ZzerozZ on Feb/16/06 said:
from what i've read here i think i like the idea of a 4-2-1 header much better than the 4-1.
my eventual goal is around 180 whp. is this unrealistic with my 2.25 exhaust?
I don't think this site has promoted 4-2-1's as being better. we've promoted hybrid headers which have the 4-1's long primaries or longer primaries but the 4-2-1 layout. there's a difference there.
stock length 4-2-1's aren't automatically "superior" to stock length 4-1's: depends on your powerband location and what you want to trade off. high powerbands with less midrange make 4-1's better if you want to keep the stock length for a header in most cases. the exception I know of is the 2.5 in. toda hybrid 4-2-1 header which has long primaries but stock length.
with longer hybrids that are a mix of 4-1 and 4-2-1 (i.e. longer = you have to cut and shorted your Bpipe to make them fit) , you have less of a trade off.
Most of the 1.8L motors that hit 180 have 2.5 in. collector headers but they also have to have air coming in first.
that's the idea here: you have to have the right minimum amount of air into the engine FIRST and foremost. once that condition is fulfilled then you realize that it has to be expelled.
it's like taking in a deep breath and not exhaling all the way when you run. you want a full inhale and exhale.
if you just open up the exhaust (exhale) it will release only the amount of power that your motor's potential is. if you breathe in enough for say 185 hp and you're only making 165 hp on a dyno because of reversion , a bigger exhaust system can help you meet the 185 hp potential.
but if you're only breathing in enough to make 165, adding a big exhaust system won't create more power to 185. you'll top out at 165 or if you have an engine with good efficiency 170-175 from the scavenging and resonance effects but you can't create something out of nothing from an exhaust system. like I said, it releases untapped potential already there that was held back by contaminated reversion, it doesn't create new hp.
if you're asking us whether you should sell the 2.25 cat, I'd say yes. There's a ton of b18b owners who can use it. those motors top out at 170 whp and a 2.25 hi flow cat can help them get there.
seriously, put it this way: it'd be easier to get to 180 with a 2.5 in. system as long as your intake side is bringing in enough air. you're just making your task more difficult with the 2.25. not impossible but more difficult.
