SHEEfan Posted February 28, 2011 Report Posted February 28, 2011 I currently have big bore CPIs on my new 4mill super cub (472cc) because they were on my bike when I got it.. Would it be a big hp gain to go to a small bore shearer or something else small bore? The bike is set up with lowered port timings for more mid range power because I dune it a lot. (Dynoed at 89hp with 53ft lbs of torque on gas with 34mm carbs) saw the results in the dyne section and there was an 11 hp gain on a 421 from big bore CPI to sb shearer.?? That's huge? Quote
WINDYCITYJOHN400 Posted February 28, 2011 Report Posted February 28, 2011 My 472 Cheetah is fully drag ported and made 81HP with the CPI Big Bore In-Frames. Switched to Shearer Small Bore In-Frames and it jumped to 95HP. Also the low end power matched the CPI's low end. So I'd say get the SB Shearers. Quote
SHEEfan Posted March 1, 2011 Author Report Posted March 1, 2011 Yeah that's a big gain in hp!.. anyone else have these results with a cub? Quote
mopar1rules Posted March 2, 2011 Report Posted March 2, 2011 how are the cpi big bore pipes, holding that much hp back? i thought those were suppose to be good pipes? would the cpi small bore inframes suite you better? Quote
J-Madd Posted March 2, 2011 Report Posted March 2, 2011 With the lower exhaust duration, you will be better with the Shearers. CPIs are great pipes,just depends on the porting. I have a 10 mil Cub that picked up hp at all rpms with BB CPIS vs RDZs. The exhaust port duration is 200*+. I have another 10 Mil that likes Shearers due to much lower exhaust duration (THough I admit I haven't dynoed it with anything other than SB and BB Shearers). You may also look into getting some Sniper Pipes. Quote
camatv Posted March 2, 2011 Report Posted March 2, 2011 are you SURE they are actual BIG BORE cpi's? the bic bore cpi and small bore cpi look VERY VERY similar as far as i can tell the only differ is the stinger tube diameter. if i could post pics i just happen to have a set of both inthe garage and can show the diff. the BB shear adn SB shear are actually 2 differnt designed pipes and are easy to tell apart. the bb shear is a grunt pipe and wont hold as much heat. the SB sheare is a RPM/ overrev pipe but can hold some more heat.. if you can find a set try them out and see what you think.. i really like the BB shears on the larger motors. and the cpi ACTUAL big bore pipes on even 350's Quote
SHEEfan Posted March 2, 2011 Author Report Posted March 2, 2011 (edited) They are deffinately big bore CPIs.. I had Cameron at redline set this motor up and he Told me I could gain a few hp by switching to a sb pipe.. But after hearing some people talk and looking at some dyno results and seeing huge 10 hp gains from the switch to sb pipes I was curious if that was typical? The cub is not ported just cleaned up the flaws.. And it has lowered port timings to retain some mid-range power.. Even with these changes I'm thinking the sb shearers would be the pipe for me.. Or the snipers but I'm not sure how they would do with the lowered port timings? Edited March 2, 2011 by SHEEfan Quote
J-Madd Posted March 2, 2011 Report Posted March 2, 2011 I don't think the 10 hp gains are typical. Also, it was most likely a gain in peak or high rpm hp; which you're not looking for. You could just as easily gain some peak hp by raising the ports, which you also probably don't want to do. Was the bottom decked? Are you running without a base gasket? Quote
J-Madd Posted March 2, 2011 Report Posted March 2, 2011 are you SURE they are actual BIG BORE cpi's? the bic bore cpi and small bore cpi look VERY VERY similar as far as i can tell the only differ is the stinger tube diameter. if i could post pics i just happen to have a set of both inthe garage and can show the diff. the BB shear adn SB shear are actually 2 differnt designed pipes and are easy to tell apart. the bb shear is a grunt pipe and wont hold as much heat. the SB sheare is a RPM/ overrev pipe but can hold some more heat.. if you can find a set try them out and see what you think.. i really like the BB shears on the larger motors. and the cpi ACTUAL big bore pipes on even 350's The CPIs I was referring to are the non stamped version. I'd almost call them hand coned - the have many more seams than the stamped pipes. Quote
SHEEfan Posted March 2, 2011 Author Report Posted March 2, 2011 (edited) I don't think the 10 hp gains are typical. Also, it was most likely a gain in peak or high rpm hp; which you're not looking for. You could just as easily gain some peak hp by raising the ports, which you also probably don't want to do. Was the bottom decked? Are you running without a base gasket? Yea he told me he set it up with no base gasket.. That's exactly what I have non stamped bb Edited March 2, 2011 by SHEEfan Quote
SHEEfan Posted March 2, 2011 Author Report Posted March 2, 2011 except mine are inframe.. they are the pipes in my sig. Quote
SHEEfan Posted March 3, 2011 Author Report Posted March 3, 2011 J-madd, what were you curious about when you asked if I was running without a base gasket? I know that's how he set it up but not sure what the advantages/disadvantages are of it? Quote
J-Madd Posted March 3, 2011 Report Posted March 3, 2011 The only way to lower the ports is to deck the bottom of the cylinders or run without a gasket, that's all. I was just wondering how you knew the ports were lowered, but that is the answer. Quote
SHEEfan Posted March 3, 2011 Author Report Posted March 3, 2011 Yea that is how he said we should set it up to keep some mid range power.. I will keep it this way for a while. I am trying to get everything possible out of it but still keep it duneable at least for a few years until I can get another dune bike and make this one into a hill shooter Quote
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