Having had some exposure to flat (horizontally opposed - boxer) engines via my previous life with Chevy Corvairs (flat 6 - aircooled), I was surprised to see the WRX dealer brochure show a cutaway of the engine with counterweights on the crankshaft.

I thought the whole point (one of them anyway) for horizotonally opposed engines was that they were inherently balanced. Thus, no need for crankshaft counterweights.

Anyone care to enlighten me on this?

JL

I don't know the answer to this, but you could probably get one if you post this question in either the " Factory Forced Induction," or "Transmission (AT/MT)" forums.

You still need a balanced rotating assembly on all engines (think of an unbalanced assy like an unbalanced wheel... whole lotta shakin going on! :).

I think they mean a flat four or flat/inline six is "balanced" as in forces are all counteracted by another opposing force (one cyl fires, and quickly, a cyl opposite to it will fire), which is not possible on a 4 stroke INLINE 4 cyl engine, and why many higher quality inline ones have balance shafts.

Flat fours also have a tiny crankshaft compared to most other engines! Can you say "rev fast?" and tough? hehe.

__________________
Vineet Singh
http://www.eaglecars.com/

is there a schemtic view or cutaway view of a REAL subie flat four (not just a little animation or simplified drawing) anywhere?

I wanna see!

go to your dealer, and get the wrx literature...its in there..


get a bunch of copies (there free) and sell em on ebay. :rolleyes:

Also, the extra weight is added to our crankshafts because without hte weight, they would be so light that the car would be very hard to drive. i.e. in between shifts the rpm's would drop so fast that every shift would be very jerky :)

Eric

So then would it be convievable that one could shave down a little of the weight ? For a quicker revving engine, kind of an addition to a lightened flywheel? Or instead of the lightened flywheel?( I know, the flywheel would be much easier )
Or is the whole thing completely ill-conceived?

Imprezinator, that's what the flywheel is for. You want the lightest possible internals (that will withstand the forces encountered, of course).
tcs007, not ill-conceived, just harder to accomplish. To do all that you'd need to hook up with a reputable race shop. You can't take your crankshaft down to the Napa machine shop and say "lighten this, please." There are better/lighter internal parts, however they cost a mint. A flywheel has been recommended enough on the list to possibly be worthwhile, but unless you're rebuilding the bottom end of a motor anyway, I'd doubt you'd see enough benefits (especially on a NA motor) to make the cost worthwhile.

But remember, the flywheel is only part of the clutch system. If you lighten the flywheel by 1/2 (for the sake of this sentence) don't expect your motor to be able to rev twice as fast. You've also got to take the pressure plate into account, along with all the other rotating bits.

Here's a closeup of a disassembled STi Ver 3 crankshaft (with a crack):
http://www.demeis.com/images/mcrankcrack.jpg
For more, see http://www.demeis.com/motorsport/hardware/wrxstory.html

Originally posted by Imprezinator
Also, the extra weight is added to our crankshafts because without hte weight, they would be so light that the car would be very hard to drive. i.e. in between shifts the rpm's would drop so fast that every shift would be very jerky :)

Eric

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Why not keep the counterweights off but add the poundage to the flywheel?

I don't buy the answer. Corvairs rev'ed just fine with no counterweights.

JL