850 supercharged

    Zitat von Genius

    stevep840, what is the performance of your car after all the mods?



    The 0-60 is around 5.2 secs, not timed the 0-100 but definatly between 11 & 13 secs, top speed is down due to my installation of the 3.91 lsd from the e34 m5 i would not be at all surprised if 135/140mph is my top speed :(

    Those who risk nothing,achieve nothing,become nothing.

    A quick update on the cars performance


    I recently got hold of a G tech pro performance meter & so far have recordered the following


    0 to 60 5.36secs 0 to 100 12.1 secs V impressed was i :D


    If any one would like to borrow the gadget (with a deposit ,just in case) let me know :wink:

    Those who risk nothing,achieve nothing,become nothing.

    Zitat von stevep840

    i would not be at all surprised if 135/140mph is my top speed :(


    That is still not a bad number in the real world...unless you take your car to a track. Useable power is more imporatnat than theoretical top speed, IMO.

    I'd love to hear what its like. My original 850i is impressive enought. I can't imagine what putting a supercharger under the hood would be like!

    Always look at the bright side of life!

    Zitat

    I recently got hold of a G tech pro performance meter


    I've looked this thing up on the web and it appears that it measures RPM by connecting to the cigarette lighter. Does this really work? :shock: If so, this is a cool device. It measures BHP, Torque, 0-60 and 0-100 (miles/h) time and a few more variables.....


    Anyone else with experience regarding G tech?


    Peter

    The Vortech supercharger is an internally gear driven blower so it will normally give a whine, especially at low rpm. The centrifugal supercharger however is fluid driven and so apart from any induction whistle, will be silent in operation.
    The 850 can be supercharged with either a single or twin superchargers and the M70 engine is a very good basis for a forced induction motor with its inherent low compression ratio of 8.8:1.
    This should allow an induction pressure of around 5-6 psi without any form of charge cooling, although ANY cooling is better than none and anything beyond this pressure will require it to reduce the onset of detonation.
    The CSi with its higher compression ratio is very similar but the onset of detonation will be at a lower boost pressure.
    The 840, with its 4 valve heads and improved design is more sympathetic to forced induction and can withstand more boost before the onset of the "death rattle".
    There are other ways to offset detonation such as water injection and further lowering compression but in the context of this discussion, I have assumed neither cars discussed have these systems.
    The power output of the 850 seems very low for this boost level at just 381bhp, unless this is rear wheel horsepower rather than crank power.
    An M70 with 0.9 boost will be running a volumetric efficiency of around 170-180%, so if running an appropriate rich stochiometric fuel ratio of about 12.7:1, and without detonation, it will produce about 630bhp at the crank.
    The power draw of the Vortech would be around 60bhp I would expect.
    However you look at it, 381bhp is very shy of this so I would suspect the engine is not fuelling correctly, or the timing is excessively retarding on boost to prevent detonation. A 5.6 litre M70 on 14psi boost makes 695bhp!
    That is turbocharged, so without any supercharger power take off.
    What size injectors are you running Michel? Do you know the Lbs/hr of them? Are you running additional injectors to add the extra fuelling or using a rising rate fuel pressure regulator? All will work to a certain degree.
    Stevep840... are you running 6 psi boost or 0.6 bar boost. 0.6 is a LOT of boost without any intercooling/chargecooling and I am not surprised the car is quick! I calculate around 450bhp for your car, less the power draw from the blower and reduced charge density due to increased charge temperature, so 400bhp is correct for this car. It must be a joy to drive a car with the power of a CSi, more torque and less weight.
    The "ignition timing reduction" referred to by Michel, is the retardation of the ignition timing as boost increases to prevent detonation, this will have been re-programmed into your ECU when it was re-mapped Steve. I would be interested to know how Michel is achieving this, as his could also be done through the ECU's, but assume from his question that he is not, possibly a piggy-back timing controller?
    Interesting thread........keep it coming.


    8Tech.

    Zitat von peter1980

    I've looked this thing up on the web and it appears that it measures RPM by connecting to the cigarette lighter. Does this really work? :shock: If so, this is a cool device. It measures BHP, Torque, 0-60 and 0-100 (miles/h) time and a few more variables.....


    Anyone else with experience regarding G tech?


    Peter


    The Makers don't claim it to be 100% but very near as to make no difference :wink: I've tried on another car E30 325i & the results were on par with what is expected so it's got my vote :D

    Those who risk nothing,achieve nothing,become nothing.

    supercharger


    Hi 8Tech,


    Boost on my car is about 0.8 to 0.9 bar. The injectors are original and I am using a rising rate fuel regulator. The air/fuel ratio has been checked at all RPM ok. I installed a MSD boost timing master on each side reducing the timing as boost increases. I hope this information will help you.


    Michael

    very interesting thread.


    A question i have is the reliability. As i came from the jap modified car scene, it was always a precarious route to have a (turbo) transplant as the car itself was not properly "set up" to deal with the power increases that the doner car was built with (such as flywheel, clutch etc if i remember correctly).


    Everyone who went down this road had experienced varying problems - i know the 8 is a different car but surely same principles apply?? :?


    I was running my 2-litre tubby (mr2) at 0.6 bar which is standard boost dynod @250bhp (flywheel) - but i know the standard turbo, without modification can take upto 1.2bar through a boost controller.

    Frix


    (Another) 1997 Velvet Blue 840Ci Sport...with a Greek attitude to driving!!

    Hi Michel,


    If you are using stock injectors, there is no way they will flow enough for your requirements. Your stock injectors whether they are Bosch or Lucas are only 14.7 lbs/hr and with a rising rate fuel pressure regulator, you would massively exceed the pressure delivery capability of your fuel system before you attained sufficient flow and you would exceed the pressure capability of the injectors. Your stock base fuel pressure is 3 Bar.
    To get the fuel delivery from your 14.7 lb injectors would require a fuel pressure of...............wait for it.............205-210 psi!!!
    Most injectors will fail and jam above 100 psi and your pumps will only run to about 120 psi also.
    24lb/hr injectors will allow approx 450 crank horsepower but you would need in excess of 30lb/hr injectors for the fuel requirements of 600 bhp at 3 Bar.
    All the above is with an 80% injector duty cycle and a brake specific fuel consumption of 0.55 for a supercharged engine.
    I do believe we have found your problem.
    I strongly recommend you recheck your fuelling on the rolling road.
    If you need accurate calculations on any of these points, please feel free to ask.
    Hope this helps,


    8Tech.


    Yes, you are partly correct.


    The M70 engine is a very strong unit and without any modification is capable of handling 500 bhp very easily and reliably. With the Jap cars you refer to, you are making big horsepower from small capacity engines so the stress is much greater. As a very wild approximation, and just for comparison, an MR2 with 1.2 bar boost would make what? 350bhp? or about 175 bhp/litre. So in the same state of tune/stress, the 5.0 M70 would need to be making 875 bhp!
    True, a 6 speed 850 will require an uprated clutch and possibly flywheel for anything over 400 bhp, even the CSi, but the auto is generally good for 450 bhp and the remainder of the transmission is certainly robust enough.


    8Tech.

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