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M40b16 Turbo Project

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    M40b16 Turbo Project

    Good evening to everyone. Lately I've become an owner of a BMW E30 M10 chassis with M40b16 engine. I got this car by trading a Punto turbo. Obviously is much more of a car, but it lacks power. Going from ~225hp to merely 100hp, is a bit of a chaos.

    So I'm thinking of turboing the M40. I've read many articles, but can't get to a conclusion. I want to avoid swapping a 6-cylinder engine (or 1.8is) for many reasons (taxes, fuel consumption, heavier front-end etc) .

    What about reliability of a turbo m40? It is in excellent condition (no oil consumption at all, or noisy valves). I want to keep it full stock (head gasket, studs, all stock for the beginning) and about 0.5-0.6 bar of boost with a t25-t28 turbo (injectors, cooler, reprogramming are all in the budget).

    Has anyone done it before? Aiming at about 170hp, but will be happy with 150hp (I think :p )

    Some people can't keep a standard m40 "reliable" whilst others ring its neck with a big turbo and seemingly "don't have any problems".

    Reliability is 100% about the owner. Can you keep in front of all the potential issues to keep the car on the road with 100 odd more horsepower than it ever came with and components that never came standard?

    Do you know how to fabricate stuff for a turbo conversion? can you tune an aftermarket ecu? can you diagnose issues while tuning to make it work? have you got any experience in proper automotive wiring?

    I personally wouldnot bother turboing it. Put an M20 in it. You;ll get close to your 150hp for alot less than its going to cost you to turbo an m40 PROPERLY.


      M42 swap, then turbo? The M40 seems to be a bit of an unknown quantity turbo wise but it has many detractors, the M42 has a big detractor (me) but it's definitely better in all ways than an M40.
      '91 318is, M20B25, T3/T04E 60 trim (18psi), megasquirt, coilovers, Z3 rack, cold AC
      [b u i l d]
      [Car of the month: April 2018]



        The world of tuning is not something new for me. Me with help from some friends - mechanics, built my previous car from stock (130hp turbo 1.4) to almost 230hp.
        Tuning and everything else done from us. Also I have let's say respect to what I build so I try to keep it in the best condition I can.
        I am sure that most off the engines are capable of 0.5 bars o boost. My limit for stock engine will be 0.8 bars as it is something that Ive read many times. Just want an opinion.
        I won't bother changing engine at all, as I won't be sure for its condition. That's why I insist on turboing this one (and for keeping the budget low) . In Greece is something common, but usually the use a different head gasket. About engine block, many say that it's reliability is close to m10' s


          A little update. I finnaly decided to install a supercharger (eaton m45) with intercooler.

          I would like to know, what is the maximum pressure that, stock internals (and gasket) can handle. With some calculations, it'll give about 0.6 - 0.7bar. Is it safe?

          Of course biggers injectors, reprogramming and fuel pump will be used.


            whats the compression ratio?

            also maximum boost depends on where in the rev range. 10psi at 3000rpm is not the same as 10psi at 6000rpm.

            on a turbo car you can use a waste controller to keep boost manageable at low/mid ranges, and boost it up at the high end.

            not sure if there is an equivalent with a roots blower. you will have to choose the pulley size accordingly.
            ---E30 320i Hennarot 1984 Sedan---


              It will run on stock compression (8.8:1 i think). With a sc puley of 8.8cm and crank puley at arount 18cm (i will measure it for sure tomorrow), according to many different calculations founfd on the net, it will not get more than 0.7 bar (more possible to be around 0.6). My only fear is having a head gasket blown, so it will be upgraded as soon as possible. That's why i woold like to learn what is the max boost for a stock engine.
              Also the only way of controlling boost is installing an external wastegate on the intercooler piping, or any other valve that opens on boost.


                After a bad attempt (I forgot to unplug the oil tube from the throttle body), I ended up with a bad rod bearing. So, as the motor now is apart, I am thinking for forged pistons, better gasket and a bigger camshaft.

                I am thinking of going about 14 psi and max out the blower. Is it necessary to buy a set of forged rods? As far as I know, the are the same as M42's.

                Will they be OK at 0.8 to 1 bar? Consider that this kind of pressure will be on, at full throttle, at any engine speed ( even it is 2000rpm or 7000rpm).

                Because blowers have always the same speed to speed ratio. All this, according to some mathematic formulas, found on the net and proven surprisingly accurate (I confirmed them, before my engine broke).


                  Hello mate (although I'm Greek too,i write in English so everyone can read this) I had a Eaton M65 on my previous engine (m40b18) without intercooler and stock pulley. I had 0,4bar on 5,5k rpms (I adjusted the afm's spring so i can't rev more than 5,5 because was lean,due to stock injectors) Also had an adjustable fuel pressure regulator and a wideband O2. With 4,4 welded dif i had some good time by burning rubber. Nvm,now I swapped to M50B20 and want to use again the blower with bigger pulley, intercooler and bigger injectors. My only concern is,should i use a BOV to idle bypass,or a bypass valve from a mini Cooper S? With a "Forged" bov and mild spring,i had compressor surge,was TOO loud while deceleration,and it was overheating,u could fry some eggs on it. Do you think that idle bypass valve would work better than a BOV?