beneEE9

Hey there,
i have been reading here alot that people go in 3" exhaust with all motor builds.
Are there any dyno runs or something that show the differents of these different sizes on the same engine?

I am searching for this because i am planing my custom exhaust on my engine:
B18c5
CP pistons high comp
Portflow b18c1 head full job
Buddyclub internals and spec 6 cams
Jenvey ITB's

what would you guys say?

greetz from germany

TheShodan

iTrader: (14)

Most people here will say 3", in order to get maximum peak power (at the last 1000 or so RPMs) and are worried about dynomometer numbers and drag racing. Being from Germany and the world of smaller, wonderfully "twisty" motorways, and a more universal use of the car, I personally would use the 2.5" to get a combination of the same peak power with a bit more use of the better rpm range. Most street applications need a little bit of back pressure to keep the engine responsive in between shifts are you're going through those wonderful turns.

However, if the purpose is for NA drag racing (something I doubt in Germany) only then would a 3" be warranted.

The posts following mine will more than likely have someone where they said they or their cousin's sister's brother made XX peak HP (then posts the dynomometer chart), and say something in the realm of 3" FTW!!!, or something just as obnoxious.

Think of the use of the car, and apply the right system to it.

beneEE9

thx Shodan
yeah we have nice motorways ;-)
thats what the car will be for. its a good weather car and a tracktool.
thats what i was thinking, 3" sounded very big for me.
i have a bisimoto header with 2,75" and was first planing on a 2,75 exhaust system. or should i rather go to 2,5"?
nnaaa drag racing is not so much here. lots of people who want to, but not enough tracks. most drag tracks here are old airports or other places with shitty streets.
everyone here dreams of tracks like you guys have!
But we have the Nürburgring ;-)
ok back to topic...
any dynos to compare?

96dxB16

I totally disagree on the back pressure. I road race my Honda and have a 3" exhaust. Here is my dyno, I made power everywhere. Keep in mind this is going from a dc4-1 JDM header (2.5" col) with a 2.25" exh to a RMF Narrow copy header and a 3" crush bent exhaust. I can't say how much was from the 3" and how much was from the header.

beneEE9

What are your Mods and what Engine?
Well you have the 2.5 and 2.25 in Front so that gives you backpressure allready.
Anyone Street Racing the complet System in 2,75" or bigger?

96dxB16

Engine is a B18C5 with CTR (PCT) pistons, Blox HSL cams and E85.

00Red_SiR

Mar778c has demonstrated how a 3" exhaust will make more power everywhere, through the powerband, even on a B16a. Backpressure is just another word for restriction. 3" is the way to go, but the exhaust is usually louder than a 2.5" so it's up to the end user to decide which is more important.

96dxB16

I'm running a 22" long resonator with a magnaflow muffler (no cat) and it is not very loud, seems quieter than my 2.25" with no cat, no resonator and similar muffler.

00Red_SiR

long resonators are key...is your muffler straight through? what brand resonator?

DDTECH

VRS true 3'' exhaust piping, with a Solo res 13'' , with a solo muffler, 3'' in and 3.5'' out.

Its quiet at cruising speeds but loud as fk when i get on it.. its tolerable for me because mine isn't a real street car, but i do daily it.

I find, two small resonators will tone the loudness down a bit, rather then one big one, but i didn't have enough run for 2 under my EG.

96dxB16

Muffler is like this one:
http://www.google.com/products/catal...1600&bih=1010#

Resonator is Magnaflow as well

Ya, the single large one takes up a lot of space, i don't think I could fit 2 small ones. The wheel base is even shorter on a Del Sol vs. an EG hatch or coupe.

DDTECH

We actually went with a company who does mostly domestic stuff for our res and muffler setup.. my friend / business partner runs their stuff on his GXP sol and it made a great deal more power and sounded much throater..

96dxB16

Mine was also done by this domestic muffler shop near my house. Def sounds throatier. The 2.25" sounded like buzzing bees at high rpm, this one sounds a lot better and seems quieter (if that's possible?). I'll post up my incar video from this last weekend at thunderhill running this exhaust and another vid using my old exhaust. I haven't listened to the new one yet, so might actually be louder. Hard to tell with a helmet on.

DDTECH

flesh199

guys...look for a dynomax vt muffler if you want to be quiet.I run a 3 inch exhaust with a dtr megaphone header and a dynomax vt 3 inch muffler.Its quieter that my old mugen twin loop...Its insane

beneEE9

yeah but he has a 2,5 col on the header. i was asking about a 2,75" or bigger all the way, from the header col. to the end.
he reached more power, but only 4 NM more then the standert b18c5 engine.

TheShodan

iTrader: (14)

That was pretty much my point. The loss in backpressure wasn't worth the racket or power increase on an NA application. I'm just old.

tianporn

I wish there were some back to back dyno comparisons with 2.5" exhaust tuned vs 3" exhaust tuned. All other factors constant... hmmm

TheShodan

iTrader: (14)

I'm using this from a practical perspective throughout the rev range and the purpose of the car. All a dyno is going to show is exactly what was shown above. One Gear, one rpm, specific conditions, and PEAK POWER. In other words, I never stated that a 3" wasn't going to make more peak power due to the less backpressure, but at the same time, that's all a dyno is going to show. What it won't show is any significant benefit for the type of driving this person from Germany does, taking a combination of good sound and aggressive power throughout the rev range. All that noise and bullshit, for 7-10 peak additional horsepower? Really? Now in a forced induction situation, where 30-40whp is at stake, different story.

This is why I stated for his needs 2.5" to 2.75" what he has is more than enough. He's streeting the car, no circuit racing.

96dxB16

Did you even look at my dyno chart? It does not show just peak HP at one RPM.

Shodan,
Please provide some data to prove your point. I provided my testing results. What do you have besides rhetoric?

beneEE9

Yeah i See it the Same Way. Was just looking if there is any proof for this.
I think i explaned it wrong. I do drive this Car on Track days sometimes.
Greetz

TheShodan

iTrader: (14)

ONE Gear, I didn't say one rpm.

And no, this whole thread lacks anything scientific other than one dyno chart (sorry that I didn't find it the most impressive when others may have), because its not based upon the OP's needs... This was an opinion-based thread. But if you feel offended, you'll be fine once you get over it.

After about 10 years of circuit racing, you come to realize where you are in the cars powerband most, and where you aren't. There's no practical way to show 50mb of data to show use of powerband. So requesting for further "proof" is moot for the purpose of the OP's needs. For the OP, I think he's looking for a balance of power, sound, and utility for his application in Germany.

96dxB16

Oh, you didn't?

No one getting offended her except you since you brought it up.

I have been road racing since 2000, I don't know what argument you're trying to make. If you're saying back pressure is needed, that is false. Proper scavenging from the cylinders is what makes more power which is typically dictated by the design of the header.

I'm just pointing out that you said 3" will make peak power only, which is clearly not the case. My dyno sheet is indeed in one gear, but it is making power throughout the entire rev range.

00Red_SiR

Here is a direct quote from Dave (SMSP):

"Tell me what will happen if I place a tank that is pressurized to 10 psi gage pressure and place it in a sealed room that is at 10 psi gage pressure and then open the valve on the tank? Now what will happen if I take the same tank and put it in a room at standard atomospheric conditions?

Back pressure resists the motion of the piston and thus increases pumping losses and that is bad.

Back pressure can also cause exhaust gases to dilute the new A/F mixture coming into the cylinder and thus decreasing power and that is bad.

Back pressure reduces the pressure difference between the cylinder and the exhaust which reduces the scavenging effect and that hurts volumetric efficiency and that is bad. Volumetric efficiency is maximized when the header and exhaust system actually cause a vacuum in the exhaust port right before the exhaust valve opens to help suck the spent gases out of the chamber.

Why does a stock ITR dyno at 160whp and then after a JDM ITR header (65mm collector vs stock 50mm), a 2-1/2" cat (stock 2") and a 2-1/2" exhaust system (stock 2-1/4" with some bad bottle necks) dyno at 182 whp? I'll tell you it isn't because there's more back pressure.

SMSP - Who, like iloveracing, thought the back pressure myth was killed a while ago.

_______

David Stadulis, Owner



I challenge anyone to show me a dyno graph where ANY power is lost in ANY part of the powerband, from using a 3" exhaust vs something smaller on a Honda All Motor car. This theory about exhaust sizing comes from old school domestic cars people but real life testing has shown the opposite on Hondas at least and probably domestics with properly designed headers.

I run a 2.5" exhaust on my 1.8L vs a 3" because of noise issues and trouble with the law and visual inspections. If it wasn't for that and I could find a decently quiet 3" exhaust that doesn't have a straight through muffler (but still flows like one), I'd install it for the extra power.

TheShodan

iTrader: (14)

Again, we'll just agree to disagree. I'm not at all offended at all in the slightest. I simply believe that a dyno graph such as the one presented doesn't give the whole story in the "entire rev range" for all applications like the OP was utilizing. An exhaust only does not a great car make.

If you must continue this debate, you can always PM me please. Bickering has ended.