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| Questions about cr? https://www.ausmini.com/forums/viewtopic.php?f=2&t=68969 |
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| Author: | austinseven [ Sun Feb 20, 2011 6:24 pm ] |
| Post subject: | Questions about cr? |
The engine is a 1114cc with a 12g940 head, and a 649 cam. I will run the car mainly on bp 98 ultimate, but may have to run on 95 sometimes. I have calculated the cr at 9.98 currently with a swept volume of 31cc. I have been reading Vizards book that suggests with a long duration cam that you have to have a high cr. I dont want to go too high and make my engine pink all day, but dont want to sacriface alot of power. 1. What cr should I run? 2. With standard chambers is there any rule that tells you how much skimming the head reduces the cc's? Any advice would be appreciated |
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| Author: | GT mowog [ Sun Feb 20, 2011 7:00 pm ] |
| Post subject: | |
A 649 cam has a pretty long duration for street use. Aprox what RPMs does it come on the cam? |
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| Author: | simon k [ Sun Feb 20, 2011 7:01 pm ] |
| Post subject: | |
A lot of people over here with 1275's would be running > 10:1 without realising it. Most of us use Hypatec pistons, which are meant to give 9.75:1, but it usually works out at about 10.2:1 Wait for the experts to reply, but as long as you keep fresh fuel in it, and the ignition is spot on, I'd suggest anywhere under 10.5 is fine I say keep fresh fuel in it, because (assuming your fuel 'quality' is the same as ours) it can lose a few octane points in a matter of weeks which will get you detonating quick smart I don't know if there is a rule about skimming, but you could rub a piece of graph paper over the chamber and add up the squares, then multiply by how many 0.mm you think may do the job till you get the volume you want |
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