421 cub with big bores?

[bugnut]

I got some Shearer Big bores in on trade and was thinking about putting them on the cub. Will this net me less or more power? I know small bores are better and that is what I thought I was getting but they turned out to be big bores so now I have them. Will I lose some bottom end or is the power just not going to be right with these pipes. They are oof's. The is race ported and fed with 39's. Current main jet is 175. That jetting is just right with 50 degree temps and 1200 ft elevation. Since I have the pipes I might just throw them on to see what it does. Just looking for some insight as to how they might do.

[Darthwall]

try them out just dont get too crazy make sure and check your plugs those might change alot with the pipes to do serious racing I would swap them out for some sb's but do some testing

[Bansh-eman]

It all depends on the porting. Some builders want you to run the BB pipes with their porting, while others like the SB.

[Wheelman Chassis]

i have a 4mm cib on methonol, 34mm pjs,fast clean up port, custom redline domes, i have cpi silenced bb oofs and i love them they may give up a bit on the bottom, but when you are drag racing i think they work better.

 

you might notice more if you run just gas, try them and keep us posted

chris

[bugnut]

I tried them out on the street and it feels like I gained a lot more top end. Feels like it breathes better up top. I know I was a little lean too on the top end. I was on the edge with the inframes. As for the bottom to mid range I need a lot more tunning or I just lost a lot with the new pipes. I think I am a little lean at half throttle. I have the stock needles in and on the 5th clip. What is the next needle to richen me up around 1/4 to 1/2 throttle. So far I am liking these oof. Now I just need to get them in the sand. I will do some more test on the street to get the mid range to feel right.

 

Also got a question about my plugs. My last set of plugs would not let me stay in the top end. I would hit third then start to bog out. Like it was running out of fuel. I put new plugs in (br8es) and was going to do a plug chop to see where the jetting was with this bog. Well I had no top end bog and it pulled like crazy. Now at the end of the day I started to feel this bog again. Just like it was going lean and running out of fuel. What would cause me to burn through plugs. I take them out and cant see anything broke or out of the ordinary. Should I try a colder plug like a 9. My ignition is all stock.

[shanYE west]

On my 421 I gained bottom end from the big bores.. not top.

[bugnut]

I am thinking why the bottome end is gone is the jetting right now. I don't have this thing anywhere near close. Once I get it close here at home I will test it out on the sand.