I posted on another thread that i made my own catback out of 2.5 in pipe with a Mazda speed muffler on the end. A few people responded saying the pipe was too wide and would hurt the performance due to low backpressure. I checked around for aftermarket catbacks. And found that some do come in a 2.5 in pipe for the fit. For example, Skunk 2. I plan to leave the cat on it as is. No gutting or bypassing. And install headers. The in\out on the cat is 1.75 inches. Wouldn't that be small enough to keep the backpressure?

 

dont think u gonna get 10hp out of a bolt on exhaust !
NA cars are very picky about exhaust flow, that's why u see GOOD NA header would cost over $2k
most aftermarket exhaust for FIT is 2.5mm 60mm, and yes you will loose power if you just bolt it on, happened in my case, with intake + exhaust i made 79whp on dyno(AUTOMATIC)
one thing is a MUST is a ECU TUNE, it is very important to any modifications you do, to let the computer know that u have these mods in place, so they can adj it self.
Greddy emanage is the cheap solution for tuning ur car with basic bolt on...anything else after that u must up grade to get the best result

if u plan to cheap out on ECU tune then i suggest not doing any mods at all...but u will loost performance and loost MPG

hope that helps

 

you wont lose performance... And about the ECU tune... only do it if your boosted or have EXTENSIVE amount of motorwork done... the $300 you pay for a tune and a gain of 3whp is not worth it on boltons. And as far as a good NA header costing $2000+ not true... some of the <300 headers out perform the more expensive ones.

 

Man i'm glad i got some good news from SOMEBODY. I was startin to think i'd have to spend more money and time putting together another exhaust. I'm not trying to make my fit into the fastest mofo on the road. Just wanna make it a lil more efficient and if possible, add a few horses. Anything i can do to add power without losing mpg is what i'm after. I've got a short ram intake and the catback so far.

 

2.5" (62mm) is a bit much for the L15A in stock NA form or even with mild bolt-ons(intake). If it was a boosted L15, I could see the possibility for going with 60 or 62mm piping. There's a reason most of the Japanese made exhausts for the Fit come in 50mm piping (2") as this has the least detriment in low-end power. I would like to see some 54mm exhausts made. The car already doesn't have very much low, mid or upper end power, and considering one is usually in the lower to mid portion of the powerband when driving, it would suck to lose power there.

The L15A doesn't flow like say the K20 or F20/22 where they see nice improvements going up to 70 and 75mm diameter in NA form. There is such a thing as having too much exhaust diameter. One other thing, what is the stock diameter, I believe it is 46 or 48mm. If 62mm was good for the L15A, Honda would have at least given the car a 56mm exhaust from the factory.

 

like said before... you can have a exhaust too big.. but 2.5 isnt too big. most companys dont make a 2.5 exhaust because they all make axlebacks. I ran 2.5 with header and cat delete before i boosted... Low to Midrange was noticeably better. You can go even bigger when boosted.. 50mm is really restrictive when boosted. Your fine with your MS3 cat-back.

 

Most definitely 50mm is too restrictive when boosting. If the OP plans on boosting down the road, then without doubt go with the bigger piping. A 25% increase in exhaust diameter on the L15 which doesn't have very good flow characteristics, not bad, but not reallly good is a bit much. People have stated even just going the full J's setup which is only 50mm they felt a decrease in low-end power. I don't know if that is really the case as a dyno would need to come into play, but when I spoke with J's staff and I asked about the exhaust sizing, they said it was the best all around performer and they tested various diameters before settling on the 50. I still believe a 54 would be optimum for a stock L15, but I'm just guessing without any hard data.

 

Wish i had my old dyno, but I picked up 10whp on the setup, with most of the gain in the low-midrange. i've been there, done that with a few different exhausts and the 2.5 worked really good. this thread is about the 2.5 being too big... and it is not the OP isnt losing any performance like his question stated.

 

Very interesting Chris. I would love to see dyno's of different diameter exhausts. Like I said, I don't have hard evidence, just going by what I was told by J's themselves. They could be full of it?!?!

 

Thats exactly what i wanted to know. Whether are not it was "too wide". I'm not boosting it. Just intake, catback and maybe headers in the future. As long as the 2.5 pipe is not reducing my power or gas milage. I'm leaving it on. I havnt clocked the mpg latlely. But i usually get between 37-43 on the interstate depending on how heavy my foot is. And it does seem like its a lil more opened up when i get on the pedal. Could just be my imagination. But o well.

 

It won't hurt.... But the problem is, it won't help a lot... I think i would start with an Intake (Stock is a choke!), Denso IK20\IK22 (Effective, not expensive!), Pulley (Look at the fat torque gain below!), Header (Stock is a Joke! x2), reworked Intake Manifold (There is power to be gained there, i'm sure!) and then start to look into an exhaust!! Begining with an exhaust won't give you large gains vs. the price you're gonna pay for it... But when you're gonna get more involved into the motor, it should begin to choke it a bit!



Marko!!

 

A 2 1/2" axle back and straight through muffler works well across the power band but is strongest in the upper end..... Trust your butt dyno......

 

Sorry, i don't want to highjack this thread, but DOHCtor do you have all the mods you listed? I know you have the fujita intake, but what about the rest? i fear i might have problems in winter with colder spark plugs... as for the pulley, it's interesting, but it does make the car a little harder to drive... altough you're auto if i remember correctly...
lol... we should gather some fitfreaks for a meet in qc city

 

that is the honda tuning fit dyno chart. They have a ge8 build.

 

I don't have all the mods listed. I gave an ''Mods Order'' based on my experience with cars and also with what i would do personately!! On my car, i only have the Fujita intake, IK22 spark plugs, DC Sports Header and an Axleback! But i've had Pulleys on my neons! It felt like a sightly lighter flywheel!! As the Unorthodox Racing pulley is only 4 pounds lighter it won't have a negative impact on driving... or at least, not like a 15 pounds lighter flywheel!! You should feel a little more power across the entire range, more perceptible in 1st gear with diminishing results in upper gears.... Personately, i didn't had any problems last winter with my IK22 but i think IK20 could be a better choice on N\A Fits!! Good mod for 50$!! My Fujita intake game me some gains, mostly in the upper revs and was a real bargain at 200$ shipped on Ebay!! The Axleback also gave me some gains but it's very subtle... maybe because an AT transmission makes it harder to feel gains in the order of 2 or 3HP (at best AND to be optimistic!) on a 1150kgs car that only have 80Whp to start with!! I Think that my best mod to date is my DC Header! The car feels torquier when going uphill! Before, it had to downshift in 3rd in steep grades and still, it had a hard time!! Now it still downshift in 3rd but it feels stronger! I can actually gain speed now... As for the 2½ inches exhaust.. i truly think that below something like 230HP it wont do anything!! Granted it's not a Fit but i had a dynoplot lying somewhere about a cammed Neon with a Standalone and ITB's that gained something like 2HP by changing it's stock 2¼ catback with a highflow muffler to a 2½ catback....

As fot the dyno chart, it's from a GD3!! Check their website!! I know they have a GE8 project....

Marko!!

 

Oops didn't had the ITB's and standalone back then!!




Crane 16 cams, blackdog manifold, mopar race header, 11:1 compression, race afx pcm. yada yada yada

Marko!!

 

Thanks! looks like i'll have to look into headers next summer :P is there a reason why you chose DC instead of Weapon R? WR seems to be the one most people are going with... the only downside is you can't wrap it in insulation... btw no CEL when you installed it?

 

No since i didn't delete my Cat! Someday soon i may want to try to fabricate some sort of backpressure tester to check out how much there is in the system before the cat!! Of i may take the lazy way and loan one in a garage...

The reason why i took the DC was because Julien Performance could have it at a ''Not so expensive price!''... Well around 300$ if i remember correctly... I ported the collector to remove some obstructive materials that were in the exhaust stream's path and installed it with my 80k km old stock gaskets!!! If you want to see it someday (Or even maybe test drive it!) let me know!!

Marko!!

 

lol... you bet your ass i do! :P
damn there's not enough fitfreaks in qc... i think the only one i ever saw was you,so when is the next meet?

 

Even with 10PSI boost I found that there was a loss of low end power with Megan header, 2.5" pipe and cat deleted compared to the stock B pipe, cat delete and 2 1/2" axle back... There is still plenty of low end with the larger straighter pipes and straight through 4" core muffler that I now have and power is much stronger than before at higher revs all the way to the limiter which is now raised to 7200 RPM.... The exhaust sound a little uneven at highway speeds at 20 to 25% throttle but is fine above or below that except for being deafeningly loud. After an hour or so it can be overwhelming.