How to get that boxer rumble?

[ryude]

I love the deep burbly note a boxer makes, but every video of the brz sounds like a regular 4 cylinder. Does anyone think the aftermarket will make something to give us that sound?

[Mr.Jay]

Yea its called UEL (unequal length) Headers and you are good

The FR-S/BRZ are coming with EL headers which devoids the car of the "boxer rumble" but is more effictive and makes better numbers.

So its sound vs performance

[old greg]

Originally Posted by Mr.Jay

So its sound vs performance

Well, it's not quite that black and white. All else being equal, a UEL header on an N/A car will be down a bit on peak power but will have a bit broader of a torque curve. For turbo engines though, it's EL ftw.

[Caliban]

just take the whole exhaust system off (cat-back section).

[old greg]

No, then it will just sound like a Honda

[Dimman]

Originally Posted by old greg

Well, it's not quite that black and white. All else being equal, a UEL header on an N/A car will be down a bit on peak power but will have a bit broader of a torque curve. For turbo engines though, it's EL ftw.

Would part of the problem be a tuning one? If we're using UEL, we're getting different scavenging effects on different cylinders, right? But the ECU is getting averaged signals for MAP and UEGO. So the tune will have to be safe, which means the whole engine will be tuned to the limits of the 'weakest' cylinder, which may not be optimal for power on the others.

So question is: if we have individual cylinder fuel/spark trim and say EGT feedback, how much closer will an UEL get to EL power-wise when all the cylinders can be tuned better for their individual peak power?

[old greg]

Originally Posted by Dimman

Would part of the problem be a tuning one? If we're using UEL, we're getting different scavenging effects on different cylinders, right? ... if we have individual cylinder fuel/spark trim and say EGT feedback, how much closer will an UEL get to EL power-wise when all the cylinders can be tuned better for their individual peak power?

It's not so much the fuel or timing that does it, it's more that different cylinders will reach peak VE at different engine speeds. So lets say when cylinders 1&3 are at peak VE, cylinders 2&4 might only be at 95% of peak. When an engine with EL headers reaches peak VE it is moving more air than it could with UEL headers, but to either side of that peak the UEL headers could be tuned to maintain a fairly steady overall VE where VE with an EL header would taper.

[ryude]

Would it be possible to make the same horsepower, but more torque with the unequal length headers?

[old greg]

Only if the UEL header was better designed/built than the EL header. Versus stock? probably. Versus an equally good aftermarket EL header? no.

[Mr.Jay]

Originally Posted by old greg

Well, it's not quite that black and white. All else being equal, a UEL header on an N/A car will be down a bit on peak power but will have a bit broader of a torque curve. For turbo engines though, it's EL ftw.

Did not know this tho I've never seen unequal length headers before on a NA car.

Originally Posted by ryude

Would it be possible to make the same horsepower, but more torque with the unequal length headers?

I believe this could be done but most likely it would be because you arent extracting the max out of the headers tho for me this is all "in theory"

[KeepGuessing]

UEL exhaust headers will raise torque due to some of the cylinders keeping higher backpressure than others...the top end will be lost due to the same reason...Much like chosing a long runner intake manifold vs short runner...


As for making the SAME horsepower but more torque...it would depend on what the constants are there.

Do you mean the same horsepower as "brand X manifold" or the same horsepower as you would make using a dynamically identical manifold just one made using a UEL method...

If the choice is ONE..then yes of course, you can produce more HP and more torque than a particular brands item by having one produced to suit YOUR car your climate and the rest of the modifications done to your car...

If the choice is #2..then no, because the majority of the design will carry over thus keeping the limitations/gains similar in all area's EXCEPT UEL....

The real question is, when will a company produce some variable length headers (i remember seeing a design/patent offer for this a while ago but it was completely unpractical..probably tripling the weight of a standard cast type)

[ichitaka05]

Originally Posted by Mr.Jay

Did not know this tho I've never seen unequal length headers before on a NA car.

Really? This is what I have on my Impreza

[catharsis]

Originally Posted by old greg

Only if the UEL header was better designed/built than the EL header. Versus stock? probably. Versus an equally good aftermarket EL header? no.

What he said. /close thread.

Seriously the only way to get it is with UEL headers, and it might be better than the stock header, but still worse than a good aftermarket EL header.

If sound is such a concern, will you to be getting a device that makes a "Woosh" sound so people think you got an ubercool turbo?

[Dimman]

Originally Posted by old greg

It's not so much the fuel or timing that does it, it's more that different cylinders will reach peak VE at different engine speeds. So lets say when cylinders 1&3 are at peak VE, cylinders 2&4 might only be at 95% of peak. When an engine with EL headers reaches peak VE it is moving more air than it could with UEL headers, but to either side of that peak the UEL headers could be tuned to maintain a fairly steady overall VE where VE with an EL header would taper.

I guess that's kind of the same thing. With different VEs the averaged fueling and ignition leaves some cylinders under-performing.