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I'm new here and that's my first post, so on very begining I would like to say Hello to everyone and thank You for reading this thread!
I've got 2 general questions and I would be gratefull to hear Your opinion about my considerations:
I am at the middle of building my old good E46 328Ci, the car passed all requred modifications for: suspension, (brakes still waiting), intake system, exhaust, differential and ECU. Meanwhile because of high mileage I want to make engine rebuild to make sure car is going to handle the power and will stay reliable for next years.
Making rebuild makes allso a consideration about some engine and exhaust modifications:
1) I'm thinking about building slightly different engine than stock, which will be able to REV till 8000~8500 RPMs (stock max is 6500). In thoose engines It's not a problem to increase rev limiter till 7K rpm because they handle it without issue. I know from 7200 valves start to float.
To archieve desired rev limiter I am considering to swap:
- cams: for greater duration and lift
- valve springs: which be able to handle till 8K RPM
- forged pistons: because they're able to handle the speed
- forged rods: because they are able to handle much higher rpms
- head porting: for better flow
- crankshaft bearings: of course because of rebuild but allso because swap from stock to race aspirated, propably: copper lead
Here are 3 questions:
a) Should i worry about my forged 84mm stroke crank ? There is possibility to swap crank to forged 74mm stroke.
b) If I swap to 74mm stroke forged crank I will have 10mm difference at the top of engine which will slightly reduce compression. If I'll install high compression pistons I'll be able to loose like 3mm. Maybe It will be possible to get thinner HeadGasket, but this will provide me max 0.5mm. Do You have ideas about dropping thoose (at least) 5mm ? Does resurfacing head and block is the last option ?
c) What about timing chain ? Isn't it better to replace timing drive to belt ?
2) My personal automotive "fetisch" is high pitch sounds like F1 and I'm allso interested about some exhaust modifications to archieve this kind of effect.
Many of people on zillions of forums told me this is archievable only with:
- flat plane crank: FAULT, because many cars does such effect with crossplane crank; ex: M3 e92 or M5 e60.
- high rev engine: FAULT, it's not required to rev engine till 10 or 13 thousands RPM's to achieve high pitch; ex: 350Z or again M3 e92 or M5 e60
- many cylinders, at least V8: FAULT, because there's many V6 which does that, like many rally Lancia or 350Z.
- It has to be V-engine, because of cylinder degree: FAULT, because supra's does that too and many old 280Z.
- equal length headers: TRUE: and here my considerations are mostly related to. Is there anythink else I should consider to get high pitch exhaust sound then just a equal length of headers (6 to 1) and decent exhaust diameter ? Anythink with lift, lobes etc ?
If You get till here, I would like to thank You very much for involve and I hope You'll be able to add some of Your opitions :)
Best Regards !
Some of these questions may be better asked on BMW forums - particularly those focusing on the in-line 6 engine, however, my 5 cents worth (might be due some change...). I assume the engine is going to be NA - NOT super or turbo'charged?
1/ Summary looks good in principle.
a/ I would expect the crankshaft to be up to the rpm increase. The shorter stoke crankshaft will bring the capacity down to ~2.5 litres.
b/ The pistons will be 5mm lower in the cylinder, not 10 as the change in crankpin offset is half the stroke. With the '28 length 'rods and pistons (with same deck height), there will be a huge drop in compression and would be a foolish move, not just because of the loss of swept volume and affect on torque and power. However, if you are just concerned with rpm, you could use the 74'crank' with longer rods for a better ratio and more rpm.
High compression pistons, as such, won't affect the piston position, but you may be able to locate some with the correct deck height.
machining the block would potentially compensate, but it may weaken the block - not recommended! machining the cylinder head will have a small affect on the compression but, again, NOT recommended.
2/ If someone says you need a flat plane crank in a six cylinder engine - STOP listening to them, they are ****ing idiots!
Depending on what you mean by a "high pitch", you really need to turn the rpm - however, you can get a lovely howl from a six even at those rpm. You will need to keep the exhaust primary, and collector, lengths as close as possible. There is also a rather nice 'ring' given off by tube manifolds/headers, which should add to the aural experience.
True, a flat plane V8, or a cross-plane with cross-over exhaust manifold should be 'better', let alone a V12, but a similar affect is certainly possible with a six, as you say.
A six into 1 is a LOT of hassle, 6>2>1 is as effective, if you keep the lengths the same - perhaps a little more mid range and a little less peak?
A BIG part of the sound is the intake system - you should run independent runner throttle bodies, with independent filters rather than an air box, as the intake can actually be louder than the exhaust for some applications!
I would also suggest checking if the oil pump is sufficient?
Oh, timing chains shouldn't be a problem, with new components, but check the BMW forums for any issues - regardless, a conversion to a timing belt is a MASSIVE AMOUNT OF WORK, and you certainly don't sound like you have the experience to even think about it - I certainly wouldn't!
It sounds like you are looking at the right components to increase the RPM -- but I don't hear you talking about the peak piston speed. Research that and you will find that piston weight/strength are the limit and Engine Speed and Stroke (plus rod length) define what the speed actually is.
Unfortunately BMW forums are mostly about 2 topics: "How much boost handle stock engine" and "how much boost can handle engine block". Not many people willing to rebuild character of engine, most of them focus just on power, which is very easy with thoose engines. They usualy hold double or tripple the power (without great hassle), after small modifications and they like to beeing abused.
Primary i was thinking about Turbo (like every bimmer) but high pitch thing is going to be harder to archieve this way. Characteristics will change and I'm not realy sure about boosting engine. I'm not building my car for client, it's allso not a track machine. For daily use 225pk on short differential is allready very fun to drive and indeed I would like to pop up the power a bit but that's not greatest point. I know Supra or Skyline are able to make this pitch sound preaty damn good, even with turbo but I need to take a look closer into build of thoose headers and setups. If I would be able to "reconstruct" it, I would be very interested about low boost at arround 7psi; because that would provide me 300+ bhp, which is fair enough for me.
- Indeed You're right about half of stroke, that's my bad. I guess my problem here is much smaller than i suspect, if turbo - the problem doesn't even exist because I will need lower compression.
- Indeed I would reduce capacity to 2.5L, but that's absolutely fine.
- If I will do "sandwitch" headgasket, which is 2mm thicker than OEM I would loose arround 2 points of compression. That's why for fast counting I'm suspecting 1mm is like 1 compression point. If there's high compression ratio pistons I'm preaty sure they are higher or valve cut's are much smaller - which makes allso smaller capacity of the cylinder; I guess I can "fast count" it allso like every 1 CR point = 1mm.
- Are You sure 6-2-1 can handle this kind of sound ? I though it's only obtainable at 6-1 constructions - indeed they are much more hassle.
- At intake point You are completely right, I was testing some of airboxes at my cars and ITB would be awesome but I've found one "geometry" of air-filter which increase a pitch noise and it's working together preaty promising.
- I was thinking about extra loop for oil cooling with thermostat. When oil get warmer it will get into big and efficient cooler; and while oil keeps OEM temperature it stays in standard route, to make sure I won't reduce operating temp's.
- Indeed I am aware meaning of timing drive swap and that's the last option I would like to go with. I have few interesting ideas to make it simplier but at this point I would like to preffer stock system. Only question is: old BMW has realy thick and solid chains and as we know big and thick stuff at high speeds like to fly away, that's what I'm a bit scared of.
That's some calculations about piston speeds:
Af far as i know most of stock pistons are OK till +/-4000fpm, forged pistons are able to get till 5500fpm.
- 84mm stroke +6,5k REV = ~3500fpm
- 84mm stroke + 8k REV = ~4400fpm
- 74mm stroke + stock rev = ~3200 fpm
- 74mm stroke + 8k REV = ~3900 fpm.
Thank You very much for Your opinions and time You spend on my case. I'm very glad to hear such acceptable conclusions and agreement - that's indeed a bright light for my project.