Exhaust Guru

[free2d]

Hi,

Got a question about the catback system.

Why some catback like 5Zigen, Spoon have tappered shape from the inlet flange of the cat-converter?

Does the reduction in size in the inlet decrease power and flow?

Thanks.

[LSD Motorsports]

Hi,

Got a question about the catback system.

Why some catback like 5Zigen, Spoon have tappered shape from the inlet flange of the cat-converter?

Does the reduction in size in the inlet decrease power and flow?

Thanks.
Hey there mate,
not sure if i understand exactly what you are saying, but if your asking why the exhaust systems such as 5zigen or spoon have reducers it can be for a few reasons. Most of the time, the majority of exhaust manufacturers make what makes sense to the majority of the market. Meaning a nice tone thats not to loud, a nice finish, a reasonable price and a fairly easy install. Well, often times in order to meet these requirements, they have to use small piping then ideal for clearance and fitment issues. There will also be times where the exhaust is much bigger then the outlet of the cat converter which doesnt hurt anything as far as flow, however if the exhaust is to big, you will reduce back pressure to much or to nothing which can have a negative impact on performance. So basically what im saying is, if your exhaust system is not the same size throughout the whole thing, it is ok. The important things are to minimize turbulence and not disrupt flow.

Cheers

[preludacris]

umm

i'm pretty sure it tapers down, for the sole reason, so that it can fit stock cats. Not everybody buys a catback system and also upgrades the cat and even header.
when they do get a bigger cat, they just cut the tapered part off, and reweld.

[VT3C]

free2D I think some might have misunderstood what you meant.. it tapers AFTER the cat convertor.

http://www.tokyo-express.co.uk/spoon/exhaustpipe_b.jpg

If you look at the SPOON Exhaust B-Pipe for DC2 (from their catalogue), you'll notice going into and out of the mid-resonator the piping appears to bottleneck..then comming out of the resonator it increases diameter again before tapering down again for the axle-sextion.

I too was wondering about this as I dont want to spend ~$1k on an exhaust system and find that it makes less power than my old (custom) system..

[free2d]

free2D I think some might have misunderstood what you meant.. it tapers AFTER the cat convertor.

http://www.tokyo-express.co.uk/spoon/exhaustpipe_b.jpg

If you look at the SPOON Exhaust B-Pipe for DC2 (from their catalogue), you'll notice going into and out of the mid-resonator the piping appears to bottleneck..then comming out of the resonator it increases diameter again before tapering down again for the axle-sextion.

I too was wondering about this as I dont want to spend ~$1k on an exhaust system and find that it makes less power than my old (custom) system..



Thanks for the clarification VT3C.

If you look at Spoon Catalog under exhaust. The N1 kit, the pipe to the cat is tappered. Thats is what I meant.

Any reason why they do that?

[sivic]

honestly after looking at a few off the shelf catback systems i would definately choose a custom system.
the biggest thing i've noticed is the restriction in the resonators with the off the shelf systems. many taper down to 2" inside the resi, and on top of that have fins sticking out into the passage. this reduces the overall straight through cross sectional area in the resi's to about an inch. my brother had the resi's on his tanabe system replaced with 2.5" ones. the difference in top end was very noticeable.

[bennjamin]

the taper is probably for a backpressure aim ~ for bottom/mid range performance rather than all out top end ?

[nipnip]

the taper is probably for a backpressure aim ~ for bottom/mid range performance rather than all out top end ?

yep... thats what i thought too, PROBABLY why my vision catback makes vtec kick in with a noticable BANG and a lil pull (compared to my mates fujitsubo that is)... again i stress the word probably...

[free2d]

I got this reply from another forum.

"Tappered shape is to help push the exhaust gases through, thus giving it a higher flow rate."


What do you guys think?

[silver_screen]

that sounds silly

That would only decrease air flow as a speed. think about it.. ur blowing through a tiny redrooster straw as hard as u can.. ur straining, but the speed of the air comin outta the other side is pretty fast... not much air volume. but speed wise its fast.... put a fat maccas straw on the end of it.. ull notice that "less" air seems to come out.. its just that the speed has slowed because it has to fill a great volume of space and when u do that.. it slows down... so it doesnt have to get exhaust gas out....

Custom systems are always the way to go because they dont have anyone else to please but u. so it will do exactly what U want it to do. It doesnt have to meet any laws or anything like that. Off the shelf types are all made to suit a greater no. of ppl, so they will be quieter and have more low/midrange kick due to those taper things.

I personally wouldnt get one. Ive got a custom system in my civic and i love it

[sivic]

uh that last post kind of contradicted itself (That would only decrease air flow as a speed. think about it.. ur blowing through a tiny redrooster straw as hard as u can.. ur straining, but the speed of the air comin outta the other side is pretty fast... not much air volume. but speed wise its fast)

anyway, free2d - thats basically true. it would increase the gas velocity of the exhaust at certain parts of the rev range.
as is usually the case with these sorts of things its a compromise. in this case the taper is probably to optimise torque at lower/mid range.

either way, in my brothers case the benefits recieved in top end power far outweighed the slight loss of lower end torque (on a DC2R).

[90LAN]

i would only get a custom exhaust if there wasn't one i could by of the shelf!
why would one of the best honda tuners design something that was going to lose power? they improve on the design, in this case the spoon one has oem fitment, has a nice sound to it, and is lighter than the factory one! if you check the original spoon catalog it actually shows the flow rate of the n1 axle back over the original. try getting your exhaust shop to do that!!
by the way im running the spoon N1

[EGB18CT]

its tapers pruely for the reason of back pressure. Spoon does this so they maintain mid power. Otherwise if your looking at drag racing ur car, u want the top end so the bigger un-taperd exhaust will help in this case the downfall being losing some lower end power.

Kinda like if u want the 4-2-1 headers for low to mid or the 4-1 for all out top end.

I belive honda have taped down some of their exhausts around the header flange to aid a bit of back pressure but i could be wrong. I believe vtec engines love to breathe so if you are custom making it use mandrel bends and as few bends in it as possible. If u want it quiet put one or two resenators in it but ull lose a bit of power otherwise dont run any and it be massive loud!

[sifoo]

Guys dont kid yourself

The reasons why there would be tapers in an exhaust system is to save time and money when welding them.

[sivic]

i would only get a custom exhaust if there wasn't one i could by of the shelf!
why would one of the best honda tuners design something that was going to lose power? they improve on the design, in this case the spoon one has oem fitment, has a nice sound to it, and is lighter than the factory one! if you check the original spoon catalog it actually shows the flow rate of the n1 axle back over the original. try getting your exhaust shop to do that!!
by the way im running the spoon N1

lol. the JDM marketing has made its mark. don't believe all you read in such catalogues. if we all took it as gospel we'd all have little gadgets like the top fuel power neo's on our cars in the belief we'd be making power.
a lot of these companies put a lot of consideration into making exhausts reasonably quiet as well, hence they make a compromise between performance and being able to live with the noise.
i'm sure the spoon N1 does an ok job but theres no reason a decent local exhaust fabricator can't match the performance.
in regards to other brands i've seen back to back comparisons on dyno's showing locally made systems making significantly more power.
frankly i think ppl get too bogged down on what catback they're running. imo the focus should be on the header.

[TODA AU]

Guys dont kid yourself
The reasons why there would be tapers in an exhaust system is to save time and money when welding them.
Ditto... :thumbsup:

lol. the JDM marketing has made its mark. don't believe all you read in such catalogues. if we all took it as gospel we'd all have little gadgets like the top fuel power neo's on our cars in the belief we'd be making power.
a lot of these companies put a lot of consideration into making exhausts reasonably quiet as well, hence they make a compromise between performance and being able to live with the noise.
i'm sure the spoon N1 does an ok job but theres no reason a decent local exhaust fabricator can't match the performance.
in regards to other brands i've seen back to back comparisons on dyno's showing locally made systems making significantly more power.
frankly i think ppl get too bogged down on what catback they're running. imo the focus should be on the header.
Give that man a New... :thumbsup: :thumbsup: :thumbsup:

[free2d]

Bro Toda,

So you think all these are crap? Tappered or not tappered doesnt matter at all?

Toda dont make exo fot CL7?

[sifoo]

english?

[sivic]

tapers are not needed in the catback section. it's mainly a fitment and noise issue.
a lot of these companies put a large emphasis on noise levels and will do what they can to achieve "accpetable" db readings so they can get their coveted JASMA badge and therefore help get more systems out the door.
the ol' JASMA approval is a big selling point in this market, however if you have a good look you'll see a lot of the genuinely better products/brands out there (one in particular) don't actually carry the badge of "approval".