Increasing compression ratio's
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  1. #1
    Member Simon888's Avatar
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    Default Increasing compression ratio's

    I've just read an article saying that you can use (smaller = less thickness) Copper gaskets, and improve compression?
    Note: Apparently not a good idea generally as it will corrode eventually.
    Any of you Mechanics got any thoughts on this?

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    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by Simon888 View Post
    I've just read an article saying that you can use (smaller = less thickness) Copper gaskets, and improve compression?
    It will increase compression ratio but that may not be an improved compression ratio of your car pings like crazy.

    Jo

  3. #3
    Member Simon888's Avatar
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    Quote Originally Posted by jo proffi View Post
    It will increase compression ratio but that may not be an improved compression ratio of your car pings like crazy.

    Jo
    Ah "pinging", my favourite sound. thanks Jo, noted.

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    1000+ Posts schlitzaugen's Avatar
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    Quote Originally Posted by jo proffi View Post
    It will increase compression ratio but that may not be an improved compression ratio if your car pings like crazy.

    Jo

    I think that's what you mean, Jo?

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    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by schlitzaugen View Post
    I think that's what you mean, Jo?

    I'm retarded. I was looking and looking at it about 20 times, thinking yes that what I said, before I notices the "o".
    Thank you for fixing it up.
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    Cometic and Permaseal do multi-layered steel (MLS) shim type gaskets. They end up about half the thickness of a usual gasket - I've use them on sprint car builds and they're the only things that don't blow with the compression we run. Whether or not you'll get one for your application is another story, although I know they do make 1-offs if you were mega-keen (it costs a few pennies).

  7. #7
    bob
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    G'day,

    Triumph/Vanguard at one time used a shim steel head gasket to provide a higher c/r model, a single thickness of shim that was impressed around all the holes and went on with a fair bit of gasket goo.

    They worked well provided everything was nice and clean and flat - 4cly iron block & head.

    Jo, most "moderns" would have anti-knock sensors wouldn't they ? our fugs have them and they're pretty old.

    cheers,
    Bob

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    The proper way to go would be to take measurements to make sure there was enough valve to piston clearance, put it on a dyno to make sure it didnt knock, and preferably retune the ECU if it did. I'm not sure you can rely on a factory knock sensor to protect you.

    I wouldn't mind increasing the CR of my 505 from the std 8.5:1 to around 9:1 but there is plenty to do already on the old girl without going down that road.

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    1000+ Posts robmac's Avatar
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    Quote Originally Posted by Nisspug View Post
    The proper way to go would be to take measurements to make sure there was enough valve to piston clearance, put it on a dyno to make sure it didnt knock, and preferably retune the ECU if it did. I'm not sure you can rely on a factory knock sensor to protect you.

    I wouldn't mind increasing the CR of my 505 from the std 8.5:1 to around 9:1 but there is plenty to do already on the old girl without going down that road.
    Another way is to weld up the combustion chambers and reduce the volume. Sometimes this is easier, especially if the head is to be reconditioned or to be hard seated.

    Domed or welded up pistons will also increase CR, but you need to check out possible grid lock with valves.

    Both of the above methods allow a standard head gasket to be used provided astronomic compression ratios are not required.

  10. #10
    Real cars have hydraulics DoubleChevron's Avatar
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    Even the factories messed with this stuff. The old ID19's have flat top pistons, the DS19's had domed pistons.... Not quite a dome, but a swirl. I imagine the idea was to get the air/fuel mixture swirling to get a more even burn at the same time as increasing the compression ratio.

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  11. #11
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    Long stroke D's could be fitted with domed pistons, and allied to the eight port head could be made to go rather well.

    However, the crap that is now sold for fuel in Australia does not readily take to the compression ratios that any decent Euro car has from standard.

    Why make the matter worse by increasing the comp ratio?

    Regards,

    Fento

  12. #12
    1000+ Posts Frans's Avatar
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    Quote Originally Posted by fento View Post
    Long stroke D's could be fitted with domed pistons, and allied to the eight port head could be made to go rather well.

    However, the crap that is now sold for fuel in Australia does not readily take to the compression ratios that any decent Euro car has from standard.

    Why make the matter worse by increasing the comp ratio?

    Regards,

    Fento
    Hi All,

    I was wondering if the fuel in Aus is a lot worse than in NZ.
    We have BP 98 octane here and it is only scarse when you're about 300km away from Auckland.The
    A110 Targa car runs purely on that. It has a CR of 11.75:1 and yes, I have limited the advance a bit. It will not exceed 30 - 31 degrees. This engine is modified extensively and still produces 190 FWHP with its 1800cc reliably.

    Regards
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  13. #13
    1000+ Posts PeterT's Avatar
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    The XU5/XU9 engines lend themselves particularly well to copper gaskets as the liner protrusion bites into the soft copper creating a good seal. If liner protrusion is poor then expect leaks. The XU10 engine, being an iron block with no liners, needs to be o-ringed to seal effectively.

    In regards to corrosion, 3yrs is about the maximum life between rebuilds before the aluminum eats away. So it's not really suitable for road cars.

    It's great for track cars however, where an increase in CR is desirable. For example, if you had an XU9J4Z with only 9.7:1 and wanted to do some budget track work, a 0.5mm gasket would get you to 10.4:1 and still have plenty of clearance at TDC. More of this is covered on my website.

    Optimax 98 is definitely the worst of the high octane pump fuels in Aus. and Caltex 98 the best in my experience. I run 11.8:1 and 24 deg. in my 16V 205 for approx. 220hp , but it probably has a much better chamber shape than an A110.

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    1000+ Posts PugMonkey's Avatar
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    Funny you mention that Peter. I have been experimenting with 98 octanes. Different brands over a period of three weeks (three fills per tank)

    Shell was first with very little change from the standard stuff. In fact I was thinking that this is a waste of time. Then I tried Caltex 98 and I could not believe the very noticeable difference. Rev smoother and did not seem to growl during normal acceleration like the shell did. Now i'm on BP 98 and can' wait to get back to the Caltex.

    Remembering this is a standard 1.9 twin cam engine with 180,000 k's
    ....now watch a Peugeot turn into a corner!

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    Quote Originally Posted by fento View Post
    Long stroke D's could be fitted with domed pistons, and allied to the eight port head could be made to go rather well.

    However, the crap that is now sold for fuel in Australia does not readily take to the compression ratios that any decent Euro car has from standard.

    Why make the matter worse by increasing the comp ratio?

    Regards,

    Fento
    You can't get 98 octane where you live?
    Graham

  16. #16
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    Yes, Graham, I can, and with a few brand variations.

    However, I carry an 11mm flat ring spanner in the glovebox to alter the timing when travelling. Lack of performance means advance the timing, preignition means retard the timing. The adjustment takes only one to two minutes, but is a pain in the arse. I appreciate the time when you were provided with a manual means of adjusting the ingition timing, as in tractions, etc.

    I have yet to find any brands that that offer the same performance characteristics, pump to pump, with other brands since the greenie vote forced government to legislate against leaded fuels.

    I maintain that the quality of the newer / greener fuels are far inferior to the older super / standard leaded originals, with a loss of consistency, added increase of carcinogens and added costs.

    Sadly,

    Fento

  17. #17
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    If you are worried about copper gaskets, for around $140 (AUS) you can get a stainless steel gasket in 3 different thicknesses from Wossner in Europe. Worth a look. I have some hi comp pistons going in my engine and will be using a standard thickness gasket to maintain valve clearance. Having measured the standard set, I agree with Peter, looks like plenty of clearance on original pistons for a 0.5mm gasket.

    Cheers.

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