Increasing torque with out forced induction
 

Hello all. After reading the last part of the EVO review (BRZ vs. Impreza), it got me thinking. I seems that low end torque is the key to the "fun" and the lack of it was what they all had an issue with. My question to all the mechanically inclined folks out there, other than forced induction (turbo/supercharging, which has been much talked about around here), are there any other ways of increasing an engine's torque? From my basic knowledge, a reflash (ie Cobb, etc.) may have some gains, but I'm not sure how much for a non-fi engine. I know engine mods like boring-out and a more aggressive cam can give a little bit but I'm not quite sure how all this applies to a smaller 4-cyl, let alone a boxer engine.

Put simply increasing air flow in and exhaust out, reducing mechanical losses and improving combustion efficiency.

Intake, exhaust, stronger igntion system and lightened flywheel are a few easy methods. Beyond that I'll start getting on nerdy on the engineering work I'll be carrying out within the engine.

Increasing displacement...

A tune would most likely would bump the TQ in places where it's lower (like the dip between 3500-4500). But to gain gobs of peak TQ would mean what 3MI said, making the most of what's there. Intaking more air, adding more fuel, and letting out that air in an efficient manner. Basically the engine is a pump, with tradeoffs.

Sacrificing gas mileage for more power, for example.

+1

If only they made it a 2.2 stock.

What about I/E Manifold Porting/Polish? Did previous Subaru engines gain from this?

I think anything to do with the intake will gain torque but for example on my 350z when i did the dc headers i actually lost torque down low but gained hp. So you might want to wait on getting headers till someone does a dyno test. Boxer engines are know for their low end torque so i think the engine should be very responsive.


Light flywheels are know to decrease inertia meaning more torque will be needed to break traction or get off the line quick. Everything else you said makes sense. ;)

Nice to see a fellow w204 owner here :)

If the 2.5RS is any indication of boxer NA engine tuning, it is going to be tough. There are very few EJ251's(zzyzx for example) running at 300whp NA and it had such a wide array of parts such as racing cams, ported and polished heads, throttle body, and intake manifold, racing pistons, lightened crankshafts, lightened rods, etc.

I'm guessing the FA20 will probably top off somewhere between 240-250whp with general mods such I/H/E/T and that's just well wishing. That's exactly fine with me as that's perfectly where I would want my 86 to be in.

Thank you all for the input. To me, NA seems to be more fitting for this car, not that I wouldn't consider a turbo in the future (for Subaru sake) so all these tuning suggestion are great.

It seems like 240-250 hp/200 lb-ft is the magic number for a lot of the posts I've seen around here, which sounds around what I would like it, but who knows, maybe once I get my hands on one for a test drive, maybe all the other reviews maybe right about the engine being "just right"...

There fixed it for ya.

I seriously doubt we'll be seeing 240-250whp without FI, unless you go with an E85 tune or replace internals to significantly bump up the redline. I'd be impressed if we got much over 200whp reliably.

Not really. It's not really a common mod because most people are tinkering with the forced induction (since all performance Subarus are turbos). The power gain per dollar was more reasonable.

I'm not saying it won't work (it should), it just wasn't very common.

more timing down low will add torque but will require race gas or E85,

more compression will help (~7% per pt of Compression) but 12.5 : 1 is already pushing the pumpgas envelope.

a light flywheel will reduce engine inertia and make you drive like a clutch monkey, it is a tradeoff of the first order, anyone who tells you otherwise either hasn't driven one or is arguing for the sake of the argument,

Most gains to lowend torque cost HP up top, I think the key to this car is going to be sorting out the torque dip of doom, otherwise the engine makes an incredibly flat torque curve for a 2.0L 4Cyl. upsetting that would be a mistake unless you are adding gobs of HP (a gob is equal to or greater than a metric fuckton)

eh, yes and no. The only way the lightened flywheel gives interial force to the tires is when you dump throttle or are disengaging the clutch (like launching the car). It does allow the engine to accelerate more rapidly as it requires less energy (power) to accelerate it's (the flywheel's) mass. So as I stated, it will give you power the same way reducing friction will. I never said a lighter flywheel would aid in force to launch a car or break traction.

So you were close but a bit off. I keep my customers with straight line cars on heavy flywheels for this exact reason. My track/auto-x/time attack all get light flywheels.