Twin GT35's on 4psi

Any reason why the 5.2 SHOULDN’T be able to handle 80-90hp per cylinder?

I figure most VW/Audi’s can safely handle ~100+ am I right? Seems so measly, but when you put it in the perspective of 10 cylinders… just seems absurd.

…Anyways, here’s to the first twin turbo (I think) BXA engine… tubing, flanges, and piping are coming in later this week and it’s time to have some fun. Or move me to the “unrelated” sub; either way, we’re all about to find out what a 12.5:1 engine will do on some 4-5psi wastegate springs and a 6sp manual transmission


Good luck. Wish you the best. If you’re successful and I hit the lottery, I’ll be looking to shoot for similar power levels. I’d probably want to do a huge supercharger to keep the sound, but the extra theater from twin BOVs would probably make up for it.

My biggest fear at the moment is detonation… with it being such a high compression ratio, the lower the boost/timing the better.

Even then if I have to run it without charge pipes until I can source another motor and throw some 4.2 rods and compression lowering pistons in it, we’ll make it work!


Turbos came in. Made a jig to keep T4 flange in place while I make a set of log style manifolds. Custom cut flanges should be coming in later this week; all the 1 5/8’s tubing/elbows are on standby.

Really going to try and keep this updated as I go.

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First side is tracked and holding under its own weight.

I originally designed the manifold to account for the 1, 5, 2, 3, and 4 firing order, but had to modify it slightly as it laid where the headlight needed to be. That said it more or less follows the factory 2-3 split headers and will be worlds better than the RS6 log manifold.

At least, one could hope…

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More progress today. Driverside is all fitted up. Still have to notch out the merge into the 2", but I’m expecting to have this side done this weekend…

Moving right along! Next step will be to figure out the oiling; potentially pull a tee off the factory oil pressure warning sensor location since I don’t use it?!

Manifolds are done minus the welding part.

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This is absolutely awesome and quite motivating to follow:) I am curious tho, how are you dealing with the potential bottleneck effect on the exhaust when you are unable to do equal lengths, especially on the 3->1? I assume the 2->1 is fine, due to a combination of equal length on the 2-1 and the pipe diameter increase on the last merge, but what about the 3-1 section? Since originally its equal lengths to avoid the bottleneck. Or did you line it more up with firing order with some fancy maths? I saw you said you changed the original design, so was wondering about the end conclusion. Cheers man, and good luck, this shit is gonna be good!

Originally I had the firing order in mind, but due to space constraints I had to run a straight section of 2" instead of 2 90°s merging together (which wouldn’t have had any bottleneck.

Unfortunately, it won’t be perfect in terms of scavenging, but then again what log style manifold (c6 rs6) is?

Got the frond end assembled for mock-up, I think I’ll get the manifolds welded this weekend and then figure out if I can go with twin 38mm wastegates or if I need the 44’s.

I’m just happy it’s symmetrical as fuck and everything fits!


Looking good too! What are you doing for a harness?

Still running the factory harness and ECU’s. I think Jackalmotorsports has had success on tuning the stock B7 RS4 ECU’s for boost so the MED9.1.1’s should be capable of it aswell.

I will send the car up there for dyno tuning; remote tuning as I’ve done in the past isn’t as feasible for a bespoke (more so just complicated) swap as this.

Also, both manifolds have been welded up, next on the list is downpipes… full 3" downpipes are going to fit, but before that I need to have some fun with hood dumps.

Buying the oil line fitting tonight (Tee’ing off the factory low oil pressure sensor threads and welding on AN bungs for the return lines into the lower oil pan)

After that there’s no reason why I shouldn’t be able to start it.

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Little update video. Should have it running by the end of the weekend!


Tial 38mm wastegates came in this morning. Got the manifolds drilled out and plopped them on, tacked them, and welded them. Also made the dump pipes for them as well; so all around A LOT of progress today… (thank you in-laws for watching the toddler!)

Still waiting on that pesky -4an line for the oil feed to the turbos, but as far as I can tell it’s ready for the first start!

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Harness is on. Everything is done. Installing the 4psi wastegate springs, filling the engine with oil, and connecting the engine harness to the chassis tomorrow after work.

On a side note, I want to remake the entire harness from scratch, did anybody have a list of necessary connectors and connector pin part numbers?

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This thing sound so fucking insane around 5000rpm.

That is all.

Twin Turbo setup is alive and very well. Still a bunch to do, but have a listen to those GT35’s in the meantime.


Those extra 2 cylinders made a huge sound difference, stoked to see whats next!

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Lovin’ the sweet sweet sounds this thing is making. So, I had to pull the motor out to revamp the coolant lines (going from water pump to back of engine, the rear crossover, and from the back up to the radiator) it’s just easier to do it with the motor out. Finished that up and tucked them under the manifolds.

Got the Ringer Racing Stage 5 clutch back on and reinstalled it into the car yesterday. Tonight, I went ahead and reinstalled everything so I could mount the intercoolers and fab up some piping (again, gotta keep it symetrical)

Ordering a ChaseBays Dual Master manual brake setup (already made a 1.5" thick spacer for it) so theoretically I should be able to drive it once those are done.

The only thing after that is to install some HPX maf’s and mount the coolant bottle.


Front end went back on for test fit. Need to do some final once overs and torque checks on everything before final reassembly and radiator drop in (staying the same).

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