Adoniram Posted February 9, 2011 Share Posted February 9, 2011 So I've been reading that the flat-4 engine design usually is smoother than an inline 4 due to the fact that the pistons are directly opposed (although slightly offset). However, because the pistons are 180 degrees apart, there's an actual pause between power strokes. Inline 4 engines will start a power stroke before another piston finishes, making smoother power. Also, because the rods are slightly offset on the crank, there might be a slight "wobble" in the engine, due to power being applied to different lengths of the shaft. What are your thoughts on this? How do you think the flat-4 in the fourth gen compares to inline 4 engines, in terms of smooth delivery, vibration, etc? Link to comment Share on other sites More sharing options...
rao Posted February 9, 2011 Share Posted February 9, 2011 The Subaru engine pretty much feels like it belongs in a tractor so I would rate the whole "magical balance" thing as a bunch of BS in practice Rob IF YOU CARE ABOUT YOUR CAR YOU SHOULD NEVER DRIVE IT Link to comment Share on other sites More sharing options...
Draco-REX Posted February 10, 2011 Share Posted February 10, 2011 Actually, there are "ideal" cylinder bank angles when designing an engine. You divide 360 degrees by half the number of cylinders (because in a 4-strone engine, you're firing once every other rotation). So a V12's ideal is 60, 10 is 72, 8 is 90, 6 is 120, and a 4 cylinder engine is best at 180 degrees (i.e. the boxer configuration). It's not a matter of smoothness, but in efficient power delivery. It's one reason why our engines feel a bit more powerful than an equivalent displacement I4. (I know there are other reasons, but this is one) Followers of Formula one in the past will have heard about 72 degree V10s vs 90 degree V8s. Also keep in mind that our engines don'e require balance shafts whereas most I4s do. Link to comment Share on other sites More sharing options...
ouch1011 Posted February 10, 2011 Share Posted February 10, 2011 By comparision to other 4cyls, the boxer layout is pretty smooth. As was said, most other I4s of similar size require balance shafts to feel smooth, and some don't even with that (ever driven a Nissan with the 2.5? Yeah) But if you are comparing the H4 to other engines with more cyls, then it might not seem as smooth simply because the frequency of the firing impulses is much lower, so you are more likely to feel it. Thats just the curse of a 4cyl engine. Try driving a 3cyl...lol Link to comment Share on other sites More sharing options...
matt Posted February 10, 2011 Share Posted February 10, 2011 The 2.4L I4 in a Mitsubishi I once owned was quite smooth for a 4 cylinder, certainly comparable to the EJ25, but it had a balance shaft. Link to comment Share on other sites More sharing options...
Adoniram Posted February 10, 2011 Author Share Posted February 10, 2011 It seems it's really just up to personal opinion... some of you say it's comparable, some say it belongs in a tractor! My friend has a 2010 Impreza (regular non-wrx) and his CAR feels smooth, but when you grip the stick to change gears, it feels like you're holding onto a miniature jackhammer. Link to comment Share on other sites More sharing options...
PoisonousBeef Posted February 10, 2011 Share Posted February 10, 2011 You get into a huge number of variables when you start talking about a driver's perception of an engine's "smoothness." Even ignoring all the internal differences of the engines and their balance, just think of the physical mounting differences between a FWD I4 (where both the engine/trans mounts are confined forward of the firewall) and our cars, where the motors are both on a different axis but also have drivelines right along the passenger compartment. You are asking a question that has an incredibly complex answer. Link to comment Share on other sites More sharing options...
RabidWombat Posted February 10, 2011 Share Posted February 10, 2011 The BMW I6 is frequently described as being one of the smoothest engines, and its not a magic configuration. There's a lot more involved than just basic engine layout. I'd say the Subaru flat-4 is better than most economy cars, and slightly rougher than most V6 luxury cars. Link to comment Share on other sites More sharing options...
GTTuner Posted February 10, 2011 Share Posted February 10, 2011 Some will argue an inline 6 is the best configuiration in terms of NVH and power delivery. I tend to agree (IMHO), even an old Chevrolet 250ci straight six, or the AMC 232/258ci were pretty damn smooth running motors. Also, I hear people refer to the Subaru engine as "horizontaly opposed". If you look it up that is not correct, the boxer has one crankshaft, a true horizontally opposed engine has two different crankshafts opposed in a boxer configuiration. Link to comment Share on other sites More sharing options...
matt Posted February 10, 2011 Share Posted February 10, 2011 My friend has a 2010 Impreza (regular non-wrx) and his CAR feels smooth, but when you grip the stick to change gears, it feels like you're holding onto a miniature jackhammer. That's an interesting way to measure it, and not what I had in mind. If you go by shifter vibrations then that Mitsubishi of mine was FAR smoother than any Subaru, since the Mitsu had no discernible shifter vibration and every MT Subaru I've driven has had some. But I think there's too many variables affecting shifter vibration to draw conclusions about engine smoothness from it. Take engine and transmission mounts as an example. I guarantee you that my Mitsubishi had softer mounts than my STI, and probably softer than my LGT. I sometimes missed WOT shifts in the Mitsubishi even though it only had 162 lb/ft at the crank. My LGT and STI both made more than that at the wheels. If they had equivalently soft mounts I would have been missing shifts in them left and right. PoisonousBeef is right on the mark when he says that there are so many variables involved in the perception of engine smoothness that you cannot accurately judge it by driving the car. The BMW I6 is frequently described as being one of the smoothest engines, and its not a magic configuration. Actually the I6 layout is inherently balanced, same as a boxer engine. And with 6 cylinders it will be smoother than a 4 cylinder due to the more frequent firings as earlier posters described. Link to comment Share on other sites More sharing options...
Draco-REX Posted February 10, 2011 Share Posted February 10, 2011 You can't compare engine vibration by the shifter feel. Most I4s are transverse mounted, so the transmission is entirely in the engine bay. This means that the shifter is often mounted to the body. Some don't even have a solid link to transmission and instead use cables. Subaru's engines and transmissions are in a more classic, longitudinal, layout. So your shifter is mounted directly to the transmission. You're going to feel a lot more vibration through the shifter because of that. Personally, I like that I can feel the engine's revs and the synchro engagement through the shifter. Link to comment Share on other sites More sharing options...
Adoniram Posted February 10, 2011 Author Share Posted February 10, 2011 I guess I wasn't clear enough... I was really just trying to get opinions of vibration in the driver's perspective. I wasn't trying to measure things scientifically, just simply the driver's or passenger's experience. That makes a whole lot of sense about the shifter being mounted to the trans directly; I didn't know that, and it explains a lot. Link to comment Share on other sites More sharing options...
PoisonousBeef Posted February 11, 2011 Share Posted February 11, 2011 I guess I wasn't clear enough... I was really just trying to get opinions of vibration in the driver's perspective. I wasn't trying to measure things scientifically, just simply the driver's or passenger's experience. That makes a whole lot of sense about the shifter being mounted to the trans directly; I didn't know that, and it explains a lot. In that case I'd agree that based only on driver perception, yes, the boxer in my GT seems to transmit more vibration to me than most of the other cars I've driven. Link to comment Share on other sites More sharing options...
RJS5689 Posted February 11, 2011 Share Posted February 11, 2011 Actually, there are "ideal" cylinder bank angles when designing an engine. You divide 360 degrees by half the number of cylinders (because in a 4-strone engine, you're firing once every other rotation). So a V12's ideal is 60, 10 is 72, 8 is 90, 6 is 120, and a 4 cylinder engine is best at 180 degrees (i.e. the boxer configuration). It's not a matter of smoothness, but in efficient power delivery. It's one reason why our engines feel a bit more powerful than an equivalent displacement I4. (I know there are other reasons, but this is one) Followers of Formula one in the past will have heard about 72 degree V10s vs 90 degree V8s. Also keep in mind that our engines don'e require balance shafts whereas most I4s do. The flat-4, inline-6 and V12 are the only engines that don't need balancing I believe, yea? From what I remember of our BMW's I6, it was a really smooth engine. Our Infiniti 3.7 V6.... let's just say it vibrates a tad more, haha. I've also found the Subaru boxer to be somewhat lumpy at idle, but I find it smooths out through the rev range. It's a really hard sound to try and describe to someone who asks. I just tell them my car kind of sounds like a tractor at times . Link to comment Share on other sites More sharing options...
sigsegv0x0b Posted February 11, 2011 Share Posted February 11, 2011 From wikipedia: However, the flat-4 does have a less serious secondary imbalance that causes it to rotate back and forth around a vertical axis twice per crankshaft revolution. This is because the cylinders cannot be directly opposed, but must be offset somewhat so the piston connecting rods can be on separate crank pins, which results in the forces being slightly off-centre. The vibration is usually not serious enough to require balance shafts. Known fact about flat-4. So your engine vibrating within reason is perfectly normal. Subaru does not put counter-balance shafts on their engines. However H6 subarus' should be smooth as butter. As I6 and V12. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.