General Exhaust Question

Just a quick question:

Assuming a flat four engine:

Advantages / disadvantages of having a 4 into 1 collector as opposed to a pair of 2 into 1 collectors going into a 2 into 1 collector.

regards

the swordmaster

 

How long is a piece of string...

Seriously though, there is more to it than just saying that 4-2-1 makes more torque and 4-1 makes better topend. Pipe diameter and length, bend radius', primary vs secondary length, collector design, all make a difference.

Andrew...

 

And also whether it's NA or turbo. Take it you're thinking of having some custom made headers for your sport?

 

Thats correct, but more of a holistic approach to the exhaust rather than just the headers, oh and it is neither NA or turbo. :wink:

Mark @ TT is planning to go for 4-1 (equal length), the original plan was 4-2-1 with crossed pairs (front from one side with bottom of other and vice versa).

Just thought I would stir up the grey cells out there and get your comments

regards

the swordmaster

 

As to Pipe diameter, yes it should be not too big and not too small

the swordmaster

 

Not sure if this is any use to you, but TWE make a set of "Equal Length Super Charger Racing Headers"

http://www.xcceleration.com/engine-rs.performance.html (scroll down a bit)

TWE have a reputation for good power gains.

 

Very interesting Fiwek, like those bends.

Still it is not balanced, but the borla, megan and Haywatd & Scott ones arn't either.

My question still stands is 4-2-1 better than 4-1?


regards

the swordmaster

 

Some more info for those interested.

http://www.cobbtuning.com/tech/exhaustdesign/index.html

regards

the swordmaster

 

I'd go for 4-2-1, but the big effect is on the entire exhaust system designed as one, as with a NA engine (i know you've a SC but the exhaust will be treated as a NA) you need to consider the overall ID along its length, too large and gas speed will be slowed and scavenge will be lower, too small and too much BP will be created, and that's the problem with that set of Borla's with the loop over the crossmember, that bank will have higher BP due to the flow restriction on the 180 loop back down. I'd try and route the manifold under the crossmember so flow would be equalized. Generally each flow junction will require a step up in ID to keep the gas speed the same and minimise BP, and also equal length, so it'll look very complicated but should flow really well.

 

Here's a piccy to give you an idea of another setup, MRT's 4-2-1 with decat:

http://www.mrtrally.com.au/shop/images/ ... lne233.jpg

Is this what you mean by "balanced"?

 

I must admit I'd forgotton about the MRT one, I've seen that before. That is not what I mean by balanced. When I spoke to Mark @ Tube Torque his method of 4-2-1 on a flat four was not to pair the two tubes on each side but pair the front pipe on one side with the rear pipe on the other, more dificult but more balanced (I'm sure Jim and Andrew can elaborate on this).

As to regards method Mark is suggesting a 4-1 system as due to no turbo the pipes can go straight back. The MRT system illustrates that it can be neatly done keeping all pipes equal length and fairly straight (I know that those fitting borlas and the like want the unequal length to get that 'turbo' burble as they put it, but to be honest standard headers give the burble anyway).

As to pipe diameter, I'm told that 2½" can cope up to 280Bhp which is more than enough for my likely top bhp figure.

regards

the swordmaster[/u]

 

A 2.5" system will do a HELL of a lot more than 280bhp. Whoever told you this doesn't know what they are talking about.

 

As above my99 uk is doing 350+ with a 2.5 inch system

 

I suspect I probably misheard, I suspect it was 380bhp?

I'm sure that Mark will get the power required out of my car, 250bhp has always been the most I expected (on a good day after winning the lottery :lol, can a good exhaust system be expected to gain 50Bhp?

Nice to hear from you Godzilla how is life treating you?

the swordmaster

 

50bhp is asking a lot.

You can get 30 or so from decatting a turbo (sometimes a bit more) but that's by removing a sizeable restriction. You don't have that hurdle to overcome.

You might find 10 or even 20 in an exhaust swap but I'd be surprised if it was more on a car with around the 200bhp mark. Looking it as a % of your current bhp, 50 is a lot.

Get the NOS out big fella :wink:

I'm doin ok ta. Eagerly awaiting the arrival of Godzilla Jnr (supposed to be this Sunday) but if he's owt like his dad, he'll arrive when he's ready, not when everyone says.

Hope you are ok. Glad to see you are still tinkering. My tinkering days are over til I've stopped buying cots, prams, clothes etc etc.

 

Sounds like there's hope for you yet Rich... :wink:

 

I appear to have a sizable restriction, the power dies at approx 5000rpm. Mind you 20Bhp would be nice. Still the most powerfull non turbo :wink: .

NOS.......sush the wife might hear :shock:

Glad to see Jr. is on the way

How about this



regards

the swordmaster

 

@TM

Oh yes, I'm down, but far from out. A 300bhp Mk2 Golf will be on the cards when I can get to it. 975kgs Only 2 wheel transmission loss. Should be interesting. Just bought coilovers for it! LOL

@Swordmaster

LOL. Like the clothes but with me not having a Subaru any more, he might look a bit daft.

Maybe your restriction is on the inlet side too. Sport inlet manifold runners are quite narrow aren't they? Just a thought.

Have you got yourself in a magazine yet?

 

If power is dying above 5K I would suspect heads or cams.

Do you have to pull a lot of timing as well?

Andrew...

 

as in exhaust headers?

standard cams

Not sure, I don't think so. Which map would show this?

Just to chuck some more info into the mix. At one of the previous rallies, Solberg crushed part of his exhaust causing a loss of power. As I'm still running standard sport headers, where the sport is standard at 123bhp, I'm currently at 197bhp, perhaps the headers are a restriction?

regards

the swordmaster