I ask because it seems to struggle in producing reliable high power when compared to the more convential 4 pots in the EVO and Cosworth. Why is this? Too much of a compromise for a low centre of gravity and a nice sound? I wonder if Subaru will continue with the boxer for many years to come? (This isn't an anti Impreza thread by the way - I've got a WRX...)

 

The cossie has a cast iron block if i am not wrong, hence why the massive power figures can be gained. The cossie engine is basically a de-tuned rally engine, where as the scooby engine is being streched.

mcbrun555

 

It's a tolerence thing, rather than design. Road car engines aren't designed to see how much power can be pulled from them, they're designed to produce the amount of power the overall designer wanted.
So you could say that the Cossie engines are a bad design as they're hugely overdesigned for the job (the road use type )
There's also manufacturing quality to take into account. If you're confident of your manufacturing skills, you can cut 'closer to the bone' than if you're not (i.e. if your manufacturers are somwhat suspect, then the design is stronger than necessary for 'normal use' just in case there's a dud).

 

I believe the 'boxer' engine is a good design from a balance/stress perspective, so perhaps as the previous thread suggests the strength of the engine block, bearings etc are manufactured to a cost and weight proportionate to what is expected to cope with ?

Out of interest I think the exhaust sound you refer to is a result of the unequal length exhaust manifold/header pipes rather than the boxer layout, the firing order will be the same as any 4-pot, it's just that some of the exhaust 'pulses' from one cylinder bank take slightly longer to reach the downpipe than the other side and hence are slightly out of phase...

 

Ditto the points above. The Impreza really has been designed to work well as it is. You can't really blame a manufacturer for not building in a huge margin for tuning now can you???

Anyway, I'd rather have a lower powered, nice handling car vs a highpower stright line mobile anyday!!!

The Evo seems to be a good compromise between these two stables

Matt

 

Well the boxer engine has its own disadvantages, including:
- It's unbalanced (therefore produces vibrations)
- It has two heads, 4 camshafts (if 4 V per cyl.), double belt system, ecc, therefore more frictions.
- It's more thirsty and less ecological

Adv:
- I has a low center of gravity
- the crankshaft is positioned longitudinally as the tranmission reducing converting gears.

but i do agree it has a special noise and poise. So does the air cooled 911.

C.

 

Yes and no!

A boxer engine is fundementally better in terms of balance than a straight four, offer a lower centre of gravity, and is simpler to avoid sealing problems.

However, the Scoob engine is not perfectly designed for high power applications. It is designed for a reasonable level of power (300 BHP in an STi), but has been kept down to a low weight and reasonable build costs.

To compare the Scoob to a Cosworth Sierra / Escort engine is not fair. The Cosworth uses a modified version of the Ford Pinto block (to strengthen it), and as standard comes with a crank and rods designed for 8,000 rpm and 400 BHP. Other than that, the only special thing was the standard Cosworth head design that has the benefits of being a known factor and being capable of being used with all the standard cams etc.. However, it is not correct to compare a standard Turbo or WRX engine with this, more with a 2 litre Pinto. Maybe it is fair to compare the STi with a Cosworth? Probably not - I don't think Subaru aimed for that kind of power even from the STi.

Duncan

PS. A happy WRX owner - as a road car it is still streets ahead of the Cosworth.

 

Agree with most of the above.
The engine was designed for production runs of many tens of thousands. It has been developed to reliably produce good power (300bhp or so) given with what are compromises in mass production ( ie. time and cost) it is very reliable under normal use. This said the 'Cosworth' read Ford lump is a modified unit (pinto) that is produced in relatively low numbers on a special production line.
They cannot be directly compared.
The 'boxer' layout is inherantly good in many aspects but does have other drawbacks. The exhaust note is a product of the exhaust layout not the engine design (unequal, read bad, but cost effective exhaust manifold).

 

Point taken about the exhaust but I've read the sound described as a 'flat 4 thrum or a 'boxer beat' etc. Does it sound exactly like an EVO if it is has an equal lengh manifold then? While I'm on the EVO how does this take higher power so well being a mass prduced engine unlike the Cosworth?

 

The EVO engine is as to a standard Lancer/Mirage engine as the Cosworth was to a standard Ford.

Duncan