racerx260 Posted June 13, 2006 Share Posted June 13, 2006 How much compression can you have and run 87 octaine?.At what timing on an na motor. Would you rather have higher compression or more advance to get the most tourqe on 87 octaine?Building a n/a daily driver and want as much low end as I can on regular.WOW me with your wisdom. Quote Link to comment Share on other sites More sharing options...
zeiss150 Posted June 13, 2006 Share Posted June 13, 2006 it depends on what kind of head you are gonna use the later heads (P79,P90) have a better design and are less pron to detination. If you go with the F54 block with flat top pistons and the P79 head you get a stock compression of 8.5:1, and I'm sure you would have no problems running that while running full timing. I run 9.2:1 CR on my N/A setup, but I put in 91 oct and I also have a mild cam. I would think it would be a better plan to have a little lower compression and run the total 35 degrees of advance, there is a lot of power in that last bit of timing. If you wanna bump up the CR a little use a 1mm head gasket that will get you to 8.7:1 ... as far as the max CR you can run on 87 oct ... I don't know... maybe 9? a total guess. Good luck, I hope this helped Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 13, 2006 Share Posted June 13, 2006 Wow us with your searching of this subject that has been discussed so frequently here. You might be careful spelling octane because that will get you better results. Quote Link to comment Share on other sites More sharing options...
Pyro Posted June 13, 2006 Share Posted June 13, 2006 You need to be figuring out dynamic compression ratio vs. octane. There are a lot of free dynamic compression ratio calculators on the web to choose from. 8 to 8.5:1 dynamic compression ratio (DCR) would be a good range to try for with 87 octane. An engine with 11:1 static compression ratio can have 8.5:1 DCR if the cam is big enough (late intake valve closing point). So, pick a cam that you what to run. Then run the calculator to figure out how much static compression you can run. Low speed torque can be made with gears or low a rpm torque engine or a combo of both. A 3.90 gear with a early 5 spd and flat top 2.8L with a P79 head and a 260/260 advertized duration cam should make for a nice runner with 87 octane. When you use the DCR calculator, input the pistion sticks out of the block 0.010", the head gasket is 6cc volume, and no valve reliefs. Quote Link to comment Share on other sites More sharing options...
TheNeedForZ Posted June 13, 2006 Share Posted June 13, 2006 Choose a flexible compression ratio(as in not on the edge), then play with timing in different situations(summer, winter, humidity and altitude change etc) Timing can be changed easily, CR cannot. If CR is pushed to the edge, then you will be forced to use more retard when it knocks. More ignition retard = less torque. Quote Link to comment Share on other sites More sharing options...
racerx260 Posted June 14, 2006 Author Share Posted June 14, 2006 Thanks guys , first use spell check, second advance more important than cr for torque with low octane Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted June 14, 2006 Share Posted June 14, 2006 http://forums.hybridz.org/showthread.php?t=110913&highlight=dynamic+compression Quote Link to comment Share on other sites More sharing options...
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