M42 Forced Induction Advice please.

[ShepsM3]

Hi all,

I am new here, but am quite active on a few other BMW forums. I have a few 318is M42's as project cars and I have just purchased one which I would love to Supercharge. I want to use a Rotrex Centrifugal Supercharger as I know them pretty well having converted a few other cars. They give damn good results and are very compact and reliable.

What I want to know is, how strong is the M42 engine for taking boost? I don't really want to play around with the internals and just want to bolt the Rotrex on, large front mount intercooler, raising rate with boost fuel pressure regulator and loose the AFM through using the latest Dastek's Unichip version Q and use a MAP sensor instead. May go larger injectors too, depending on how off the fueling is under boost. I would love to push 10-12psi if the internals can take it?

I understand that the crank and rods are steal and the pistons are forged already, so BMW did the hard work here. I am not worried about the high compression ratio either, but am worried about the top piston rings and head gasket.

I also know that in order to carry out this conversion, I have to upgrade the crank pulleys and water pump, alternator pulleys for the later M44 type to be able to use a multi-vee belt for the supercharger. I will mount the SC where the AC pump would have gone if it was fitted.

I have done a quick search, but its late here and I thought some of you guys maybe interested in what I want to do and offer some advice up before I go ahead.

Thanks in advance.

Paul

[WeirdYo2]

here is my experience with my turbo m42.  My car has a stage colder plugs and the thickest headgasket you can buy from the bmw dealer, I forgot the actual thickness.  I have been through a few setups already but I use to run about 6psi with the stock injectors and a rising rate, my injectors were maxed out and it started running really lean at about 7psi.  It ran good then but i kept getting beat and needed more power.  So now i have 42lb injectors and run about 10-11 psi on the same setup.  As far as tuning goes, i have the stock ecu, factory timing and everything, all i did was mess around with the mass airflow a little bit rev it up in the garage a couple times to make sure it wasnt huffing black smoke and left it.  For some reason it ended up working pretty well for over 30k miles.  I dont see any problems running 12lbs or more with a good tune and knocking back the timing.

[ShepsM3]

here is my experience with my turbo m42.  My car has a stage colder plugs and the thickest headgasket you can buy from the bmw dealer, I forgot the actual thickness.  I have been through a few setups already but I use to run about 6psi with the stock injectors and a rising rate, my injectors were maxed out and it started running really lean at about 7psi.  It ran good then but i kept getting beat and needed more power.  So now i have 42lb injectors and run about 10-11 psi on the same setup.  As far as tuning goes, i have the stock ecu, factory timing and everything, all i did was mess around with the mass airflow a little bit rev it up in the garage a couple times to make sure it wasnt huffing black smoke and left it.  For some reason it ended up working pretty well for over 30k miles.  I dont see any problems running 12lbs or more with a good tune and knocking back the timing.

That sounds good, I am suprised it's not pinging with standard ignition timing though, how much thicker is the head gasket to the one you took off?

Ok looks like the injectors will be the limiting factor here. Does anyone know what cc the standard ones are?

Whats the limit boost wise for these engine with standard internals, assuming the head isn't comming off yet?

[ludiagsm]

That sounds good, I am suprised it's not pinging with standard ignition timing though, how much thicker is the head gasket to the one you took off?

Ok looks like the injectors will be the limiting factor here. Does anyone know what cc the standard ones are?

Whats the limit boost wise for these engine with standard internals, assuming the head isn't comming off yet?

hi on E30 m42 standard injectrors are 215cc , with standard internals , m42 can take 0,7 bar of boost in 10:1 cr without of problems ,but you must tune afr ratio and advance retart sheets with SMT6 pigiback or somthing else megasquirt and more if you do everithing write you must have 270-280 hp and 320-340 NM. on engine

[tim_s]

looking forward to this paul! btw m42 pistons aren't forged iirc. look forward to seeing you soonish with the latest tweaks to mine (if i hang onto it)

[ShepsM3]

hi on E30 m42 standard injectrors are 215cc , with standard internals , m42 can take 0,7 bar of boost in 10:5 cr without of problems ,but you must tune afr ratio and advance retart sheets with SMT6 pigiback or somthing else megasquirt and more if you do everithing write you must have 270-280 hp and 320-340 NM. on engine

That sounds great! I thought the standard injectors were only 170cc - which I thought was a bit low for a standard 318is. Also are they really 10.5:1? Again, I read somewhere they are 10:1... My info could be wrong though?

Hi Tim... I'm looking forward to it too lol. I've been looking for a low mileaged 318is for a while quietly and got this one pretty cheap, but it needs work in the suspension area and some bodywork too. I've also found it pretty dire on fuel too compared to my mothers. Can get 34mpg on a very gentle long run, but driving with some spirit drops it to 26-27mpg. I was getting more than that out of my M3!!  I am not too worried about the fuel economy, but I want issues like this sorted as I think something is slightly amis, certainly before I start forcing air through the intake! lol Want to talk to you about painting my Cam cover and intake manifold too, you did a neat job of yours!
Looking forward to seeing you again.... and lets crack 200bhp this time

EDIT:: Oh BTW, Appletree from the E30Zone I am sure said the standard M42 pistons were forged?? Or have I got everything wrong about this car? LOL.

[an318is]

Also are they really 10.5:1? Again, I read somewhere they are 10:1... My info could be wrong though?

The compression is 10:1, think that was probably just a typo.

EDIT:: Oh BTW, Appletree from the E30Zone I am sure said the standard M42 pistons were forged?? Or have I got everything wrong about this car? LOL.

Im pretty sure the pistons are not forged. Basically the only bit that isnt.

[ShepsM3]

Thanks An318is,

If they are not forged, I guess that gives me an excuse to get in there and enlarge the displacement too

[ludiagsm]

Sorry for cr :eek::eek:,they are two modifications он м42 10,5:1 and 10:1 the diferense are in piston forehead.

[rob_e30]

The motor I built is not a complete basis for comparison as it's custom pistons and a lower CR but I do have stock rods.  We had a problem with the wastegate while on the track last time and were seeing up to 27psi.  There appear to be no long terms effects and we've had the car back on the dyno since then.  It's making the same numbers without coolant leaks, oil consumption, or any temp problems.

The quick answer is that the block and heads will take boost.

[ShepsM3]

The motor I built is not a complete basis for comparison as it's custom pistons and a lower CR but I do have stock rods.  We had a problem with the wastegate while on the track last time and were seeing up to 27psi.  There appear to be no long terms effects and we've had the car back on the dyno since then.  It's making the same numbers without coolant leaks, oil consumption, or any temp problems.

The quick answer is that the block and heads will take boost.

Rob, is your headgasket, headbolts and everything except pistons standard? What CR did you end up with and who's pistons did you use? Any links to it?
27psi is going some!

[rob_e30]

We were not happy with 27.  I designed the setup to run up to about 23 but can hit our HP goals well below that.  We're using ARP head studs and a MLS head gasket.  The pistons are 8.5:1.

Here is a link  http://www.r3vlimited.com/board/showthread.php?t=96456

[ShepsM3]

Thanks Rob, makes for some interesting reading. I think I'd like to keep the high CR but if I need to change the pistons to forged ones I would probably just go down to 9.5:1 to make the car nice and driveable down at low RPM's. The SC I will be using is a Rotrex centrifugal type, so increases boost with RPM. Obviously the ARP Head studs and a nicer head gasket is the way to go. Also while I am there I will replace the big end and main bearing cap bolts/studs? with ARP items too.

Power wise, I want to see around 275BHP at the flywheel. So maybe I may need to loose some CR to run a bit more boost than 10psi, although I don't think I will be far away?

[rob_e30]

I honestly don't remember if we could find main and end cap ARP bolts, but if you can then get them.  I think you'll need to run more than 12psi to make the power you would like.  You're also going to have to think about injectors, fuel pressure, and regulating fuel.  If the engine is solid now, I'd recommending you run it at 8-10psi until you blow a head gasket and then worry about the upgrades on the rebuild.

[2002is]

i found this about the m42

http://www.esatclear.ie/~bpurcell/318isengine.html

it says
forged crank, forged rods, but only lightened pistons.
also says compression is 10.1 nothing about 10.5.1
and injectors are 173cc

but who says this site is correct?