Fre530d Posted November 30, 2006 Report Share Posted November 30, 2006 Hey Guys Got a question. I run a Noss coolhead with 20cc domes at sea level and use 98 octane of fuel. I just bought an adjustable timing plate. How much can I increase timing to be safe? Thx Fred :beer: Quote Link to comment Share on other sites More sharing options...
Bansh-eman Posted November 30, 2006 Report Share Posted November 30, 2006 Hey Guys Got a question. I run a Noss coolhead with 20cc domes at sea level and use 98 octane of fuel. I just bought an adjustable timing plate. How much can I increase timing to be safe? Thx Fred :beer: whats kinda compression do you have? your going to be ok with +4 but before i say you can go higher you need to do a compression test... Quote Link to comment Share on other sites More sharing options...
HotCarl Posted November 30, 2006 Report Share Posted November 30, 2006 whats kinda compression do you have? your going to be ok with +4 but before i say you can go higher you need to do a compression test... I've seen you say the samething about 10 times a day, and i wondering what the cut off pressures are for when you should upgrade your fuel or change your timeing. I know the way i do it is by listing to my motor, but is is the common accepted values? Quote Link to comment Share on other sites More sharing options...
Bansh-eman Posted November 30, 2006 Report Share Posted November 30, 2006 (edited) cutoff is around 160-170 ... but i go lower then that to be safe and shoot for 150... the extra insureance of spending 30 bucks more at the pump to save my motor is well worth it imo then trying to be a cheap skate and run 93 oct until you hit 170 psi do your self , your wallet, and your motor a favor go to sears and get your self a 60 dollar compression tester... only thing i dont like about those craftsman didnt think too well while making it , the threads dont have a nut to screw the tester in with... you have to use pliers and it chews up the head... but for 60 bucks its dead on... Edited November 30, 2006 by Bansh-eman Quote Link to comment Share on other sites More sharing options...
dajogejr Posted December 1, 2006 Report Share Posted December 1, 2006 There is no 100%...only averages and best guesses. Once you're in the 150ish range with timing, usually you need a 50/50 mix of pump/race gas. Over 165ish and timing, race all the way. You only need octane to the point your motor doesn't detonate...and if you have a good ear and are willing to check plugs often, you can always mix it 75/25, 50/50, 25/75...etc. But, you get to a point when enough and you just throw full race in there, run some real timing and get some good compression... There is always alky... Quote Link to comment Share on other sites More sharing options...
Washburn Posted December 1, 2006 Report Share Posted December 1, 2006 I plan on being in the high 150s when I install my timing plate and Im going to run 1 gallon of VP110 to 3 gallons of 93. That should be plenty. I dont think its to good of an idea to have above 160-165 in a stock ported engine. Thats major wear on your crank first and foremost and your running that race fuel without running as strong as you can run. Im breaking my own rules running a 25% blend in mine. Gotta save up for shocks though :biggrin: Quote Link to comment Share on other sites More sharing options...
BlazinOne Posted December 1, 2006 Report Share Posted December 1, 2006 (edited) There is no 100%...only averages and best guesses. Once you're in the 150ish range with timing, usually you need a 50/50 mix of pump/race gas. Over 165ish and timing, race all the way. You only need octane to the point your motor doesn't detonate...and if you have a good ear and are willing to check plugs often, you can always mix it 75/25, 50/50, 25/75...etc. But, you get to a point when enough and you just throw full race in there, run some real timing and get some good compression... There is always alky... You need to compare apples to apples and baselines like this are not accurate. I've been running 180-185 for years and i can get away with 50/50.Ive even ran tanks of 75% 94 and 25% 108 and showed no signs of detonation with +4 timing Your dome shape is the deciding factor.I have found with an aftermarket head you can get away with alot more than a stock head.Porting/port timing/ignition timing/compression/jetting all contribute to octane requirements. You can always play the safe side and just do the race gas thing,but if I did that,I would have traded my stroker crank kit for peace of mind.Thats what the extra race fuel would have amounted to in one season. 150 with timing will timing will do just fine with 94.If you need a bump,add some good octane boost. Edited December 1, 2006 by BlazinOne Quote Link to comment Share on other sites More sharing options...
Bansh-eman Posted December 1, 2006 Report Share Posted December 1, 2006 You need to compare apples to apples and baselines like this are not accurate. I've been running 180-185 for years and i can get away with 50/50.Ive even ran tanks of 75% 94 and 25% 108 and showed no signs of detonation with +4 timing Your dome shape is the deciding factor.I have found with an aftermarket head you can get away with alot more than a stock head.Porting/port timing/ignition timing/compression/jetting all contribute to octane requirements. You can always play the safe side and just do the race gas thing,but if I did that,I would have traded my stroker crank kit for peace of mind.Thats what the extra race fuel would have amounted to in one season. 150 with timing will timing will do just fine with 94.If you need a bump,add some good octane boost. umm i think that is what da is saying... that there is no 100% its no were set in stone being all the differant factors... its just best guessing and running what others have ran to get him close until he gets it spot on with how his motor runs Quote Link to comment Share on other sites More sharing options...
csrmel Posted December 1, 2006 Report Share Posted December 1, 2006 just as a reference point im running +4.5 timing and 22cc domes at sea level. ive got a fresh motor and 149psi of compression. ive ran 98 octane before and not had any detonation, although on a 2 stroke i dont know if i could hear it. but my plugs had no aluminum specs and my motor still runs... although just to be safe i awalys try to run 93 and fresh 93 at that (i dont let fuel sit around longer than 1 month). Quote Link to comment Share on other sites More sharing options...
Fre530d Posted December 1, 2006 Author Report Share Posted December 1, 2006 I've got about 160PSi measured with a motometer tool. Quote Link to comment Share on other sites More sharing options...
dajogejr Posted December 1, 2006 Report Share Posted December 1, 2006 The octane debate could go on and on...and everyone is different. However.... I think it's best to start out safe. While you don't need race gas on a bone stock machine, once you start upping the compression and/or timing, it's always best to start off with more than what you need, and slowly and carefully work your way down. Quote Link to comment Share on other sites More sharing options...
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