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Thread: m20 Engine options for PRC regulations.

  1. #1
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    m20 Engine options for PRC regulations.

    hey guys,

    im after some food for thought in regards to m20 engines, and performance upgrades.

    to start off with what the goal is, is im taking my 82 323i, and building it for forrest rallying, and tarmac. its being built to Production rally car regulations...
    there are two options that i can see:

    1. I try to extract as much power as i can out of the 2.3 block,

    or two, swap in an engine. below is an extract from the cams regs, its a bit of a read, but basically if i was to replace the 2.3, it would have to be with something thats produced before 86, and not more than a 17% increase of capacity.. ruling out the 2.5.








    3.1.7 Substitute Engines
    (a) In exceptional circumstances and at its absolute discretion ARCom may approve a substitute engine. An
    applicant must demonstrate that a substitute engine would provide a cheaper and more durable option,
    without a significant performance increase, when compared to the original engine. Additional limitations may
    be placed on such substitute engines.
    (b) Early PRC Substitute Engines: Substitute engines may be permitted subject to application to and approval by
    ARCom.
    The guidelines for replacement engines, approval of which is at the sole discretion of ARCom, are that the
    engine shall:
    (i) be produced prior to 1986 unless otherwise specifically approved by ARCom;
    (ii) be produced by the same manufacturer as the original;
    (iii) have the same number of camshafts in the same location as the original;
    (iv) have the same number of cylinders and general configuration;
    (v) be made of the same material as the original;
    (vi) be able to be fitted in the same general location as the original. No body modification is permitted to allow
    the fitment of the replacement cylinder block.
    Each substitution shall be approved by ARCom and published in the PRC regulations (or via bulletin) prior to
    use in competition.
    Cars with substitute engines are not permitted the full range of modifications otherwise acceptable under
    Article 3.4 of these regulations. The following modification limitations apply:
    • Capacity: A maximum of a 17% increase in capacity over the original/recognised engine is permitted, or
    alternatively, a substitute engine which keeps the car in the same PRC capacity class as it would be with the
    standard specification original/recognised engine may be permitted. The standard stroke must be retained.
    • Cylinder Head: Modifications may be made to the cylinder head and related components only in the following
    areas:
    - inlet and exhaust ports may be modified by the removal of metal only;
    - inlet and exhaust valve sizes and valve seats are free. The minimum modifications required to fit these
    items are permitted;
    - valve guides may be replaced by others of alternate materials.
    A car which incurs a capacity alteration due to a substitute engine, together with permitted modifications,
    must compete in the capacity class pertaining to the new capacity.





    Cheers,

    Chucklez.

  2. #2
    Join Date
    Sep 2005
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    75 2002 77 323irace 91M5
    I would just use the 2.3 bore it 17% over or as big as you can with some 12.1 compression pistons and a 885 head or a ported 731 head with the 885 valves in it.Whats interesting is the 2.3 has a 76.8 stroke and the 2.5 is 75mm stroke. All done up with a independent runner intake I think it would
    make a nice rally motor.


  3. #3
    Join Date
    Oct 2011
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    Victoria, australia
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    BMW E21 323i
    Cheers mate,

    Well if i was to put a diff engine in its limited to a 17% capacity increase where as if i modify my current one basically i can do what i want...

    The 885 head, isnt that the 325i one that uses the different pistons?

    Is that your engine it looks sweet i like it

    Cheers,

    Chucklez.

  4. #4
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    1982 323i, 1997 318iS
    The 885 is from the E30 325i. As rare an engine as you can try to find in Australia. Probably not as rare as the S14. That head is also better suited to the pistons in the M20B25, BMW changed there thinking on combustion chambers at that time and slapping the 885 on there would significantly lower the compression ratio. If you could find one.

    In all the research I did I found that the bigger valves don't flow all that much more and the 731 head is a very good compromise, it is the way that I went. Having reread your original question, though, you would probably want all the extra power you can get. I believe the 885 valves are 2mm larger than the 731 and 200 heads. I believe you could probably go slightly bigger than that, but that's actually a question for the machinist.

  5. #5
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    So no 325i cars in Aus. thats a bummer there all over here I think I guy was selling one on here a week or so ago cheep. The only reason I said 885 head
    is the first thing I think of for a 2.3 rally engine is get some over bore 12.1 custom pistons.Pic of some 12.1 CP pistons I had made for the 885

    The motor in the pic is my old 323i with sport motor. The 731 head is in some ways the best casting to start with like a blank for shaping. The 885
    the factory already did all the work in the casting.

  6. #6
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    Oh, you see the occasional 325i, but the people that own them know that they have something special and treat them as such. I've absolutely never seen one in the wreckers, including E34 525i's, so it's really not cost effective.

  7. #7
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    Thanks for all the info guys, ive never built a performance piston engine before so its a first for me.

    Another thing ive been toying with to get power is turboing. But im not sure how difficult that will be with the whole rhd thing.

    The other idea i had was go back to the 4cyl m10 as theres heaps more off the shelf bits for them...

    Cheers,

    Charlie.

  8. #8
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    The 17% refers to increase in displacement? 2316cc * 1.17 = 2709cc. A 2.7 block would fall within that rule.

  9. #9
    Join Date
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    1979 323i BMW. 2003 GTI 20 V Turbo
    In my new engine I used the 885 head and Plus 1 ferrara valves and I got them to work fine. So plus 1 valves can work on the 885 head.
    "..Horsepower is a measure of work done over time, or the rate at which work is done."




    http://www.cardomain.com/ride/579694/1


  10. #10
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    This is whats listed at the start of the regs, not sure if i posted it originally.

    (link to regs) : http://docs.cams.com.au/Manual/Rally...PRC_2013-3.pdf

    RALLY / ROAD
    Group 3C – Production Rally Cars (PRC)
    Production Rally Cars are eligible subject to the vehicle meeting the description below and the General
    Requirements for Rally Cars in Schedules A and R (see “General Requirements for Cars and Drivers” in the CAMS
    Manual of Motor Sport).
    Note:
    These regulations apply only to events where PRC are eligible. For events listed on the FIA International
    Sporting Calendar, FIA group cars must comply with Appendix J of the FIA Yearbook.
    1.

    GENERAL
    1.1

    Modifications:

    (
    a
    )

    Any car, which has a minimum seating capacity of two persons, of which more than 500 have been

    produced worldwide in the same specification; or





    I would be interested to contact alpina and get the exact numbers of the cars they made. this could be an avenue to go down. i could of sworn ive seen someone else running their car as an alpina replica.



    @hdx, i was under the impression you couldnt really bore the 2.3 motors out, thats why no one bothers with them?


    @m20 powered,

    I must of stuffed up the maths when i originally looked at that (dont know how ?) I am going to try and find out how to contact arcom. and apply for the engine swap. and if i get it, whether or not its still acceptable to turbo that engine.

    Thanks,

    Chucklez.

  11. #11
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    Hi, what break booster is it?

  12. #12
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    1982 323i 2003 325it
    Quote Originally Posted by Louis287 View Post
    Hi, what break booster is it?
    Hi, this thread was last posted on 5 years ago, so i don't know if you'll get a response. just so you know.
    Past, Present, and Future

    1974 BMW 2002tii (RIP)
    1995 BMW 325is w/ FULL S50 swap, track prepped (SOLD)
    1988 BMW 325ix Zinno/Black (RIP)
    1988 BMW 325ix Alpine/Black (Sold)
    1988 BMW 535is Alpine/Pacific Blue (Going Away...)
    1982 BMW 323i (Current Project/Paper Weight)
    2003 BMW 325i Sport Touring (Daily Driver)

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