Would like to ask what may seem a daft question, but when aiming for High power, is it necessary to have a larger diameter exhaust?

 

my current setup is decat-downpipes with 2 free flowing JDM 4.5 inch single exhaust back box tips.

 

with this being my daily driver, at night this is abit loud so bought a mongoose 2x3 inch double exit quad system, will this be free flowing enough for 500HP + potential, or am i better off not fitting it?

I think I've read somewhere a 2.5" straight through exhaust is good enough for 800bhp, so I would say all is fine.

its not so much how muc air can be moved in one go but how smoothly this process occurs. this is where the difference between quality and cheap arises, how the bends are bent some are simply rolled this reduces the diametere in the corners causing restrictions. this is the sort of thing you are paying the money for. that and the material and welding quality. i would likly think the 2.5 inch system is good for about 600 hp. as a guess dont forget thats a 2.5" exit per 3 cyldenrs. the back box shape can also have a bearing on the process, single exits process gas easier than twin exit. (per back box) in reality you probally better off looking at your maifolds etc rather than fixating on the exhaust itself, another point worth noting is that without enough back pressure within the system it will effect your torque and affect spool up times just as equally as too restrictive.

Also, if you go down the twin exit route, be sure to fit an X pipe, and not a H pipe at the centre.

 

Alz.

..................... another point worth noting is that without enough back pressure within the system it will effect your torque and affect spool up times just as equally as too restrictive.

 

I seem to remember reading once that on a turbo car, bigger pipes to remove back pressure are fine. However on an n/a car then you need a bit of back pressure - so the kids who fit dustbin-size exhausts to their Corsas and Saxos etc are actually reducing performance.....

 

......Like i said, it was a long time ago when I read it; so no doubt someone more knowledgable will step in and correct me if I'm wrong!

 

Richard:arabia:

n/a does need back pressure turbos need less as its more restrictive, but within reason, but when upping the power i need to know the limit, as i dont want to sacrifice for no reason.

Also, if you go down the twin exit route, be sure to fit an X pipe, and not a H pipe at the centre.

 

Alz.

 

out of interest what makes an x pipe worse than an h pipe

out of interest what makes an x pipe worse than an h pipe

 

I'd be interested to know this too - even though mine actually has neither lol just straight pipes from each cat to each back box.

In reality no car 'needs' backpressure as such, but the more backpressure (to a point) lowers the powerband. BP is more useful in NA cars because they don't have wolloping amounts of torque to make use of the mid-range. You go from a stock system on a 300 to a free flowing 3" decat and 3" exhaust with only one box at either end and you'll notice a drop in torque/power until the turbo's kick in, but hopefully a significant increase in power shortly after the boost kicks in. I've run straight pipes on NA cars before (bit noisy!) and they run fine, they are slower though until higher revs, but by that point - there's no point (short of having a 10,000 rpm peaky engine pushing 200+bhp). Running a cannon on the back of a corsa probably doesnt reduce the power any more than its likely to increase the power, but little engines make more use of more backpressure for a bit of low-down 'nip'. Same story with big induction kits, rarely they increase performance unless your running turbo's or have a high-hp engine which can make use of the extra air.