is this necessary? first thing im going to do is get full exhaust system, w/Dual N1's, so i was wondering if i could go with a 3" downpipe/midpipe setup....and if it would be better than 2.5"?

or you can just give me your opinions on whats best....i dont mind the loudness, im just looking for max HP!

thanks,
chad

 

I'd go for 2.5".....

 

That Is wide open for a na. You'll lose plenty of torque with a diameter of 3''. 2.5 seems to be the consensus. However, I went with 2.25 and I can't complain.

 

ok, so 3" is too big....i wont lose any power with 2.5"? i want to get max HP out of it....so what do you think?

 

If you want max hp then I would go for the 3" piping, that's won't neccessarily give you the best power though. I would go for the 2.5" piping (but since you're going with dual exhaust then I would do 2.25") since it'll give you more torque and hp in the low/mid range area as well as high range. The larger piping will create power up high but decrease power down low.

 

2.5 is perfect for NA's dont get anything bigger

 

On my GSL-SE both of my primaries collect into a 2.5" collector and then expand through a megaphone to 3" before going out through a 3" internal straight through muffler. It works great. I had it running out through a 2.5" system before and it did work very good as well but I personally prefer the expansion to 3" since it broadened the power band a little.

 

I am going 2 1/4 based on my engine builders recommendation

 

naw man dont go over 2.5 on a n/a that thing just will be loud as ****. wont do anything different realy than the 2 1/4 or 2.5 would do!!

 

rob from pineapple said anything over 2.25 is a waste

 

header is 2.5 and the presilencer is 2.5 you might as well go 2.5 the whole way

 

Guess who built my engine!

 

little elves? naw i know...pineappleracing
i think Rob meant 2.25 after the main cat flange i.e. y pipe because everything else is a 2.5 diameter
I am only running one muffler so i use 2.5 all the way

 

I run 3" all the way back.

Brad

 

ok cool, I think i'll go for 2.5 all the way then....I know I want to get the Dual N1's, but what headers and catback do you guys reccomend? again I want MAX HP....sorry I dont know much, I haven't had any experience with exhaust systems...

 

Dave Wood of Dave Wood Mazda, here In T.O, has been racing 7's for a long time. He Insisted to go to 2.25. He also said, as Banzai aswell, anything more Is a waste.

 

seriously I think the 2 muffler thing is unneccessary on a 13B i mean feel the exhaust pulse out of each muffler very very little at idle you can barley feel it....with a single I notice alot more flow at idle and an increase in torque..

 

really?, hmmm maybe i should go 2.25 then...anyone else care to shed some light on the subject? does he mean 2.25 all the way? because samps said header and presilencer is 2.5... im lost...

 

well, i would go single, but i dont like the way it looks, the rear bumper has 2 indents for dual exhaust, and when it only has a single it looks weird....but then again if it will increase performance then i am definitely willing to go single...if i did go single does anyone know anything about the N1 Titanium?

 

single is lighter too....does really matter how the rear end of your car looks? as long as the dude your racing is looking at it thats all that matters my car looks like *** right now but it'll blow the door off 90% of the cars on the street

 

I just measured the exhaust on my race car. The road race headers are 2" OD (each) from the motor for about 35". They then collect (into a 2.5" OD pipe for about 18" before meeting up with the Apex N1 single (claims to be 54mm? ID). It has a nice rumble at idle and is very loud at WOT.

Because my next car is going to be built to SCCA ITS specifications I have been following that class for a while now. The deep pocket racers in that series spend many many hours on a dyno trying different exhaust setups that will give them the most power between 4 and 8k RPM. Becuase that is time/money they have spent to extract an extra 5hp from their car their exhaust systems are a closely guarded secret. And they are not about to give away a speed secret to a competitor.

The description of one exhaust system I read about that was spied on had very short primary header lengths (the distance before they collect) with a small collector (no specific size given). The ehxuast diameter then slowly expanded to a large size (no specific size given) before contracting into a smaller pipe. It also did not go straight out to the rear of the car. Apparently it made a curve out to the center of the car and curved back to the passenger side before exiting out a standard race muffler. The only thing I can imagine for the change in pipe size is to compare it to the "expansion chambers" you see on the modified 2 stroke motorcycles. If you look at them they can start off at around 1" and expand to what appears to be 8" and then back down to a .5" tip. And the extra curve in the exhaust may be necessary to get the right length to maximize the scavaging (sp) effect for a specific RPM range.

Long story short... if you are looking for "Max Power" it is not going to be an off the shelf part

 

thanks for the info trader, but im no hardcore racer, and its not that big of a deal to spend so much time on getting the absolute most HP possible....i just want the most as to where i can buy it off the shelf.

so is single better than dual? besides the weight?

 

There's no proof that the single makes any more power than the dual other than in true dual exhaust where the duals make another 5-10hp on the top end with considerable loss of torque below 5K.

I'm running the RD street header with custom 2.5" dual all the way out. (some guys use 2.25" in the Y back portion of the duals) I had excellent luck with the setup. Running open flow through mufflers and no cats it is insanely LOUD. I can't rev it over 2700rpm next to a cop without fear of a ticket. EVERYONE knows where I am at all times when I drive it too. I didn't believe my friends untill I loaned it to a buddy and could hear him at every stoplight for a mile. So, I'm curently thinking of ways to mute the damn thing without killing the power.

I'm also thinking about forsaking the N/A and going 6 port turbo now though. One of the main reasons is that my stock computer can't keep up with my street port so I need a new ecu and figure that a turbo will only cost me another 600 bucks and that was what I would be spending on nitrous anyway.

 

My 90 NA has a stright pipe 2.25 from the exhaust manifold to the stock y-pipe and mufflers. It made a big difference up high and down low. Still sounds good. I know someone that has a single N1 for sale with a straight 2.5 pipe from manifold back for $350.00, complete exhaust. Sounds bad *** without being THAT loud. Pm me and I'll give you his info if you want.

 

Id use 2.5, 3 will give you very small gains in top end for very large losses in bottom, not to mention no one makes a fully 3 inch system for NA's. Mazda went with a y-pipe because it reduces noise and the duels looked good. 2.25 would work fine too sacrificing a lil top end for a lil more bottom end, but racing beat and mazda trix preech 2.5 so id go with that