MZR 2.5/DISI Swap Internals Question

Hi all, the 235000km engine in my 2008 Mazdaspeed 3 recently started knock knock knockin on heavens door, so i've been looking into the 2.5/DISI hybrid swap. Eventually I want to make somewhere in the range of 450whp. I've found some Molnar rods for the 2.5 bottom end that would hold up to that kind of power that fit the stock wrist pin. I was wondering if that power range necessitates upgraded pistons as well? I havent heard anything about piston failure in these engines, but then again, I havent seen any >400whp builds without upgraded pistons.

 

If your going to build a motor why wouldn't you build the 2.3. The only reason anyone uses the 2.5 bottom end is that it's a cheaper way to get back on the road. There are no other advantages to the 2.5 bottom end

 

Where I live decently low km 2.3 DISI engines cost upwards of $3500. I've put together a parts list that includes the 2.5 short block, a full bottom end rebuild, VVT parts and a clutch/flywheel kit for <$2800 If I was looking for crazy power I would definitely go for the 2.3, but im not

 

Why can't you just build the 2.3 you have?

 

Because there's a hole in my block? Wouldn't be asking about the 2.5 if I could rebuild mine

 

Ahh you said knock and I thought it was running with rod knock

 

The pistons on the stock 2.5L are weaker then Speed 2.3L pistons.. The power potential of a 2.5L comes from Miata world with port injection/not as knock prone.... That doesn't mean people aren't having success running a 2.5L swap on stock pistons.. If you are going to rebuild the motor and put rods in it.. Then don't short change yourself.. Do pistons as well...

I was in the same boat as you. I did a forged 2.5L build for my speed6... My stock motor melted down and destroyed the block.. It was almost the same cost to buy a used 2.3L as it was to buy a 2.5L and all the parts to rebuild it...

 

mr sassy pants here expects us to be able to mind read information that wasn't posted already when all you said was you had knock on your OP. Some people opt to go 2.5 because "cheap".

2.5 is weaker, don't bother I know it's recommend on Facebook frequently but if you want anything more than stock power ever don't go 2.5, which you said you do so time for a built 2.3 block. You want 450 yeh I'd be upgrading pistons and rods.

Do people not search for other 2.5 threads here? They all end in the same way; users recommending against the 2.5 swap unless you want stock power to get your car back on the road. If you want to make power and don't have the budget then it's time to get a beater and save until you do.