrio has that the donor Jetta GLX doesn鈥檛, like power top, less door/window switches because two door, etc. I鈥檇 think everything behind the firewall would work correctly with existing panel. I could be dead wrong though. There鈥檚 other little gremlins to solve too. The mk3.5 Cabrio headlight harness sockets are different and I assume I鈥檒l have to splice. 3.5 cabrio鈥檚 also have a running/fog light in the actual headlight housing as opposed to the bumper fogs from donor GLX, that I assume is a splice. Cabrio has side marker repeater turn signals in front fenders, donor Jetta doesn鈥檛; I assume that鈥檒l be a splice or separate run to make those operational. I鈥檝e got the VR6 MFA stalk ported over but trying to figure out if I also have to port over the MFA stalk loom, and if I do, where it plugs in. Similarly I鈥檓 working through if I can reuse the ABA gauge cluster harness with the VR6 gauge cluster since for sure ha to be ported over. Also, I don鈥檛 really want to destroy the ABA wiring harness, but I鈥檓 deciding if I鈥檇 rather chop it close to firewall or pull the Cabrio dash since I really don鈥檛 think I鈥檒l get the ABA harness out with the dash in place, it proved damn near impossible on the donor GLX. I got frustrated enough I literally cut out the donor dashboard. I鈥檓 leaning towards chopping the ABA loom.

I鈥檓 also sorting through the hydraulics for clutch and brake stuff. Still figuring out if I can use the existing Cabrio ABS sensors and ABS loom or if I have to port the VR6 stuff. I鈥檓 staying 4lug and ABA brakes so I鈥檓 thinking use the Cabrio ABS stuff. Should be able to reuse the Cabrio brake fluid reservoir since it literally has a break off tab for the VR6 clutch slave cylinder connection, iirc.

A parting note- it is borderline unbelievable to me how complicated the windshield washer fluid assembly is. And cruise vacuum stuff. Hard delete. Car鈥檚 only getting driven in sunshine after a detail. And I never use cruise control.

I鈥檒l take and post some current pics tomorrow or Sunday when I head to the garage.

22 Posts
Discussion Starter · #5 ·
I鈥檓 about to do a write up about some engine electrical stuff, some of the issue I鈥檝e solved or am in the middle of solving but first let鈥檚 do a picture update from the last handful of weeks.

Immediate aftermath of engine pulling.

Out of sheer frustration I sawzall鈥檇 the donor dashboard. Felt so wrong, yet so right.

Forge coolant lines are on. Ended up bypassing the heater core by looping the furthest right hose back to the block. And bypassed the small lines that run in/out of the throttle body.

New water pump is in. I also have the Veltsport metal crackpipe in and a new belt tensioner. I also lopped off the bottom 2/3rds of the alternator bracket since PS/AC delete. It turned out REALLY clean.

New oil pan is on. Internals looked SUPER clean fortunately. Previous owner must鈥檝e been religious about oil changes, fortunately.

For oil pan install, I wire brushed the gasket mating surface removing all debris and surface rust and used a factory gasket and per instructions used a bead of gasket sealer at each block seam, there鈥檚 4 places. Torqued to spec and the final looks super clean and hopefully doesn鈥檛 leak anymore.

Started detailing the engine bay.

New stupid-stiff engine mounts in. I also sent off the front crossmember to have the poly bushings pressed in.

Power steering delete rack loop installed.

Rapidly growing pile of deleted garbage. All I see is weight savings off the nose

And next post, we are going to dive into what quite exactly is going on here with the VR6 wiring harness. There鈥檚 some really specific stuff related to 12V OBDII VR6 wiring into mk3.5 Cabrio鈥檚 that I want to have documented since I am certain will be helpful to someone doing this in the future. And resources are otherwise limited or scattered across a bunch of different places.

Cheers for now. Hit me with any comments/questions.

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