Dreams of a supercharger...:D

[Nay]

I've been contemplating this for a while....

F/I or N/A.... early high comp 325i.

I still dont know too much about FI apart from the principle of how it works.

I noticed a while back, Ant's Rotex supercharger kit. Its £3k. Now could that be fitted easily whilst my engines out, by home mechanics (:P) and then have MS and a remap etc done by pros for a fair bit less than £4k?

Also, my plan is to get a BTB3 manifold (to accompany my new Z3 rack) and also a hot cam and lightweight fly etc.. Will the superchager go hand in hand with these or will they not really be compatible. Do you need a special manifold for a charger, as if my knowledge is "on target", you need a special "turbo" manifold when turbo boosting...

Also it will be coupled with a full engine rebuild... to the extent of my budget.

Just trying to locate some info on building a S/C 325i. I take it you need a blower (Like in Ant's Rotex kit, which is a 'Contrifugal' charger... which has characteristics similar to a Turbo?), a pipe from the charger to the throttle body, sort out the air intake (MAF? And does that feed into the charger), MS then a remap... Thats as far as I can make out, but I'm sure theres much, much, much more. What else is there?


Can anyone please help out a Boosting newb who's asking a question which has blatently been done to death, but struggling to find some good resources?

TYAI!

[rix313]

Loads of good books out there dude, there's a thread on it in this section some where.

You can use the standard manifold for the charger so you can keep costs down by not making a whole new one.

The fly wheel and exhaust will go perfectly with it but you need to make sure that the manifold and indeed the rest of the exhaust will flow enough exhaust if you're going for more power, don't want you're efforts strangeld by a narrow exhaust.

You will need an intercooler to cool the charge air down too.

Read Geoffbob's thread on supercharging the M42 (there's an Eaton one and a Rotrex one), although a different engine the principles are the same.

[m_jermyn]

centrifugal blowers work just like a turbo but dont use the exhaust to spin the turbine, they are belt driven. So you can have a your btb3 manifold. So the blower sucks in the air, compresses it, you can then run strait through to the motor or via a cooler if you want higher boost then through to the motor.

Like I said looks just like a turbo but is driven by the belts on the motor instead of the exhaust.

Mike

[m_jermyn]

http://auto.howstuffworks.com/supercharger4.htm

This should help you out heaps

Mike

[Nay]

Much apprecitated.

OK, so you start with say an air filter, which goes into a supercharger (which is constantly spun by the belt (is that a new cambelt with an extension for S/C?)). The S/C then sucks in and compresses the air into the throttle body which essentially forces air into your engine? And this can "optionally" run though an intercooler to cool the air down?

Ok, as I'm really comtemplating a S/C kit from Ant (as the engine build goes on in the future!).

Just want to know whats involved outside of Ant's kit and also what is actually included in the kit as well!

[ShakeyC]

I would not bother with a fast steering rack atall the standard one gives you half a chance to catch an ooops moment especially with the power delivery of Rotrex. You can change to Z3 rack at a later date ofcourse once your used to it be a wiser move.

You don't need a special manifold if budget is a concern it be one of the things i would leave out or put money towards properly rebuilding your engine to suitable spec maybe 2.7 although standard is fine too you do not need fancy crap for sake of it! Infact if it aint broke leave it alone. An intercooler, catcam, set of injectors and megasquirt is enough to start off with.

pics of the kit
www.fastbimmer.co.uk/projects/projectE30rotrex.html

A pulley is attached to the front of crank to drive the Rotrex via seperate wide belt, as revs change so does speed of the charger BUT the boost created is not linear as traditional superchargers its an exponential rise due to the way Rotrex works its more efficient. The kit is well designed to make it easy as possible to fit even with engine in situ.

[Nay]

Cheers Shakey.

This isn't a budget build at all. I'm already looking a £10k minimum for just the current plans.

Its going to have a pretty much full engine rebuild, bar new pistons etc. The cylinder head will use the original rockers and shafts, but thats about it. new cooling etc. Fast rack, BTB3, all new bushes, bearings, suspension, brakes etc. Let alone the interior, exterior, spray job and alloys

Living in Jersey, 2.7s and monster top end cars are useless, its about the rapid acceleration in the few areas we may get a chance to be a prick. The rest is massively fun windy little county roads.

I'm a competant enough driver to not get into the situation of "whoops" moments round corners, I dont aim to do it, but I have enough experience in the sideways department to know what is going to happen and when... but thats not what I want to to, as even the most experienced drifter will have his off days... and on public roads is a bad idea! Oh, and personally, I hate the standard steering racks, and they really dont help when the back does break loose!

The point is just a completely custom, nice to drive E30 that will come out to play in cool evenings and nights, and maybe a few meets in the UK.

I want a car that low down is simple and easy to drive, but can be a handfull if you push it. Thought about turboing, but the lag puts me off.

[ShakeyC]

If your rebuilding the engine a 2.7 build its not just for top end it gives worthwhile gains low to mid range too not just all about top end which is more dictated by the cam profiles you choose. A 2.7 build is not much more expensive than rebuilding 2.5 as you are anyway in the grand scheme of things?

Im not saying your incompetant driver at all, im making sure your aware with the power delivery and punch a rotrex gives on a motorway at 70mph if you punched the throttle it will spit you across 3 lanes in the dry. A quicker steering rack just makes it that bit more difficult to predict and catch easily end up over correcting making the results worse when you least expect it.

[Gunni]

What have you set aside as money for engine power?

[Nay]

ShakeyC - Cheers that sort of punch is what I'm truely after (for the occasional show off moment ). Luckily we dont have motorways for such a devastating high speed punch! Speed limit is 40mph, but the country roads prove fun for the occasional loud pedal fettling!

Gunni - As much as it needs mate. I currently (and hopefully for the duration of the build) can punch out a rough budget of £400-£500 per month free for the car (lucky still under the parents roof for a few more years!:D). That budget will resume after christmas now, as a mate is getting married in december. Need money for that, money for the stagg doo in november in Prague (we think), so moneys is tighter this side of the year.

Trying to cap myself where possible. Maybe a top of £3k for the rebuild, and some other associated parts that are directly connected. £3k for the supercharger and £1k for MS and remap and fetteling.

£1k for possible rust hunting. Classic places are ok. Innards are still a bit of a mystery. Scuttle is begining to bubble due to the long time its been sitting outside
£3k for the suspension, bushes and so on. £1k for wheels and tyres.
£1k for electrics
£1.5 for the retrim, dying carpets and sorting all little trim as well.
£1.5k-£2k for a top spray job.

That £15k-£15.5k (inc supercharging )...

Hoping to push that down as I go. If thats good, pull to pieces, refurb, put back together, test and reuse. So hopefully that will start cutting on prices of parts throughout... hopefully closer to the £12k mark would make me happy. But I'm not going to skimp, only reuse A1 parts and A1 spares. Actual prices may well shift to more expensive one place, cheaper in others.

But this is going to be a lifetime toy and properly insured for serious money. I'm trying to do essentially a kit-car E30, whilst I'm young, can rob my dads garage and dont have many bills pay!!! I fear once I get a tadd older, into my job and life, this will start to become unviable!

I'd rather drive a shitter as a daily and have something like that to roll out on a nice cool weekend evening/night than buy a boring newish car. There isnt enough "standout" cars in jersey bar some barry boys in fibregay shitters!

As this progresses though, I'm preparing myself (we'll see how it goes) to get the bodywork (rust hunting), suspension and engine done and price up the rest and finish it all with a £5kish loan. Also, my work offers a brilliant bonus where if I pass a proffessional exam, I get a grand. Also, hoping that upon gaining some proper qualies will see a pay rise = more funding faster!

Even if this takes me 3 years or something, I'll get it done!

[dlatch]

i would concentrate on getting the engine and car its self rebuilt and running happy.
this will also give you time top tune the handling and brakes to your preference and get used to driving the car.
the super charger kit is retro fit anyway so if you have a fresh engine with free flow exhaust you will get good results when it see's some boost.

[Ant]

^^^ fookin hell, thats a username from the past !

hello Duncan

[dlatch]

lol hey mate
how's tricks?
nothing to report my end same old ect ect

[Nay]

dlatch - Ye, the order is remove the engine and interior, rust hunt and fix. Then rebuild the engine and the suspension. Test everything is good. Supercharge, MS, Remap. Then continue with all the little bits and bobs, such as replacing parts within the anchillaries, and brakelines, fuel pump, fuels lines, tank etc...

Once the car is tip top, respray it and fit new wheels (to make sure about rolling arches as it gets final bodywork done). Then sort out the interior properly, whilst fitting new features (hopefully heated seats, a built in computer, etc) and making everything work like it did from the factory (sunroof, windows, OBC, etc). Massive, Massive job


Now, another S/C query, - How do you determine the amount of boost from a charger (which I assume is the major factor in how powerful the car is... can this be controled by the ECU/MS? I spoke to people a while back as I was curious about having two different maps, 1 for normal everyday conditions (which still pumps out some respectable power) and one for just pumping out the best map we create for performance. As if I could say (example, not real figures) drop the boost from the S/C to 5psi for driving (to give some boost, but not send me out of control!) and then bump that up to 15psi on the press of a button, whilst opening up the rev limiter, more fuel/air and so on....

Could something like that be done?

[Steve]

lol hey mate
how's tricks?
nothing to report my end same old ect ect

Wow, Hello Duncan !

I wonder how many members on here remember you? would be interesting !

/Nay sorry for jumping in

[e301988325i]

Nay, a few things to consider if you're doing s/c conversion.

Boost is determined by charger rpm (size of driven/driver pulleys relative to each other) and obviously the charger itself. So it's not an option to limit power other than with the throttle itself.

A facelift 325i lump has forged pistons (required) and a lower compression ratio (also required) and is a better bet for FI, + this standard bottom end will take a lot of boost with a 2mm decompression plate between head and block. Randomdave325 on here built one in an E21 with big power from a rotrex charger.

BTB3 will be ideal for S/C

Custom exhaust manifold required for turbo charging for two reasons, one you have to bolt the turbo to it, and 2 it needs too be designed so that the turbocharger recieves equal exhaust pulsing for optimum efficiency, although number 2 isn't strictly necessary.

You'll need bigger injectors too.

[Nay]

Ok, so the pully you attach to 'your crank?' to power the supercharger, and the one on the s/c itself determines the rpm of the blower, which in turn is how to determin boost. I may be completely off, but does that mean it works with the same principle of bicycle gearing, where if the cog on the end of the crank is smaller, the one on the S/C will spin faster (but build up smoother?) meaning more boost?? Or am I waaaay off

For a start, doesn't Ant's S/C kit work quite well with stock internals? With forged pistons, does that mean having a lower compression ratio will effectively allow more boost in the car with less strain on the engine? Also, would stronger rocker arms be a wise idea as I've heard hitting 7k rpm on frequent occassions will cause a rocker to snap. With a hot cam and S/C, I'm sure the car would hit that quite easily?

Finally, is MS required? Is the supercharger in anyway connected to the fuel management system? Otherwise, is the fact that you need an MAF or MAP box over the AFM and to judge fuel/air ratios whilst air is effectively forced into the engine?

TIA

[e301988325i]

Ok, so the pully you attach to 'your crank?' to power the supercharger, and the one on the s/c itself determines the rpm of the blower, which in turn is how to determin boost. I may be completely off, but does that mean it works with the same principle of bicycle gearing, where if the cog on the end of the crank is smaller, the one on the S/C will spin faster (but build up smoother?) meaning more boost?? Or am I waaaay off

Yes. but has nothing to do with smoothness. it's directly proportionate.

For a start, doesn't Ant's S/C kit work quite well with stock internals?

yes, but the later engines are better suited.

With forged pistons, does that mean having a lower compression ratio will effectively allow more boost in the car with less strain on the engine?

Forged pistons are stronger and better. Strain on the engine is based on torque output. To high a compression ratio will result in compression ignition like a diesel engine and will break any engine.

lower compression ratio = safer, or more boost before pinking (pre ignition).

Also, would stronger rocker arms be a wise idea as I've heard hitting 7k rpm on frequent occassions will cause a rocker to snap. With a hot cam and S/C, I'm sure the car would hit that quite easily?

I'd advise a low to mid range torque band for where you live, you don't want a high revving engine with a high power band you'll never get to use over there. The standard cam works fairly well with FI, you need a specific FI cam if you're going to change it.

Finally, is MS required? Is the supercharger in anyway connected to the fuel management system? Otherwise, is the fact that you need an MAF or MAP box over the AFM and to judge fuel/air ratios whilst air is effectively forced into the engine?TIA

It's doable on standard ECU, but you just wouldn't.
You could use the standard AFM but again you just wouldn't!

Basically upgrade to MS or equivalent with MAP (manifold absolute pressure) or MAF (mass air flow) or both perhaps I'm not sure but definitely ditch the AFM.

[rix313]

You do need MS (or something similar) as you're changing the way the engine runs. You're cramming alot more air and fuel into the cylinders and the ECU needs to know what to do with it in simple terms.

The Rotrex chargers have interchangable pulleys so you can get the gearing set up properly although I'm sure the one Ant supplies will come with the right one or he can sort you with one to suit what you want. I'm not sure what size crank pulley the M20 uses but for example on my M42 I'm going to be running a 140mm crank pulley. Because I don't want to be pushing my standard engine too hard I need to look at running a 100mm S/C pulley which means the charger is running at 82,000rpm which is fairly slow compared to it's readline of 120,000rpm.

[Nay]

Right,

So, having the earlier engine means I really should look for some forged pistons? Also, are the pistons and compression ratios the same for pre and post facelift M20s? (as in with the new pistons, is it the old pistons that make that stock difference in CR?).

The plan is to have a high revving, preferably nutty, engine. If the car is powerful low down, you wont really use it either. You'll go too fast straight away! With a speed limit of 40mph, I dont really plan to be doing stupid speeds anyway in Jersey. Its for the UK (going to meets, meeting mates), maybe santa pod, and possibly the odd track day. I find mid range power makes you edge up gears when cruising around (like dumping it into 5th at 45mph.), but I would rather a car that forces you to use the right gear, even if it means cruising a 3-3.5k rpm. Its hard to explain! High top end, just enough below.

So, stronger rocker arms? Also, would a shrick cam (e.g 272/272, 288/288) not be good to use? Will these not go with FI?

Right, so S/Cs (obviously) affect the levels of air going into the engine. Which is why MAF (and possibly MAP as well? Is it one or the other, or both?) are used. So can you get away with using this miller WAR chip, which I'm still yet to hear reviews or experiences with, which is a remappable chip that uses he standard fuel injection system. Having the older engine (but in a facelift car) which injection system would you think is in my car? Any way to check?


What I was on about with the "gearing" for the S/C and its smoothness, I was saying that with a smaller cog, surely it would be be slower to start off with, but progress much more smoothly and have a higher boost at the end. A larger one would spin the boost faster, so more of a kick?


Again, thanks lads, but this project is going to take masses of studying and I dont want to go off an do something, only to find out its wrong for the finished product!

[rix313]

Think you got the gearing the wrong way round, a smaller pulley will spool the charger faster and a larger pulley will spool it slower.

You need to gear it so that the charger isn't running over 120,000rpm at your engine redline. If you fit a smaller pulley to spool it up faster, you'll end up redlining the charger earlier meaning you have a silly low engine redline too so you don't nuke the charger so no advantage at all.

You only need one or the other when it comes to MAP or MAF sensors.

[Nay]

Ah ok. So does gearing it take trial and error, rough judgment or is there a way to figure it out?

[Morat]

You're deliberately building a peaky top end screamer for a country with a 40mph limit?

[rix313]

Ah ok. So does gearing it take trial and error, rough judgment or is there a way to figure it out?

Good god no.

This is the equation you need to work out the pulley ratio:

S/C RPM at desired airflow
Gear ratio of charger x engine redline

[Nay]

You're deliberately building a peaky top end screamer for a country with a 40mph limit?

Country is a massive overstatement.

Again... this car is NOT a daily, is not for just poking round green lanes in jersey (a 50cc mopeds good enough for that!). Its a car that will be over in the UK a bit, be an occasional trackday toy. It will oneday (hopefully) say hello to the nurburgring and probably a few of the larger zone/E30/BMW meets in the future in the UK. An elaborate toy, if you will

I think I'll be buying a 328i sport or an M3 or (god forbid) a Golf or something for my everyday rampages, when its time to replace my 320i auto (which will probably be replaced by another tatty E30 when it sees the barvarian heaven, untill the project is finished and funding is released again ).

I'd only take it out of the garage once or twice a month depending on the weather. Probably only on weekends and holidays when I can go wake people up in the early hours of the morning!

[e301988325i]

So, stronger rocker arms? Also, would a shrick cam (e.g 272/272, 288/288) not be good to use? Will these not go with FI?

Right, so S/Cs (obviously) affect the levels of air going into the engine. Which is why MAF (and possibly MAP as well? Is it one or the other, or both?) are used. So can you get away with using this miller WAR chip, which I'm still yet to hear reviews or experiences with, which is a remappable chip that uses he standard fuel injection system. Having the older engine (but in a facelift car) which injection system would you think is in my car? Any way to check?

What I was on about with the "gearing" for the S/C and its smoothness, I was saying that with a smaller cog, surely it would be be slower to start off with, but progress much more smoothly and have a higher boost at the end. A larger one would spin the boost faster, so more of a kick?

Building a supercharged engine for constant high revving is rather missing the point, especially on a 2 valve per cylinder head. Go turbo if you want top end, and then rockers. As I said above, upgrade NA cams are the WRONG choice for FI. And again as I said above, although it's technically possible to use the standard ECU, DON'T.

A supercharger trys to give equal boost across the rev range, it's a mechanical pump pyhysically attached to the engine in a directly proportionate sense, as rpms rise, pumped air flow increases, and at the same time the engine needs more air. . .

For an example at 2000rpm the engine is using say, 200CFM (cubic feet per minute) the charger is pumping say 300CFM (150% more) creating boost, because the two are linked, at 4000rpm the engine is using 400CFM and the charger pumping 600CFM (still the same ratio at 150% more).

I've plucked those numbers out of thin air as an example and in no way are accurate or calculated, neither do they take into account varying efficiencies across the rev range, I'm just trying to give you an idea. Basically a supercharger that doesn't work low down won't be working up high either.

[dlatch]

lol hey mate
how's tricks?
nothing to report my end same old ect ect

Wow, Hello Duncan !

I wonder how many members on here remember you? would be interesting !

/Nay sorry for jumping in

hehe hey steve still around yourself then

[Nay]

So, stronger rocker arms? Also, would a shrick cam (e.g 272/272, 288/288) not be good to use? Will these not go with FI?

Right, so S/Cs (obviously) affect the levels of air going into the engine. Which is why MAF (and possibly MAP as well? Is it one or the other, or both?) are used. So can you get away with using this miller WAR chip, which I'm still yet to hear reviews or experiences with, which is a remappable chip that uses he standard fuel injection system. Having the older engine (but in a facelift car) which injection system would you think is in my car? Any way to check?

What I was on about with the "gearing" for the S/C and its smoothness, I was saying that with a smaller cog, surely it would be be slower to start off with, but progress much more smoothly and have a higher boost at the end. A larger one would spin the boost faster, so more of a kick?

Building a supercharged engine for constant high revving is rather missing the point, especially on a 2 valve per cylinder head. Go turbo if you want top end, and then rockers. As I said above, upgrade NA cams are the WRONG choice for FI. And again as I said above, although it's technically possible to use the standard ECU, DON'T.

A supercharger trys to give equal boost across the rev range, it's a mechanical pump pyhysically attached to the engine in a directly proportionate sense, as rpms rise, pumped air flow increases, and at the same time the engine needs more air. . .

For an example at 2000rpm the engine is using say, 200CFM (cubic feet per minute) the charger is pumping say 300CFM (150% more) creating boost, because the two are linked, at 4000rpm the engine is using 400CFM and the charger pumping 600CFM (still the same ratio at 150% more).

I've plucked those numbers out of thin air as an example and in no way are accurate or calculated, neither do they take into account varying efficiencies across the rev range, I'm just trying to give you an idea. Basically a supercharger that doesn't work low down won't be working up high either.

I understand that, but different chargers work differently.

I've heard rotex (contrifugal) superchargers act a lot more like turbos. Different blowers work differently forcing more air into the engine at different peak points. A blower could continuously force 150% more air in proportion to what the engine is wanting, but some might say give you 110% at the bottom, 130% by the time your revving 3.5k/4k and 160% nearer 6k. So the boost rises as the revs increase, but still at a constant % increase. Meaning there is more top end, but it is still giving boost at the bottom.

This, coupled with cams and other little toys could help effectively make the top end much more playful than the bottom, making a high up revving beast... but still not like a powerful turbo with nothing, nothing, nothing, a little, shit....

This is the explaination I have been getting around the place with s/c and 90% of people are definiately backing the s/c over the t/c for a fast, powerful car, but helping avoid the lag patch in the bottom end, which in Jersey is not very good. You want low end grunt, at least to make the slow driving fun.

I think I've explained myself somewhat conherently