gotta_goatsfast Posted March 7, 2011 Report Share Posted March 7, 2011 ...a higher octane fuel burns cooler and slower. I promise you. Quote Link to comment Share on other sites More sharing options...
volcrano Posted March 8, 2011 Report Share Posted March 8, 2011 it still cracks me up when people use compression gage readings to determine octane required for the engine. elaborate please.i thought over 160 psi u needed race fuel to prevent detonation.what other method to determine what octane to run for ? compression is there.im not being a turd.im curious to know if im misinformed. Quote Link to comment Share on other sites More sharing options...
beebs Posted March 8, 2011 Report Share Posted March 8, 2011 The higher the compression the more octane you need, and I think 160 is normally the cut off for pump fuel. Your builder would give you the info on what fuel you need to run, or will build your motor to what fuel you plan on using. As for the other comment I think it was talking about the squish for determining the octane requirement (tighter squish=higher compression=more octane). Quote Link to comment Share on other sites More sharing options...
volcrano Posted March 8, 2011 Report Share Posted March 8, 2011 The higher the compression the more octane you need, and I think 160 is normally the cut off for pump fuel. Your builder would give you the info on what fuel you need to run, or will build your motor to what fuel you plan on using. As for the other comment I think it was talking about the squish for determining the octane requirement (tighter squish=higher compression=more octane). ok.so what new information are you stating that wasnt already known.over 160 psi,race gas,got it.higher compression=need for more octane,got it.higher compression=tighter squish,got it.so whats the other way to determine what octane to run besides compression? Quote Link to comment Share on other sites More sharing options...
vulvafan537240 Posted March 8, 2011 Report Share Posted March 8, 2011 compression ratio Quote Link to comment Share on other sites More sharing options...
Burt Reynolds Posted March 8, 2011 Report Share Posted March 8, 2011 If you run 110 in a motor thats built for 93 not only will you not see a power improvement,you will probably see a power loss. Quote Link to comment Share on other sites More sharing options...
beebs Posted March 8, 2011 Report Share Posted March 8, 2011 ok.so what new information are you stating that wasnt already known.over 160 psi,race gas,got it.higher compression=need for more octane,got it.higher compression=tighter squish,got it.so whats the other way to determine what octane to run besides compression? Sorry, what other method you ask? Instead of a compression gauge like was said, you can use how tight the squish is or cauculate your head volume. Both those mothods I think would be more accurate than the compression gauge. Its all based on compression and just diff ways to determin it. Compression and timing are to only 2 things you base octane requirements on. Someone correct me if i'm wrong. Tks. Quote Link to comment Share on other sites More sharing options...
volcrano Posted March 8, 2011 Report Share Posted March 8, 2011 Sorry, what other method you ask? Instead of a compression gauge like was said, you can use how tight the squish is or cauculate your head volume. Both those mothods I think would be more accurate than the compression gauge. Its all based on compression and just diff ways to determin it. Compression and timing are to only 2 things you base octane requirements on. Someone correct me if i'm wrong. Tks. ok,i understand.so at what psi do u need straight 110 or 50/50?is it somewhere like 180 and up to run straight race fuel?bear with me,im learning Quote Link to comment Share on other sites More sharing options...
gotta_goatsfast Posted March 8, 2011 Report Share Posted March 8, 2011 Sorry, what other method you ask? Instead of a compression gauge like was said, you can use how tight the squish is or cauculate your head volume. Both those mothods I think would be more accurate than the compression gauge. Its all based on compression and just diff ways to determin it. Compression and timing are to only 2 things you base octane requirements on. Someone correct me if i'm wrong. Tks. No and no. The squish band-although an important measurement-is not the area of the dome you cut to produce more (or less) compression. The combustion chamber (void area around the sparkplug) will be cut to a specific volume. The quish band is simply the clearance between the piston crown and dome. Too little clearance will most likely result in contact. Too much clearance will defeat the purpose of a squish band and cause detonation as the squish band is designed to rush air/fuel away from the perimeter of the cylinder where fuel is more likely to ignite and "clash" with the flame front ignited by the spark plug. That clash between two flame fronts is very violent... detonation. Why is cranking compression (and dome size) only a small consideration to octane requirements? Well, its easier to link you something than to type a book myself. lol so read ME Quote Link to comment Share on other sites More sharing options...
gotta_goatsfast Posted March 8, 2011 Report Share Posted March 8, 2011 ok,i understand.so at what psi do u need straight 110 or 50/50?is it somewhere like 180 and up to run straight race fuel?bear with me,im learning I encourage you to read the link at the end of my previous post, also. There are other explanations that include math formulas and what not, but this one is very easy to read/understand. Quote Link to comment Share on other sites More sharing options...
mopar1rules Posted March 8, 2011 Report Share Posted March 8, 2011 you need to know the compression ratios of the engine.....UCCR (uncorrected compression ratio) and CCR (corrected compression ratio). UCCR is full stroke compression ratio (like a 4 stroke) and the CCR is the ratio of volume, between the roof of the exh port and above, compared to what's above the piston, when its at top dead center. usuaally 15:1 is when you need 110 octane. guys, also remember that the squish band is still very important. a squish band that yields higher MSV (squish velocity), will require higher octane too. throw some advanced timing at it too, and you need better fuel too. you can have 2 engines with the same bore, stroke, and head cc volume, but 1 will have a higher exh port, and that one will show less psi on a compression gage (lower cranking psi), but running comprssions will be higher than cranking. see, don't get caught up on comp gage for dictating octane. this is what trinity does and they suck. Quote Link to comment Share on other sites More sharing options...
volcrano Posted March 9, 2011 Report Share Posted March 9, 2011 I encourage you to read the link at the end of my previous post, also. There are other explanations that include math formulas and what not, but this one is very easy to read/understand. holy shit.very interesting.now,so is the proper way to see what fuel to run dependant on exhaust port height with xx? size domes.now since it says the higher the port,u will have lower compression with same domes as a motor with lower exhaust port,due to the larger charge,scavenging and crown temps.so how do u know what octane to run compared to exhaust port height?i know with my port on my 4 mill,the exhaust looked huge for a aggressive trail/dune port,i have standard base gasket and domes cut to 20cc.ive been running 93,and compression is around 140 psi.i havent had detonation issues,but wonder now the formula to figure octane to port height since compression ive learned isnt the way to accurately know.am i in the ballpark of figuring this out lol??mopar,i saw u replied as i was writing this.so uccr is that hooking up the gauge and kicking like how everybody checks?how do u find the volume number between the roof of the exhaust port and above (i believe u mean roof of the ex. port to the top of the dome?),and comparing that to whats above the piston at tdc (i believe this is the squish??). Quote Link to comment Share on other sites More sharing options...
beebs Posted March 9, 2011 Report Share Posted March 9, 2011 Thanks for the clarification Mopar1 and Gotta-gofast. Seems like alot of information needs to work together to decide correct octane requirements. Quote Link to comment Share on other sites More sharing options...
Derrickc14 Posted November 28, 2013 Report Share Posted November 28, 2013 (edited) If I ran ethanol, how many sizes up on the jetting should I start with if anyone has experience with it. I know in my gsx awd eclipse I had to dump a shit load of fuel with fic 1450 injectors and duel pumps to get fuel air ratio right. And would it even be worth running it since it would run out of a gas almost twice as fast?! I'm assuming I'd have to buy bigger carbs to do it. Edited November 28, 2013 by Derrickc14 Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted November 28, 2013 Report Share Posted November 28, 2013 This ain't your DSM.... Alky requires a few simple yet necaccary parts/mods. First you need to gut the gas cap diaphragm, install a fuel pump, modify or buy the carbs set up for alky. The carbs should have the needle and seat set up for the fuel pump. There is some drilling needed on the dump tubes as well the jets. Install power jets and bigger bowls also. There are a few well known places to get already set up carbs if you have money to foot it. Quote Link to comment Share on other sites More sharing options...
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