Wheeler Posted January 9, 2006 Share Posted January 9, 2006 OK, so it is a compression ratio question.... I've done quite a bit of reading on compression ratio both in magazines and on this and other forums. Most things I have read say that you should not go much higher than 10:1 (static ratio) if you want a smooth streetable engine that also runs on 91 or so octane. If you look at a lot of new cars being sold (Audi, BMW....) they have compression ratios of up to 11.5:1. So what gives here. I understand that if you run a more exteme cam you can get away with higher compression ratios but then they dont idle so well. What am I missing -C Quote Link to comment Share on other sites More sharing options...
JMortensen Posted January 9, 2006 Share Posted January 9, 2006 Combustion chamber design, fuel injection, and ECU's have come a LOOOOONG way in the last 20 years or so since the end of L series production. Bigger cam will reduce the dynamic compression but will also throw off older FI systems. There's been a lot of talk about this subject in a recent thread. Search MN47 and you should find it very quickly. Quote Link to comment Share on other sites More sharing options...
Pyro Posted January 9, 2006 Share Posted January 9, 2006 Engine design has improved over the past 30 years. Better head design and better electronics to control fuel and ignition curves. Fast burn cylinder heads don't require as much timing to begin with so more cylinder pressure can be used. Plus the new cams are designed to be used with high compression and low octane. New engine cams most likely have very wide lobe seperation to reduce overlap and a late closing intake valve to reduce cylinder pressure. A low amount of valve overlap makes a smooth idle and low emissions. Z cam are designed to work with 9:1 cr and are made to generally increase cylinder pressure (early closing intake valve) So you could could get the results that you want with a 11:1cr Z engine using a cam with wide lobe centers and a very late intake valve closing point and then use a high tech efi system. I'm sure there are many more reasons but these are some of the biggies. Quote Link to comment Share on other sites More sharing options...
1 fast z Posted January 10, 2006 Share Posted January 10, 2006 BTW, I run a 12-1 compression ratio on my 3.1 liter, and my car is driven EVERY day, sees, at least 7 grand EVERY day, and NO detonation. This is on 91 crappy Arizona gas might I add. So you can run that much compression if all varibles are set up correctly. Quote Link to comment Share on other sites More sharing options...
RedBeauty84ZX Posted January 10, 2006 Share Posted January 10, 2006 Engine design has improved over the past 30 years. Better head design and better electronics to control fuel and ignition curves. Fast burn cylinder heads don't require as much timing to begin with so more cylinder pressure can be used. Plus the new cams are designed to be used with high compression and low octane. New engine cams most likely have very wide lobe seperation to reduce overlap and a late closing intake valve to reduce cylinder pressure. A low amount of valve overlap makes a smooth idle and low emissions. Z cam are designed to work with 9:1 cr and are made to generally increase cylinder pressure (early closing intake valve) So you could could get the results that you want with a 11:1cr Z engine using a cam with wide lobe centers and a very late intake valve closing point and then use a high tech efi system. I'm sure there are many more reasons but these are some of the biggies. Pyro, what part of SA? I live in Schertz. Quote Link to comment Share on other sites More sharing options...
Pyro Posted January 10, 2006 Share Posted January 10, 2006 northwest, near I10 and Loop 1604 Quote Link to comment Share on other sites More sharing options...
RedBeauty84ZX Posted January 12, 2006 Share Posted January 12, 2006 northwest, near I10 and Loop 1604 Should of gone to the Z meeting last night. Quote Link to comment Share on other sites More sharing options...
Pyro Posted January 13, 2006 Share Posted January 13, 2006 I'm too busy right now for car clubs because of work, cars, and new baby. Quote Link to comment Share on other sites More sharing options...
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