Reddon

iTrader: (2)

I have been searching around here and am researching all I can. I have very little knowledge about exhaust systems but do know what I learned here; That I want the highest flow possible and that can be very noisy. I am going to be changing out the stock exhaust next week and am in need of some advise as well as 2 questions answered.

From what I read here expansion chambers are very good for our cars, but does that limit me to a single pipe system? I've been told that a single pipe system is better performance wise, true?

I am wanting to get a good system but not looking to spend money where I do not have to so I am considering buying the header (Maybe the rotaryworks 2.5) and muffler(s), a Y-pipe, as well as some sort of resonator to keep the noise down. This will be a no cat system and the only modifications I have is a K&N filter. I was going to have the rest of the piping done at a local shop here because it seems it would be much cheaper, from what I see I'll want 3" all the way to the muffler. Thanks for your help and advice.

j9fd3s

iTrader: (3)

its true that free flow and loud is easy, freeflow and quiet is hard.

i don't see why an expansion chamber would limit you to a single exhaust, it may need to Y after the chamber but you should be able to keep dual mufflers.

as for building a system, ive got a couple of suggestions. this is based off of some testing i've done on a couple of stock FC's. actually when in doubt make a backpressure tester, it doesn't have to be fancy either. more backpressure = less power.

1. the inlet of the header needs to be a little bigger than the exit of the exhaust sleeve, i think the sleeve is 48mm ID, and the RB header is 44mm, which is bad. there is enough meat to open up an RB header. the stock manifold inlet is 50mm

2. the 44mm ID of the RB pipe actually seems to be a very good size for a 13B. they use 43mm ID on the P port engines, i see no reason to go bigger. the MFR PP engines actually have a smaller exit than the street engines do, so the MFR uses a 43mm pipe and it matches the port, while the street engine has a 48mm exit.

3. header length. i don't know, i'd use the short length in the RB catalog. ideally you'd try a few lengths on the dyno.

4. the stock FC system is 50mm ID from the manifold to the Y, and this seems to be fine, if it became 60mm ID, i think that would be good too. especially on a stock port engine. i'm not sure that going bigger is needed.

5. you want a muffler in the center if you chose a short header, and it should be something that can take the pounding a rotary dishes out.

6. rear mufflers; ideally they should be straight thru, and it needs to flow enough for the engine, but 2x2" straight thru actually should be plenty, dynomax has the flow numbers in the PDF catalog on their website. as far as silencing goes the bigger the muffler the better.

Laxfreak3557

If you end up fabricating a header you might as well consider going 3" or so straight out of the flange before making your first bends. This is often brought up by many as one of the reason the rb header isn't optimal. Just a thought

j9fd3s: have you ever thought of using anti-reversion cones on a rotary header? I remeber reading about them in a racecar engineering book somewhere and liked the idea, but i've never seen them on rotary headers before.

to the o.p. I just re-read your post and if i recall the rotary works 2.5" headers you mentions have 2.5" primaries! That is way too big, i don't even think a pp engine needs primaries that large.

j9fd3s

iTrader: (3)

if you look at the RB header and how it addresses the sleeve on an FC engine, the bend in the front pipe actually does make the port match weird. i think the big benefit for the header being straight is that it'll line up with the port better, but that is just speculation. no other engine needs to be 3" straight out, the 787B isn't, F1 cars aren't. not that straight isn't good.

it turns out that the stock sleeve and manifold actually DO make an anti reversion thingamajig, and the RB header ruins it because its the wrong size, and the bend makes the pipe oval.

i agree on pipe size, the 787B runs 4x 43mm ID* pipes, into a 75-80mm ID pipe, and its making 172hp/rotor so i'm not sure you'd need to go bigger... especially on a stock port street car

i think if you considered just these basic things, you'd end up with an exhaust that worked really well, without some endless experiment/speculation.


*i haven't fisted those pipes...