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high durations wwill usually make the powerband peak much higher. and cna also narrow the band up.

 

more transfer duration will make the tq curve come up BUT can lead to issues with the burn mixture and possible - pressure in the transfers. also differnt pipes react differntly to higher and lower durations. head profiles can affect the power output as well. and of course PV motors like a completely differnt port timing and can do things fixed ports will never be able to live with.

 

rider weight, bike weight, fuel used, bike condition will all atribute to what a motor "feels like" with a higher port timing. i cannt say it enough just "porting" isnt the only thing you should concern yourself with..

 

 

also i have played with transfer velocity's / intake designs and gotten all kinds of differnt power "feels" out the same port numbers..

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Cub motors scavenge very well with the right pipe setup. IMO exhaust numbers that high are unneccessary and will only hurt the curve. Most of the power in porting a cub is in the tripples and transfers. Much will also depend on what pipe you are planning to run. With a cub most of your power gain is going to be found in the dome design once you have a good clean port layout. Going beyond 198 is a waste IMO.

-Brandon

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Cub motors scavenge very well with the right pipe setup. IMO exhaust numbers that high are unneccessary and will only hurt the curve. Most of the power in porting a cub is in the tripples and transfers. Much will also depend on what pipe you are planning to run. With a cub most of your power gain is going to be found in the dome design once you have a good clean port layout. Going beyond 198 is a waste IMO.

-Brandon

 

is there a point to where you LOSE power if the exhaust is taking to high?

 

 

i know of a stock cylinder 4mil on alky running 208 ex/135 trans and it runs HARD!!!

 

im not sure i want to take a cub that high

 

most say to leave trans at 130 but thats stock on a cub so that cant be the best power numbers on the trans

 

 

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good lord!! if i did that the motor wouldnt even get out of the hole!!

 

ive never ran a cub over the 198* exhaust either. i ahve rode a few with higher exhausts and yea they hit harder but to me they were much slower overall.

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Its hard to compare durations from stock jugs to a cub. Cubs have tripple ex and transfers, stockers do not. Im not saying oem jugs cannot run hard cause they can. Even in stock stroke form they can be fast.. Dont forget that bigger isnt always better. Velocity is something that often is forgotten about.. I just did a set of stockers at 194/128. . It should be fun for a stock stroke

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Dont forget to take into account your stroke. You cant compare stk, 4 mill to 7,10mill. You piston speed on the long stroke is going to be faster requiring lower operating speeds for the pistons and rods to live. This means lower timing numbers. I agree with the others and wouldnt go much over 198. Also tranfer port roof work is more important than a number

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