JohnEd

iTrader: (1)

JBRADY, Jamie and all,

I removed my center cat that turned out to be a resonator. It was a SS can filled with SS wool with a straight piece of perforated pipe running through it. It worked, as my exhaust note is deeper and only a tad louder. The result is what I "feel" is a significant increase in power down low and up on top. I always suspect people of wishfull thinking but this time it is me and really!!!! This mod only cost me $50 and I think I got a hp gain and another mile per gallon.

I am running Mich Pilots A/S and the tire has excellent ratings for traction. If I hold the brake and give it some gas and then release the brake and at the same time floor the gas I just light up the tire and sit there and spin and smoke. If I just mash the gas at launch I get a lot of spin half the time. To use my Gtech I have to feather the gas off the line. This is not normal for a stock 93 SC400, I am told. Something has changed for the better.

When I first tested the stock system I installed a O2 sensor bung, actually a 18 mm nut with a thread pitch of one thread per mm. aka 18x1, in the center section after the resonator and between the rear resonators and the "Y" and after the resonators. I used the O2 sensor hole in front of the first cat to get an idea of the total back pressure for the system. In those tests I read 2.5 pounds for the total system and 1 pound for everything after the center resonator.

After the resonator was replaced with a piece of 2.5 inch pipe I took readings and got a surprise. The back pressure for the rear half was down to "ZERO" psi. I made three runs to be sure. My explaination for this is that the center resonator was causing so much turbulance that the rear Y and everything after became restrictive. Without the resonator the gases flow smoothly. My best guess. I checked the pressure at the O2 port in front of the cat and found it still read the full 2.5 pounds psi of back pressure. You never look for an answer till u have a question. The answer is that that bung has a serious forward lean to it. I think the gasses are being ram charged into the fitting connected to my pressure gauge. I can't loose 1 pound in the rear half and still have the same pressure in the total system so the front reading is bogus. If the rear Y works so well I can assume the front Y is also non restrictive and I WILL NOT ditch my cats. Maybe "hi flo" in the future, but I will run them.

I will hit the dyno in a couple of weeks and get a reading on the stock system. In the meantime: can anyone tell me what a one psi drop in exhaust back pressure should represent in RWHP increase.

Almost forgot, I ran her up to 5.8Krpm, held the road speed constant with the foot brake and opened the throttle wide. That is the max flow condition I am sure.

Next up is the UNICHIP install.

John

dejacky

iTrader: (2)

John,
excellent work and thanks for informing all of us of your findings . One thing I noticed with replacing my sc300 restrictive oem catback exhaust with my aftermarket catback exhaust was the following:

engine revs much smoother and quicker

In general, the engine feels like it breathes a lot more effortlessly, which is what it sounds like you're also experiencing. This is more affirmation that our stock SC exhausts systems are very restrictive and choking the engines' performance to some degree.

JohnEd

iTrader: (1)

Mr. Dejacky,

I read your posts with pleasure and I have gotten a lot of great info from your generousity. With that said, I was not making a point of critisism of the stock system. On the contrairy, I feel I "fixed" the stock system by simply replacing the center section resonator with a piece of 2.5 inch pipe. I note you said you have a SC300 and anything I said was applicable to the 400 only. After replacing my resonator I think the only exhaust work that would bear fruit is to get rid of that ex. manifold. The stock system, sans resonator, is providing no back pressure to a normally aspirated 4 litre without nitrous.

I am open to criticism here. My view is that the stock system provides no tuning or scavanging after the first "Y" combiner. If that is true, isn't zero back pressure the objective? The only objective except volume and tone considerations?

Thanks Dejacky

John

SUPRMSC

iTrader: (7)

The SC300 exhaust system from the y-pipe out isn't very restrictive at all. The only areas that you need to address is the catalytic converter on the headers, and the center midpipe.

As for the "power loss" for not enough back pressure. Its pretty redundant, you don't actually lose any power, but rather shift the powerband to another area.

MJHSC400

I've seen this argued so many times, and it always seems that the smart guy ends up saying that zero-loss means zero restriction-- which would sort of kill the opinion of back pressure helping torque--

It makes good sense too as when you add better flowing headers and a less restrictive system you get more torque and more hp-- almost even gains for both--

kyoso23

Anyone using stock piping with the resonators all removed? If so, was there a noticeable gain in gas mileage, power, and sound?

MJHSC400

I'm working on that one right now--

JohnEd

iTrader: (1)

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

turbochris

I just cut out the resonators and welded a piece of pipe on mine a few days ago. I then cut off the mufflers and welded a set of cheapo turbo II mufflers from autozone on there to give it a little beefier sound. Then I just pulled off the stock tips and rewelded them in place so you couldn't even tell there was any exhaust work on the car. After it was all done I painted the mufflers with a black heat paint and you wouldn't have a clue. It made a little bit of a difference as far as throttle response goes and I might of picked up a few HP but nothing to drastic. Only reason I did it was because the car was so quiet it scared me. Its still to quiet but once I get the turbo system on it all the stuff I just did will be tossed to the trash......My wife keeps telling me to leave it alone but I cant.....lol.


chris w

turbochris

the mufflers

sc300gte

how do the turbo II mufflers sound? I was thinking about doing the same thing with my car

turbochris

Believe it or not they actually sound pretty good.

I figured for 40 or 50 bucks it worth a try to hear them. I am happy with it.


chris w

KC95SC400

iTrader: (3)

Hey,

Am thinking about doing an exhaust mod and hope to get some input on my plan.

I live in North Carolina where it would be illegal for an exhaust shop to remove a cat. Even if it really is just a resonator, I'd probably have a hard time convincing someone to do it for me, it sure looks like a cat. So keep in mind that I'll be cutting it out myself, putting some temp piping on, and then later taking it to a shop for welds and better piping.

Here's my plan:

Cut a bit before the cat, and a bit after the rear y split. Using a combination of autozone bought flex pipe and solid pipe (remember temp), run dual 2.25 (stock diameter) pipes to join the front and rear of the system.

Basically totally eliminating the center cat and pipe, and using a true dual exhaust. Would most likely have a crossover put in when I get it welded.

Any theories on how this would sound / perform are welcome.

Any other ideas welcome.

Thanks

BTW. I have new "A traction" tires on mine, and no, I couldn't spin dry if my life depended on it, LOL.

$C300

iTrader: (1)

i just straight piped it after the resenators, do The resenators look more restrictive in side them the muffler?

jgscott

iTrader: (1)

You are not going to notice much difference until you do sometrhing with the Intake like BFI, and let the stock ECU learn the new change.