ej205 engine rebuild for a daily driver
 

Lastly, the engine in my blobeye wrx said bye bye (something got into one of cylinders when engine was running). I decided not to gamble, and instead of buying a secondhand engine, I will have my engine rebuilt.
The shop that will be doing it, checked and measured my engine:
- cylinders will be rebored;
- crankshaft is in very good shape and can be reused;
- bearings will be changed to ACL Race (this is what the shop recommends);
- pistons need to be bought new for rebored cylinders; the shop recommends using stock ej205 pistons (HBR); the other option that they are practicing are MAHLE 4032 pistons;

Currently my car is running on WRX PPP map. I would like new engine to handle as much as 300-330BHP. I have plans to install td04 hybrid or vf 35 or simillar turbo. For sure nothing bigger, I don't have plans to change gearbox to 6 speed (however, I have stronger JDM WRX 5speed gearbox). The car is my daily driver, I often use it on short distances (I have about 5 miles to my job).
Shop says that HBR pistons are enough for that power, but if I want they can mount MAHLE pistons instead (this would cost me 200 pounds more).

What pistons would you advise me to use? Will MAHLE give me anything more at that power level (they should be more resistant to knock?), with stock ej205 crank, on 5speed gearbox? Will they perform good on short distances and can I expect as high mileage from them as from stock pistons?
Or should I just get stock pistons?

These are just my opinions, and I'm not an engine builder etc, but I think Subaru must have done something right when designing the 2.0 turbo lumps.

The reason I say this is that there are a lot of high mileage ones knocking about on a standard engines, so they do seem reliable even on standard components PROVIDED the engine is run within the design parameters. I.e. if you're sticking to PPP+"a bit" level power, and you want longevity, then I think there's something to be said for sticking to the subaru components.

I don't have any hard data to back this up, but my "general, wavy-hand, feeling" is that there aren't as many high mileage forged engines about, at least not having undergone "refresh" (which IMO sounds almost like a complete rebuild, really...).


Also, if you stick to Subaru components, you can use the rods and pistons from e.g. the 2.0 litre STI engine - both of these are apparently stronger than the WRX counterparts, and if you're buying new, then there might not be a huge difference in cost between an oversize STI piston vs and oversize WRX piston. For rods, you could probably get away with a used set of STI rods from a 2.0 (or used 2.5 rods from either STI or WRX), which should be possible to source for under 100 pounds (both the ej25 and ej20 rods are the same length, as far as I know).


Most people would probably instinctively say "go forged", but IMO it *might* not make sense if it's a daily driver, and you only want a modest 350bhp max.

I'm not sure on stock power of these blob wrx but say it's 250bhp,looking to increase to 350 is hardly modest,that's around 40% increase.
I would personally go forged pistons.
Again I'm no engine builder so just my opinion.

i should clarify, for the 350bhp level, i'd go with the sti pistons/rods.

Can buy 2.1 stoker kits for 1700 pound very cheap

Cheapest and most reliable for your goal would be to fit a ej207 short block, circa 1k to buy plus labour to fit

Or fit a brand new ej207 circa 2k with peace of mind that you know the history/condition :thumb:

Unless you are planning to keep the car for a very long time, I personally think you're mad shelling out £2.5k+ (which it must be for a decent rebuild) on what will still be a WRX motor (same heads, cams, non-avcs etc). Especially when you are only looking for 330bhp. I certainly don't think you'll see any benefit from forged pistons at that power level (VF35) if it's mapped correctly.

You could probably buy and fit 2 second hand ej207 motors for the same cost.

Don't get why you would pay over 1k for a used and possibly abused motor when you could pay 2k for a brand new zero mileage motor :wonder:

As I mentioned, buying a second hand lump is not an option. Have you ever seen ej207 which has done more than 160k miles? I personally haven't. These engines are not long lasting, especially because of how they were used (of course every seller will tel you that he only drove it to church on Sundays :) ).
Let's assume I buy a beatifully looking ej207. I cannot easily check the bearings condition. So I buy an engine and swap it, I invest my money and in a couple of thousands of miles I could hear sweet sound of spun bearing :) And then I would need to pay for a full rebuild (more than I have to pay now).
Main benefit for swapping ej207 would be to get AVCS (at that power level I don't see any benefit from high flow heads). But to get it I would need to buy a full swap (including wiring, ecu, turbo, etc.) so the cost would be closer to 4000 pounds, and still this is a second hand lump with unknown history and internals condition.
Plus to use a full potential of ej207 I would need to swap also 6speed gearbox, that's another 3000 pounds. And it's still a WRX wagon :)
On the other hand, for my engine repair I am getting a warranty - 2 years or 60.000 miles. The cost of repair should be about 2.500 pounds including reconditioned heads, ACL bearing, and OEM other parts (I don't need to buy crankshaft and rods which are in mint condition).

About using ej207 pistons and rods: rods could be considered, but are they really that stronger? How much torque can handle stock ej205 rods and how much ej207 rods? About ej207 pistons: they are very expensive (1 pc is more expensive than a full set of HBRs) and I don't know how would they influence the compression ratio?

Nobody has any real life experience with MAHLE pistons (4032)?

I have mahle 4032 on my 2.5 running mid 400hp. They're quiet for a forged piston and oil usage is virtually nil.
Trev

How much torque can stock ej205 connecting rods handle? And how much more can be handled by sti/ej207 rods?

You're gearbox will be the limiting factor. 330bhp/lbsft are considered "safe" for both.

My stock gearbox has been swapped for a 04 WRX JDM gearbox (AFAIK it is the same as P1 gearbox), so it should handle a little more torque/abuse.
So is there no difference between ej205 and ej207 rods strength?