But as you're supercharged, you should have maybe 3 - 4Psi max in the low-end!! It's RPM dependent!!

This is from neons.org and not from me!!

These are general guidelines I calculated from David Vizard's formulas.
1. For avoiding significant restriction from back pressure, the pipe should flow at least 2.2CFM per horsepower produced.
2. A straight pipe will flow ~115CFM per square inch of area (using inside diameter of the pipe)
3) I used the formula: (115*pi(diameter/2)^2)/2.2
4) The pipe size will become more restrictive the further you go above the zero loss horsepower.
5) Similarly, try not to go too big on piping for your set up. I think Vitor dynoed 2.5 vs 2.25 on a 160whp set up and had very minimal gain. Putting 3" on your stock Neon will be very loud for no good reason!
6) Add length as a factor.
7) Each 90° bend will reduce airflow by 8%!

Exhaust Diameter (inches): 2
Zero loss Horsepower 164.22

Exhaust Diameter (inches): 2.25
Zero loss Horsepower 207.84

Exhaust Diameter (inches): 2.5
Zero loss Horsepower 256.59

Exhaust Diameter (inches): 3
Zero loss Horsepower 369.49

Exhaust Diameter (inches): 3.5
Zero loss Horsepower 502.92

Exhaust Diameter (inches): 4
Zero loss Horsepower 656.88


Based on this, 2¼ shouyld be more then enough for FI \ Nitrous Fits! Maybe 2½ if turbo! Going the harder all motor route!? 2in should be more then enough... Fact: My 1995 Mazda 626 that had a V6 from the factory had a 2inches exhaust pipe.... it generated 164Hp Stock! 2¼ - 2½ - bigger then that and all motor? you make noise \ kill your power for no reason as the pipe is too big to properly scavenge the cylinder on exhaust due to less exhaust stream velocity!! Too many people don't really understand that backpressure is bad and don't know anything about gases velocity and assume that by putting a big ass pipe and killing low end torque they automatically assumes that it's because they eliminated backpressure when in reality it's because they eliminated \ drastically reduced gas stream velocity and as a result, reduced scavenging of the exhaust gases...

search ''scavenging'' on google and learn!

Marko!!

 

well on the subject of exhaust size, does any one know the diameter of the spoon exhaust?

 

I have been messing around with all kinds of engines since before I got out of elementary school and have a hard time with the horsepower output being the determining factor to use when choosing what diameter and length of pipe to use... I have found that engine displacement, boost, compression ratio, camshaft duration, intake flow characteristics, bore/stroke, air/fuel ratios, number of cylinders, power band width and so on in combination as a whole can change what size and length pipe is needed. Exhaust scavenging is all about flow velocity and the things I listed all have an influence on that.

 

Absolutely correct!! But i still think that an NA fit should'nt an exhaust bigger then 2 inches!! 2¼ should be fine for a FI Fit in my opinion!! The best would be to take an identical car with all bold ons possible and then dyno the stocker VS 2'', 2¼, 2½... then add a supercharger and re-do the same tests!! Without that, it's hard to tell... But personally, i think that if a built 2.0 neon engine spinning to 7500Rpm didn't had serious (If any!) power improvements by swapping the stock 2¼ over to a 2½ Dynomax unit, i seriously doubt that a 1.5l L15A without any camshafts or headwork available spinning to 6500 - 6800Rpm would benefit from a 2¼ or 2½ pipe unless seriously boosted... Plus a 2½ Cat back bolted to the stock catalyst or 2'' test-pipe is worthless IMHO!!

Marko!!

 

I am kind of laughing at what I am thinking right now because it sounds crazy as hell.. I keep thinking that a 1.75" pipe from the header back to a 24" long reverse cone megaphone would be about as good as it gets... You would have to wear ear protection to get within a city block of the thing without suffering some degree of hearing loss... I used a 2 1/2" catback with a 10" glass pack, went back to the stock pipe and it slowed me down in the upper mid end of the RPM range I would be in when passing slower moving vehicles on 2 lane highways... The stock B pipe minus the cat with the same 2 1/2" axle back was super strong on the low and mid range to the extent that 2nd gear tire spin was inevitable even at partial throttle with 10 PSI boost but not as strong as it is with 2 1/2" at higher revs in 3rd,4th,and 5th gears.... It is about time that manufacturers utilized the ECU to adjust the exhaust flow like a person would with a water nozzle because it is almost impossible to have an exhaust configuration that is going to be optimal throughout the power band from lowest to highest revs. Most of my experimentation has been on motorcycles but I still have things that I am going to try on my Fit that will hopefully allow me to even things out some.... It is definitely best to use the smallest pipe that you can use that still allows good acceleration with a load at high revs... It has been too hot outside to get anything done this summer and even the afternoon at a relatively low 93 degree temperature the temperature heat index was 100 degrees. It's hard on an old man.

 

automatic opening exhaust cut-out in the upper rpm ranges... do it.

 

pretty sure its 50mm

 

I saw an ad for Skunk exhaust somewhere and it said they come in 50mm and 60mm sizes.

 

I think anything above 60mm will just being louder on the small engine..

 

**BUMP**

This is EXACTLY the type of information I was looking for just now for the Fit. Thank you, Thank You, THANK YOU! The 8% horsepower loss per 90 degree turn is especially interesting. Even more will be lost with a mandrel bend. Was trying to judge if my midpipe decision helped compromise this situation by going 2.5" with 2 90 degree bends before tapering off to 2.25" afterwards.

 

I just went through a good deal of 1/4 mile tickets on different tracks with different exhaust setups and different videos I've taken inside of the car.

The general consensus I've come up with is that 2.5" is TOO BIG. I lost 3-4mph on my top end and 3 to 4/10ths in the 1/4 mile by going with a 'B' pipe that is 2.5". The ONLY part I had that I opened up to 2.5" was the 'B' pipe and this is what I saw.

I need to gather some more data to make this even more conclusive. I'll be changing my 'B' pipe from 2.5" to 2.25" this Friday. I have a 2" J's Racing Cat delete that will go to 2.25" B-pipe and 2.25" out to the muffler. I'm thinking.....hoping this is the ticket to getting my mph back and get my 1/4 mile times back down. HOPING for a 15.1-15.2 consistently if I'm lucky.

It's all speculation! I need more data, lots more runs and lots more time to make it more worthwhile information. You can't go wrong with 2" all the way out though. I think 2" is the best option overall. I'm willing to sacrifice a tiny bit of low end for more top end.