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Thread: Short or Long stroke

  1. #21

    Sleeper

    Just the way I would want it if it was mine and I wanted it 2,5L.

    IMHO the 901 case is a beautiful piece and besides being the strongest, best, affordable 911 case they look really good with all the beautiful cast aluminum pieces that came on them originally - and not that cheap looking die cast magnesium stuff that looks straight out of Wolfsburg as found on the later engines.

    A 901/02 built to these specs looks exactly like a little 2,0L S motor except for the twin plug - tough to tell it is a hot rod without crawling underneath to get a peek at the part numbers on the 70T heads.

    The exhaust note, however, would be a little throatier.
    Early 911S Registry
    Looking for engine 960 168
    Looking for gear box 103 165

  2. #22
    Senior Member
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    Flunder.
    For myself i have already built a 2.3 ST with EXACTLY the same specification you wrote ( and something else , of course) starting from alu case.

    Raj.
    i saw at least 2 italian original racing SWB with 2.5SS with alu case (in 1970 they were 2.3,in 1972 2.5). they bought only cilinder and pistons and reworked case and heads. nothing else. More power and torque in a very cheap way.


    NOW:

    I see that Targa Florio's real racing cars have those combinatons:

    Alu 2.0 (906)SS 1968-1969
    Alu 2.2LS 1970
    Alu 2.3SS 1970
    Alu 2.4LS (very rare, 1971)
    Alu 2.5SS 1972
    Mag 2.2LS 1970
    Mag 2.3SS 1970
    Mag 2.5LS 1971

    (with 901 or 911 gearbox, with or without coolers)

    and when i spoke with some italian racers they told me " we mounted all the Porsche news trying to maintain all the old pieces we can (eg engine case) because Porsche pieces were extremely expensive !!! "

    i understand that, apart OFFICIAL cars , everybody made lot's of experiments trying to pay less money as possible!!

    That's why my confusion about the best solution.

    I understand some things:

    1) Alu case is better looking than mag case without doubt. Mine seems new.

    2) Mag case is absoultely ok for a SWB, like Raj perfectly said.

    3) Mag case (in 7R version in my opinion) thanks to his weight is better for car's rear control (and it's important for a swb...)

    4) 2.5LS may have problems with flywheel due to vibrations... (are we sure about this?)


    I can imagine there is no ONE best solution.... everybody has his experience...

    of course, thanks to all....
    Registry Member #1414
    NOSGRUPPE

  3. #23
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    Raj

    about engine, as soon as it'll be ready i'll post the datas. We expect at least 10-15 hp more than Porsche in 1970...

    about photos: i have tons of Targa car's photos. But no engine photo. I know it by talking with the drivers and sicilian friends. I'll try to find something interesting...

    BTW, yesterday night i spoke with a foumous italian racing driver of the 70ies.
    He told me: ALL the early racing engine were in MAGNESIUM , no question! SO forget ALUminium!

    confusion is big under the sky!!
    Registry Member #1414
    NOSGRUPPE

  4. #24
    Senior Member super9064's Avatar
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    At a cost of $20,000 and up for a comprehensive rebuild, I would want use the strongest case available, Porsche had the luxury of a rebuild after every race. Weight and winning were the priority not longevity. Just because Porsche used Magnesium for their race engines does not mean it was the best for street/ track cars. Just my opinion, for what its worth... very little
    Rob Abbott

  5. #25
    FACT: Aluminum cases are less prone to shuffling as well as cracking up the back.
    -Marco
    SReg. #778 OGrp: #8 RGrp: #---
    TLG Auto: Website
    Searching for engine #907495 and gearbox 902/1 #229687

  6. #26
    Intended use is the key. If you were building a 2.5L that would only be driven on the street and not blasted out of corners on sticky tires repeatedly, then a pinned mag case (even a lowly 3R) would probably be fine. But if you were building that same motor for three seasons of racing - especially if it's a long stroke that would experience increased torque at low rpms - well you would not want a spun rod bearing to ruin your expensive rod, crank, case, oil pump, piston, head, cylinder- not to mention the cost of an unforseen rebuild. It has happened enough times that when I researched this for my long stroke race motor, every experienced racer/mechanic I spoke with advised me to use an early aluminum case and shuffle pin the chain covers. The increased weight and cost of using the alum. case was not enough to offset the disadvantages when used in this application.
    Randy Wells
    Automotive Writer/Photographer/Filmmaker
    www.randywells.com/blog
    www.hotrodfilms.com

    Early S Registry #187

  7. #27
    Quote Originally Posted by varunan123 View Post
    As a side note some of the rally engines back in the day were single plug.

    Raj


    Have noted this in my reading as well. Rally spec engines appear to have been much less stressed. I assumed this had to do with the relative traction limitations and tire sizes typically run in rallys but not sure.
    Erik

    Early S # 1107

    All my german equipment is either busted or sold...sigh....in the market for a decent non-sunroof tub!!!!!!! Help me get back to autocrossing!!!

  8. #28
    Quote Originally Posted by varunan123 View Post
    Marco

    Why does this occur,is it because of the magnesium itself,is it the relative expansion of the three metals,is it the design.If it is the magnesium what about the magnesium causes this.Thanks marco

    Raj
    I honestly don't know for sure, Raj.

    Common sense tells me it may have something to do with thermal expansion and metalurgy, but my curiosity never took me that far.

    I do know - from personal experience - that a mag case will shuffle before an aluminum one, but I also know of a 7R-based 2.8RSR-spec motor that went A LOT of miles before the bottom end started shuffling (street motor that sees 8K from time to time). It got pins on the rebuild and will never shuffle again.

    A pinned 7R (or any other mag case, for that matter) should be just as durable as a non-pinned early aluminum case over a short period of time ... but since you are rebuilding a race motor fairly often it becomes a moot point.
    -Marco
    SReg. #778 OGrp: #8 RGrp: #---
    TLG Auto: Website
    Searching for engine #907495 and gearbox 902/1 #229687

  9. #29
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    Here in Germany, a well known engine builder recently told me that the mag cases are simply getting soft with age. He allegedly has a dozen 2.7RS cases that are no longer usable in his warehouse. He is buying all 2.7 cases he can find to keep his customers' RSs on the road.

    Same story with the mag wheels of the 964RS: the surface gets bubbly over time as gas seems to evaporate from the metal. We do not use the stock wheels in anger anymore.

    I once saw a Ferrari 312T F1 car from the early 70s. The car was being restored. The mag engine case looked as if a mouse had eaten away parts of it: the magnesium metal had simply "melted" away.

    But sorry, I do not have a scientific explanation for this effect!
    Keep up the speed!

    Anatol

    '68 911S coupe
    '92 964 RS NGT
    '09 987S Boxster

  10. #30
    Quote Originally Posted by varunan123 View Post
    here are some sights regarding magnesium,and alloy metal properties-interesting read atleast for crazy me.I can't believe there is an international magnesium organization.

    Raj


    http://www.matweb.com

    http://www.intlmag.org
    Would you mind providing a link to the actual article/fact pages that you are referring to? I am having trouble navigating the sites. All I can seem to find are graphs but no writen analysis explaining the material properties of Magnesium and why it is considered so much weaker/porous/etc than Aluminum.

    I find this metallurgy interesting as well as you do.
    1971 911S, 2.7RS spec MFI engine, suspension mods, lightened
    Early 911S Registry Member #425

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