down pipes

[zielritter]

Guys, it's a well known fact if you read around the forums that Hyundais run "pig rich" from the factory. This helps keep cylinder temps down and prolongs engine life (good for a company offering 100k powertrain warranties) so it's by design. Removing both cats essentially allows this excess fuel to be dumped unimpeded directly into the exhaust pipe where it burns.

I can tell you from experience that my Elantra (2.0L beta) and Tiburon (2.7L delta V6) smelled like shit after deleting the cats. I wouldn't even call it a fuel smell as much as would call it an excessive combustion smell - like normal exhaust amplified by many factors. I don't think you'd want that in a car like the Genesis (sedan).

 

[dmitriylm]

Guys, it's a well known fact if you read around the forums that Hyundais run "pig rich" from the factory. This helps keep cylinder temps down and prolongs engine life (good for a company offering 100k powertrain warranties) so it's by design. Removing both cats essentially allows this excess fuel to be dumped unimpeded directly into the exhaust pipe where it burns.

I can tell you from experience that my Elantra (2.0L beta) and Tiburon (2.7L delta V6) smelled like shit after deleting the cats. I wouldn't even call it a fuel smell as much as would call it an excessive combustion smell - like normal exhaust amplified by many factors. I don't think you'd want that in a car like the Genesis (sedan).

Pig rich generally refers to open loop operation and most OEM's tend to run rich particularly with forced induction. Closed loop pretty much always targets 14.7 so you'll see AFR bounce round that region. I was getting that smell primarily during idle at stop signs and lights while the car is in closed loop. The only way to reduce the smell at that point would be to run even leaner than stoich.

 

[2011 Genesis 4.6]

Guys, it's a well known fact if you read around the forums that Hyundais run "pig rich" from the factory. This helps keep cylinder temps down and prolongs engine life (good for a company offering 100k powertrain warranties) so it's by design. Removing both cats essentially allows this excess fuel to be dumped unimpeded directly into the exhaust pipe where it burns.

I can tell you from experience that my Elantra (2.0L beta) and Tiburon (2.7L delta V6) smelled like shit after deleting the cats. I wouldn't even call it a fuel smell as much as would call it an excessive combustion smell - like normal exhaust amplified by many factors. I don't think you'd want that in a car like the Genesis (sedan).

great point, and no I would much rather not smell fuel burning in the exhaust. Though another good point with cracking the 4.6 ecu I wonder how much we can improve fuel mileage just by not letting it run pig rich.

 

[dmitriylm]

great point, and no I would much rather not smell fuel burning in the exhaust. Though another good point with cracking the 4.6 ecu I wonder how much we can improve fuel mileage just by not letting it run pig rich.

I don't expect any fuel major fuel mileage difference as most driving is done in closed loop and the car is already targeting stoich there. Mileage at WOT can be improved as this would be open loop conditions but most people aren't on the throttle often enough to make it matter.

 

[2011 Genesis 4.6]

I don't expect any fuel major fuel mileage difference as most driving is done in closed loop and the car is already targeting stoich there. Mileage at WOT can be improved as this would be open loop conditions but most people aren't on the throttle often enough to make it matter.

While true I am thinking stop and go traffic if your idling more often then moving maybe some savings could be seen?

 

[dmitriylm]

While true I am thinking stop and go traffic if your idling more often then moving maybe some savings could be seen?

In order to improve mpg's at idle or cruise you'd have to set a leaner closed loop target AFR. Stoich is already fairly lean and I'm not sure I'd like to target leaner AFR's.

 

[zielritter]

Pig rich generally refers to open loop operation and most OEM's tend to run rich particularly with forced induction. Closed loop pretty much always targets 14.7 so you'll see AFR bounce round that region. I was getting that smell primarily during idle at stop signs and lights while the car is in closed loop. The only way to reduce the smell at that point would be to run even leaner than stoich.

You're right. But I would especially notice the smell after driving hard and coming to a stop where the fumes would coalesce.

 

[zielritter]

You're right. But I would especially notice the smell after driving hard and coming to a stop where the fumes would coalesce.

And I'll also add that my Mazda RX-8 did not have the fuel smell running catless.

 

[Rey]

We've had this debate over gas mileage increase for some time. Some say that as long as the closed-loop fuel mixture is fixed at 14.7 there can be no gas mileage change by reason of cat removal.

I don't think this is true, and my belief is based on a lot of direct experience not only with Hyundai Genesis, but also other closed-loop injected autos. Check with any major turner such at Lingenfelter, Hennessy or TPIS and they will confirm this. What is achieved is a reduction in pumping losses. The motor has to work less extract exhaust gas. This makes the motor more efficient.

I have not removed downpipes. My experience is limited to removal of the secondary cats, which I have done on four Genesis and now an Equus. They all use the same secondary cats. I use the Motorsports Authority Cat Delete ($109). Motorsports Authority claims a 6hp increase at top rpm, which is not enough to notice by one's "seat of pants dyno". Some increase is shown over the entire rpm range. For example, assume a 65mph steady state cruise. I have seen figures of less than 20 RWHP required to maintain this. Now, if a cat delete at say 1800rpm delivers just one hp that represents a 5% power increase at that rpm level, which in turn is reflected in better gas mileage. My own experience shows about a one mpg increase at cruise.

You can thank the California Air Resources Board (CARB) for the present inefficient exhaust. Many years ago CARB realized it took a bit of time, less than a couple of minutes, to "light off cats". They require high heat to light off. To reduce start up emissions CARB has required cats to be as close to exhaust valves as possible so as to accelerate light up.

Now the cats require a certain amount of restriction to slow gas flow to heat. I think, but have no data, that the secondary cats may be there to restrict gas flow on start up. They are not part of the closed loop control system.

I won't be removing my downpipes anytime soon as it is a hassle and a bother to fool with the emission system, when the same can be achieved with just a cat delete for the secondary cats. At this time no long tube headers are available for Hyundai V8s, and I doubt that any will ever be produced. Manufacturers need a market, and the market for our headers is very, very small.

I wonder if anyone has checked Hyundai V8s world wide to see if there are examples of more efficient exhausts in markets not as restrictive as California?

 

[84FordMan]

Well not to deviate from the discussion of AFRs, I finally got time to follow through and check my spare Coupe down pipes against the 4.6 Sedan's.

They will not fit.

Chiefly, the 4.6's are considerably shorter by several inches. That and the hanger bracket at the secondary cat end is angled wrong.

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