89LSED

Shoot me a text and ill get you some pix
530-957-1019
If you like the work then we can work something out!

rhymeshark916

Ok. Once I get my car to frickin' pass smog/bar referee, I will let you know. Can you just upload some images?

todahead

finally i found a custom 2.75'' used for 200usd hope it wont be a huge different between 3''

HdeucedeuceA

From one of the links posted earlier.

"Using terms like "backpressure" is funny because it makes you look like a fool. It is a non-quantifiable term given to a resistance to flow. It literally does not exist. It is unitless. It is just a word used by people who do not understand exhaust flow and exhaust dynamics. It does not exist in any index of any engineering or fluid dynamics text."

Going from OEM to a 3" manifold back on my AP1 was just WOW. My butt dyno liked it VERY much. A 70mm manifold back has been proven to make gains on the s2k's. Huge gains are had with proper tuning.

cibao2ner

i know 3 inch is the new religion and i agree...im going 3 inch thermal on my allmotor cause i already had it from my turbo days..but i was watching on speed channel how a bmw team actualy gain power from going smaller..on an m3...according to them the smaller diameter gain more velocity and cars were making more power...but those were road racing cars...on something u drag race top end is all that matters...

todahead

hot gasses can move faster than cold.
then a smaller pipe can keep gas temps on hi levels i think that counts only on headers piping.?

88Hatchy

BMW's are very limited on header design and tuning software. The M3's that I have seen built all have the largest exhaust possible, which is usually a 3".

an2ny888

i agree back pressure isn't needed, but what about exhaust velocity? wouldn't a smaller diameter piping increase exhaust gas velocity and promote scavenging?

88Hatchy

That's why header design is important.

ddd4114

Backpressure is just the gauge pressure at the beginning of the tubing.

egb18c5

although i never made a header, but done some research, i can say this, you dont want any back pressure. think of it this way, if there is back pressure, the exhaust gases would have a tough time going through the pipes. the size and length of the pipes "helps" the gases move freely while having a "vacuum/scavenging" effect. besides the fact that length also plays a role, there's a point of diminishing return when it comes to the ID of the pipe, and thats when you go too big.

if i used any terms incorrectly, please point them out.

94eg!

iTrader: (2)

FYI: Tubing is measured by it's OD, and piping is measured by it's ID. Exhaust typically uses tubing and that's why they are almost always 2.5" OD...

PyroProblem

Interesting...I didnt know this. Thanks!

vsexhaust.co m for some good prices on 3" exhaust kits.

C_Rock77

that's www.VRSexhaust.com

I second that notion. VRS has some great stuff. They KILL anyone else's prices for exhaust tubing kits.

1.5Slowmatic

vrs

i'll say this and i believe this is where the mis-conception comes from. if you go that big with the exhaust; you NEED a custom tune. you cant just bolt it on and make more power everywhere. Morons who buy it and throw it on than it goes slower because they are to cheap to get a real tune come on here and say its bad to go that big. Get your **** tuned.

ddd4114

Yeah, I second that. A mixture that is too lean will hurt power much more than a little more backpressure. I was running in the 13.9's with a 2-3/8" exhaust on a very mild build (before tuning).

PyroProblem

Thanks for the correction.

willister54

what exactly do u mean by "scavenging"? I have a del sol with a jdm b18c and went to a honda shop where they made up a 2.5" exhaust from the header back, and no more cat. what im feeling is power at the high revs, but just daily driving the gasses seem to get held up and i gotta tap the throttle to resume acceleration. Ive been hearing alot about velocity vs, backpressure but not sure. what can i do to get that velcity back w/o buying a whole new exhaust. any ideas? thank you, willis

RootBur

I did a back to back test on a 12v vr6 for what it's worth.

http://forums.vwvortex.com/showthrea...t-back-to-back.

thundernoodle

Nice test

HdeucedeuceA

Nice to see an all motor, non-Honda making power with a 3". Not that I'm surprised though.

met

I wish I would have know this a few years back before I got my 2 1/5" exhaust. I made about 380 with it at 12psi on a gt35 b18c 83mm. I was at the tunner this last week he went up to 16psi and only went up to 412. I am wondering if its time to get a 3" now. I have a fueling issue so he turned it back to 12 psi till I get that fixed. I have seen simular setups hitting about 450 with the same boost and close to 500 with 20 psi.

S1LENT94D00R

this thread has me thinking. im having trouble finding a full exhaust for 94 integra gsr. the big problem is thats its a 4 door. ill have to look into these thermal exhaust. any one on here running it? good fitment? no sagging low? any sound clips?

5OHinaEK

yup.. The 2.5 will keep your power band in the lower rpms . But the 3 will bring the torque way up in the rpms. If your worried about noise. Then use 2 long resonators inline. Will not effect flow. Thrush glasspacks have a good smooth sound with no rasp or pop ..more like a turbo muffler but with straight through flow and takes up less space. Gotta ask for em at your local parts house. They keep em in back ..

HdeucedeuceA

It's funny, that after my post everyone is still using the term "backpressure". I guess engineers are ignorant fools.

The idea that going to a larger piping will loose power in the low RPM's and gain power in the high RPM's, is false. If you look at any 3" vs 2.5" test, power is made EVERYWHERE in the powerband. Although, this is only half true. If you don't have an EMS or your computer can't compensate for the increase in VE, then no power will be made. This isn't the exhaust's fault though, just the limitations of the OEM EMS.