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Post by 427malibu on Mar 25, 2009 16:07:24 GMT -5
Selecting a camshaft for my motor and a few things came into mind. Since you are adding apprx 30% more fuel you have to have more spent gasses right? Do you need more duration/lift on the exhaust to compensate compared to gasoline? Maybe a even widen LSA and open the exhaust valve a few degrees early? Any idea on what dynamic compression to shoot for>?
Looking for some thoughts.
James
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Post by tomscharger70 on Mar 26, 2009 16:50:07 GMT -5
Im not in any way a great engine builder, not even close... But here are my thoughts for what its worth...
About the cam. It depends on so many variables, like what kind of engine do you want? Street, Street/Race or Race??? Is it a SB or BB??? What intake.. heads.. etc.. etc..
Any way, about the compression. I know for a fact that there are a couple of engines out there running close to 16.0:1 compression on E85, but that may be pushing it and it also depends on what kind of combo your building...
It al comes down to what kind of engine are you planing on? If your just going to use it for mostly cruising and once or twice at the track, you can just buy something what ever fits your combo and you may like. Doing things more complicated then nessessary will only make you bang your head against the garage wall in the end..
I run a tad over 12.5:1 comp. in my 426 Hemi. I droped the compression using a .40 thick head gasket. Im planing on raising the comp back up to around 13.7:1. The reason to lower the comp was that may be I could run it on 99oct. unleaded, but then I decided to convert my carb to E85. Im gonna change out the head gaskets come next winter...
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Post by 427malibu on Mar 26, 2009 22:17:57 GMT -5
I understand and appreciate your input. I am really intersted in what amount of Dynamic compression can be tolerated. Valve timing/duration is what ultimately determines your true or Dynamic compression. A 12.5:1 motor with a big cam with lots of duaration with a late closing intake valve may have a dynamic ratio of 8-8.5:1 to tolerate 93 octane premium fuel without detination. If you decide to run race fuel or in this case E85 you can raise the dynamic ratio by changing valve timing/duration and produce more HP/TQ. (http://www.forcefedperformance.com/TechDynamicCompression.asp) I am not sure what E85 is tolerant of and this can be a place to pick up a few or many ponies. My other thought is if more fuel in/more waste out. Removing exhaust gases out of the cylinder is crucial in making power in normally aspirated motor. If E85 is producing more exhaust gas then cylinder head/camshaft/headers/exhaust selection can be critical when building a motor for maximum performance. I am building a E85 bbc nitrous street/strip motor. 95%strip .
James
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