Mazdaspeeding's 2012 ~400whp engine rebuild

mazdaspeeding

mazdaspeeding

Greenie N00B Member
So I've owned my 2012 Mazdaspeed3 since it was brand new. I did a bunch of little "stage 1" type things right off the bat like rear motor mount, short ram intake, hpfp internals, Cobb AP +OTS tune, stainless steel brake lines, shifter bushings + short shift plate. It was very reliable for about 130,000 miles. I had just replaced the suspension with Bilstein B6's when I developed rod knock due to low oil and now I'm planning an executing a rebuild with a ~400whp power target in mind.

I've got ~$10,000 to make stuff happen here and get my speed3 back on the road. While the engine is disassembled for the rebuild, I also plan to replace the clutch and fix the second gear pop out problem. I think I'm going to add a CST4 turbo with the EWG setup, a corksport intake manifold with additional fuel rail, an ETS TMIC and also replace the motor mounts. I don't want the car to be very loud at idle or around town, so I intend to replace the downpipe but keep the exhaust stock past that. I'll also fix some things like replacing the skid plate I lost, swapping sway bar bushings and getting new tires. I'll keep it updated as I intend to start ordering parts this upcoming week and having the car back together within the next 2-3 months at most.

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Welcome, and great to see!

I'm a huge sucker for the Focus ST Manifold, since all-in you are half the price of the Corksport IM, and it should work perfectly at your power levels. You just need to modify the FMIC piping a bit to make it work - you can see that on my build thread if you are interested.

I would also look at a CST5 or BNRS4 if you want to hit 400 without really working the turbo too hard, and it's a pretty insignificant cost difference.
 
Welcome! I have the CST4, and it will top out at 400. CST5 is where you may want to look. I have my motor in rebuild status, both CS manifolds, CS FMIC and TB, 3.5" intake, CST4 IWG, CPE DP, CS 3" exhaust. I am hoping for 400. No port injection, E85, or meth. Just a 93 tune.
 
jdab555 said:
Welcome, and great to see!

I'm a huge sucker for the Focus ST Manifold, since all-in you are half the price of the Corksport IM, and it should work perfectly at your power levels. You just need to modify the FMIC piping a bit to make it work - you can see that on my build thread if you are interested.

I would also look at a CST5 or BNRS4 if you want to hit 400 without really working the turbo too hard, and it's a pretty insignificant cost difference.
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This is good to know. Although the info below about the intercooler is new for me and I'm going to have to do some thinking.

Raider said:
Welcome! I have the CST4, and it will top out at 400. CST5 is where you may want to look. I have my motor in rebuild status, both CS manifolds, CS FMIC and TB, 3.5" intake, CST4 IWG, CPE DP, CS 3" exhaust. I am hoping for 400. No port injection, E85, or meth. Just a 93 tune.
Click to expand...

I want to keep the car as a daily so I'm thinking a CST5 might be just a bit "too big" and I'll probably just have to revise my power goals.

Easter Bunny said:
The corksport intake manifold has no provision for mounting a tmic fyi
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Now this is exactly the kind of information I needed. I'll look more into the FMIC options and other intake manifolds maybe.
 
If I revise my power goals to ~350hp-375hp I wouldn't need extra fueling so the intake manifold becomes less of a worry to begin with.

My philosophy for this rebuild is just making everything as good as it can be while staying (mostly) within OEM packaging and the realm of "bolt-ons". I'd like another 100k miles out of this car with proper care hopefully.

I'd initially thought about keeping the cost down and just doing the engine rebuild w/ forged internals, the clutch/transmission fixes and swapping the K04 for like a S3/CST3 for reliability more than anything else. But tbh, I want the EWG for the novelty factor more than anything else. That's what's pulling me to the CST4 over the BNRs or the CST3
 
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If you're going built motor and big turbo your car deserves a FMIC, it is a noticeable and appreciable drop in BAT, especially if you are using it as a daily.
 
If you're running a built motor and big turbo and a higher % of ethanol your car doesn't care if it has a FMIC or a TMIC. Vash made 550 wheel with a TMIC, and I made about 380 with no intercooler at all (but did have WMI).

Edit:
The CS intake mani does have TMIC mounting provisions but if you're going to use a TMIC with PI you may need to run the stubby injectors; this is one thing I've not tested yet. I'm also not sure *which* TMICs you can run with the rail in place, though the CS TMIC would probably work out since it's quite thin and sits a bit higher than, say, a CPE (which is what Vash ran).

Side note number 2: The bigger the turbo the more efficiently it can make boost. Running a 500 WHP turbo at 400 WHP with a TMIC may actually be a good compromise, as the turbo outlet temps into the TMIC should be lower (depending on where on the map you are).
 
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I'd definitely buy a quality IC and absolutely abhor ebay.

So far, I don't ever plan on going past ~500whp, my mechanic is recommending a mostly stock bottom end with upgraded head studs and bolts. At most I want to do a CST4 turbo with full supporting mods. I'll almost certainly do the manifolds and full 3"+ intake and exhaust
 
I realized my intake is actually only the 2.5" inch Corksport intake and I'm debating how far I want to go with 3" vs 3.5' and having to move the battery
 
If you plan on going bigger turbo later, get a 3.5". No reason not to, and gives you a whiff of more topend on the baby K.
 
I plan on going to the CST4 and no further. Beyond that I'll just optimize the car and I'll probably buy a second car in the next year or two but I won't get rid of the speed.

I just don't see the point in a 500+ hp FWD car but that's just me. I'd build the car for AWD before I'd swap a bigger turbo on personally.
 
As far as the clutch goes, I've been pointed to South Bend or Xclutch. I'm leaning Xclutch but I'm not sure if I should spring for the street plus over the street. They say peak tq holding in the street is ~440 and I don't think the CST4 can really top that but I'm not sure if the extra overhead of the plus would be worth it.
 
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