Im running a high comp b20v, plan on getting a street sweeper header from sigma six racing, what diameter exhaust size is better to run with? 2.5" all the way or 3" all the way? If end up doing 3" will probably use WS2 80mm muffler or 2.5" with magnaflow. any thoughts?

 

You'll make more power up top with the full 3 inch system, but the lower end might lose a bit compared to a 2.5 inch setup. What compression ratio? What cams? Any head work?

 

theres no point of doing 3" with a 2.5 axle back... ill say max for a b series do a 2.75

 

that sounds like a mean setup...go 3 inch all the way...

 

here's my set up:

B20v setup
gsr head stage 5 port
b20b block 84.5 mm bore
weisco 13:1 pistons
eagle rods
gsr crank
acl race bearings
skunk2 internals
skunk2 pro 3 cams
itr tb
omni 70mm tb
competition stage 5 clutch and ultra light flywheel
aem fuel rail and fpr
RC 750injectors
Gsr tranny

 

3"!

 

2.25 with a cutout at header....nice streetability and you can open it up anytime

 

3''

 

3 inch.

 

Nothing less than 3" just did full 3" with my stock B20V and love it, lost a little down low but nothing terrible.

 

3"

 

I found this article that you should check out about exhaust.

https://honda-tech.com/forums/all-motor-naturally-aspirated-44/article-exhaust-system-basics-2970428/

 

WHY 2.5'' or 3'' exhaust OR 2,75'' or 3'' exhaust ?
3'' in my stock b18 feels good.

 

You def need to go 3". The less obstructions (bends, flex pipes, mufflers, etc) the faster the exhaust gas can exit. Get some 304SS 3" and roll with it

 

2.5" all motor all the way baby!!

 

For what might as well be a race motor?


Air in and air out. Think about that

 

2.5'' why ?

 

I do wonder though why do several race teams and such use smaller piping? TODA Racing exhaust is clearly labeled off road use only and their intent is to make the most out of a race motor. A Spoon N1 is a race exhaust and wasn't intended for street use yet the outlet is only 2.5". I understand tracks have sound regulations but there has to be something more to it.

 

big reason why alot of people use 2.5 on their all motor set ups is because the flow needed for maxium hp is enough. plus its just a way lighter exhaust set up. thats why the bc spec 2 is made that way and only exits at about 3"

but dont get me wrong, i've seen ppl throw on 3" set ups on their all motor and put down some decent numbers. if ur taking EVERYTHING into calucation though like weight, efficiency, etc then i would rec 2.5" for a solid na.

sidenote: is there any heavy block work being done?

 

The weight between a 3'' and 2.5'' system is minimal. 3-4 lbs isn't going to slow you down.

 

thanks all for the input going 3"