Predator 212 hemi head 9k plus rpm timing? And how much compression?

#1
Hey guys this is my first post on here, I’d like to go ahead and thank you all for any and all replies and help, now, i have a modified hemi predator 212 that I run on kart dirt circle tracks of different sizes, my engine specs are stock bore/stroke, stock crank, arc billet flywheel 32 degrees timing, arc plus .020 rod, dyno cam running around 380 total lift and around 260 duration on exhaust and around 255 on intake, stainless valves stock hemi sizes with automotive retainers and 36 pounds springs, head has been ported and polished may but not too much for the stock valve sizes and has been milled down to first fin and between 0 to .005 piston deck height with a .020 head gasket, 1.2 nr roller rockers, cm push rods, 22mm round slide chikuni on methanol(I have read that the 22 have the same size Venturi as a 26mm), stock flat top piston that I cut valve reliefs into, I have had this revved to almost 9200 on the stand with no clearance issues but sounds like that’s about all she has and I was trying to get to 9500 just to see if it would just for the heck of it, so what could be causing the so called “wall” around 9200, from my research I should be able to turn 9500 on the stand and also could someone give me a ballpark figure of my CR? I have tried to cc the head with a ml syringe but I’m getting around 13-14cc and I don’t think that’s right with a hemi head even though I have Milled it down around .120-.130, it’s basically on the first fin now. What do you guys think I should do to get a coupe more hundred rpms out of her? I’m not worried about it blowing, I’m doing this build for fun.
 

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SAS289

Well-Known Member
#2
Hey guys this is my first post on here, I’d like to go ahead and thank you all for any and all replies and help, now, i have a modified hemi predator 212 that I run on kart dirt circle tracks of different sizes, my engine specs are stock bore/stroke, stock crank, arc billet flywheel 32 degrees timing, arc plus .020 rod, dyno cam running around 380 total lift and around 260 duration on exhaust and around 255 on intake, stainless valves stock hemi sizes with automotive retainers and 36 pounds springs, head has been ported and polished may but not too much for the stock valve sizes and has been milled down to first fin and between 0 to .005 piston deck height with a .020 head gasket, 1.2 nr roller rockers, cm push rods, 22mm round slide chikuni on methanol(I have read that the 22 have the same size Venturi as a 26mm), stock flat top piston that I cut valve reliefs into, I have had this revved to almost 9200 on the stand with no clearance issues but sounds like that’s about all she has and I was trying to get to 9500 just to see if it would just for the heck of it, so what could be causing the so called “wall” around 9200, from my research I should be able to turn 9500 on the stand and also could someone give me a ballpark figure of my CR? I have tried to cc the head with a ml syringe but I’m getting around 13-14cc and I don’t think that’s right with a hemi head even though I have Milled it down around .120-.130, it’s basically on the first fin now. What do you guys think I should do to get a coupe more hundred rpms out of her? I’m not worried about it blowing, I’m doing this build for fun.
9500 RPM. Wow.

You may want to open a thread in the Honda/Clone/Predator category in the Engines section. It would get more responses there. Just copy and paste what you have here.
 
#4
are you free reving the engine on the stand? Which dyno cam? You have minimum piston to head clearance (.025) and we need to know what you measured for piston to valve clearance on overlap, especially the exhaust. The 22mm chikuni have a effective bore of 22mm however the mounting flamge opening is 26mm. They flow 87.3 CFM @ 28" on my bench and for reference a 24mm OKO flatslide flows 90 CFM on my bench.
 
#7
are you free reving the engine on the stand? Which dyno cam? You have minimum piston to head clearance (.025) and we need to know what you measured for piston to valve clearance on overlap, especially the exhaust. The 22mm chikuni have a effective bore of 22mm however the mounting flamge opening is 26mm. They flow 87.3 CFM @ 28" on my bench and for reference a 24mm OKO flatslide flows 90 CFM on my bench.
yes it’s on the stand as I mentioned, I didn’t clay or anything to get my measurements I just went by my piston deck height, head gasket thickness and went ahead and cut around .065 deep valve reliefs in piston, still had to cut a little deeper after taching it up to 8800 but have cut deep enough now that it doesn’t hit at 9200 and should be good up to 9500. I also had to make a relief for the spark plug. I’m running a dyno 310 cam on 1.2 rockers. I’m going to get a 26 or 28 flat side later on so that should help along with welding the head and putting bigger valves in but for now I’m just trying to see if I can get it to tach 9500 with this setup on stand.
 
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