CrimsonSC3

So I've been thinking about modifying the factory exhaust on my SC300 (without spending a lot). I was looking to produce just a little more volume and flow. So today i had the second cat removed and straight pipe put in its place (if anyone was wondering it only cost $75 to do), before i got it done I already figured I would loose a little bit of low end torque, which it turns out I did.

So my primary question is anyone have any good suggestions to add a bit of back pressure back into the system without decreasing too much flow... Also I didn't get as much volume as I was looking for so I'm also looking at deleting the resonators and just having the primary CAT and mufflers.

thanks guys

EDIT: if you aren't reading all the posts I've realized my problem isn't back pressure but exhaust steam velocity... any input on how i can achieve a high ESV with the new lower back pressure I have would be great

thanks

1997Soarer

iTrader: (1)

in order to gain some exhaust velocity to regain torque, you could get a header that replaces the primary cat. A header is pretty cheap (OBX) and works until you have the $$$ in the future to go turbo.
You didn't say if you had an exhaust or not. If you are still running a stock exhaust, that could be your problem...

1WILLY1

iTrader: (9)

hmmmm i would of thought u would of gained power, guess i was wrong.

If thats the case u shouldnt of taken it off, im sorry but its just how i feel.

CrimsonSC3

yeah i had a full stock exhaust system on it... and the full stock one performed really well with the NA motor... but now i just have to balance the flow with back pressure now that the second cat isnt there to give any resistance

you can gain power without gains or loss to the torque... and like i said its just the low end i felt the loss in... and yeah i thought that i should have just left it alone but oh well... now just to figure out what i can do for a little bit of back pressure

CrimsonSC3

after doing some other reading its not necessarily the back pressure i need to be worrying about... more so high exhaust stream velocity... what im experiencing right now is low back pressure with low exhaust stream velocity... so now i need to figure out how to remedy this issue... a thought i had is that even though the diameter of the pipe is factory size, with out the cat there the stream velocity make be to low now... so looking into a slightly smaller diameter pipe might help me solve this

1WILLY1

iTrader: (9)

sorry i didnt mean to knock your descision to delete the cat.

I was thinking of doing the same at one point but I didnt realize it could cause these sorts of issues --so i dont think i will end up doing it.

Good luck with it all i hope it works out

CrimsonSC3

no worries... i didnt think you were being rude or anything... as it turns out deleting the cat is a great way to improve power and lower the back pressure but you just need to make sure you have high exhaust stream velocity... the best analogy i have seen for this is a garden hose with water running out of it, just an open ended hose is free flowing but very slow (low velocity), but if you place you thumb over the end the water shoots out and high speed (high velocity)... so its this we have to try to mimic in our exhaust systems... in this instance the cat is the thumb over the hose and now ive removed it... so to fix it i think i will either try to put a smaller diameter pipe on it or tapper the pipe to give it this effect...

if anyone has any experience with exhaust systems and the type of manipulation that im talking about, input would be greatly appreciated

FatBrian81

iTrader: (2)

I think putting in a smaller pipe is your best bet. The stock piping was sized to achieve high velocity with the backpressure of all the installed components. Now with less backpresuure you need a smaller pipe to maintain the correct velocity. Even though its counter intuitive paired with everything we learn about how to up a cars performance its a simple concept of flow dynamics. Ask a plumber about the importance of have a properly sized sewer outfall. The line has to be big enough so that the drains inside don't back up but small enough to have enough speed to move solids effectively down the line.

CrimsonSC3

yeah I couldn't have said that part better myself... people are learning the wrong things about NA exhausts... I have read a lot (this includes myself) about people thinking they need to increase back pressure to improve torque on their naturally aspirated cars... but yeah i think will will get it replaced with smaller diameter piping... I'm thinking 2'' dia with do the trick... too bad i don't have the time or money to try different things out and get an actual reading to give hard data... however, since I'm going to be deleting the resonator, if I did a smaller pipe where they went if that wouldn't give the ESV desired... like I said too bad I don't have the time or money to get true data on a dyno

t70 supra

iTrader: (-4)

i had this same problem what i did was removed the second cat 50.00
added a box header for 225.00
nrg ti exhuast

i have notice lots of gains the best step would be to get the header first that will delete ur first car and make is a 2.5

CrimsonSC3

i wasn't trying to mess with the headers or mufflers right now... but i will def look into something like that in the future... plus i have a 9mo girl and dont want the exhaust too loud because she falls asleep in the car all the time... on a side note some people think its odd i purchased a SC300 for a family car but my MK3 supra was only a two seater

t70 supra

iTrader: (-4)

i would looking into the header with the top speed exhuast

CrimsonSC3

will do... thanks for the help

FatBrian81

iTrader: (2)

I don't know what the inspection laws are like in Florida usually as long as you are past the cat you can use clamps instead of welding things in. You could take out the straight section you put in and use clamps and reducers to find the correct sizing and then have it welded in when you do.

soarer13oy

iTrader: (13)

How about a exhaust cutout for when you are actually on the pedal.