has anyone run 3 inch exaust on there all motor application?
just wondering..have they seen benifit, i don't want to know if 2.5 inch is enoughi just want to know if 3 inch has been used.

 

i know a couple of peopel that had three inch thermal research exhaust when they were turbo and have since switched to N/A. It works fine. A little loud, but fine. Seems a bit sluggish off tthe line to- no back pressure at all.

 

unless you have 230 whp or more a 3" exhaust would give loss all the way to redline. the highest i seen was 2.75 and that motor was dyno at 245whp. 2.5" is the perfect setup of course only if you have a 2.5"-3" header collector or else you would loose power.

 

you know of people that have seen a loss going from 2.5 to 3 inch?
unless you have something to back that up i don't see that happening.

 

i was wondering the same for my setup ...i was think that 2.5" mite not be enough ...ill have to look into this more ...

 

if i remeber correctly didn't "lip" have a 3inch exuast on his teg??

 

You would NOT lose power going from 2.5 to 3 inches. You would lose some lower end torque and maybe some mid range horsepower due to lack of back pressure but the top end may benefit slightly.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by asubennett &raquo;</TD></TR><TR><TD CLASS="quote">You would NOT lose power going from 2.5 to 3 inches. You would lose some lower end torque and maybe some mid range horsepower due to lack of back pressure but the top end may benefit slightly. </TD></TR></TABLE> I don't know about 3" pipes and if there is a negitive or positive effect on an all motor Honda engine, but I do however know there should NEVER EVER be ANY backpressure in your exhuast! That is one of the biggest myths about exhuasts it's all about flow, and the speed of it.....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92 civic VX B18c &raquo;</TD></TR><TR><TD CLASS="quote"> I don't know about 3" pipes and if there is a negitive or positive effect on an all motor Honda engine, but I do however know there should NEVER EVER be ANY backpressure in your exhuast! That is one of the biggest myths about exhuasts it's all about flow, and the speed of it..... </TD></TR></TABLE>

Werd.

You don't see race cars running exhausts do you?
I'm going to be running a open header with a qtec on the street. You think I will loose horsepower open header?? I'll bring you a dyno in a few weeks.

 

you wont lose power due to a decrease in back-pressure, you will lose power because of the loss of exhaust velocity

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92 civic VX B18c &raquo;</TD></TR><TR><TD CLASS="quote"> I don't know about 3" pipes and if there is a negitive or positive effect on an all motor Honda engine, but I do however know there should NEVER EVER be ANY backpressure in your exhuast! That is one of the biggest myths about exhuasts it's all about flow, and the speed of it..... </TD></TR></TABLE>

i couldnt agree more, i think what people are unconciously refering to as 'backpressure' is more of a scavenging effect created by exhaust pulses, this is similar to what takes place in 2 stroke engines and in 4 strokes using valve overlap. what happens is as intake charge passes into the cylinder the pressure forces the exhaust out, and the vacuum created by the exiting exhaust in-turn pulls in the intake charge, when this is applied to exhaust its all about timing the exhaust pulses, i guarantee if you were to ask any major header retailer what they consider in designing a header they would tell you among other things timing the exhaust pulses, so that one pulse that is moving down the header helps to 'pull' another pulse out, this can continue down the exhaust pipe effectivly increasing efficiency, i realize this is mostly in layman's terms so if anyone wishes to correct or elaborate, please do

 

You guys.........

There is an optimum velocity to make the most horsepower. You want those exhaust gasses moving fast. By increasing the diameter of the pipe, the same amount of air moving at that particular RPM, the velocity will be slower, hence the loss of power towards the bottom end of the powerband.

If you guys switch to a 1.75", the air would be moving really fast at lower RPM (hence more power down low), but at higher RPM, it's a restriction (hence lose power).

That's why boost makes power w/ a 3" exhaust. It's due to the fact that it's moving more air (compressed air) than an N/A engine of similar setup and of the same RPM.

Think of it as a straw. Drink out of a big straw, and you'll see the liquid move slower than drinking out of a small straw. But try drinking out of a coffee straw, and hence why too small is bad. Drink out of a big boba straw, and the liquid flows slower.

 

although i agree with some of the things you are saying .

"If you guys switch to a 1.75", the air would be moving really fast at lower RPM (hence more power down low), but at higher RPM, it's a restriction (hence lose power)."

this is wrong as anyone that has dynoed there car with there exhaust on and straight pipe will tell you that it makes more power with the exhaust off everywhere even at 3000 rpm.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by cpforyou &raquo;</TD></TR><TR><TD CLASS="quote">You guys.........

There is an optimum velocity to make the most horsepower. You want those exhaust gasses moving fast. By increasing the diameter of the pipe, the same amount of air moving at that particular RPM, the velocity will be slower, hence the loss of power towards the bottom end of the powerband.

If you guys switch to a 1.75", the air would be moving really fast at lower RPM (hence more power down low), but at higher RPM, it's a restriction (hence lose power).

That's why boost makes power w/ a 3" exhaust. It's due to the fact that it's moving more air (compressed air) than an N/A engine of similar setup and of the same RPM.

Think of it as a straw. Drink out of a big straw, and you'll see the liquid move slower than drinking out of a small straw. But try drinking out of a coffee straw, and hence why too small is bad. Drink out of a big boba straw, and the liquid flows slower. </TD></TR></TABLE>

Well said..... This is what it boils down to. So yes, you will see a loss of power and torque if your exhaust is too big for your setup. The only way to ever find out for sure just HOW MUCH you will be losing would be to dyno your car with the 2 different exhaust sizes on. But as a rule of thumb, I've always heard that cars that are under 250 hp (flywheel) should stick to 2.5 inch. Any higher than 250 and a 3 inch would probably be more beneficial. But once again, the best thing is to actually get your car dynoed.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by AllMotorMark &raquo;</TD></TR><TR><TD CLASS="quote">although i agree with some of the things you are saying .

"If you guys switch to a 1.75", the air would be moving really fast at lower RPM (hence more power down low), but at higher RPM, it's a restriction (hence lose power)."

this is wrong as anyone that has dynoed there car with there exhaust on and straight pipe will tell you that it makes more power with the exhaust off everywhere even at 3000 rpm. </TD></TR></TABLE>

SMSP says otherwise.

 

well i can tell you every car i have dynoed with the exhaust on then exhaust off made more power even down low

 

**** ive seen charts on an internally STOCK b16 where 2.25 and 2.5 exhausts were used.....guess which one made more power throughout the entire rev range including at 2500 rpm?

now tell me a smaller exhuast makes more power down low.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by AllMotorMark &raquo;</TD></TR><TR><TD CLASS="quote">well i can tell you every car i have dynoed with the exhaust on then exhaust off made more power even down low </TD></TR></TABLE>

I dont know about everything else, but I agree with this. Every time some guy on the dyno makes 195-198whp with a 2.5" exhaust. The first thing they do is drop the cat-back so they can try to reach the magical 200whp mark... Works like a charm every time.

Race cars run open header for a reason. And who cares about power at 2500rpms? I know that when I race my motor NEVER EVER sees 2500rpms. What's the importance of power @ 2500rpms? A 220whp 2.0L motor with high compression will have more then enough power to get you around at 2500rpms whether it has a 1" exhaust or a 4" pipe.

 

.....IMHO, bigger is better.

Open header makes more power than any exhaust in my experience:

https://honda-tech.com/zerothread?id=213963

As for 3" exhaust; go for it. Leaves you room to grow.....

MINIMUM of 2.5" for allmotor - even a b16, imho.....

 

I run 2.75 till my cat and 3 from the cat back on my crx. I have no problem making power down low.

 

Back press. is a MYTH.
I run 3" on my car and it works great, I've ran the same times with or without exhaust.

 

A slightly bottlenecked exhasut will fell and drive better for everyday driving. For all of you guys running straight pipe and 2.5 inch exhuast go put your silencer in the muffler and tell me what 0-4000 rpms feels like. It will significantly "slow down the speed" of the exhaust- if thats what you want to call it. I'll call it backpressure- and the car will fell more responsive but then up high 4500- and up it feels choked off. It is all relative. I think 2.5 is the perect compromise for low and high rpm ranges but open header would be best for the track. And for those who say restrictions in exhaust is not considered backpressure- define backpressure as websters does and it is referring to exactly what is happening inside your exhaust pipes.

 

t- bone and nonvtecallmotor,

have either of you tried other exhaust setups?
really curious

 

There's really no need to test all kinds of exhaust if you can stand the noise open header is the most power that you can ever get from your motor. 3in is only 1-2 hp diff. from open header and thats nothing. Theres no such thing as back pres. theres no gain or loss in lowend power ether.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nonvtecallmotor &raquo;</TD></TR><TR><TD CLASS="quote">There's really no need to test all kinds of exhaust if you can stand the noise open header is the most power that you can ever get from your motor. 3in is only 1-2 hp diff. from open header and thats nothing. Theres no such thing as back pres. theres no gain or loss in lowend power ether. </TD></TR></TABLE>


.....everything here is dead on.


Ideally, the "perfect" exhaust would be the same size as the outlet of the header and gradually increas in larger diameter till exit. Ex: 2.5" header collector, to 2.5" piping, increasing to 2.75" piping, increasing to 3" piping, and finally ending in 3.5" piping and muffler. I'll see if I can dig up the article.

And once again for those saying you'll lose "backpressure" or low end, I have dyno'd back to back and found the opposite to be true. GAINS EVERYWHERE IN THE POWERBAND WITH OPEN HEADER.