GNN60GT500

OK- Ill shed some light on the subject- I work for Magnaflow-

1. For the most part, dynos are fun, but they dont tell you much unless the dyno shop has paid the big money to create an actual controlled environment-

Some of the variables that need to be taken into consideration are-

1. Head temperature- most dyno shops dont check
2. Coolant temperature- most dyno shops dont check
3. Oil temperature- most dyno shops dont check
4. humidity
5. air temperature

Our R&D center can actually change dyno results on a 200hp car by as much as 4-5 hp just by manipulating head temperature and collant temperature-

Heat soak into the heads is the biggest reason for a loss of performance-

Cars will also dyno differnent numbers at different times of the day due to humidity and temperature as well-

Also the "learning curve" of a cars computer needs to be looked at as well- as in order to effectively guage a mod, you need to let the car learn the new mod in order to fully understand how that mod effects the vehicle-

Lets look at the options for a stock IS350

1. True Dual Exhaust- no cross over
2. X pipe Dual
3. H pipe dual
4. Single Exhaust

An X pipe exhaust will outperform a true dual, or H pipe due to scavenging, so lets concentrate on single vs X pipe exhaust-

The first big factor is that due to firing order, a V6 will not take advantage of an X pipe in the same way a V8 will- hp wise- the X pipe will however provide the car with a more exotic sound quality, and will also help with interior noise-

the reason behind that is the faster acceleration of the gasses through an X-pipe causes them to flow in a linear fashion parallel to the walls of the tubing rather than tumbling. This "laminar" flowing gas is much quieter than tumbling gas, resulting in an exhaust tone up to 8 decibels quieter than a traditional H-pipe


Each one has disadvantages-

X pipe- i

ncreased friction of exhaust against pipe due to larger surface area of 2 smaller pipes compared to one larger pipe-

not enough back pressure?



Y pipe into single-

turbulences caused by forcing the two pipes into one

too much back pressure?

The first thing to consider is what kind of power to we want?

peak hp? peak tq? power under the curve?

In order to gain the most power- our goal should be to increase the total area under the hp/ tq curve by the largest amount possible-

Peak gains sound impressive and help sell product, but not if they sacrifice power in other places of the RPM range-

If product A averages 7rwhp throught the RPM range, peaking at 8rwhp gain

and Product B averages 5rwhp through out the RPM range peaking at 10rwhp

one might think B is better then A, because it has a higher peak-

however A is better then B, and in a drag race A would beat B-

After testing oh 100s of V6 motors, I can tell you based on the past-

A is a single exhaust on V6 motors

B is a dual exhaust using a cross over-

dual exhaust "might" provide a few more peak hp, but for overall gains a single is the way to go-

In fact if you look at the Nissan VQ series, you see all of these companies making "dual" kits using catch phrases like "X pipe" and so on-

But if you look at the system Nismo Japan made, its a single exhaust-

There is a good reason behind this-

Remember- Magnaflow does not make intakes, exhaust, suspension parts, exc- we spend 100% of our company resources on understanding exhaust theory-


Now I know we dont make a cat back for the IS350- however- so this doesnt apply- but for those that want to know more-


To take this a step further, in order to design a real exhaust system, you need to look at how the air flows through the muffler and design the internal preforations of the muffler on a straight through design to best take advantage-

We actually use extremely expensive testing equipment designed specifically only for exhaust that lets us look at how the exhaust pulses flow through the muffler so that we can change the size, shape, and number of preforations internally inside the muffler to make the most power, while reducing noise-

basically custom designing a muffler specifically to the car for optimal power-

OK- i think Ive bored everyone enough-

combfilter

iTrader: (3)

You didn't bore me at all GNN60GT500. This was good information to know. Thanks!

Gernby

iTrader: (1)

Thanks for the comments. I guess sticking with the 6-2-1 configuration might be best then. I'm also tempted to just run a single muffler, but I don't think I could stand the way it would look. It would be a nice weight savings though...

07Txlex

Hey gernby.. I admittedly do not know much technical info about all this, however I was thinking this. Removing the 2nd cats somehow, piping to an x-pipe to the mufflers.. If this sounded bad due to the stock mufflers I was thinking of purchasing the "new" non lexus HKS exhaust and implimenting that with the cats removed.. I the HKS exhaust will sound the "least rice" as my buddy comb likes to call it. lol The only person who actually has posted owning the new HKS non lexus is HUTCH27 who has it on a 250, I think the HKS will sound similar to this on a 350 http://www.youtube.com/watch?v=21YS52IBrkc without the cats removed.. If you read HKS's website the Carbon Ti is basically the HI power exhaust with a carbon can and tip so that's why I think the above clip is so close

al503

This is just about the only reason I would change the exhaust at all. If there was a way to extract enough power to make a real difference in performance, then the manufacturer would have probably done so as there aren't huge deltas in $ between the available designs.

As mentioned by GT500, I never take the dyno results from manufacturers without a huge grain of salt. They can be:
1. manipulated, and
2. peaky gains can be negated by loss of aggregate power under the entire rpm range.

So, given that I won't alter/delete the existing stock cats, the only real advantage (that doesn't rely on dynos) is the weight loss from a lighter single or dual muffler design. As most of the flow/backpressure characteristics are determined by the stock cats and resonators, you don't have to worry about a significant loss in power down low from too much flow and you may gain a slight benefit higher in the rev range. They'll probably cancel each other out if anything.

However, there is no arguing with the laws of physics. Without going into a discussion about where the weight is gained or lost, lighter is better and will help almost every aspect of the car's performance, not just acceleration.

My ideal exhaust mod would be a relatively quiet, single ti exhaust that weighs about 10 lbs v. the 40 lb stock muffler (offset with a lighter battery up front and/or draining your washer fluid, etc., to maintain weight distribution.)

caymandive

iTrader: (2)

Nice thread Gernby! Seems like we have lots of great minds here and the input from GNN60GT500 is very helpful. I'd love to do a single exhaust myself. Something lightweight, possibly use a flowmax inline muffler and have it pipe out the right rear side with a nice exhaust tip would seem optimal. If looks were a huge deal, then for the other side just put the same exhaust pipe/tip there or have a body shop fill it in somehow. I was curious to see how bad the car would look with a missing muffler so I photoshopped it out. Not too bad, but not great either.

caymandive

iTrader: (2)

Here is a photoshop with one side filled in. That would be cool if a body shop could fill it and then have a nice size tip on the right for the single exhaust.

al503

Thanks, James. That pretty much sealed the deal for me on a dual muffler. The additional weight loss isn't worth that....

07Txlex

Yea thanks for giving us an idea, but I agree it just doesn't look right without 2 so I hope we can all reach an agreeable solution for 2

lobuxracer

iTrader: (2)

A decent bodyshop could make that whole second arch disappear. Reworking bumpers isn't all that difficult as long as you have the talent for it.

I'd like the single, but again, much as al503 says, I don't think there's a lot to be gained without upsetting things. The biggest gains will be had from putting equal length primary tubes into a good quality collector. Possibly enough to really **** off the engine management scheme because our VVTi programming depends on the exhaust behaving like the stock unit. The improved scavenging could make the natural EGR effect fail to work as intended (and essential for NOx emissions) even with the cats in place.

As I said in the other thread, this is a development project and getting the most out of the engine will be a challenge for sure. While I fundamentally agree more area under the curve is a good thing, the most correct answer to the problem is more area under the curve in the most useful rpm range. All engine tuning starts with a power goal, then determing the rpm range most likely to make that power goal, then making the torque curve as high as possible in that range of rpm. Cam selection, intake tuning, exhaust tuning, and a small host of other variables all get chosen based on this desired outcome.

So, figure out where you want to make power, THEN start your exhaust tuning process. And NO - idle to redline is NOT a reasonable rpm range!

caymandive

iTrader: (2)

Glad I could be of some visual help.

Why not just keep the current stock setup and cut the rear cats out and replace with straight pipes. I'm sure the gain would be there and the car would still remain fairly quiet with the stock mufflers.

**EDIT** Nevermind that would be boring

Gernby

iTrader: (1)

Regarding dynos ... the ones I posted are not from the manufacturers. Regarding their value of the results ... everyone has their own opinions, and the subject has been beaten to death in other threads.

After the discussion here, I think going with an X-piped dual exhaust would be too big of a commitment without a known outcome. It would also prevent the use of the current bolt-on axle back exhausts. What I'm leaning toward now is to simply remove the secondary cats and see if I like it. If I do anything else, it will probably just be the HKS axle back. Of course, it would be pretty cheap to do a custom, light weight single just for fun...

BTW, I just saw this video clip with the rear mufflers totally removed, and I must say it didn't sound that bad (or loud).

caymandive

iTrader: (2)

Would love to see a dyno before and after the secondary cats are removed. I'll pitch in. Now of course the hard part is finding a shop or person to do the job.

07Txlex

2nd cats alone or 2nd cats and the resonator like that diagram you have previously posted?

iSuxeL

iTrader: (21)

Are you saying that HUTCH27 has that IS350 in the video? If you are than youre wrong, cause thats jinetix's car. Sorry I dont mean to ***** talk just wanted to clarify that up. I too am running the HKS Carbon Ti, the sounds is awesome, from what Ive been told on jinetix setup he is only running a custom axle back with the HKS's.