Danjo

Watched a podcast by Flatirons on the Subaru long rods (+2mm and +4mm) and I notice that IAG offer +2mm rods in all of their bigger power EJ25 builds, but why the fascination?

Of course the decrease in rod angle means there’s less side loading on the piston skirts and cylinder walls, is this their way of getting around the thin liner issue on the EJ25’s and why the US seem to be so successful in running these stock linered case halves to much higher power hp than we seem to be able to achieve here without failure?

I keep seeing them mention rod ratios and having an engine with the ability to rev, but again, why the fascination with this? To me it almost feels like trying to fix an issue that doesn’t exist. Yes a longer rod will increase the rod ratio and therefore allow the engine to rev higher, but at the expense of lower torque levels. Yes it gives the piston a longer dwell time but at the expense of being more knock limited. And an EJ25 has a rod ratio of 1.64, that’s hardly a poor ratio for revs considering an RB26 has the same ratio and is known to rev quite happily to over 9k when built properly. Surely there’s better EJ’s to use of you want to build a high revving race engine?

Am I missing something?

matt-c

iTrader: (5)

I've wondered this as well. If it was so good, surely all would be built this way.

I think I have only seen +1mm rods over here.

96sti

I run +2mm longer rods back when the build was done few years ago it was un common had to have them made by Corillo in America ran with the ej20 75mm crank faster reving with the displacement of a 2.5 ltr so mine is a destroked 2.3

Danjo

I’ve not seen much in the way of data to actually prove that it’s worthwhile. A 2mm longer rod lifts the rod ration from 1.64 to 1.69, so it’s not exactly a big gain in rod ratio. I think I’d rather the low end grunt and the ability to spool a larger turbo at lower revs. It seems +2mm rods would just shift everything to the right on the graph for not much gain.

Danjo

What was the reasoning behind this rather than going for an EJ22 with the 79mm crank?

96sti

For the faster revving and to prove it works and to be different I geuss plus couldn't source a ej22 case at the time. 490bhp and 520ftlb @1.2 bar and still more to go just started getting valve bounce in the heads

Danjo

Thats fair enough, I know it’s a fairly common theme in the US to destroke.