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lt1bird

small bore pipes on big bore engine....

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Wondering if anyone has used small bore pipes on a big bore engine? Im just wondering how it ran? Ran out of steam up top? lacked max power acorss the whole rpm range? maybe someone who actually has done this can chime in. small bore being stockish 350, big bore being around 500cc... guess im wondering how much hp is lost due to too small of pipes.

 

Thanks!

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I have no actual experience trying this but a lot of builders prefer the small bore shearer up to the 10 cub(465cc). A few of the fastest builders also like to use the big bore on that motor including mine(a&s racing). M

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The small bore on anything bigger than a 10 mil Cub would probably hold too much heat. The BB should get rid of heat better; however I've ran both on my 10 mil Cub and didn't make any difference at the track. It ran leaner at part throttle with the BB pipes, so that probably negated any effect on the heat. On the dyno the SBs peaked about 400-600 rpm higher, but the max hp was about the same. THese results will vary depending on exhaust duration, of course. Mine is only about 192*. Neither pipe utilizes the potential hp of my engine.

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I ran a set of big bore pipes on a 10mil cub and a set of small bore pipes (both from same manufacturer) and it definitely ran better with the small bore pipes. But we ride at 7200ft elevation, so there isn't much air up here to begin with.

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Thats really cool info. Now the pipes you tested, were they drag pipes or basic pipes?

Thanks!

 

 

MIne were both OOF Shearers (drag pipes) out both sides. I ran back to back passes. 3.89@ 78-80 mph on both. MOtor was on alky, if that matters.

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Pretty intersting....I have a 535 and Im wondering if the big bore pipe is really the best choice....regular race gas.... so far its looking like small bore!

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sb for more bottom bb for top I haven't run bb pipes but a 446 with sb drag port was like a dune port nice all around power

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At 535cc I think you're above the mark for small bore pipes. I know the 465cc Cub can run well with either as I ran both on mine. At 535 I think you're going to have to run big bore to get the heat out.

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if i'm not mistaken.. i beleive matt shearer told me he designed the big bore pipes for the 535.

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sb for more bottom bb for top I haven't run bb pipes but a 446 with sb drag port was like a dune port nice all around power

 

 

The opposite was true for mine on the dyno. Peak hp at about 9,000 rpms with BB and 9,600 rpms with SB. Just my experience on 1 particular motor.

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The opposite was true for mine on the dyno. Peak hp at about 9,000 rpms with BB and 9,600 rpms with SB. Just my experience on 1 particular motor.

 

 

 

^^^^also on mine, few hundred more rpm but comes on a lil less hard, about the same hp

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all depends on how you want the motor to pull. i like more lower rpm hit BUT i also like a high revving engine. small motors like to REV bigger motors are more lower rpm's so the pipes are fitted to work on what they are intended. the 535 cheeta i have i use the big bore pipes it looses less hp as it heats up (dune racing) and will launch a hell of a lot harder when you load the shit out of the motor. that is bigger gearing heavier rider and lot more tire..

 

a lil 350 can rev and make power well into 11000 rpms the big bores will really fall off after 10000 i know on mine i use 7500-10500 rpm range ( its also powervalved) a 535 i would choose a big bore pipe and gear it up tire it up.

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