Guru

Precisely. Thank you very much. I hate it when people say loss of backpressure causes low end torque. Loss of backpressure is ALWAYS good. Just keep velocity up and reversion/turbulence down is all. On this car I have not experimented but even on a 1.8 liter I have gotten 3 inch exhaust systems to work without any loss of torque above 2000 RPM.

Gstt

U know, its funny because i had a 99 Gs300 first and my boy had exactly your car. white 89 240sx with SR-20 DET. That **** ****ing killed me and had 3 cars on my. He pissed me off so much that i had to trade in my gs3 for a gs4 and i'm the one whose laughing now

but he crashed the white one, put it in a 94 and i rape him again. (i raced him @ 12psi of boost and still killed him.

but his car is not running properly (timming). Good luck with the swap on both cars. Man if only i knew @ that time, i would have used that ****ing money and tried to do make a GSTT 6sp.

JBrady

I checked out your links but didn't find a picture of the Greddy off the car. The phrase "cat back" was created because it is generally accepted that it is legal to do anything AFTER the cat but not before it. Most cars cats used to be underneath in the middle of the car but with stricter emissions many new cars attached the cats directly to the exhaust manifolds. I have yet to see a true cat back on a Lexus. The JIC comes closer than most I have seen as most just replace the rear mufflers (Borla, RM and LSportline). A true cat back would start at the CATs and would include a "Y" or "X" pipe, center resonator upgrade and everything else shown in the JIC pictures. EXPENSIVE.

Contrary to common opinion the stock cats flow OK. The parts of a stock system include: manifolds(3-into-2 on I6s)(4-into-2 on V8s), cats(2), Y-pipe into single center resonator assembly OR center cat on some California cars(2-into-1), Y-splitter and dual resonator assembly (1-into-2), rear mufflers (2).

So, any pictures of the available systems OFF the car would be appreciated.

zenki300

iTrader: (3)

I must have worded something wrong in my statement... Nonetheless, here's a good link that gives a simple explanation about ideal exhaust setupsbackpressure myth and exhaust setups

It's one of the more "easier" to understand explanations of exhaust systems and the backpressure myth, but still a bit of reading.

Now I need some sleep, it's causing me to make stupid remarks... ehhrrrroooo.

LexusRules

yes sorry i dont have pictures but cat-back means CAT BACK.. apex'i, Greddy, as well as tom's and JIC, plus many more from japan. these are all CAT-BACk

my exhaust has a Y-pipe that bolts onto the CAT ITSELF right off the headers. and then 2 rear sections each with a canister attached. I will look for a pic.

mumbles

Lots of folks have their opinions on the backpressure thing, but even the link that zenki300 posted shows that backpressure does play a vital part in tuning and engine.

JBrady

Eric, actually no, the link labels both negative and positive pressure as backpressure and that is confusing. The writer was using atmospheric pressure as ZERO when in fact it is as much as 15psi. 20psi would be positive pressure, 10psi would be negative in the article. True ZERO reads apx 30in/hg of vacuum.

The important point to gather from the link is that the LESS pressure the better. If you could achieve true ZERO pressure after the exhaust valve you would maximize flow. Now, the problem is the ASSUMPTION that larger pipes have less pressure. Don't forget that the faster a gas travels the lower its pressure. Larger pipes slow the flow at low RPM and actually increase pressure, turbulance, reversion, etc and this is why they hurt low RPM power. Now, at some point the total volume of flow will cause a smaller pipe to become a restriction and the pressure goes up. At this point a larger diameter would lower the pressure and improve power, but only above that RPM and its respective volume of flow.

GS400_PUSHER

I think someone here gots the JIC exhaust and it was recently. do a search!!!

Kajukenbo

PV=nRT, 2nd law of thermal dynamics.....

as pressure goes up velocity goes down assuming the other end equation stays constant.

JBrady

I checked with JIC, Greddy, Apex'i and NO one had a true cat back. Could you please send a link for the system that actually includes the Y-pipe that bolts to the cats. A picture of your Y-pipe would be great. Along with Japanimal I am trying to source one and will have to build my own if I cannot find one. Any help would be appreciated.

LexusRules

the GS300 has 3 cats, 2 in teh headers and one after teh downpipe. You CAN get a downpipe for japan for the S300, however that is before the last cat, after the two others.. so cat-back is relative to which cat you are talkinga bout. My exhaust system has a Y-pipe two rearsections attached to two mufflers, it is NOT the same as the borla or l-tune, hks or blitz system. It IS the same as JIC, Fujibitsu, Apex'i, and some other JDM company.

JBrady

Hmmm... I know that some California spec SC400s have 3 cats as you describe and the others have just 2. On the GS400s I have seen there are just the 2 cats bolted to the header manifolds.

Here is a picture I took of a GS300 on a rack but I admit it is inconclusive and I can't remember specifics but I thought I remembered the part right before the twin resonator Y pipe as being a resonator. The GS400 I looked at the same day was definitely a resonator.

JBrady

Here is a picture of a true Japanese cat back for the GS300. What I would like to find is the Y pipe off the V8 engines twin cats.

http://www.fujitsubo.co.jp/search/pr...namID=00000403

LexusRules

ya racing aristo showed me that, it would only work for the S300 and v300 not hte GS4. it removes the last cat so its a 2nd cat back.. not a lastcat back like the greddy and most exhaust. The greddy is a last cat cat back exhaust including y-pipe and rear sections. The GS400 and GS300 have hte same last cat therefore any exhaust will bolt up that is last cat back.

JBrady

So, the GS300 uses a cat in the position just prior to the Y diverge section? Interesting as the 400 uses just a straight through resonator here. The 400 having 33% more displacement and power would be taxing the system more than the 300. Of course the more you try to flow through a given area the greater the resistance. The 400 NEEDS a better exhaust more than the 300 (unless a turbo is involved )

So, as you stated, even though from the 2nd cat back is a true cat back on a 300 it is not a true cat back on a 400...

I know that at least one company offers the Y pipe

https://www.clublexus.com/forums/sho...5&pagenumber=1