imported_magicguy

i just brought an Axle back for my Car
its 2" diameter
no mid pipe , Cat or header
just the muffler part
so...i'm planning on getting a header and a midpipe now to make it a full exhaust system
but i have to get the 2" diameter to fit the Axle back rite?
the header can't be 2"25 or something like that rite?

imported_bevboyy

You should run 2" from the header back. Running 2.5" then have it reduced to 2" is pointless. Unless you are running turbo, 2" will flow more than enough for your needs.

imported_magicguy

so whats the different between 1 piece header or 2 pieces

imported_BoOsTd

just as it says, one piece has no bolts its all welded. 2 piece the collector and downpipe are seaperated (easier to install)

4ever

deleted

imported_magicguy

um...i went to a garage today
i told them i want to order a custom 2" midpipe for my car
they told me that having a 2" exhaust is just the same as the stock one...why bother to change it.......it won't do much...
and i was very dissapointed of what he said...
so..bascially...what should i do now.....?
J.C can u plz come out and discribe about it?

imported_magicguy

i duno wanna spend around 700- 800 to increase 2-3 HP
thats useless
i rather get a Header cost me 600 and get about 7-8 horse power increase at least

cibs

magicguy... IMO if you have 2" at the muffler, what's the point of having a larger midpipe? if you go out to 2 1/4 at the header, go 2 1/4 all the way back no? i'm no engine expert but if you have a smaller diameter at the end of your exhaust you'll bottleneck and you'll still have higher backpressure...

imported_bevboyy

magicguy, your stock exhaust is 1 5/8 - 1 3/4 diameter. Your muffler installer is wrong. That extra 1/4 inch diameter will flow better. You do need some back pressure in your system to keep the scavenging effect in check. What is important to keep in mind is that you trade off torque and off the line performance when you increase the diameter of your piping. When you go 2.25 you lose bottom end, and if you go 2.5 you lose more and develop a nasty flat spot from 3000 rpm to about 4500 rpm. What this translates to is if your driving style is one who likes to keep the engine in "vtec land" often - and I do mean often, you can go larger diameter. If your driving style is like most of us, a combination of everyday street putting around and the occasional "blast out the carbon" then the 2" application will be a better overall performer. Remember the key word here is OVERALL. There is a whole wack of data,easily found on the net substanciating this theory.

Let me further clarify that the 2" diameter is compromise over the 2.5" With 2" you do gain better bottom end off the line response - which you notice most, but when you are around 4500 - 5500 rpm you will not have that much of an upper hand than running 2. 25 or 2.5.

It's a system - you MUST couple this with a well designed header and a free flowing resonator in order to reap the benefits (Ask Mourad - he's proof). Just putting on a header, but leaving your stock resonator will do SFA for you.

imported_magicguy

ic...so..just put on a header and leave the stock midpipe there? should i custom make one?

punkindrublic

dont forget to get a larger cat if your increasing the pipe size

imported_magicguy

SIR cat coverter is a 2" inlet & outlet and muffler is also 2" inlet
found it on Honda's 2000 SIR spec page..so....confusing now

imported_bevboyy

Magicguy...no worries. The SiR is blessed with a relatively high flow cat. You save $$$ here. Catalytic convertors are usually high-flow in design from the get go.

The most restriction found in your system is in the exhaust manifold, stock resonator and stock muffler. Majority of the restriction is in the resonator and the muffler secondary...

Your situation is simple. Use a good header. Use your SiR cat. If the mid pipe is 2" - keep it. Get a hi flow resonator, and then use that twin loop..

You've got nothing to worry about..

Chigga1

SIR's running a 2" exhaust from header.

going 2" is pointless for what???? i just did mine.
2 1/4" stainless from header back....

my 1 piece 4-2-1 DC header was not a biatch to install at all, they did it fine, goes through a high flow magnaflow cat and through the midpipe with no resonator to the magnaflow muffler...

its loud as fukkkkk.... im putting a resonator on it. make sur u do it especially with the ERASE program happening

imported_bevboyy

It totally depends on how you drive (as I mentioned before..)

I took this from Honda Tech as it was very susinct...

"Exhaust pulses at low rpm travel faster in a smaller exhaust pipe- which would create a vacuum behind each pulse- the faster the exhaust gas pulseses travel, the more vacuum is produced. Each pulse creates a vacuum for the next pulse- which would "pull" the next exhaust pulse behind it. This is effective at low rpms only because as engine speed increases- the exhaust becomes restrictive and the vacuum effect doesnt help because the exhaust pulses are pushing each other instead of pulling. With a bigger exhaust- the opposite happens- at higher RPMs the exhaust begins to create larger vacuum pulses at a certain point- incresing efficiency. At low rpms the exhaust doesnt travel as fast in a larger pipe so the vacuum is not as strong"

Ergo...

Low rpm's = less air, which necessitates a smaller pipe for it to actually flow reasonably fast, flowing fast being good for the reasons that are described.

High rpm's = more air, which would try to flow way too fast though a small pipe, creating too much restriction. Therefore you want a larger pipe.


As I have said - if you are using your car as a daily driver and you spend the majority of the time doing spirited highway and city driving, then 2" will function very well.

If you so choose to drive your car - constantly at 4000 rpm and above, then a larger diameter pipe would be necessary.

"Backpressure is bad. Smooth exhaust flow is good. Too small exhaust diameter is bad. Too large exhaust diameter is bad."

That is why I mentioned an "overall" use. Pipe diameters are always a compromise of best overall performance in context of need.

I can only speak from my own personal experience here as I do my own exhausts.

imported_bevboyy

Also to further the debate - a quote from SCC


"What engines need is low backpressure, but high exhaust stream velocity. A fast-moving but free-flowing gas column in the exhaust helps create a rarefaction or a negative pressure wave behind the exhaust valve as it opens. This vacuum helps scavenge the cylinder of exhaust gas faster and more throughly with less pumping losses. An exhaust pipe that is too big in diameter has low backpressure but lower velocity. The low velocity reduces the effectiveness of this scavenging effect, which has the greatest impact on low-end torque.
Low backpressure and high exhaust stream velocity can be achieved by running straight-through free-flowing mufflers and small pipe diameters. The only two exceptions to this are turbocharged engines and engines optimized for large amounts of nitrous oxide. Both of these devices vastly increase the exhaust gas volume and simply need larger pipe to get rid of it all.
Some stock mufflers and exhaust systems have up to 18psi of choking, power-robbing backpressure. In direct contrast, a well-designed, high-performance street exhaust system typically has about 2-6psi of backpressure. For an interesting comparison, an un-muffled straight pipe on a "real racecar" usually has 1-3psi of backpressure."

Also...optimal diameter sizing based on displacement (Normally Aspirated - non turbo/supercharged)

1,500cc - 2,000cc = 2-inch
2,100cc - 2,500cc = 2.25-inch
2,600cc - 3,000cc = 2.5-inch

here endeth the lesson...

imported_magicguy

ic....so...where can i get a good header outside?
which is the 2 inch one to fit my catback
any suggestion?

imported_magicguy

btw, i learned a lot from u ^^