ackebous

I have been reading a lot of posts here over the last month. Can someone help me understand why a catback exhaust can yield a 10 hp gain, but doing a stage 3 mod will not give any? Is it that the factory mufflers are so restrictive or is it the difference between the stock 2 1/4 " piping verses 2 1/2" ? Just curious. I did the stage 1 and to me it feels more responsive.

Timb227

iTrader: (3)

From what I understand, removing or adding mid mufflers and resonators do not add, or free up any hp. So by taking them off any exhaust, it will not yield any performance. Likewise with adding a resonator, it does not reduce performance.

I believe with an aftermarket exhaust being 2.5", and stock being 2.25", it creates a much more free flowing exhaust. The larger piping as well as the smoother bends and Y pipe, also add HP.

SpiderX1016

Well, Changing the Resonator won't give you any power and removing the muffler will be a very little increase in power.

The difference of 2.25" and 2.5" won't really be much either.

TL|GTX

Yes actually changing the size of the piping does make most of the diff.

tlmaster1

go with 3'' flange back to factory mufflers the best sound ever i love it on mine better then g35 or g37 animal

keystonegreg

Does after market j-pipe and catback exhaust improve fuel economy ?

greco9885

iTrader: (1)

3" is way to big for an n/a car. u are actually loosing some tq since the obvious lack of backpressure

and how did u turn 2.25 inlets to the mufflers into 3" inlets?

princelybug

iTrader: (16)

^


OP, any stage (1-4) won't do anything for you performance-wise. Doing this is strictly for sound. Stage 4 is basically a straight pipe. This will give you the best "flow" but you'll get a lot of rasp.

princelybug

iTrader: (16)

On a N/A car, going any more than 1/4" larger than stock diameter in the exhaust piping is going to be counter-productive.

I hate cars

With stock precats in place you could run a dual 6" exhaust all the way back and see no loss in low end.

Backpressure will still be higher even if you cut the exhaust off after the precats than it would be with PCD and a good cat back.

Even when torque is lost, it's not really lost, it's just shifted higher in the powerband.

You guys are being way too conservative about backpressure in these cars.

ackebous

That seems consistent with everything I been reading on this forum. But, I was just wondering specifcally what gives the HP gain in the catback systems from ATLP, Excerlerate, ect. Are the catbacks 2 1/2 all the way to the mufflers? What is the size of the oem from the y split to the mufflers? It would be interesting to understand the effects of different size pipes. For example, what size is the tubing of say the ATLP J pipe. What kind of volume would this have? For example, if the J pipe uses 2" that would be 2 pipes each being 2" collecting into oem 2 1/4 or 2 1/2" catback system pipes back to the Y and ?? after that. It just seems like the exhaust gases are being compressed and then decompressed again at the Y. So bottom line, what gives the hp gain and can it be achieved at a fraction of the cost of a catback system?

JackSampson

iTrader: (2)

Ok so going with any stage 1-4 yields no performance gain. So lets assume a TL-S is set up with stock precats, RV-6 J-Pipe, RV-6 Test Pipe, stock piping and mufflers after stage 3 exhaust. Now would changing out the last bit of piping and stock mufflers give any kind of performance gain?

chinkwapin

iTrader: (1)

im 99% sure my comptech catback is 2.5 in to the y-pipe then 2 in to the mufflers. the 1/4 in difference from stock is what makes the difference, so technically you could get a 2.5 in catback custom made for cheaper than aftermarket catbacks and still see about the same results.

Blown

The difference is actually a lot more than you would think because we're talking about a 23% increase in the cross-sectional area of the pipe.
The amount of gain yielded by an exhaust mod all has to do with how restrictive the part being replaced is relative to the rest of the system. So it just goes to show that the factory mufflers and resonators are decent but the pipe is smaller than optimum and the stock J-pipe design is restrictive.

princelybug

iTrader: (16)

^
+1.

princelybug

iTrader: (16)

Be careful. If this was the case, no one would purchase name brand aftermarket exhausts. There is a LOT to be said about materials used, quality of welding, and mandrel bends.

chinkwapin

iTrader: (1)

true but im just saying that it IS possible. obviously custom jobs have many variables to factor into the cost, while name brand products come with a higher price tag, they are backed by warranty, support, R&D, etc. you get what you pay for i guess?

Blown

If you go to a shop to get a custom exhaust made just make sure they are using mandrel bent stainless pipe when they quote you and if possible take a look at some of their previous work to make sure they have good welding skills.

AccordtypeT

hey I don't want to argue with you but I saw few honda prelude put 3" piping and made sinificant gain over 2.5 piping about 5-10 whp and it's just 2.2liter so don't you think that a 3.5 liter need bigger than 2.5

Blown

According to David Vizard, who has written many books on making hp, you can break down exhaust sizing like this:
Pipe should flow at least 2.2 cfm per hp produced.
Straight pipe will flow ~115 cfm per square inch of cross-sectional area.
Bends restrict flow and a muffler with the same size inlet and outlet will flow less than pipe of the same size. How much less depends on the design of the muffler and severity and quality of bends in the system.

So for a stock base TL, ideal exhaust diameter comes out right at 2.5". That's why there are good gains to be had with a 2.5" catback. If you back calculate for 3" it would be ideal for 370hp or so.

JackSampson

iTrader: (2)

Good info. So just go to an exhaust shop and have them install 2.5" mandrel bent pipe and new mufflers from the axle back? What kind of gains would this produce on a TL-S?

el_ache_veintidos

Honda's love big exhaust. On a full bolt-on h22, k20, k24 or f20c you can run a 3" exhaust with minimal low end losses and get a couple more hp on the top end over a 2.5". I have seen gains of up to 8-10 whp from this. It have been dyno proven again and again and you can still see a LOT of people that keep telling others that a 3" exhaust is to big for a h22/k20/f20c without any facts to back up their claims, even after seeing dyno graphs that prove that they are wrong! Our engines obviously lack the high-revving DOHC vtec and even worst is that our exhaust manifolds are cast on the head limiting greatly exhaust flow and reducing the possibility to improve exhaust scavenging. Not all engines have the same needs, even when they have the same horsepower and displacement, so no mater what some books might said, there is no fancy formula to calculate the correct exhaust diameter. All that being said, I can't tell you for sure if a 3" exhaust will provide gains on our j32 engine, but when I do a custom single exhaust on my 04 6-speed it will be 3" because I believe it's not to big for an engine that displaces 3.2lt and can produce well over 260whp with bolt ons. I'm not a master builder nor have write any books, but I have work with hondas for over 10 years and have being part of every major honda forum out there, and on my h22 civic I have a 3" exhaust and on my previous car, a 07 civic Si (k20z3) I used to have also a 3" exhaust, both with good dyno proven gains over the 2.5" that were on the cars before. It's not back pressure what you are looking for after the header collector (j-pipe collector on our cars). If this was the case, you will lose horsepower by running open exhaust, when in real life you will normally see bigger gains that what you will see from any exhaust install. This don't mean that bigger is better because dumping exhaust directly to the air after the header collector it's not the same that dumping it in to a straight pipe. You have to keep exhaust pulses organized so they don't lose speed, that is what really restricts how big the diameter can be. If the exhaust pulses enter a exhaust that is to big for them, they start "bouncing" on the walls of the exhaust and lose speed and you lose power ;-)

el_ache_veintidos

Arggg! my post was divided in paragraphs just before I click post message :-/