E21 323 without silencing
Discussion
Yesterday one of my housemates and I removed the diff and prop shaft from the E21 he's breaking. We had a few access problems so decided that as the exhaust pipes were fairly rusty that they might as well be removed. Took them out right back to in front of the central silencer. He looks over and says "I wonder what it'd sound like...".
10 minutes later we have fuel, a battery and the fuel lines are hooked up for one last time. The engine turns over fairly slowly at first, but then it starts to get fuel and nearly starts a few times. A few seconds later it goes. WOW, WHAT A NOISE! Anyone who has never heard a BMW straight 6 unsilenced I can assure you that it is most certainly a supplier of aural pleasure of the highest degree.
Even better, one of my housemates girlfriend had her digital camera videoing when we fired it up. With a bit of luck I'll be able to get the video online soon!
10 minutes later we have fuel, a battery and the fuel lines are hooked up for one last time. The engine turns over fairly slowly at first, but then it starts to get fuel and nearly starts a few times. A few seconds later it goes. WOW, WHAT A NOISE! Anyone who has never heard a BMW straight 6 unsilenced I can assure you that it is most certainly a supplier of aural pleasure of the highest degree.
Even better, one of my housemates girlfriend had her digital camera videoing when we fired it up. With a bit of luck I'll be able to get the video online soon!
The M20 2 valver engine on open exhausts is one of the BEST sounding engines I've come across, and I've done work in OEM vehicle NVH (noise vibration harshness)quality. Most folk know a straight six is superbly refined and smoothed due to very low moments of inertia in both horizontal and vertical planes.
The E21 323i in particular has more potential to sound better than any E30, because it has dual side pipes, that exit at each side. This is like having speakers but spreading them apart- unlike the dumb E30 arrangment where they are together (like placing your speakers together!).
The other factor in favour of the E21 NVH is that the each bank of the system is UN-EQUAL length- as both pipes travel down one side for ages before splitting up and exiting at opposite sides. This gives some "half order modulation" which is a flash way of saying- some richer character. BMW obviously achieved this unwittingley on the E21, but it's interesting that their NVH specialist in Munich recently wrote a paper describing this characteristic and how the Z3s and Z4s have embraced this philosophy NOW by design. [ SAE paper 2001-01-1428]. This paper also describes that BMW straight sixes make a good noise if they have most of their silencing at the rear rather than distributed in the middle resonator as well.
The 2 valve layout also makes the car sound rortier than the later M50 4 valve engine- due to the earlier Exhaust valve opening event and larger overlaps. My car has gone for a 2.7 litre motor and to this I've added a schrick 284 duration profile. I've had a specially fabricated stainless steel exhaust system made up. All these combined make the car sound incredible. I would honestly put it above a racing Jaguar E type and almost on a par with the oldstyle Masserati straight sixes in terms of noise. The 2.7 litre with the race cams made a huge difference in terms of noise over the stock 2.3 litre when attatched to the same fabricated exhaust.
If I stay the M20 2 valve route- I'll go 3.1 litre capacity, go for my own design of 292 period cams, and evolve the exhaust design further- I'm hoping to get a real PEACH of a sounding engine.
The E21 323i in particular has more potential to sound better than any E30, because it has dual side pipes, that exit at each side. This is like having speakers but spreading them apart- unlike the dumb E30 arrangment where they are together (like placing your speakers together!).
The other factor in favour of the E21 NVH is that the each bank of the system is UN-EQUAL length- as both pipes travel down one side for ages before splitting up and exiting at opposite sides. This gives some "half order modulation" which is a flash way of saying- some richer character. BMW obviously achieved this unwittingley on the E21, but it's interesting that their NVH specialist in Munich recently wrote a paper describing this characteristic and how the Z3s and Z4s have embraced this philosophy NOW by design. [ SAE paper 2001-01-1428]. This paper also describes that BMW straight sixes make a good noise if they have most of their silencing at the rear rather than distributed in the middle resonator as well.
The 2 valve layout also makes the car sound rortier than the later M50 4 valve engine- due to the earlier Exhaust valve opening event and larger overlaps. My car has gone for a 2.7 litre motor and to this I've added a schrick 284 duration profile. I've had a specially fabricated stainless steel exhaust system made up. All these combined make the car sound incredible. I would honestly put it above a racing Jaguar E type and almost on a par with the oldstyle Masserati straight sixes in terms of noise. The 2.7 litre with the race cams made a huge difference in terms of noise over the stock 2.3 litre when attatched to the same fabricated exhaust.
If I stay the M20 2 valve route- I'll go 3.1 litre capacity, go for my own design of 292 period cams, and evolve the exhaust design further- I'm hoping to get a real PEACH of a sounding engine.
Marquis_Rex said:
... 3.1 litre capacity ...
Is it possible to get these engines this big without major work being done to them. I have read with interest your posts regarding BMW engines and your project car but had missed this little detail! If you're interested here's a video of the car being played with
www.tombrimble.co.uk/E21%20Sound.mpg
ginge said:
... 3.1 litre capacity ...
If you're interested here's a video of the car being played with
<a href="http://www.tombrimble.co.uk/E21%20Sound.mpg">www.tombrimble.co.uk/E21%20Sound.mpg</a>
Thanks for the links, I'll have a listen to them later.
It is possible to stretch the M20 engine- my collegue in california has stretched the M20 up to 2.9 litres by using a US-M3 crankshaft and 325i M20 rods and custom pistons- he's also bored the unit out.
In answer to this (:P), I have obtained an EURO S50 engine (the Euro M3 engine has bigger con rod journals- up from 45mm to 50mm). From this I intend to offset grind the crank to go from the 85.8 mm stroke to 86.8 mm. Although I wouldn't reccommend it, I'm going to bore out to 87mm, which only leaves 4 mm between bores. I've done my calcs and compared to a few engines and think It will be ok. I've had a block sonic tested before- and there's enough metal there. You have to start off with an 84mm 325i or 525eta block as the 80mm 320/323i blocks have water ways between them. The other issue is if you want to go for a sensible rod to stroke length ratio ( I want to use the 139 mm rods from the S50) the M20 block is only 206mm tall. This leaves only 23.8mm for compression height of the piston to get your ring pack into. I'm going to tackle this by using a custom-spacer cylinder head gasket to accomodate specially forged pistons.
There are some clearance issues with the crankshaft/rod bearing wipe line fouling the auxiliary shaft (the one that drives the dizzy on the E21)but I think I should be able to relieve this.
To use the M50/multivalve crank you have to use a special washer so that you can accomodate the belt drive sprocket on the nose of the crank.
The other challenge will be trying to accomodate large engine valves into the M20 325i cylinder head. I've made a vinylmold moulding of the combustion chamber and ports and reckon I should be able to squeeze 45mm valves (from 42) and 37 mm exhausts ( from 36).
So it's not an easy undertaking, and one would probably reap better results fitting a late alloy block 330 ci engine, but it wouldn't be as much fun nor would it be an exercise in engineering which is partially what I'm after.
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