apeik Posted August 21, 2013 Report Share Posted August 21, 2013 what's a somewhat optimal squish for a 421 cub on pump gas? it was .62 with the custom cut domes i had and a .012 base gasket(152 cranking psi), and detonated pretty reliably so i didnt run it, but im going to change it to a .020 base gasket and different domes. Should i be shooting for .45-.50 like most race gas cubs? or is it different for pump gas. Thanks in advance, couldn't seem to find a direct answer to this, and i have 2 months to figure this motor out. Quote Link to comment Share on other sites More sharing options...
J-Madd Posted August 21, 2013 Report Share Posted August 21, 2013 If it detonated at 0.062", the squish wasn't the problem. It was probably the pump gas. Quote Link to comment Share on other sites More sharing options...
apeik Posted August 21, 2013 Author Report Share Posted August 21, 2013 i was running costco 91, mixed 30/70 vp 110 and it still backed a plug out once after a hard long wot run, even while rich. Both sources of gas were fresh. All i can guess is the custom cut domes with their weird angles(4), had something largely to do with it. It detonated terrible on anything under 100 octane, and after it backed a plug out at 100+ octane and only 152 psi kicking compression, i parked it since it was the last trip of the season. ill throw up a pic of the domes just for refrence. They were supposed to be specifically for pump gas only. Quote Link to comment Share on other sites More sharing options...
dirtydownunder Posted August 21, 2013 Report Share Posted August 21, 2013 im running pump at .045" squish. Quote Link to comment Share on other sites More sharing options...
robert0762 Posted August 21, 2013 Report Share Posted August 21, 2013 Who cut the domes? Quote Link to comment Share on other sites More sharing options...
J-Madd Posted August 22, 2013 Report Share Posted August 22, 2013 Yea, those domes don't look right for 573 series pistons. All of mine look more like this, minus the bashing from porcelain. Quote Link to comment Share on other sites More sharing options...
apeik Posted August 22, 2013 Author Report Share Posted August 22, 2013 I don't want to name names, just wanna get it running right. I have a set of 24cc domes that look identical to those jmadd. Once I get my cylinders back from milennium Mayne ill see what kind of squish/comp I have with that set, and if need be have another set cut that are more normal. Quote Link to comment Share on other sites More sharing options...
BANSHEE HP Posted August 22, 2013 Report Share Posted August 22, 2013 that dome is fucked. name the names. Quote Link to comment Share on other sites More sharing options...
Redline Racing Posted August 22, 2013 Report Share Posted August 22, 2013 I think diesel would detonate with that dome. I'd go .050-.055 on squish. That is safe and still makes good power. Tighter will make little more power but can cause issues if everything isn't perfect. Quote Link to comment Share on other sites More sharing options...
Pastrykiller Posted August 22, 2013 Report Share Posted August 22, 2013 I'm gonna go out on a limb and say that I have seen domes from wildcard, hjr, noss, pro design, shearer, fast....:never looked like that. So...is it Passion? Quote Link to comment Share on other sites More sharing options...
apeik Posted August 22, 2013 Author Report Share Posted August 22, 2013 Thanks for all the help so far guy's. Yea i suppose pastry is right, sniper domes. I'm not to worried about that last ounce of power, hence the pump gas, so ill stick with .50-.55 area then. After 3+ trips last season chasing crazy detonation and the retarded running temps and trying to jet it, on a motor with more than enough octane, and guaranteed sealed up tight with no airleaks, im kinda aiming to be able to ride this season. Because let's face it, getting out to the dunes costs a decent chunk of change, working on my bike is fun but i can do that at home. Quote Link to comment Share on other sites More sharing options...
rubberneck Posted August 22, 2013 Report Share Posted August 22, 2013 Thanks for all the help so far guy's. Yea i suppose pastry is right, sniper domes. I'm not to worried about that last ounce of power, hence the pump gas, so ill stick with .50-.55 area then. After 3+ trips last season chasing crazy detonation and the retarded running temps and trying to jet it, on a motor with more than enough octane, and guaranteed sealed up tight with no airleaks, im kinda aiming to be able to ride this season. Because let's face it, getting out to the dunes costs a decent chunk of change, working on my bike is fun but i can do that at home. let it begin Quote Link to comment Share on other sites More sharing options...
mopar1rules Posted August 22, 2013 Report Share Posted August 22, 2013 That "custom" dome is garbage. That's the problem. Get normal hemispherical domes that will yield you a 12.2:1-12:1 comp ratio and you will be fine with 93 octane and .050-.055 squish. You will also need a squish angle that's 2deg more positive than your 573 series piston crown angle. Quote Link to comment Share on other sites More sharing options...
mopar1rules Posted August 22, 2013 Report Share Posted August 22, 2013 And make sure the new domes don't have an abnormally wide squish band. Don't need anything over 55-60% on pump gas imo. Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted August 22, 2013 Report Share Posted August 22, 2013 I'm gonna go out on a limb and say that I have seen domes from wildcard, hjr, noss, pro design, shearer, fast....:never looked like that. So...is it Passion? Its not like the passion domes I have. BTW, noss domes are Jims design. Although he says sniper..... That would be Gary's handy work. Not Jim's. Quote Link to comment Share on other sites More sharing options...
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