I guess one thing to think about is that the exhaust gas continues to cool down as it travels through the exhaust piping. There can be a difference of a few hundred degrees as the gas travels down the pipe and anyone who has taken physics knows that when a gas gets cooler it contracts in volume. Thus the same mass of gas upstream will have a smaller volume as it travels downstream. Thus in theory using a smaller diameter piping further downstream shouldn't hinder performance as the exhaust gas would have shrunk in volume and in theory should keep the velocity of the gas constant. I really think you will hardly lose any power by using the Fujitsubo, may be 0-5HP worstcase senario .... something I would gladly give up for the noise level.
Oh well it seems like you have made up your mind ....

 

u will lose topend with anything that is less then a 3" exhaust. the fuji will support 500hp, but u can get more topend with a ture 3" exhaust

 

I figured 2 of the vendors I asked would know. Next time, I'll call you guys for info.

Do you know if there is suppose to be a hanger that wraps around the muffler? I saw a picture of one w/ a hanger and I don't think I got one. I will have to check my packing to see if its in there for sure

 

Wow that really sucks. Just because an exhaust has resonators doesnt paticularly mean its going to hurt power, but if it has ridiculous neckdowns like you say, especially at the muffler, its going to effect power.

To everyone saying we have this guy who made xx on this exhaust. That doesnt mean its not a restriction. Those guys making big power numbers could probably make a ton more power with a much better flowing system.

 

The vendor has vanished so I am going to install it and do some before and after road dyno pulls. I will do some AFR logging too. Anyone want to bet how much HP/TQ I will lose? Who thinks I will gain power ?

 

I would probably opine that there wouldnt be more than 5hp difference (depending on original dyno environment compared to testing with the new exhaust)

 

Put me down for 2HP lost and a dramatic reduction in noise levels ...

 

I wish I could be as optimistic as some... however, you will lose power necking down from a 3" to a smaller diameter within the exhaust system on an 03' stock turbo'd Evo (mine, and supposedly the least powerful model year). Don't take my word for it... go to the vendors forums and get the (same) opinion from the tuners with the fastest big, and stock turbo'd cars.

There have been many posts regarding the subject... including a paper my Garrett (turbos) and other manufacturers dispelling the shade tree "back pressure" (myth) misunderstanding. This also includes "low end" power vs. "top end" in relation to forced induction and exhaust piping diameter.

My personal opinion based on the experience of other shops, my, and my customer's cars is that you should run a full 3" system on an Evo for optimum performance. You can get away with a 2.5-2.75" downpipe and still make nice power, but in the end your better off going 3" when you put it on the track.

Wasn't this brought up by and shown by David in one of his earlier famous "dyno proof" threads?

 

Here's my rule of thumb: "If you want quiet keep the stock cat and get a resonated exhaust if you want/don't mind loud do what ever the hell you want"

Stock cat and resonated Apexi N1 on my Evo is dead quiet and has a very low grumble at idle. At full song she is still really quiet in comparison with most other setups.

With 20psi/dynoflash/AEM intake/walbro/stock cat/Apexi N1/Helix DP I made 256hp 265lb/ft (about a 40hp gain over stock '03 Evos on MachV's dyno)

I am moving to a highflow cat since I got the 2.3l installed but I am not looking forward to more noise.

 

What's funny is that swapping out the resonators has even less effect on sound as it does on flow. don't know why manufacturers do that...

 

makes me wanna go measure my resonator on the inside. anyone know if the invidia exhaust tapers down?

 

I'm going to stick my neck out for this one. I say no power loss that is appreciable in comparison to other inaccuracies. That is to say that if you get a 2hp loss, then that doesn't count.

In fact, I would say that you might stand to gain some power, perhaps at the lower end. I actually get this right out of my ar$e but it's good to be on the other side once in a while.

 

So youre saying you think hes going to gain power from putting on this incredibly restrictive exhaust?

 

Well, incredible is not the word I'd choose. I am hoping that Fujitsubo know what they're doing and that the exhaust isn't that bad. I think thy're one of the few companies out there that just make exhausts so I would think they know about the restriction and so on. They've been around for a while and are not normally known for carppy products.

Why are people so hung up about pipe diameter? Surely it's not just a matter of bigger being better. I mean it's not exactly diffucult to buy 5" pipes and use that. Considering you only gain typically 7hp max from going from a stocker to a larger aftermarket pipe and that the gain varies between different makes of exhausts, this suggests that the diameter is not the only variable here.

On my DC5, I had a 3" system and then changed to a 2.5". The thing I noticed most is the low end. It just doesn't exist with the 3" but with the 2.5, it pulls from a lot lower down. I am guessing that this is mainly to do with the inertia of the gas in the pipes and perhaps the effects of getting all that to flow. It's a transient thing so steady state is probably a different matter. Anyway, I'm not a fluids guy so I'm prolly way off. [I know it's an NA car but I am assuming here that a similar situaiton applies to the EVO.]

It may turn out that I am wrong. And I can accept that, and on face value, a larger pipe should let the turbo work better, but I am cusious to see if other components in the system make enough of a difference also. It's mainly idle speculation on my part, and a light hearted one at that. I am however curious to see the results.

 

Yeah well Im gonna go ahead and just say the Fuji exhaust will make the least power of any other exhaust system available for the EVO. Garbage in terms of performance.