Stock exhaust system backpressure
05-30-07, 06:12 PM
#16
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Yea
I did the intake this afternoon and electric fans yesterday. Its starting to be noticably quicker. I am just screwin around till i have a chance to get the turbo kit on.
chris w
05-30-07, 06:48 PM
#17
Lexus Test Driver
Kyo,
I replaced my center resonator ONLY with a piece of 2.5 inch tubing and my back pressure, which was measured at 1 PSI with the stock pipes, went to zero. Why would anyone do anything else at that point? I replaced my differential grease with synthetic but am running regular oil in the engine. I recently changed plugs and Toy wires. Air filter has 10 K on it. With all freeway and filled with 92 octane fuel, and the cruise set at 70, my SC400 gave me a solid 25.54 MPG with ambient of 60 degrees F. I think this is superb but it is only a one tank test so far.
The exhaust tone went a little louder but it is still a Lex in the cabin. While it growls deeply at throttle at low rpm like it always did, it becomes a snarl at high rpm. Cost me $50 to get that pipe put in and if I didn't like it I wouldn't be out much. Fact is "I FEEL" it has more power at the low and mid range and nothing is gone at the high end. If you hold your brake and give it throttle and then let off the brake (staging) does you SC400 just sit there and burn the tire? Mine does and my Mich Sports are supposed to have grade A traction. It wouldn't do that before and it is not my practice now. Cheap thrill that pipe install.
Good luck,
John
I replaced my center resonator ONLY with a piece of 2.5 inch tubing and my back pressure, which was measured at 1 PSI with the stock pipes, went to zero. Why would anyone do anything else at that point? I replaced my differential grease with synthetic but am running regular oil in the engine. I recently changed plugs and Toy wires. Air filter has 10 K on it. With all freeway and filled with 92 octane fuel, and the cruise set at 70, my SC400 gave me a solid 25.54 MPG with ambient of 60 degrees F. I think this is superb but it is only a one tank test so far.
The exhaust tone went a little louder but it is still a Lex in the cabin. While it growls deeply at throttle at low rpm like it always did, it becomes a snarl at high rpm. Cost me $50 to get that pipe put in and if I didn't like it I wouldn't be out much. Fact is "I FEEL" it has more power at the low and mid range and nothing is gone at the high end. If you hold your brake and give it throttle and then let off the brake (staging) does you SC400 just sit there and burn the tire? Mine does and my Mich Sports are supposed to have grade A traction. It wouldn't do that before and it is not my practice now. Cheap thrill that pipe install.
Good luck,
John
05-31-07, 10:38 AM
#18
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low end
Kyoso,
I think you must have awsome low end. Really!
After the first "Y" there is no "tuning" going on in the exhaust circuit. If you drop back pressure back there in the center pipe/resonator rearward portion you will just boost power across the band. Mostly in the high end but you won't lose anything anywhere. The resonator removal will drop the back pressure in the back half from 1 psi to zero. I don't know what that translates to in terms of hp and if you ever find out please pm me. The ex sound level goes up only a tad and is throatier.
John
I think you must have awsome low end. Really!
After the first "Y" there is no "tuning" going on in the exhaust circuit. If you drop back pressure back there in the center pipe/resonator rearward portion you will just boost power across the band. Mostly in the high end but you won't lose anything anywhere. The resonator removal will drop the back pressure in the back half from 1 psi to zero. I don't know what that translates to in terms of hp and if you ever find out please pm me. The ex sound level goes up only a tad and is throatier.
John
06-01-07, 03:06 PM
#19
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Hey John i have read you post thurly and am very imprested with the "zero" back pressure. but i'm curious that if and when you install the unichip or later on maybe headers, could you take another pressure readding. i can only asume that when the volumetric efficiency (more air in the system) is bumped up your will find back pressure again in the exhaust. any way i was just curious. thanks
06-02-07, 09:57 AM
#20
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back pressure recheck
ATL,
My info is that the stock system is good for the stock gas flow generated by a natural 4 liter at our redline. My measurements seem to substantiate that math. If I did cam and headers and removed the cats I would be at that limit. I will never get there caus my cats can never go and a header is too costly. If I moved the redline up and did a rad cam with all the changes I would need new plumbing, no doubt. I won't and don't think I will ever need more "room". Sound is another story and there is no accounting for taste. My friends tell me that there is absolutely no doubt as to how hard I am pushing on the gas pedal when I leave their home and still there is no noise in the cabin louder than stock. I seem to have arrived on that score, also.
I will retest this back pressure after my UNICHIP install and tune. Who knows....? I will also retest my zero to sixty times with my Gtech after each mod or tune.
John
My info is that the stock system is good for the stock gas flow generated by a natural 4 liter at our redline. My measurements seem to substantiate that math. If I did cam and headers and removed the cats I would be at that limit. I will never get there caus my cats can never go and a header is too costly. If I moved the redline up and did a rad cam with all the changes I would need new plumbing, no doubt. I won't and don't think I will ever need more "room". Sound is another story and there is no accounting for taste. My friends tell me that there is absolutely no doubt as to how hard I am pushing on the gas pedal when I leave their home and still there is no noise in the cabin louder than stock. I seem to have arrived on that score, also.
I will retest this back pressure after my UNICHIP install and tune. Who knows....? I will also retest my zero to sixty times with my Gtech after each mod or tune.
John
05-18-12, 08:20 PM
#24
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Yes, and I certainly noticed gains all around. The exhaust note using the stock mufflers really sucks. Until I got Magnaflows, it really annoyed my wife and neighbors. It's VERY raspy, almost ricish in it's annoying note.
05-18-12, 08:25 PM
#25
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Ebay is a great place. You can get some Magnaflow cats there, or off brand. It probably doesn't matter that much. I went with Magnaflow high flow cats just because I trust the name. They weren't that expensive and the car was quicker.
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