cobo10201's "Just a V6" Twin Turbo 2017 3.7L Mustang

[cobo10201]

I'll keep going back to the question of CATS and restrictive exhaust. If so, the backpressure is killing those turbos.

So I’ve actually been looking into this and talked to two local performance shops. They both told me too much backpressure after the turbo would actually LIMIT building boost because the turbine would take longer to spool up. Without getting to science-y, the turbo needs high pressure from the engine (pre-turbo) and less pressure after the turbo. The lower the backpressure after the turbo, the faster it will spool. Higher backpressure from the cats would cause it to spool slower and build less boost. They basically told me modern cats are extremely efficient and shouldn’t be causing any over-boost issues with the turbo. If anything removing the cats or getting high flow cats would increase the ability to make boost.

The main thing each one told me is unless I’m really going for max performance with track-only goals, there’s no reason to remove or replace the cats. The F-150 comes with essentially identical cats from factory and the turbos are build for that setup. One of the shops actually put my car on a lift to check everything out and they said the only thing my cats are doing is making me build boost a little slower and the current setup shouldn’t be dangerous to the turbos or the engine.

Truth-be-told I think at least one of the turbos has been bad from the start. The driver’s side turbo has always made a slight chirping sound when spooling, and it’s not a normal turbo whine. I’m thinking the combination of the overboosting issues and pushing the damaged turbos with WOT and 0-60 pulls just put them over the edge.

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[USMCtoARMY]

So I’ve actually been looking into this and talked to two local performance shops. They both told me too much backpressure after the turbo would actually LIMIT building boost because the turbine would take longer to spool up. Without getting to science-y, the turbo needs high pressure from the engine (pre-turbo) and less pressure after the turbo. The lower the backpressure after the turbo, the faster it will spool. Higher backpressure from the cats would cause it to spool slower and build less boost. They basically told me modern cats are extremely efficient and shouldn’t be causing any over-boost issues with the turbo. If anything removing the cats or getting high flow cats would increase the ability to make boost.

The main thing each one told me is unless I’m really going for max performance with track-only goals, there’s no reason to remove or replace the cats. The F-150 comes with essentially identical cats from factory and the turbos are build for that setup. One of the shops actually put my car on a lift to check everything out and they said the only thing my cats are doing is making me build boost a little slower and the current setup shouldn’t be dangerous to the turbos or the engine.

Truth-be-told I think at least one of the turbos has been bad from the start. The driver’s side turbo has always made a slight chirping sound when spooling, and it’s not a normal turbo whine. I’m thinking the combination of the overboosting issues and pushing the damaged turbos with WOT and 0-60 pulls just put them over the edge.

Bear with me here. You have to understand those turbos are made to be matched with the 3.5 engine which has a different compression ratio than the 3.7 engine. The 3.7 responds extremely well to a proper boost application, bit poorly with the 3.5 kit. It's all about the turbos and their size. Countless people who have run this setup run into the same issue as you. You cannot restrict the exhaust flow. It is true from the factory on the 3.5 setup it is optimized pretty good and return in gains isn't as great by just opening up CATS and going to bigger exhaust. But, this isn't the case with a retro fit application. Unless, you replace the turbos themselves with bigger better units the best thing to do is opening up the exhaust flow to prevent the backpressure issue AFTER the turbos. It won't improve the "performance" aspect of this build per say but will ensure longevity in the setup.

AND, your explanation above is saying exactly what I am talking about. You said, "The lower the backpressure after the turbo, the faster it will spool." This is what I am talking about. Freeing up the exhaust flow AFTER the turbos. Yes, you need pressure up front, but not after. This means bigger Downpipe, no CATS or maybe 200 cell CATS (high flow), and a bigger exhaust free of restrictive chambered mufflers. The downpipe is damn near impossible to improve on this build because of the location of the turbos and firewall since the kit isn't specifically built for this engine but a retro fit from the 3.5 engine. This leave you with CATS and exhaust.

In the end none of this really matters because the turbos themselves are the main hinge point, but even if you do attend to the post turbo exhaust side of the build you also set yourself up for the future when and if you upgrade the stock 3.5 turbos.

 

[cobo10201]

Hydroplaned in the rain and hit the barrier last Monday. Sad times. Doesn't look TOO bad, but the lower airbags did deploy. Initial appraisal from the insurance was ~$4k in damages, but still waiting for the final appraisal after the shop gets everything broken down. Fingers crossed there's no frame damage, but honestly I'm not holding my breath. I'm just happy I didn't hit anyone else and that I walked away with nothing except a seatbelt bruise.

 

[OneStrudel]

Were you ever able to fix the over boosting issue? Or did you just tune it for 11psi?

 

[cobo10201]

Were you ever able to fix the over boosting issue? Or did you just tune it for 11psi?

Hey sorry, just seeing your post. Yep! Got it sorted by running off wastegate pressure alone and tuning the wastegates to exactly 10 psi. Tuning is done and car runs like a dream. Currently just waiting to get it back from the body shop after hydroplaning and hitting a wall.

 

[308Vanquish]

Have you been able to check and see what kind of horsepower you are making? I have an older Mustang with the 3.7L and I plan on twin turbos for it soon as well, just curious what kind of gain you got with the Ecoboost F150 turbos if you happen to know??

 

[cobo10201]

Have you been able to check and see what kind of horsepower you are making? I have an older Mustang with the 3.7L and I plan on twin turbos for it soon as well, just curious what kind of gain you got with the Ecoboost F150 turbos if you happen to know??

Hey! I never got my car dyno'd, but the S550 my kit was based on gained ~100 hp and ~150 lb-ft of torque if I remember correctly so that's the gains you can probably expect once properly tuned.

 

[308Vanquish]

Hey! I never got my car dyno'd, but the S550 my kit was based on gained ~100 hp and ~150 lb-ft of torque if I remember correctly so that's the gains you can probably expect once properly tuned.

Awesome. That's pretty decent for the little turbos. My engine is already internally built pretty well, so I'm going a little bigger than the Ecoboost turbos. A lot of parts needed to set up a turbo system from scratch. I already have a pair of GT3582R's, but those are quite large for a V6. Thank you for the reply. Have you gotten your car back from the body shop yet from that last incident?

 

[cobo10201]

Awesome. That's pretty decent for the little turbos. My engine is already internally built pretty well, so I'm going a little bigger than the Ecoboost turbos. A lot of parts needed to set up a turbo system from scratch. I already have a pair of GT3582R's, but those are quite large for a V6. Thank you for the reply. Have you gotten your car back from the body shop yet from that last incident?

Yep! Got it back a couple weeks ago. Sadly the car hasn’t felt the same since the accident. It still runs and drives perfect, but I’m not having as much fun in it. I’m sure it would probably pass but I’ve actually decided to sell it. I was actually about to make a post because there were some other reasons as well.

 

[cobo10201]

So it is the end of my time as a Mustang owner, at least for the time being. An unfortunate accident in my wife’s car has left us with the Mustang as the sole vehicle for a family of 4 (soon to be 5). Unfortunately her car was a 2008 Mitsubishi Galant so the insurance is only giving us $4700 (before medical bills/pain and suffering/etc. But that comes way later). We’ve decided to sell the Mustang and the new owner actually just drove it away about 2 hours ago. I ended up selling it for more than I bought it for (still a net negative with the turbos, but I’m not mad). We’re planning on taking the insurance payout plus the money for the Mustang to get a slightly used Explorer as our family vehicle, and we have a Mach E on order that should be in around October.

It’s been a fun ride y’all! I’ve learned a lot from this community and I appreciate all the help I’ve gotten in this thread!

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