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Discussion Starter · #1 · (Edited)
Update 12/08/04:

Hey guys, I updated the title of this thread to make it more obvious as to what the thread was about (Should I keep the stock Y pipe or put on a staight through ypipe when I put on atermarket headers?). I'm working on updating this to my new format with new analysis as part of the "250 bhp IS300" Review, and am also completing another writeup: "The Importance of AirFuel Tuning (SAFC, etc)" at the same time.

Check the last post for new anaylsis from this data (40-110 mph analysis plus some teaser data form the SAFC tuning writeup)


End Update

Alrighty. I recently helped a friend here in Atlanta upgrade his exhaust system. I took the opportunity to get his car on a dyno during different phases of the upgrade to gather some data on how exhaust backpressure effects the engine output.

A stock IS300 has 3 catalytic converters: 2 on the headers/exhaust manifold, and 1 on the Ypipe. It also has a resonator in the stock Bpipe. This stock setup allows for a very quiet ride, but also makes the exhaust very restrictive (non-free-flowing). Some people say that the less restrictive your exhaust is, the more power you produce. Others argue that a bit of backpressure is good for the low end torque, but you might lose horsepower. Let's have a look at some real data!

Test Car
2002 Lexus IS300
5spd Manual Transmission
PLP Silent Flow Intake
K&N drop in filter
A lot of rusty bolts (damn you, Salty North :( )

Here are our two test setups:

Setup 1 Parts
Toyomoto Gen1 Headers
Toyomoto Gen1 Ypipe
Stock Bpipe
Toyomoto axelback exhaust

Setup 1 Backpressure
With this setup the exhaust is basically straight through from the headers back... there are no catalytic converters left in the car. This creates a minimum amount of backpressure.

Setup 1 Sound
Because the exhaust is straight through, the car has a definite rumble even when idling, and gets VERY loud under partial throttle and WOT. The exhaust note with this setup isn't high pitched (fart can)... although it gets very loud it maintains a moderately deep tone.

Setup 2 Parts
Toyomoto Gen1 Headers
Stock Ypipe
Stock Bpipe
Toyomoto axelback exhaust

Setup 2 Backpressure
With this setup, 1 stock catalytic converter is retained, as well as the stock resonator. This maintains some of the stock backpressure while still making the exhaust much more freeflowing than stock.

Setup 2 Sound
Compared to setup 1 this configuration is much quieter... at idle you can barely hear it, and even at WOT it maintains a deep, smooth sound, although it is louder than stock.


Both setups utilized the stock ECU with no additional tuning (S-AFC, etc)


Show me the money!


As you can see from the dyno results... Setup 2 (with the stock Ypipe) produced appx 2 more max torque and almost exactly the same max horsepower!

Max outputs ARE NOT the most important (and interesting) things on the graph though!


0-4000 RPMs... Setup 2 shows its stuff with some low end numbers
Take a closer look. Between 2500 and around 4000 RPMS, Setup 2 with the stock Ypipe made about 5-10 more torque, and 2-5 more horsepower. The largest differences are seen down in the lower rpms...



At 2500 RPMs, you make 11 more ft-lbs of torque, and 5 more horsepower using setup 2 with the stock ypipe! This gap decreases as you near 4000 rpms... at 3000 rpms the stock y makes +6 tq and +6 hp, 3500 its only +4tq and +3hp, and at 4000 rpms both setups are making the exact same power.

I'm not kidding when I say the exact same power. @4000 rpms:


These two dynos runs were on different days (almost a week apart) with different exhaust setups. What the heck are the chances they'd make the exact same power exactly at 4000 RPMs, especially given that the graphs are quite different at all other rpms??? :crazy:

4000-5500 rpms - Setup 1 shines in the midrange


Looking from 4000 rpms up to 5500 rpms we see the two Setups flip positions. Setup 1, with the full straight through exhaust, produces around +5 hp and +6 tq over Setup 2.

5500 RPM plus, tie ballgame
As we near 5500 rpms both setups start to line up and produce about the same power... with neither having a significant advantage. Perhaps the volume of exhaust being produced at these high rpms is enough to push through the backpressure and negate its effects.


Final Thoughts

Given the dyno results, both setups have power in their own areas... Setup 2 from 0-4000 RPM, and Setup 1 from 4000-5500 rpms. When deciding which setup you should go with you should think about your goals for your own car...

A bit of backpressure (from the stock cat) is good for low end hp and tq.
If you want the max mid range hp, and tq, get rid of as much backpressure as possible.

Setup 1 is good for a mid-to-top end, freeway car. The extra power from 4k-5.5k rpms is right in the revs where you'll be shifting down to when running at higher speeds and from a roll. Also keep in mind that this setup is much louder than setup 2... the lack of any cats whatsoever can make the car very loud when under throttle, and creates quite the drone on the freeway.

If you don't mind the sound and want a car for the freeways, a full straight through exhaust is for you.


Setup 2 is perfect for that off-the-line, stoplight-to-stoplight racer. The power down low, especially between 2500 and 4000 rpms, is far superior than setup 1 and will help you rocket off the line when the light goes green. Also keep in mind that this setup is much quieter

If you like to go at it from a dig, or don't mind trading midrange power for a quieter exhaust, Setup 2 is for you.


Also, note those air/fuel graphs. To make the most power, they should run near 14:1 for an NA car, and they're in the 12:1-10:1 range for this bolt on exhaust setup! If you just slap on headers, a ypipe, and exhaust and don't worry about the tuning, you're not getting your full money's worth on your mods! Add that SAFC and get it dyno tuned... I'll make another thread on that soon.


Special Thanks

Special thanks to Batlground Engineering for letting me use their dyno to do this comparison. If you're within driving distance of Atlanta GA and need tuning, parts, installation, or troubleshooting help with your IS300 check them out at www.batlground.com. Give them a call or shoot them an email... ask to speak to Dan or Tracy, and tell em Das sent you. :wink:

Also thanks to Jeff (Icarus on SELOC) for letting me play Dr Frankenstein with his car... can't beat a free exhaust installation, can you? :wink:
 

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Wow, this was an excellent write up! Thanks for the info! You should try these tests on your car with your s/c.
 

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Discussion Starter · #3 ·
stick said:
Wow, this was an excellent write up! Thanks for the info! You should try these tests on your car with your s/c.
:D I'm also working on one that shows stock exhaust vs untuned upgraded exhaust vs tuned upgraded exhaust... an SAFC almost doubles the gains from headers + exhaust!
 

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Very nice work and well written. I think I'd go for the low end torque as I was used to driving a LT1 before I got my IS.
 

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I'm having fun with my Toyo Y Pipe, don't want the hassle with the header...too hard to install. I do need a new exhaust though, stock is very restrictive.


Chan
 

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Discussion Starter · #7 ·
Chan said:
I'm having fun with my Toyo Y Pipe, don't want the hassle with the header...too hard to install. I do need a new exhaust though, stock is very restrictive.


Chan
Hehe did you notice the "rusty bolts" comment I made? Took us 5 hours to do the whole job... half of that was breaking loose crazy rusty bolts. Out of the 8 bolts on the exhaust system under the car, only 5 of them made it out alive.

The rest were dremel'd mercilessly. :wink:

we did manage to get the headers out the top of the engine bay though... didn't have a lift, just a lame mini floor jack. If I had to do it again I could do the headers in about an hour and a half.
 

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any chance for

Setup 3:
-stock headers
-toyomoto y-pipe-
-stock b-pipe
-toyomoto exhaust

I'm sure many of us are running just a y-pipe (xerd, toyo) with aftermarket exhaust.

Either way, Good job man, much appreciated.

I would definitely go for a "freeway" setup.
 

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dasgalloway said:
Hehe did you notice the "rusty bolts" comment I made? Took us 5 hours to do the whole job... half of that was breaking loose crazy rusty bolts. Out of the 8 bolts on the exhaust system under the car, only 5 of them made it out alive.

The rest were dremel'd mercilessly. :wink:

we did manage to get the headers out the top of the engine bay though... didn't have a lift, just a lame mini floor jack. If I had to do it again I could do the headers in about an hour and a half.
My O2 sensor on my stock Y pipe did not want to come off, sprayed liquid wrench on it waited 30mins and it still didn't want to come off. Took us 30mins to take off that damn 02 sensor.

Chan
 

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Discussion Starter · #10 ·
redlex15 said:
any chance for

Setup 3:
-stock headers
-toyomoto y-pipe-
-stock b-pipe
-toyomoto exhaust

I'm sure many of us are running just a y-pipe (xerd, toyo) with aftermarket exhaust.

Either way, Good job man, much appreciated.

I would definitely go for a "freeway" setup.
Probably not on this same car, which is what makes it a really good comparison. All work was done to the same car so we know the gains/losses were all from the mods.

If I get another car here in the ATL thats upgrading to a ypipe I'll do the same for them and get some real numbers on the gains. :)
 

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Discussion Starter · #11 ·
Chan said:
dasgalloway said:
Hehe did you notice the "rusty bolts" comment I made? Took us 5 hours to do the whole job... half of that was breaking loose crazy rusty bolts. Out of the 8 bolts on the exhaust system under the car, only 5 of them made it out alive.

The rest were dremel'd mercilessly. :wink:

we did manage to get the headers out the top of the engine bay though... didn't have a lift, just a lame mini floor jack. If I had to do it again I could do the headers in about an hour and a half.
My O2 sensor on my stock Y pipe did not want to come off, sprayed liquid wrench on it waited 30mins and it still didn't want to come off. Took us 30mins to take off that damn 02 sensor.

Chan
You need about a 3 ft breaker bar to get those suckers out sometimes. A wrench and a rubber mallet also works wonders.
 

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GOOG JOB DAS!!!!

This is the type of FACTS we need posted. Very interesting. I know I have allot more tq at lower rpms than the other stage 2 folks because I kept my restrictive L-Tuned exhaust. However, I lost more in top hp (25hp).
 

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Chan said:
dasgalloway said:
Hehe did you notice the "rusty bolts" comment I made? Took us 5 hours to do the whole job... half of that was breaking loose crazy rusty bolts. Out of the 8 bolts on the exhaust system under the car, only 5 of them made it out alive.

The rest were dremel'd mercilessly. :wink:

we did manage to get the headers out the top of the engine bay though... didn't have a lift, just a lame mini floor jack. If I had to do it again I could do the headers in about an hour and a half.
My O2 sensor on my stock Y pipe did not want to come off, sprayed liquid wrench on it waited 30mins and it still didn't want to come off. Took us 30mins to take off that damn 02 sensor.

Chan
You need to HEAT UP the 02 sensor bung. It comes off VERY easily. If you do it cold, it will give you some issues.
 

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sweet post Das!!! :D
 

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Discussion Starter · #15 ·
redline814 said:
GOOG JOB DAS!!!!

This is the type of FACTS we need posted. Very interesting. I know I have allot more tq at lower rpms than the other stage 2 folks because I kept my restrictive L-Tuned exhaust. However, I lost more in top hp (25hp).
Word... I'm in the same boat as you. :)

What you need is an open wastegate...

Anyone have any comments on the data or analysis? I have the raw dyno files so we can zoom in on different areas, discuss the a/f ratios, etc.

Still working on that SAFC tuning results writeup... spent 4 hours on it so far.. still going. Whew! :crazy:
 

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Malekreza11 said:
You need to HEAT UP the 02 sensor bung. It comes off VERY easily. If you do it cold, it will give you some issues.
Yup yup....do it when the exhaust is piping hot after a good run...and it'll come off with basic hand tools!
 

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redlex15 said:
any chance for

Setup 3:
-stock headers
-toyomoto y-pipe-
-stock b-pipe
-toyomoto exhaust

I'm sure many of us are running just a y-pipe (xerd, toyo) with aftermarket exhaust.

Either way, Good job man, much appreciated.

I would definitely go for a "freeway" setup.

exactly what i was looking for


my "seat of the pants" impressions


I went from XERD header, y pipe, Tanabe b pipe, & Hiper exh to JUST the Y pipe, Tanabe b pipe, & Hiper...adding a Stock manifold was like night / day from a low end power & torque.... i was just blown away at the difference......

I actually have been turned off on headers now as i do not run my car from 4k-6k rpm mostly when i am having fun with it ... i am more in the mid range & then the low end on tight canyon roads.. .the increase in low end power & torque when i put the stock header back on was nothing short of amazing.. . the extra 10 hp up top oi gained really was not that useable & dare i say....practical...

I felt like i gained 10-15 hp down low & lost a bit up top but really i was stunned at how much harde it pulled right off the line... headers & free flowing exh REALLY kill your off the line grunt....


thanks Das,, ,this goes along way to explaining what i have experienced as well & very close to what i was doing last year when i dropped several hundred bucks at SP engineering testing everything from Hiper Exh to Srt intake, to B pipe, to Y pipes, & finally Teck Ground kits....


it was very interesting & fun....


edg
 
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