Getting very nerdy with engine capacity options!!!

Here's what I'm thinking about!!
Bareing in mind that I am a carpenter,
EJ20's redline at 8,000 rpm, EJ25's redline at 7,000
I think maybe that is largely down to the shorter throw of the 75mm crank as opposed to the 79mm crank of the 2.5!
The popular options for more cc's is fitting a EJ25 crank to an EJ20 making the 2.1
And Boring out a Closed Deck Block (CDB) to 97mm and fitting the EJ25 crank)
Both of which do away with the revvier EJ20 75mm crank, and hence loosing out on 1000rpm, ie. one less gear change across the quarter mile line! or between bends in mondello??
Of course you gain maybe 10% more Torque, But not sure if the lack of revs would suit a short ratio 'box like a type R or RA and some Jap newages!

So, I got thinking about big bore, short stroke options, in favour of gaining capacity but keeping the 8,000rpm redline

Has Anyone ever heard of anyone doing this, and what's the results?

My own next step is 2.71L torque monster, as it suits my longer ratio 'box and I do like Torque

Torquey Options

2.5 99.5mm bore x 79mm stroke, standard 2.5

2.1 92mm bore x 79mm stroke, EJ20 with 2.5 crank

2.35 97mm bore x 79mm stroke, EJ20 or EJ22 CDB with 2.5 crank

2.71 102mm bore x 83mm stroke, EJ257 linered with custom 83mm crank

Revvy Options

2.0 92mm bore x 75mm stroke, standard EJ20

2.22 97mm bore x 75mm stroke, Standard EJ22 (22B)

2.36 100mm bore x 75mm stroke, EJ257 with EJ20 crank

2.46 102mm bore x 75mm stroke, Ej257 linered with EJ20 crank

Dan

Surely the crank size is not limiting the RPM limit on the ej25? You've lost me there.

as far as i know crank stroke does limit redline to a certian extent!
be interesting to know this, would like to keep my ej20 crank and have a 2.2 or 2.3 in the future! somethin iv always bien thinkin about is increasing the engine capasity.

My own next step is 2.71L torque monster, as it suits my longer ratio 'box and I do like Torque

if your worried about rev limit 2.7 isnt the way to go as id imagine ud lose another 1000 rpm over 2.5 option
im building a 2.33 rev limit 8000/8500rpm undecided yet tho best of both worlds i suppose in a way, can rev out and extra cc`s over the 2ltr option

Get a 2.7 and spend around 4k on your heads and you will have all the revs you want, dont think revs and the forester will go hand in hand, you need bigger displacement

I personally would favour the non revvy torquey 2.71 long stroke option for the Forester
If I had (when I have) a type R or spec c I would be looking for revs!

Dan

whats stopping you having big displacement and revs? I don't know why you think you need to trade one of the other?

As above, bare in mind, I am a carpenter, not an engineer or mechanic!

My reasoning is,
Standard EJ20 revs to 8,000rpm
The EJ25 revs to 7,000rpm

I thought the longer the stroke/bore ratio = less likely to to want to rev,???
ie. It is known that stroking an EVO form 2.0L to 2.4L looses the willingness to rev!

If that is not the case, what's makes the 2.5 less revvy!

Dan

It will do less revolutions alright because its longer but it doesn't mean its limited to how many revolutions it can do...thats down to mechanical failure

longer stroke makes the engine "SLOW" to rev, but again as i said you can have a fast reving big cc engine aswell, but you will have to spend money on heads, Heads are as important or even more important at some point than the block.
I have a mate whos brother is big into muscle cars in OZ, and he would think nothing of spending 5k on a set of heads, and in 6mnths time when a better set come out buy them and ditch the old ones, all there power is made from the heads.
The main thing with an engine/ turbo/ heads choice is to determine what you want from it.. if you want a track car, well then the smaller engine with big turbo is fine as it will be always up in revs so lag/ power band isnt an issue.. however, it would make a shite road car, road cars should be like hookers, ready to go when its put up to them, no hanging around waiting for them to get going
You have mentioned Type R Dan, if you were ever thinking of an out and out track car, leave the forester alone or even down tune back to 400/400 and use her as your tow Jeep, have your stripped out Typer with A 2.1 and 450hp Turbo on it.
If the forester is what you want then the bigger engine is way to go, but then i dont know what that will be like on track?

My thoughts exactly!
I'm still interested how a 97mm bore X 79mm (2.5 crank) 2.35L
Would compare to a 102mm bore x 75mm (2L crank) 2.35L
Dan

How would you get the 102mm bore?
Heres a thing i was told years ago, and think it was said that formula 1 engines do this, if the closer piston diameter is to rod lenght the faster the rev, i was told that formula 1 engines stroke and bore size are equal, hence there rev.. not sure if its true or not, so with that in mind the 2 options you have listed could quite end up revving the same, as there is only 1mm in difference of both... But prob would be the 102mm bore, that cant be got withouth liners and when going that far, why not go 2.7?
And now to really confuse you Dan, how about using a custom piston with gudgin pin set higher and using a longer than standard rod and upping the stroke and upping the torque

I do like threads like this!
That american 2.71 short block, uses an EJ25 block, linered and bored to 102mm, then custom 83mm stroke crank, I Imagen the rods and pistons are as you described above
So by using the linered EJ257 with 102mm bore and a short throw EJ20 75mm crank, you get 2.35,
Hondas legendery K20 has 86mm bore and 86mm stroke!!!!!
EJ 257 has bore/stroke ratio of 1:1.26, ie. the bore is 26% longer then the stroke, EJ207 has bore/stroke ratio of 1:1.22 ie. the bore is 22% longer then the stroke
Would that be enough to loose 1000rpm? Why?
I would have thought the shorter the stroke, the harder it revs? but honda and F1 obviously know better :lol:

SO If we got one of these 83mm stroke cranks and kept the EJ20 bore of 92, that's a ratio of 1:1.1 That should be the revviest possible combination?? and making a 2.2L motor??
:lol:
Do you think anyone has done anything like that?
I wonder what the Rev limit would be then?
And with such a long stroke, she should be super torquey?
Dan

If going to the expense of linering for a 102 bore, it wouldnt really make sense to then down stroke the motor... You may bite the bullet Dan, the only way to find out is to try out.. or you can go the proven route of 2.35.. rev of 2ltr torque of 2.5

I'll defo be going 2.71 torquey route next time with the forester!
I'm just very interested in options that aren't "the norm"
I would love to see someone do a revvy (Unequal length headered) build!
Dan