2.5 N/A engine build question

[MetalNeverDies]

hey guys i have a question.

would it be better to build up my stock 2.5 rs na SOHC engine?

Or to find a used or new JDM dual over head cam.

Or would it just be worth it to run a 2.5rs DOHC if i can find it for the same year as my car?

bassically ive been playing with the idea of a turbo and as fun and powerful as they may be i think i want a N/A set up. i dont want crazy power but maybe some where about 250 or 300 hp. do you guys think it would be possible to run that much power on the 2.5 engine with no turbo.

what all would i need to upgrade? pistons, bolts, gaskets, intake manifold, exhaust, headers, cams, tune, and porting. anything else?

how hard is it to find jdm engine parts if i was to get one?

thanks for any of the help.

[I Like It Sideways]

250-300hp is expensive to obtain on our NA motors. But it is doable :)


Check out http://www.rs25.com/forums/showthread.php?t=36040
Zzyzx Motorsports broke the 300hp mark a few years back

It depends on what you want, and what your budget is.

I'd rather go the NA route, money not an option. Linear torque and power delivery, along with instant throttle response. Very usable for rallycross

[MetalNeverDies]

thats a pretty sweet. build. and its on an SOHC engine? very nice.

[MetalNeverDies]

could i run high compression ratio on a stock block with upgraded springs and valves and cams and pistons? or would my engine end up getting destroyed?

[impreza_GC8]

I would recommend going the SOHC route if you go for an N/A build. SOHC heads flow very well. Have Delta make you an aggressive cam and have a shop do some machine work on the heads. Port your throttle body, intake manifold runners and heads. I would suggest upgrading the valvetrain and reflashing the ECU to a higher redline. You would prob need to upgrade pistons and rods as well. Equal length header and high flow cat. All that still wont get you 250 hp but its possible you could get 200 out of it.

[MetalNeverDies]

if i was going to swap for a wrx engine or something similar could i keep and run my stock 5 spd 2.5rs tranny.

[MetalNeverDies]

I would recommend going the SOHC route if you go for an N/A build. SOHC heads flow very well. Have Delta make you an aggressive cam and have a shop do some machine work on the heads. Port your throttle body, intake manifold runners and heads. I would suggest upgrading the valvetrain and reflashing the ECU to a higher redline. You would prob need to upgrade pistons and rods as well. Equal length header and high flow cat. All that still wont get you 250 hp but its possible you could get 200 out of it.

at the wheels? or just the crank?

[I Like It Sideways]

200 at the crank easy. More like 160-170 at the wheels

The RS tranny will put up with the abuse of a WRX motor, so long as you don't dump the clutch. Rolling on the throttle and softer shifts, you'll be fine.

[impreza_GC8]

at the wheels? or just the crank?
^^ I don't know man, probably at the crank. You'd be looking at 180 or so to the wheels but if you think about you are making around 110 right now at the wheels so it would be a large improvement.
As for the question regarding the RS trans. Yes you could totally run the RS trans with a WRX engine. I have a 4.11+LSD drivetrain on my turbo'ed Outback (should be the same or similar to an RS) and it handles the power just fine. I know of people who run STI engines with RS 5-speeds. If you are mature and understand that burnouts, doughnuts and clutch dumps are not Subaru style then that trans will last a long long time.

EDIT: Elliot beat me to it, but our responses are pretty much the same.

[impreza_GC8]

Also, check this out:
http://www.rs25.com/forums/showthread.php?t=87763

[MetalNeverDies]

^^ I don't know man, probably at the crank. You'd be looking at 180 or so to the wheels but if you think about you are making around 110 right now at the wheels so it would be a large improvement.
As for the question regarding the RS trans. Yes you could totally run the RS trans with a WRX engine. I have a 4.11+LSD drivetrain on my turbo'ed Outback (should be the same or similar to an RS) and it handles the power just fine. I know of people who run STI engines with RS 5-speeds. If you are mature and understand that burnouts, doughnuts and clutch dumps are not Subaru style then that trans will last a long long time.

EDIT: Elliot beat me to it, but our responses are pretty much the same.

lol well i do shift hard some times on acident as well as just being a retard. sometimes in the dirt i like to do doughnuts or do big take offs. as well as sliding in parking lots on a rare occasion. would an upgraded clutch help or is it the gearing that just cant take the abuse?

also could any one suggest some brands or sites to get upgraded internals and some of the other stuff i would need. what would be a decent set of cams for power/dd compormise. i dont want crazy unstreetable cams but i dont want something that feels like i wasted my money getting them because they are so calm.

[Galen]

an upgraded clutch would just put more of that power(stress) into the transmission. I would probably upgrade the tranny if your going to be driving hard in the dirt... or you could wait till the RS one goes out (if it even dose) than upgrade...

[409industries]

Id say screw making power with a NA build. (Anyone remember the Subiesport Zero to Hero build?) talk about a PITA. Just do a WRX swap and be done with it. Reliable performance right there, for a fraction of what it would cost to build up a JDM block.

[MetalNeverDies]

if i was gonna do a turbo engine swap i would still probably take apart the whole engine and put it back together from scratch so its like new. if i upgraded pistons and rods would it add to power at all or no?

[ArcticWolf]

Id say screw making power with a NA build. (Anyone remember the Subiesport Zero to Hero build?) talk about a PITA. Just do a WRX swap and be done with it. Reliable performance right there, for a fraction of what it would cost to build up a JDM block.

I remember them cancelling it, but don't remember them doing anything with it. :lol:

Seriously, though. If you're really wanting 250-300 hp, turbo's the sane way of doing it.

Yes its possible to build an NA that'll do it, but it takes one hell of a budget, that most of us don't have. Remember that NA's make power by either displacement, or RPM. Our motors aren't really blessed with either.

If you've got a NA motor, just do the typical stuff (headers, intake, exhaust) and drive the crap out of it.

[g wilikers]

Id say screw making power with a NA build. Just do a WRX swap or and be done with it.

then there is more room for additional power later or have a much bigger safety margin. unless you like to run race gas when you got to the movies or down to the store :roll:

dont get me wrong, i am all about hi compression race engines. if you are building a daily driver, running pump gas, want low maintainance & very easy to drive around town, then a wrx swap would be the way to go.

my .02

greg

[MetalNeverDies]

could i put in cams in and run like 5 or 6 psi on my stock engine if i just did a turbo kit then i know it didnt get raped. then put in like headers intake exhaust and cams and up and down pipe? or would that blow up the engine.

[me_jimmy]

is you want more N/A hp check out the H6

[Hoooch]

Or just buy an Aero :D

[409industries]

could i put in cams in and run like 5 or 6 psi on my stock engine if i just did a turbo kit then i know it didnt get raped. then put in like headers intake exhaust and cams and up and down pipe? or would that blow up the engine.

I've heard of bad things about turbo'ing motors that were originally NA. Something about the engines out of the WRX and STi that are designed to run boost have meatier mating surfaces and therefore have less tendency to have head gasket problems, etc.

In all seriousness though, a swap is the complete package, with parts that were all designed to go together with all the R&D done by FHI. :headbang:

[MetalNeverDies]

oh i know. if i was going to do a swap i would do full wire harness and every thing. probably the only stock thing in engine bay would be washer fluid container.

[MetalNeverDies]

Or just buy an Aero :D
lol im a broke college kid who is upside down on their loan thats not gonna happen haha. if i was gonna spend even more it would probably be on an sti :) although an aero would be awesome.

[Rally Jon]

Bout $750.00 for upgraded cams and carbon nitrated valves, in your custom built street set of heads. affordable H.P.
1 week turn around !

[MetalNeverDies]

is that new valves or mine recoated?
what set of cams?
would i need a tune or will it throw a cell.
would i need new rockers aswell because they had mated with the old cams?

about how much of an hp gain would this get me?

[me_jimmy]

is that new valves or mine recoated?
what set of cams?
would i need a tune or will it throw a cell.
would i need new rockers aswell because they had mated with the old cams?

about how much of an hp gain would this get me?

always tune when changing stuff from airfilter to crank size

[impreza_GC8]

lol im a broke college kid who is upside down on their loan thats not gonna happen haha. if i was gonna spend even more it would probably be on an sti :) although an aero would be awesome.
Then why did you even make this thread? Anything you could do to make decent power is going to be too expensive. Get your ish together son.

[me_jimmy]

Then why did you even make this thread? Anything you could do to make decent power is going to be too expensive. Get your ish together son.

everything starts with a dream... son...

[MetalNeverDies]

Then why did you even make this thread? Anything you could do to make decent power is going to be too expensive. Get your ish together son.

because im saving up little bits at a time for some parts. and i have been looking into things to make my car faster other than just throwing a turbo on like every one else does. i wanted to know if my car had any potential of being relatively quick... not fast or anything but just fun to drive enstead of feeling like there are hamsters in the engine bay turning the wheels. if not then i was debating trading my car in on some other cheap crappy car and then paying that off.

theres no need to flame dude.

[wolfman79]

Nothing wrong with wanting a little more pep out of your car. Nothing wrong with working on a budget either. Cams and a full exhaust would definitely make it feel like either the hamsters were on steriods or even been replaced by a couple of wombats.

[04caliwrx]

sti 2.5 engine with a 18g on low boos and u will be at that 300whp u want. I think in the long run it will cost you less and be happy with that turbo engine

[MetalNeverDies]

well at this point in my life i know there is probably a 1% chance that i would be able to do a swap. and if i was gonna go all out and get a swap it would probably be a full 6mt / 2.5 sti engine swap with dccd and every thing.

because i know a swap is 99% sure of not happening at least until im older and engine blows up i at least want to make the car sound good and have alittle more pep to it than what it does stock. i know its not fast and ive learned to accept that. out of all honesty i want to keep this car for a long time i like it alot and if i was gonna get a second vehicle it would probably be a bike cause its cheap or find a datsun 510 coupe and get into auto x with that or find an old porsche. i have always loved subies and porsche's so that would be a sweet set of cars in a garage.

bassically my goal of this thread was to find some info on exactly what all it would take to make it have more pep as well as see what all my options are and pricing. the way it looks now is that i will get headers highflow cat and put on the sti exhaust i bought a long time ago and run that. then save up and get cams and a tune. then just work on some cheap suspenssion stuff and get skid plates. and have my friend finally bend up the light bar i want and weld that on with the lights and hella 500's i have.

[impreza_GC8]

^ Why not just get into AutoX now? You're car is plenty fast now on an AutoX course assuming you don't make any dumb modifications that will bump you to a high class. Skip the high flow, stay with your stock cat, get some good tires and run in STS class.

I was a bit forward with my last post because it bugs me when people talk about making power with N/A engine mods and they don't have much to spend. If you are on a budget do an intake and an exhaust, spend the most money on your suspension setup and go race your car at SCCA events.

You're car will never be a straight line performer. Not without a major engine swap. You need to play to your vehicle's strengths which - aside from hauling groceries - is handling. Build the suspension and put on nice tires, you will be faster in the turns because you will be able to carry more speed in the turns.

My RS is slow as balls on the street, just about anything is faster but I beat turbo boys with modded suspensions on twisty roads and I routinely beat them on the AutoX course. I find that to be more important than who can beat who in a straight line. There will always be someone faster.

Plus, if I'm feeling the need for forced induction, I have a swap whore Outback to drive.

[MetalNeverDies]

i have looked into intakes some but there is only one brand that works with the 2.5RS engine. and that is injen. its like 400 dollars. no way in hell im paying that much for a damn CAI. plus i love to offroad and splash threw stuff to much to have to worry about a CAI and hydrolocking.

the problem with keeping the stock cat and running an exhaust is that you still end up restricting your exhaust quite a bit.

as for modifications that bump me up in classes in autox i think i have already made that mistake. unfortunatly stock my car comes with a 13mm RSB. its a total understeer monster. so i upgraded to a 20mm RSB and now its a little better but not much. it will probably help if i throw on some endlinks. i have sti pink USDM wagon springs aswell. i dont know if that will bump up my class or not.

also i have a SS so i dont know if that hurts me or not either.

i have debated getting some new struts sence mine are kinda gone. however, i am not sure what i want to do with them yet. i have debated tokico d-specs but i am afraid i will have to buy new rear springs and saggy but shims because they dont make tokico struts for wagons. i was also afraid i would wear them out fast because the car has been lowered alittle bit.

[impreza_GC8]

All those mods are within STS class rules. Download the SCCA Rulebook to read what you can and can't do. STS class allows tons of modifications, its a pretty great class.

Sounds to me like you need to do some more research to figure out what you want to do with your car. You've got a lot of ideas but no real plan.