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Car Forum / BMW Cars / February 2005323i V 325i engine.
Just idle curiosity. Both engines are the same size. Presumably mechanically very similar. Why the big difference in output? Mike. > Just idle curiosity. > Both engines are the same size. Presumably mechanically very similar. > Why the big difference in output? > Mike. Single VANOS against double VANOS, I think? Badger. > > Just idle curiosity. > > Both engines are the same size. Presumably mechanically very similar. > > Why the big difference in output? > > Mike. > Single VANOS against double VANOS, I think? I think it must be someting else. The 325i M50TU engine is single Vanos. 192 bhp. AFAIK the 323i engine only delivers 170 bhp. Both UK figures. Mike. > > > Just idle curiosity. > > > Both engines are the same size. Presumably mechanically very similar. [quoted text clipped - 7 lines] > Both UK figures. > Mike. Do a google groups search & you'll find out. > > > Just idle curiosity. > > > Both engines are the same size. Presumably mechanically very similar. [quoted text clipped - 7 lines] > Both UK figures. > Mike. Do a google groups search & you'll find out. > Just idle curiosity. > Both engines are the same size. Presumably mechanically very similar. > Why the big difference in output? > Mike. I suppose this is just curiosity too. My wife and I each have E36 3 Series. Hers is a 97 328 and mine a 97 323. So, theres about 300cc difference in engine size, but about 27BHP. That said, on the road hers is a demon in comparison. Cruising at 80 or so, when you dip the accelerator (gas) on the 328 the response is a firm push into your seat and off it goes. My 323 is no slouch but the difference is clearly noticeable. I regard the stated top speeds of 140 vs 147 to be irrelevant but the acceleration differences aren't. Can 27BHP make THAT much difference or is it something else? > > Just idle curiosity. > > Both engines are the same size. Presumably mechanically very similar. [quoted text clipped - 14 lines] > > Can 27BHP make THAT much difference or is it something else? Not an answer to your question, but it does draw attention to another anomaly. The 328i M52TU engine, despite it's extra cc, only delivers about the same as the 325i M50TU. A different power curve, but overall the output is virtually the same. Mike. > My 323 is no slouch but the difference is clearly noticeable. I regard > the stated top speeds of 140 vs 147 to be irrelevant but the > acceleration differences aren't. > > Can 27BHP make THAT much difference or is it something else? It might also be possible that BMW grossly underated the power on the 2.8L for insurance reasons. Makes alot of sense when you figure that the power of the 3.0 (M54?) shot up to to over 220 HP when they increased the displacement by only 200 cc. Matthew 528i Sport The 323i was a detuned version of the 2.5l engine apparently for economy & driveability reasons. Intake & exhaust are different. The naming 323 rather than 325 gives the idea that it's not as powerful. The power band is most exactly the same in shape just it's 500rpm down the rev range. The peak torque of the two cars is the same & since power is a function of revs & torque the peak power on the 323 is less. The 328 is a slightly bigger engined version of the 323. Same peak power as the 325 but more torque. If they made the 328 like the 325 engine then it should be up near 215 peak hp. With the new 330 and 325 the output is back to more like it used to be. The other thing to remember is gearing - the 323 and 328 have different final drive ratios. > The 323i was a detuned version of the 2.5l engine apparently for > economy & driveability reasons. Intake & exhaust are different. The [quoted text clipped - 8 lines] > thing to remember is gearing - the 323 and 328 have different final > drive ratios. Good explanation. Compared to the earlier 325i, the 323i is quicker off the line, with better driveablility. It may not have quite the peak power, but in everyday driving the response is improved. Also, I believe the 323i is de-stroked, which makes it smoother. It is indeed a very sweet engine, the smoothest in recent memory. The best buy in a used BMW in the US right now is probably a '98-'99 323is coupe. Everyone looks for the "hot" 328i, leaving the 323i to languish at really good prices -- particuarly the coupes, and particularly the automatics, if you like those. OK, now that I've let the secret out, I won't be able to afford one! Matt O. No the bore & stroke on the 325 & 323 are the same. The 328 gets it's extra capacity from a longer stroke. Hi all, I'll shed my light on this topic and settle it once and for all. Firstly i have a 323i and even though ive tuned the damn thing up (chip, exhaust, air filters etc) runs great etc etc...I keep seeing these 325's glide right past me. Originally i thought the answer was in the diff (stock 323i runs 2.93 open / 325i runs 3.15) so i upgraded to 3.23 LSD of 98 M3. Result...I have to treat mine like a MotherF... to keep up... Basic reasons behind architecture, bmw wanted the 323i to be economical and smooth it was never intended to be thumped! Otherwise we would all have short gear shifters! (thats a bmw blunder!!) So anyway i kept searching to push it the edge... I notice the 323 while accelerating to 4K RPM its fantastic then all of a sudden it Chokes like its gasping for air. The answer lies in the "INTAKE MANIFOLD"!!! M50 325s have larger ports...about 1/3 larger than M52 some suggest. which means u get more air in when your in need, and the reason why our a.ses always got munched the hell out of. Engines both the same, approx 2.5... The 325 gets more air in which ads to a higher torque and HP at 5,500 rpm. Whereass the 323 is restricted b/c of its small intake manifold. Hence why the 323 is a detuned 325i! But with one advantage, the 323i runs 3.0 m3 dual exhaust headers (so ive heard!) Right now with the M50 intake i can beat 325's easily (it keeps munching through the RPM's when b4 at 4000 it choked!). To beat 328's u might need a software upgrade. This is the obvious downside which costs and may have side effects depending on software version and who made it. Hope this clarrified things up :) >So anyway i kept searching to push it the edge... I notice the 323 while >accelerating to 4K RPM its fantastic then all of a sudden it Chokes like >its gasping for air. The answer lies in the "INTAKE MANIFOLD"!!! Doesn't happen with my 2000 323i. Indeed, I can feel a bit of a torque increase around 4000 RPM, presumably due to VANOS cam-timing changing. Not big bump, mind you - it's clearly designed to have a fairly flat torque curve, but it pulls good and smoothly to redline. I didn't think the 323 & 325 intakes were interchangable due to different mating surfaces at the head. That's what I read - maybe it wasn't true. I also read that the 323i has a *single* exhaust rather than the 325s dual which is why one could fit M3 mufflers to a 325 but not to a 323i. In my 325i it didn't get going until 3300 & then there was a noticeable jump in power around 5500rpm :-) If you search around the usual BMW web pages there is a scanned document somewhere that describes in detail, with pictures, the 323/328 engine. >I didn't think the 323 & 325 intakes were interchangable due to >different mating surfaces at the head. That's what I read - maybe it >wasn't true. I also read that the 323i has a *single* exhaust rather >than the 325s dual which is why one could fit M3 mufflers to a 325 but >not to a 323i. Well, dual exhausts on these (I6) cars is pretty much just for looks. Why? >Why? Because a single pipe works just fine, plus weighs and costs less. Only very powerful engines, needing to flow a lot of air, need two pipes*. Two pipes may also make sense in a V engine, which naturally lends itself to two pipes. *I use the word "need" here rather loosely. There are other factors in the decision, such as ground-clearance (where one large pipe hangs lower than two small pipes). But to take the exhaust from an I6 and run two pipes down the length of the car (or split into two pipes somewhere in the middle? Really just for looks. >>Why? > [quoted text clipped - 12 lines] > of the car (or split into two pipes somewhere in the middle? Really > just for looks. Then why do you suppose that pretty much all of them (BMW inline sixes) have them? My E36 325i has two separate exhaust manifolds and 2 pipes all the way back, except for a short section of larger diameter in front of the two (parallel) cats. I believe that the reason for this joining is the exhaust pulses from one pipe would have an effect of pulling the next one down the other pipe similar to how a 2-stroke expansion chamber works. It also allows a location for a single O2 sensor to monitor all 8 cylinders. The rest of the entire system is two parallel pipes. This doubles the effective flow area and reduces the backpressure dramatically. This is especially important considering the relatively high rpms that these engines are designed to operate at. I highly doubt that BMW engineers would have gone to the bother of designing such a complex exhaust system if it was non-functional. Sorry Dizzy, you are wrong. It's not just for looks. If it was they would just split it aft of the muffler (as many American cars do). -Fred W >If it was they would just split it aft of the muffler They do on some of them? Does the 323i have a "dual" muffler? I single large pipe would ultimately flow a similar amoutn of air (maybe more)but maybe the two smaller pipes have better low rpm characterisitics? ..or it could just be one big pipe was too big to fit in there. >Then why do you suppose that pretty much all of them (BMW inline >sixes) have them? [quoted text clipped - 11 lines] >is especially important considering the relatively high rpms that >these engines are designed to operate at. As a rule, the RPM's on BMW I6's are entirely usual, and the displacement is not large. The only ones I consider "powerful" are the M-engines, the old 3.5L "big six", and the new 3.0L. >I highly doubt that BMW >engineers would have gone to the bother of designing such a complex >exhaust system if it was non-functional. Well, it is "functional" in that it's much flatter than a single pipe with the same flow capacity. >Sorry Dizzy, you are wrong. It's not just for looks. If it was they >would just split it aft of the muffler (as many American cars do). Just for looks and ground-clearance. Certainly, the splitting at the rear for that dual-exhasut look is purely for looks. There's no reason not the run the pipe(s) into a single muffler/tailpipe assembly, except for looks. > Just for looks and ground-clearance. Certainly, the splitting at > the > rear for that dual-exhasut look is purely for looks. There's no > reason not the run the pipe(s) into a single muffler/tailpipe > assembly, except for looks. agreed. -Fred W Hi all, I'll shed my light on this topic and settle it once and for all. Firstly i have a 323i and even though ive tuned the damn thing up (chip, exhaust, air filters etc) runs great etc etc...I keep seeing these 325's glide right past me. Originally i thought the answer was in the diff (stock 323i runs 2.93 open / 325i runs 3.15) so i upgraded to 3.23 LSD of 98 M3. Result...I have to treat mine like a MotherF... to keep up... Basic reasons behind architecture, bmw wanted the 323i to be economical and smooth it was never intended to be thumped! Otherwise we would all have short gear shifters! (thats a bmw blunder!!) So anyway i kept searching to push it the edge... I notice the 323 while accelerating to 4K RPM its fantastic then all of a sudden it Chokes like its gasping for air. The answer lies in the "INTAKE MANIFOLD"!!! M50 325s have larger ports...about 1/3 larger than M52 some suggest. which means u get more air in when your in need, and the reason why our a.ses always got munched the hell out of. Engines both the same, approx 2.5... The 325 gets more air in which ads to a higher torque and HP at 5,500 rpm. Whereass the 323 is restricted b/c of its small intake manifold. Hence why the 323 is a detuned 325i! But with one advantage, the 323i runs 3.0 m3 dual exhaust headers (so ive heard!) Right now with the M50 intake i can beat 325's easily (it keeps munching through the RPM's when b4 at 4000 it choked!). To beat 328's u might need a software upgrade. This is the obvious downside which costs and may have side effects depending on software version and who made it. Hope this clarrified things up :) > Good explanation. Compared to the earlier 325i, the 323i is quicker off > the > line, with better driveablility. It may not have quite the peak power, > but in > everyday driving the response is improved. Also, I believe the 323i is > de-stroked, which makes it smoother. You may believe that, but if it was destroked, how would the displacement be the same? > It is indeed a very sweet engine, the > smoothest in recent memory. [quoted text clipped - 5 lines] > automatics, > if you like those. I disagree. I own a '95 325i and have driven 323i's and 328i's and also have a 2.8l Z3 in the garage. IMO, the 2.5l 323 engine is wimpy in both torque grunt and high rev horsepower compared to my stock '95 2.5l single vanos. Also, the 2.8l engine gives much more torque which can be easily sensed as power at lower rpms, allowing shorter shifting even during brisk driving. For everyday driving, I would suggest the 2.8l is the best choice even at a premium, which for a used car of this age is minimal. The big difference in these used car prices seems to be the increased cost of deleting 2 doors. -Fred W >> Good explanation. Compared to the earlier 325i, the 323i is quicker >> off the [quoted text clipped - 5 lines] > You may believe that, but if it was destroked, how would the > displacement be the same? Bigger bore. It's a different engine. The older 325 had a different bore and stroke. IIRC the 323 is a de-stroked 328, and the later "325" is different still. >> It is indeed a very sweet engine, the >> smoothest in recent memory. [quoted text clipped - 17 lines] > big difference in these used car prices seems to be the increased > cost of deleting 2 doors. I'm not saying the 323 is a better car (which is a marginal difference anyway), I'm saying that it's a better value right now because of market anomalies. I'm not going by KBB values or retail asking prices, but selling prices according to DMV tax/registration fees paid (which marketing consultants have some access to), as well as scuttlebutt from dealer auctions. Matt O. >> You may believe that, but if it was destroked, how would the >> displacement be the same? [quoted text clipped - 4 lines] > different > still. Ah, I see. Thanks, -Fred W > >> Good explanation. Compared to the earlier 325i, the 323i is quicker > >> off the [quoted text clipped - 9 lines] > stroke. IIRC the 323 is a de-stroked 328, and the later "325" is different > still. There appears to be some confusion. Seems to me the 325 from '89 to '95, had bore/stroke of 84 x75. Around '91/2, a single Vanos was added. The engine continued in this form, until around '95 it became the 323, with it's output reduced by about 20bhp. I'm guessing the valve timing, and fueling settings were changed. Effectively detuning it. All I was wondering is exactly how and why. The 328 would appear to be basically the same engine as the 325/323, apart from an increase in the stroke, from 75 to 84mm. Presumably it has a similar 'detuned' setup as the 323, as the bhp output is virtually the same as the single Vanos 325, even though it has 300 more cc. Mike. |
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