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Discussion Starter #1
Here's my build I going to have d16z6 with p29 pistons bizi stage 2 cam skunk intake manifold aem short air intake lite weight flywheel and act stage 2 clutch dc sport 421 single peace header but this could change if the engine needs more beathing room to a b series rewelded with a d series flange.

My question is should I use 2.25" or 2.5" mandral exhaust from catback it's going to be custom with a straight thro muffler. I should also mention that this is going to be a dd street car.
 

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thats about the dumbest answer ive ever heard and you didn't outline why you gave that asinine answer. unless he goes turbo. he wont need more than 2.5. even with a B series. 2.5 will be the max for what he is looking to do. especially with a SOHC motor. 2.5 will be perfect on a N/A B with some mods
 

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thats about the dumbest answer ive ever heard and you didn't outline why you gave that asinine answer. unless he goes turbo. he wont need more than 2.5. even with a B series. 2.5 will be the max for what he is looking to do. especially with a SOHC motor. 2.5 will be perfect on a N/A B with some mods
I have read with a good tune 2.5in catback can be beneficial for a NA d-series without too much shift of power away from the lower rpms.

If I were you OP I would go with 2.25in it is a same medium till you know exactly what your motor wants.
 

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thats about the dumbest answer ive ever heard and you didn't outline why you gave that asinine answer. unless he goes turbo. he wont need more than 2.5. even with a B series. 2.5 will be the max for what he is looking to do. especially with a SOHC motor. 2.5 will be perfect on a N/A B with some mods
Why? Why 3" too much? What makes 2.25 or 2.5" so much better?
Why why why? :wacko:
 

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thats about the dumbest answer ive ever heard and you didn't outline why you gave that asinine answer. unless he goes turbo. he wont need more than 2.5. even with a B series. 2.5 will be the max for what he is looking to do. especially with a SOHC motor. 2.5 will be perfect on a N/A B with some mods

IIRC bizimoto reccomends 3" for n/a d series
 

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http://www.d-series.org/forums/naturally-aspirated/131750-na-theory.html for reference. The last 2 civics I had for daily drive with simple bolt-ons (IEH) I kept with 2.25" mandrel for sound quality and peace of mind. All depends on you and the sound difference. Is your car slammed? I believe 2.5" hangs a tad lower and if don't mind grinning when you scrape if that's the case. Either one would be fine though IMHO. =) Pictures!
 

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http://www.d-series.org/forums/naturally-aspirated/131750-na-theory.html for reference. The last 2 civics I had for daily drive with simple bolt-ons (IEH) I kept with 2.25" mandrel for sound quality and peace of mind. All depends on you and the sound difference. Is your car slammed? I believe 2.5" hangs a tad lower and if don't mind grinning when you scrape if that's the case. Either one would be fine though IMHO. =) Pictures!
This, I smell exhaust now casue I went too big and scrapped, may have torn my flex, or resonator. Just be sure you go wth what works if this is a daily, or you will fix it more then enjoy it.
 

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http://www.d-series.org/forums/naturally-aspirated/131750-na-theory.html for reference. The last 2 civics I had for daily drive with simple bolt-ons (IEH) I kept with 2.25" mandrel for sound quality and peace of mind. All depends on you and the sound difference. Is your car slammed? I believe 2.5" hangs a tad lower and if don't mind grinning when you scrape if that's the case. Either one would be fine though IMHO. =) Pictures!
Problem is, link says nothing about header/collector design for a NA engine..
Not to mention, it's one of those "CAI make more power cause the air is colder" threads..
 

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Discussion Starter #10
So form the post so far you all think 2.5 and it dosent pull to much from the lower rpm but I'm definly not useing 3" because you lose to much volicety running thro the pipe if I was turbo maybe because you flowing twice as much or more air and this is a street car not a strict drag car and I like road corse running so lowend is a little more desired.

What do you all think of the b series header with a d flange the dc sport header I have now has 1 5/8" primary runners most b series have 1 3/4" runners and if I got the b series it would be a 4 to 1 with a 2.5" collector
 

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he will make more power with 3" than 2.5"

maybe not much, but it will make more power.

it will also be a fuck load louder

So form the post so far you all think 2.5 and it dosent pull to much from the lower rpm but I'm definly not useing 3" because you lose to much volicety running thro the pipe if I was turbo maybe because you flowing twice as much or more air and this is a street car not a strict drag car and I like road corse running so lowend is a little more desired.

What do you all think of the b series header with a d flange the dc sport header I have now has 1 5/8" primary runners most b series have 1 3/4" runners and if I got the b series it would be a 4 to 1 with a 2.5" collector
you got it all wrong man.

the collector and header is where the power is made. that is the most important part of the exahust. after that, you want it as EASY as possible for the exhaust to get out. 3" will show nothing but improvements over 2.5
 

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danz the man. i can concur with the concept of "fuck load louder" :sweatdrop:

he will make more power with 3" than 2.5"

maybe not much, but it will make more power.

it will also be a fuck load louder



you got it all wrong man.

the collector and header is where the power is made. that is the most important part of the exahust. after that, you want it as EASY as possible for the exhaust to get out. 3" will show nothing but improvements over 2.5
 

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To simplify the NA theory if its a handful to read, it sums up to this.

Here's a nice test, get a stock civic and have a 4" fart can installed in place of the stock muffler. Notice how a good bunch of your low end has disappeared. Why? Picture two hoses. One is a small 1/2" diameter while the other is a whopping 3". Now lets hook them both up to a faucet. When you fully open the faucet on the 1/2" hose, you get a nice jet of water shooting out the other end. Whereas if you use the same faucet and hook up a 3" hose, you get a slow stream that dribbles out. The jet vs dribble represents the gas velocity between stock and a large diameter exhaust system. 1.6's don't even need anything beyond 2.5 because they can only produce so much exhaust! Period. I don't even think Bisi or any race motors of the same displacement even go beyond 2.5. If they don't, doesn't it tell you something?
 

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Ah, but what happens when they re-tune the car with a 2.5-3" exhaust?

You see, I asked a similar question recently, as to why you 'lose' power with a big exhaust:

sxysweed said:
Thread:
exhaust setup for mini-me w bisi level 3 - onecamonly.com

Post:
"No, it's because going to a larger exhaust tends to lean out lower RPM fueling quite extremely, which causes a loss in torque. It comes back and gains with the fuel properly tuned. It's a function of having a excellent collector, and it doesn't hurt that you have a large cam, too."

Why does the engine lean out at low RPM when you run big exhaust (or a better collector)? Better scavenging? If so, why wouldn't it go lean at high rpm too?

The_Acid_Beaver said:
Time. There is more time for air to move in an out of the engine at lower RPM. The VE is typically higher at lower RPM. A large exhaust with a good collector exacerbates that problem.

For example, I am tuning a REAL high compression A6 now. (It is currently over 13:1 SCR. On pump gas. heh) It has a Bisi header and a good sized exhaust. I have to tune in 5+% more fuel below 2500RPM to prevent it from leaning out.... Anyway, there is a distinct low RPM bump in the fuel map with that engine. I suspect that it is the same with almost any D-series (and probably other Honda engines) as well.

I first became aware of this tendency when a friend of mine tested a 3" exhaust on his ZC (DOHC type, and back then, "ZC" WAS the DOHC . . . it's so confusing today), which was originally set up for the JRSC. (He ran a lot of autocrosses and road races, and there weren't so many turbo options that would be considered reliable and powerful.) He had access to a dyno for work, so, when he sent his JRSC to Endyn to get it modified, he did some experimenting. He hated how weak the engine felt with the BIG exhaust side (kamikazee header, modified, 3" all the way back) and was going to put a more normal H/E combo on the car but decided to try to tune back some of the power. He did, and more. He was running very lean, and that Kamikazee header was not the best for a NA engine by any means. After he tuned out the lean spots (ZDYNE Gold!), the engine felt stronger than stock (He had never dyno'd it stock) and gained 3-5ft/lbs back, which is pretty darn significant.

I'll say it again: exhaust sizes don't matter much as long as you have a good collector, and the exhaust size isn't too small to choke the collector. With a good collector, bigger is better, as long as it isn't too loud. As far as "good" collectors go, I mean a properly made 4-1 merge collector with a good choke built in, or a 4-2-1 with properly sized primaries and merges that take into account the increasing volume needing to be moved with each merge. (I prefer the long primary 4-2-1 design.)
 

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I was referring to his paticular setup. He wont need to go over 2.5 because this is considered a mid range DD build. not a mid turbo build. there are plenty of guys running 3' piping but they have 2 thing going for them. either no bottom end whatsoever or they are tuned for ultra high RPM's. just my experience. ultimatley it will come down to the tune that will determine if a 3 in exaust will be benificial for a 3 in or better for a 2.5. What he should really do is modify the collector on that DC header. that will give hime the biggest improvement. I wonder why they haven't redesinged their collector for this reason. that would give them the credibility that I grew up on.
 

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To simplify the NA theory if its a handful to read, it sums up to this.

Here's a nice test, get a stock civic and have a 4" fart can installed in place of the stock muffler. Notice how a good bunch of your low end has disappeared. Why? Picture two hoses. One is a small 1/2" diameter while the other is a whopping 3". Now lets hook them both up to a faucet. When you fully open the faucet on the 1/2" hose, you get a nice jet of water shooting out the other end. Whereas if you use the same faucet and hook up a 3" hose, you get a slow stream that dribbles out. The jet vs dribble represents the gas velocity between stock and a large diameter exhaust system. 1.6's don't even need anything beyond 2.5 because they can only produce so much exhaust! Period. I don't even think Bisi or any race motors of the same displacement even go beyond 2.5. If they don't, doesn't it tell you something?


you are not correct. your analogy is flawed. you appear to have no real world experience.

when will this back pressure myth DIE?! UGH!!!!! :3dtard:
 

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Discussion Starter #20 (Edited)
so you think that i should cut the tail off of my dc header and re weld a 2.5" collector to the end of it and new o2 bung and finish the exhaust with 2.5"

The car is going to be tune with crome gold by a good friend of mind he also told me to get a b series 4 into 1 long tube header and run 2.5" exhaust but i really enjoy the bottom end torque for a good street car that one reason I also have a conquest/Starion because 255 ft/lb at 2500rpm is really fun. Which we are going to convert to run on crome with a Honda dizy

I also want it to be fairly quiet because I drive though a town with cops itching to give any random person a ticket
 
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