bansheeryder21 Posted August 1, 2006 Report Share Posted August 1, 2006 I am running 20cc domes with stock timing and my compression is around 160. I mix race gas at 20%. I am getting my bike ported right now which is going to lower my compression and I am advancing my timing +6. My question is, to keep my compression the same and run no more than 50/50 race gas, what size domes should I run after the porting? I am thinking 19's or 18's. All you guys that have ported bikes, help me out!!! Quote Link to comment Share on other sites More sharing options...
dajogejr Posted August 1, 2006 Report Share Posted August 1, 2006 No way we can tell you that. Everyone ports different, you may ask the engine builder what they think. To be honest, I'd rather run straight race gas, one less thing to mix. Don't kid yourself, porting will only lower your PSI a few points, nothing earth shattering. Also...have you had your crank welded. I dont' trust the stocker to hold up to much more than 150 or so PSI for very long. 150PSI to 165 is USUALLY the gray valley you can get away with running mix of pump and race. Throw smaller domes in and advance the timing, why chance it? Run race gas! Quote Link to comment Share on other sites More sharing options...
bansheeryder21 Posted August 1, 2006 Author Report Share Posted August 1, 2006 No way we can tell you that. Everyone ports different, you may ask the engine builder what they think. To be honest, I'd rather run straight race gas, one less thing to mix. Don't kid yourself, porting will only lower your PSI a few points, nothing earth shattering. Also...have you had your crank welded. I dont' trust the stocker to hold up to much more than 150 or so PSI for very long. 150PSI to 165 is USUALLY the gray valley you can get away with running mix of pump and race. Throw smaller domes in and advance the timing, why chance it? Run race gas! I want to stay away from running straight race gas! I don't know if you've noticed, but gas prices are a little high. Especially in California! That's why I don't want to have to run just race gas! Yes I am getting my crank welded and trued after I get my engine back! Kevin Herr is porting my juggs right now! So then to awenser my question, maybe I should stay at 20's or go to 19's! Question, does advancing the timing increase compression? I ask that because I know when you advance the timing, you need higher octane fuel! Quote Link to comment Share on other sites More sharing options...
Animalman294 Posted August 1, 2006 Report Share Posted August 1, 2006 Contact your builder, but I would run nothin' less than AV100LL just to be safe at that PSI............... :beer: Quote Link to comment Share on other sites More sharing options...
crazybluerider Posted August 1, 2006 Report Share Posted August 1, 2006 If you buy race gas in quantity you can usually get it for about a 1.50 more than premium. gas prices have gone up but race gas has stayed pretty much the same. Its almost like race gas is getting cheaper Quote Link to comment Share on other sites More sharing options...
bansheeryder21 Posted August 1, 2006 Author Report Share Posted August 1, 2006 If you buy race gas in quantity you can usually get it for about a 1.50 more than premium. gas prices have gone up but race gas has stayed pretty much the same. Its almost like race gas is getting cheaper Race gas has gone up as well! 6 months ago it was $5/g at the pump. now it's $6/g!!! Back to my original question, what domes do you guys recommend? I know there is a lot of experience out there and a lot of knowledge! Help me out! As for race gas, no one's gonna convince me to run straight race gas!!! $$$$$$$ Quote Link to comment Share on other sites More sharing options...
dajogejr Posted August 1, 2006 Report Share Posted August 1, 2006 As for race gas, no one's gonna convince me to run straight race gas!!! $$$$$$$ Well...you made this easy then. No one is going to safely tell you what domes you can and can't run. So...buy a few pairs, test yourself, sell what you don't use. I just don't get it when you need to mix race gas and pump gas. Why...to save 15 bucks or so for a 5 gallon jug for a day's riding? If you're worried about saving that measly 15 bucks per 5 gallons, you're in the wrong sport...or have the wrong machine. :: :: After doing some math...I'm a little off. These are MI, Detroit area prices. 3.20 for premium, from 92 to 93 octane X 5 gallons = 16 4.99 for Race 110 Leaded, X 5 gallons is 24.95 Split the difference for 50/50 mix. = 20.50 So...you're telling me...that all this hub bub is worth a measly 4 and a half buck per 5 gallons. Say you go through 5 gallons every week. That is, if you ride every week. You'd save yourself roughly 230 bucks in a single year...to take that chance... Shit, 4.50 barely buys a set of spark plugs..... The only arguement you'd have is if you couldn't find race gas, or lived in an area to desolate or remote to get it. You are already mixing it 20%...which, may raise the octane 1 or 2 points... So, you have access to race gas. Again, this is the wrong sport, or make that bike, to penny pinch over this little stuff. Quote Link to comment Share on other sites More sharing options...
bansheeryder21 Posted August 1, 2006 Author Report Share Posted August 1, 2006 Well...you made this easy then. No one is going to safely tell you what domes you can and can't run. So...buy a few pairs, test yourself, sell what you don't use. I just don't get it when you need to mix race gas and pump gas. Why...to save 15 bucks or so for a 5 gallon jug for a day's riding? If you're worried about saving that measly 15 bucks per 5 gallons, you're in the wrong sport...or have the wrong machine. :: :: After doing some math...I'm a little off. These are MI, Detroit area prices. 3.20 for premium, from 92 to 93 octane X 5 gallons = 16 4.99 for Race 110 Leaded, X 5 gallons is 24.95 Split the difference for 50/50 mix. = 20.50 So...you're telling me...that all this hub bub is worth a measly 4 and a half buck per 5 gallons. Say you go through 5 gallons every week. That is, if you ride every week. You'd save yourself roughly 230 bucks in a single year...to take that chance... Shit, 4.50 barely buys a set of spark plugs..... Can you help me out with my timing question? When you advance timing, why do you use a higher octane level? Does the compression go up? Quote Link to comment Share on other sites More sharing options...
dajogejr Posted August 1, 2006 Report Share Posted August 1, 2006 Advancing the timing make the motor run better (more HP) but it also makes it run hotter. When this happens, it can pre-ignite. Or, detonate the fuel before the spark happens...when it's supposed to. Higher octane fuels have a higher detonation point... Compression is similar...more performance...higher temps, need more octane to combat pre-ignition. Compression has more to do with the need for higer octane than a small timing advance like 4 or 6 degrees. Keep in mind, the 4 or 6 degrees of timing you may advance it is above and beyond what the stock CDI already advances it...so, don't think it's only 4 or 6...it's more like 27 to 22 or so (the higher the RPM, the less it advances the timing.) So...that being said. Do you see why it's almost impossible to tell you what domes to run, with what timing and what porting, unless you try it yourself. No two builders port the exact same, no two engines run the exact same...this is not an exact science... people spend years figuring all this out...and even they can't tell you with 100% certainty how your specific machine will turn out until it's all said and done.... And to answer your second question, NO. Advancing the timing alone does not make your compression go up. Quote Link to comment Share on other sites More sharing options...
bansheeryder21 Posted August 1, 2006 Author Report Share Posted August 1, 2006 (edited) Advancing the timing make the motor run better (more HP) but it also makes it run hotter. When this happens, it can pre-ignite. Or, detonate the fuel before the spark happens...when it's supposed to. Higher octane fuels have a higher detonation point... Compression is similar...more performance...higher temps, need more octane to combat pre-ignition. Compression has more to do with the need for higer octane than a small timing advance like 4 or 6 degrees. Keep in mind, the 4 or 6 degrees of timing you may advance it is above and beyond what the stock CDI already advances it...so, don't think it's only 4 or 6...it's more like 27 to 22 or so (the higher the RPM, the less it advances the timing.) So...that being said. Do you see why it's almost impossible to tell you what domes to run, with what timing and what porting, unless you try it yourself. No two builders port the exact same, no two engines run the exact same...this is not an exact science... people spend years figuring all this out...and even they can't tell you with 100% certainty how your specific machine will turn out until it's all said and done.... And to answer your second question, NO. Advancing the timing alone does not make your compression go up. Cool thanks! Makes sence! I know all machines are different and each builder ports differently! I was just looking for an estimate of what domes people would recommend! Like I said, I'm going to try 19 or 18's! About the timing! I am getting an agressive dune port done! What timing should I run! 4 or 6? And can I adjust my RS timing plate with the flywheel on? Is there enought room to loosen the three screws? Edited August 1, 2006 by bansheeryder21 Quote Link to comment Share on other sites More sharing options...
dajogejr Posted August 1, 2006 Report Share Posted August 1, 2006 As said, I wouldn't push the issue with a stock crank... You're already at the point where I'd be nervous. Again...can't tell you what timing to run. I'd say put it at 8, but...you'll be right back to needing more than a 50/50 mix of race gas. I don't know about a screwdriver, but I do know I could adjust mine with an open end 10mm wrench with the flywheel still on. I'm going to be 100% honest with you. You're learning, that's good. We all need to. However, if you're asking basic questions about timing, compression and octane, I'm not sure you have the ear to listen to a motor and recognize pinging, preignition, etc. That few bucks you're trying to save on race gas goes right out the window when you lunch a top end because you ran it too long without the proper octane. I'm not trying to be a dick...but, I'd rather be safe than sorry... Although this is an extreme case, this very well can happen if you ignore your motor long enough, or don't know how to listen for problems.... http://www.bansheehq.com/forums/index.php?...topic=64680&hl= Quote Link to comment Share on other sites More sharing options...
bansheeryder21 Posted August 1, 2006 Author Report Share Posted August 1, 2006 As said, I wouldn't push the issue with a stock crank... You're already at the point where I'd be nervous. Again...can't tell you what timing to run. I'd say put it at 8, but...you'll be right back to needing more than a 50/50 mix of race gas. I don't know about a screwdriver, but I do know I could adjust mine with an open end 10mm wrench with the flywheel still on. I'm going to be 100% honest with you. You're learning, that's good. We all need to. However, if you're asking basic questions about timing, compression and octane, I'm not sure you have the ear to listen to a motor and recognize pinging, preignition, etc. That few bucks you're trying to save on race gas goes right out the window when you lunch a top end because you ran it too long without the proper octane. I'm not trying to be a dick...but, I'd rather be safe than sorry... Although this is an extreme case, this very well can happen if you ignore your motor long enough, or don't know how to listen for problems.... http://www.bansheehq.com/forums/index.php?...topic=64680&hl= If you look back at my second post, I said yes I am getting my crank welded and trued as soon as I get my engine back! And the reason I am asking these questions is so I don't end up with a blown motor! That's the whole point! Timing and porting is new to me! I'm trying to learn as much as I can now so when I get my motor back together, I don't do something stupid and blow the f-ing think up! Thanks for your constructive critizism!!! Quote Link to comment Share on other sites More sharing options...
BillyRay Posted August 1, 2006 Report Share Posted August 1, 2006 If you are going to run 18 or 19 domes I would start with straight 110 and jet your machine for correct altitude and air temp. Then after you get your carbs dialed in with correct needle clip position and air screw setting then you can lower the amount of octane by blending some fuel. But take baby steps when you do this and learn the sound of your motor. Once you start modding a two stroke it takes lots of steps to get to a well dialed in machine so it is smart to start on the safe side. Talk to your builder and listen and do what he says and start from there. If you are going to play with the big dogs you must be willing to pay the price. Quote Link to comment Share on other sites More sharing options...
dajogejr Posted August 1, 2006 Report Share Posted August 1, 2006 Thanks...Billy Ray. that's pretty much what I was getting at...with a lot more words. Quote Link to comment Share on other sites More sharing options...
bansheeryder21 Posted August 1, 2006 Author Report Share Posted August 1, 2006 If you are going to run 18 or 19 domes I would start with straight 110 and jet your machine for correct altitude and air temp. Then after you get your carbs dialed in with correct needle clip position and air screw setting then you can lower the amount of octane by blending some fuel. But take baby steps when you do this and learn the sound of your motor. Once you start modding a two stroke it takes lots of steps to get to a well dialed in machine so it is smart to start on the safe side. Talk to your builder and listen and do what he says and start from there. If you are going to play with the big dogs you must be willing to pay the price. Thanks! I talked to my builder and he just gave me a ball park estimate of where I should be at and what size domes to run! I going to check my compression after its built back up and see how much I lost and go from there! Like I said, porting and timing is new to me! I found out that "playing with the big dogs" is expensive real quick! Thanks for the help guys! Quote Link to comment Share on other sites More sharing options...
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