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.

first off all, the engines are completely different animals. I won't begin to compare the FA and EJ at all other than they are both boxer engines produced by Subaru.

Also, as for the zzyzx build, he didn't make 300whp. His post from WAAAAY back was that he was now making 300bhp as he was dynoing at the same power as a stock STi (300bhp).

Any news on FA/FB interchange? The mythical 94mm bore 86mm stroke FA24, possibly with 2GRFSE D4-S compatible pistons and corresponding CR reduction to 11.8:1?

Patiently waiting for results on a hybrid engine... or perhaps a stroker.

Changing the stroke can also increase the torque, but that is pretty intense change and probably not a good idea on this engine. Gotta agree with 3MI on the flywheel

Totally different engine, but the EJ strokers perform like 2.5L EJ series engines due to the favorable stroke ratio (IIRC, might something else stroke related). I'd like to see something like that in this engine, though a rebuild like that is definitely 3-5 years down the road for me.

I won't be able to say one way for sure without having the FA in my hands...or actual engineering drawings.
Pistons are going to be custom for it. They'll start off with the new materials that I'm currently developing on the EJ platform.

The most time extensive part will probably come with developing the dish/combustion work on the 94mm bore to work with an OTS FA20 head. I'm going to try and steal some time and work out the combustion modeling in Star.

-Micah

I was hoping the 94mm 2GRFSE pistons would magically fit. But even if they fit , the direct injector location and spray pattern is probably different anyways...

If you end up making custom pistons, will they be more $ than typical because of machining the little bowl/dish for the DI?

I don't agree with this. I've installed a lightweight flywheel on my past 3 cars ('97 Honda Prelude, '07 Honda Fit, and a '79 Datsun 280zx). All 3 of them were driven before & after by both my Mom and sister, without me mentioning it to them - and not a single stall. If you read deeper into a lot of accounts of people suggesting a lightweight flywheel was trickier to drive, you'll find that almost all of them "upgraded" their clutch at the same time, usually to some annoying unsprung race puck crap thing.

Maybe with an extreme 8 pound flywheel it gets trickier, but all of the ones I've done are very easy to drive. If memory serves, I had a 12lb. on the Prelude, a 10lb. on the Fit, and have an 11lb. on the Z. The Z's stock flywheel weight is almost 24 pounds.

To be honest, unless you've already got the tranny off for some reason, I wouldn't bother doing it - I think most people will be underwhelmed by the difference, and it's a lot of labor to get in there.

Lightweight flywheels are a pain in the ass. Terrible return per dollar

If you don't want FI, your best bet is probably weight reduction + bolt ons. C/F hood, lightweight battery/exhaust/wheels, remove rear seats, spare, etc. If you can shed 100-150 lbs and pick up 10 whp from basic bolt-ons, you'd have a pretty quick car (and improved handling).

The aluminum hood is really light already... just FYI. I know carbon can be lighter, but might be a big $$$/lb saved ratio

Yeah I thought about that, but since no one has actually weighed the stock alum. hood yet, didn't want to rule it out completely. You're right though, there probably won't be huge weight savings going CF there.

When I lifted the hood on the demo car, I was shocked at the lightness. :w00t:

:happy0180: We'll just have to find other ways of reducing weight on the car!

lightweight battery/exhaust/wheels like you mentioned are good

I wonder is the driveshaft is heavy and worth changing to CF or Al?

We should start a weight loss thread.

^^^I agree, once people start getting into yanking parts and chasing weight; it would be a nice thread to sticky.

Pricing should be about what my pistons currently are. They'll be starting from a custom forging to reduce machining anyway.

P.S. I never would have started with a piston for another engine. I don't cut corners.

I feel like a broken record here but given this cars weight, it just begs for a simple low boost supercharger kit. You could even skip the intercooler if the boost was low enough (5-6 psi) as I think Toyota has done this on some of their other TRD cars. All this car needs is another 40-50 hp/tq given its weight to be a rocket. a low boost supercharger kit could be a cheap and light weight way to give the car the low end kick it needs. I know some people want 300 whp but this car can get by on a lot less and be a terror.

The car can easily handle 40-50whp, all you might need are some new injectors at most. Seems like a no brainer solution for folks looking for just a bit more power down low that would be very streetable.

Which is why we have several threads on superchargers.

This isn't one of those threads...

This.

There's also several weight loss threads already.

If you use the car mostly for track days, mountain/country road or in the city centre, a easy solution to the missing torque is a reduced final ratio.

On one hand if you replace the rear end gears with quicker ration gear, I'm sure a taller sixth can't be that hard to install, with all the variations of this transmission that are supposed to be out there. On the other hand, I don't know how much it would be needed, if they needed to fit a sound tube to put some engine noise in the cabin. Time and research will tell, but I can forsee the above being somewhat common eventually.

Yikes - rebuilding a transmission with a new gear is vastly more complex than swapping the final drive gear in the diff.

In my experience, a few hundred rpm difference makes a lot less difference in your highway mpg than people would lead you to believe. Random data point: my old 5th gen Prelude got it's best fuel efficiency at close to 80mph (spinning at 4k rpms). Every drivetrain/vehicle combo is going to be different of course, so it remains to be seen how efficient these latest boxer engines will be at higher rpms.

When we're talking fuel efficiency, it comes down to how efficiently the engine can operate at extremely low loads, and that has yet to be seen. Pekingduck has said that he got 39mpg at 70 and 29.5mpg going 85-90 (yikes). With a 30% increase in the 6th gear ratio, at those load levels (we're talking about 2-3 bar MEP) it's typical to see about 10% improvement.

However, slow the car down, load requirement drops, and the difference grows bigger. Longer gears pay off more if you drive slower. Some people believe in the "de facto speed limit" of the posted speed limit + 10mph or something, so this doesn't really matter to them. Of course this depends on the engine (I imagine cooled EGR does great things for very low load operation), but you get the point.

EDIT: okay as a concrete example, I'll be looking at the 1NZ-FXE again (as far as efficiency improving features go, it's probably comparable to this engine). Notice that if you pick an arbitrary rpm, and go to the 230g/kwh mark, you'll notice that ~1/3 load reduction brings you to somewhere between 250 and 260, which is a 10% increase in specific fuel consumption. Going down to the 290 mark is another ~1/3 load reduction, so far it's following a logarithmic sort of pattern. However from here, depending on where you're looking at, reducing load ~1/4 is increasing specific fuel consumption 10%, and then it only takes a ~1/6 reduction in load to go from ~320 to ~350.

Yes, but if you do both, you can keep a similar cruising rpm. That way the noise level and your mileage wont be effected by the rear end change.

Of course you can do both. But I have to question to the efficacy of it . . . and any sane person will look very hard at the value, considering the cost of that kind of modification.

This is what jumped out at me. Again . . . yikes.