MZR 2.5 Bottom End Swap - 08 MS3

Hey All, been a long time lurker on this site to gather tips, tricks and knowledge about this platform. Fair warning this is a long read, can make alternate posts if there are additional questions.

Last Christmas I was playing with the idea of picking up my first project car. Coming from a background of wrenching and riding/driving anything with an engine, the project seemed like a good idea. I was searching around on kijiji, autotrader and the like for a good vehicle to work on, could do mechanical issues but rust is a no go for me personally, not a body repair guy at all. Then up came a 2008 mazdaspeed 3 with internal engine issues for $1500 CAD. The car had ~190k kms on the ODO and the body was in good shape (aside from a clear front bra that poorly aged and oxidized). The seller had the courtesy to be descriptive and highlight the fact that the 2.3T had spun a connecting rod and was knocking badly (turned out to be cyl 1 & 3, both of which had NO rod bearing remaining as it was in a shredded pile in the bottom of the oil pan)...


My dad and I visited the car in Hamilton, and the car had clearly been sitting for some time as the rotors were all rotten. As mentioned the body and underside were in surprisingly good shape as I know late 00's Mazda's were notorious for rear quarter panel rot. There was a little bubbling in the inner pinch welds on the underside of the driver and passenger door but nothing too critical for a project car. I paid for the car and we loaded it up on a uhaul tow dolly (front wheels lifted only) and set on our way to Windsor. No less than an hour onto the 403 (and already dark might I add) and suddenly there was a harsh drag on our family suv, and literal orange sparks coming from the rear left corner of the recently acquired MS3. After quickly puling over to the shoulder near an on ramp, I was greeted with no tire or rim on the rear left corner, nothing but a gaping wheel well and a bent lug stud, the lower control arm took the pavement like a champ. After swapping the dummy spare tire onto one of the front wheels and one of the fronts onto the rear, I realized the seller had EVERY SINGLE lug nut hand tightened, as in ~5lbft if that, its a wonder I made it as far as I did...

Fast forward to Windsor, I addressed the brakes with replacement rotors, pads, sliders and caliper slider boots on all four corners. Full well knowing the engine had spun bearings, Early 2020 was the start to the tear down process. Pulled the oil pan off to assess the damage and see whether or not the crank was remotely salvageable (if turned down and use oversized bearings). However knowing that this motor was most likely abused and probably suffered from ZZB, I ruled out reusing the 2.3 engine in my car. Note I was trying to keep this build cheap to gain experience and have a fun car at the end, was not interested in modding and taking the engine to a machine shop to push high HP.

After sitting on the car for a few months I stumbled on a post about how someone had swapped a 2.5 Duratec bottom end with the 2.3T top end (head, turbo, exhaust etc) with little to no workarounds required. Just reroute the oil feed for the turbo as the 2.5 block did not have the port drilled and tapped in the rear (nor an oil return for the turbo). Long story short I decided on this route and within a few weeks had sourced a $400 junkyard 2.5 complete engine out of a 2010 ford fusion at LKQ. The engine was out of an automatic car and had 70k kms on it.



Spending many nights and weekends removing my powertrain and stripping down both the 2.3T and 2.5 N/A was worth the cost alone just for the gained knowledge and experience.

Some more technical info for parts used in the build are as follows:

• Mazdapseed 3 headgasket
• Replaced many gaskets with speed 3 such as EGR, Intake mani, turbo to DP, etc.
• PCV system retained from 2.5 engine, intalled MS3 pcv valve to accept the aluminum intake manifold piping
• Carbon cleaned intake valves while head was off (CRC valve cleaner)
• Installed new clutch, TOB, Fork and pivot and had Dual mass flywheel resurfaced on a lathe (locked up dual mass FW to keep from bouncing around)
• Trans fluid flush, coolant flush (duh), fresh 5W30 full synth
• Stock gap iridium spark plugs
• Retained MS3 oil pan for dipstick (2.5 was straight up through the centre of the engine)
• Replaced all timing components in the engine (used 2.5 timing gear (vvt, exh cam gear) throughout as the chain is visibly more durable)
• VVT solenoid was from MS3
• Kept oil pump from the 2.5 engine
• Oil feed for the turbo via teeing off where the oil pressure sensor is installed in the oil filter/oil cooler assembly
• Used AN 4 braided line to route up over the transmission to banjo bolt on turbo (replaced copper washers)
• Retained stock bolt for turbo oil feed (some say it feeds too much oil, however my turbo was not showing signs of leaking seals)
• Retained part of the oil drain tube from turbo, cut lower flange off and used power steering hose to connect drain tube to a barbed return into the oil pan (drilled oil pan and sealed with A/C rubber washers)

Aside from prematurely replacing the MS3 MAF sensor in an attempt to pinpoint a rich condition (turned out to be coolant temp sensor, then loose MAF connection), the engine runs quite happily and makes good power. I have no clue how these cars behave from the factory but it can really move and is surprisingly quick for a 6sp hatchback.

As for longevity I can't comment as I have been driving for about a month now (~1000kms), however it is still running strong and I hope it stays that way for a while. If there are questions I will try to answer the best I can, I personally did this build along with the help of some close friends for engine removal and install (& moral support + many garage beers).

Cheers,

Derek (& sparky, as the name fits day 1 of ownership)

 

Any involvement from the infamous Matt on this build?

Sent from my SM-N975W using Tapatalk

 

Not sure who the infamous Matt is no, I did have a few guys message about the build when I sold off the ms3 block though.

 

It’s really nice to see the level of detail shared, thank you!! Gives a little less dread to the ownership of a speed thanks to a much lower cost replacement to our engines if we end up with the ZZB!

 

Thanks for the info. I will have questions in the future.

 

DID YOU USE THE CRANK FROM THE 2.5 OR THE 2.3?

 

I used the crank that was in the 2.5, my 2.3 crank needed remachining (ended up selling the old block & rotating assy together)

 

How's the 3 holding up for you? It's been quite some time now!

I'm thinking about doing a 2.5 bottom end, going FBO. I heard the block can take a good amount of power up to a safe spec of 325-350 hp with stock internals, but also read a lot from people that if you're staying stock for the purpose of reliability it's got a smoother and better low-end torque.

There's also a 2.5swap group on Facebook as well but a rare of no videos actually showing step by step on what can be transferred over ( just a how to with the video skipping to an already put together pieces each part is talked about ), I don't like reading the instructions as it may be different from each person doing the swap, I'm more of a visual guy

 

I think bottom end is all 2.5 other than the oil pan

 

Any updates on how it's running?

 

Speed3 shell with no engine, 2.5 long block, 2.3 Short block, 2.3 timing components. Rings gapped accordingly, plugs gapped properly, NGK 6510 or NGK iridium 1 step. Autotech or CS HPFP. Thats all I can think of, if you're doing a 2.5 swap on a stock N/A 2.3, You'll need to tap the oil pan for the turbo hoses, and upgrade axles , trans, mounts and other stuff if you're trying to push over 200 HP as components from an N/A 2.3 can't handle power put down off a speed3.

 

Speed3 shell with no engine, 2.5 long block, 2.3 Short block, 2.3 timing components. Rings gapped accordingly, plugs gapped properly, NGK 6510 or NGK iridium 1 step. Autotech or CS HPFP.

What was your ring gap on 2.5 block? Top ring and 2nd ring

 

That 2.5 head looks like it might be PI. Is that the case?

 

The 2.5 is pi.

 

Is the head worth a shit?

 

It flows fantastic

 

I'd also love to know what the stock ring gap was on the 2.5. I've heard it varies a lot over the years, but I've never seen concrete info on it.