I'm just curious on what people's opinions on exhaust size is for all motor applications. Car is a weekend street driven car and track ***** at the same time.
I'm not worried about noise level at all. My main concern is usable power in a drag race application (from 7k to about 9k).

What would you recommend for a motor setup like this:
Lsvtec
89mm crank, 1.8L
12:1 compression
ported/polished B16 head (race spec)
BC4 cams
ITR manifold/ITR TB/3 inch SRI/velocity stack

Or what about the same motor above, but w/ an 85mm bore, 2.0L

-Both motors will rev to 9k.

Generally, all motor guys (including myself) run complete 2.5 inch systems. 2.5 inch collector on the header, 2.5 inch flexpipe, 2.5 inch cat, 2.5 inch piping, 2.5 inch resonator, to a 2.5 inch muffler. But who the hell decided 2.5 was the best for ALL allmotor applications? It seems to be the general consensus...but just questioning why. Is it something we've all just come to accept and haven't put any real thought into it? For the REAL all motor guys, it's either 2.5 inch exhaust or open header. That's it. I was just toying around with the idea of upgrading to a header w/ 3 inch collector and complete 3 inch exhaust including the flexpipe, resonator and muffler. Is there more power to be had w/ running a 3 inch complete exhaust over just running open header? I mean, there should be a fine line where running a complete larger exhaust would make more usable power than an open header right since it would still at least help w/ scavenging exhaust gases somewhat? I mean, I think it would be interesting to do a dyno comparison of a car with a similar motor as the one above or even just an ITR motor, and do both open header, 2.5 inch exhaust, and 3 and 3.5 or 4 inch exhaust comparisons. It's a well-known fact that tuning header length and collector size can greatly affect power output, but what about larger exhaust piping w/ a matching larger collector? We've all tested different size intake piping diameter and length, different size header primary diameter and runner length, different size collectors, etc. But no one has really tested exhaust size on an all motor application versus open header, at least not anything above 2.5 inch. I know a test like this could only happen in my dreams though as that could get very expensive.

What would be better for power? It would be cool to get guys like RMF (even though he's now banned) and Dave @ SMSP in here or any other exhaust/header experts. Or if anyone has any dyno sheets of allmotor cars that went from 2.5 to 3 inch complete exhaust.

TIA.

 

every big allmotor setup run 3in exhaust.I would like to know what smsp have to say about this question..

 

Not necessarily, 2.5" is fine for all motor, I guess with NA motors the larger the piping diameter there tends to be a loss in TQ but slight gains top end.

anyone else want to chime in?

 

I would also like to hear some quality feedback on this. What about for a 89x95 H22? Does bore and stroke play a big part in exhaust piping diameter requirements? I'm running an RMF header and in the process of building a 2.5" system with ES oval, should I go with 3" instead?

 

I think the reason why so many people use the 2.5" exhausts is because most of the Honda Engines have similar displacements, rev ranges and make power in similar fashions. It's not like we have domestic small blocks that vary greatly in engine displacement, rev ranges and the types of things they are used for (towing vs. racing). For "us", 2.5" is the best size for power on most built B-series engines. A 3" exhaust might give slightly higher peak numbers on some engines but it's usually at the expense of lower/mid-range power. Everyone knows that it's usually the car with the greatest amount of average power that beats the car with the highest peak power. From my experience a 3" exhaust on a Honda is overkill unless you're running a decent turbo setup.

 

2.5 inch is more than enough for an all motor car. I am still waiting for suggestions on the proper muffler to purchase. Im in the same area looking for a good 2.5 inch exhaust. The easy way out is to say hytech - but they arent building them anymore, and the mugen ones ive looked at for an EG arent 2.5 inch soooooo while i wait for suggestions ill try to piece together a custom 2.5 inch system.

 

Switched from the T1R 65mm to the new T1R 70mm and picked up 4.5hp. No tuning done.

 

We usually advise our customers to run 3" if they are looking for maximum useable power. 2.5" is usually on the small side and often times will restrict the flow. It just depends what exactly you are looking for....

general rule of thumb is 190+ WHP = 3" exhaust if you dont mind the noise.


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by diesel32 &raquo;</TD></TR><TR><TD CLASS="quote">2.5 inch is more than enough for an all motor car. I am still waiting for suggestions on the proper muffler to purchase. Im in the same area looking for a good 2.5 inch exhaust. The easy way out is to say hytech - but they arent building them anymore, and the mugen ones ive looked at for an EG arent 2.5 inch soooooo while i wait for suggestions ill try to piece together a custom 2.5 inch system.</TD></TR></TABLE>

Depends on the All Motor car we ran 4" on a street stock car.

Losing bottom end torque when changing to a larger exhaust is usually a tuning issue not an issue of the tailpipe size being too large

but then again i'm not rmf or smsp so who knows


Modified by Ekasey at 3:50 PM 11/13/2006

 

I read an old article from honda tuning where they put mahle pistons with 11:5 cr to a H22. Upon switching from a header with a 2.5" collector to a header with a 3" collector they gained about 25-30whp. I forgot what cam they had in.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by camlob &raquo;</TD></TR><TR><TD CLASS="quote">I read an old article from honda tuning where they put mahle pistons with 11:5 cr to a H22. Upon switching from a header with a 2.5" collector to a header with a 3" collector they gained about 25-30whp. I forgot what cam they had in. </TD></TR></TABLE>




If that's the case, it's probably safe to say my 60mm BC Pro Spec exhaust was robbing a couple ponies at least....Any other H series guys running 3" exhaust on their all motor setup?

 

john (jd3jdm) runs a 2.5 RMF out to a full 3 inch on his prelude (we made it rsr style too) but too bad it drags on everything...also the engine was tuned open header

brad @ RLZ was pretty adament about running 3 in on h22's...he said they flow more air stock than most give credit for

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by diesel32 &raquo;</TD></TR><TR><TD CLASS="quote">2.5 inch is more than enough for an all motor car. I am still waiting for suggestions on the proper muffler to purchase. Im in the same area looking for a good 2.5 inch exhaust. The easy way out is to say hytech - but they arent building them anymore, and the mugen ones ive looked at for an EG arent 2.5 inch soooooo while i wait for suggestions ill try to piece together a custom 2.5 inch system.</TD></TR></TABLE>

As well as everyone else who said 2.5 was adequate for most all motor set ups.....

What makes you say 2.5 is more than enough for all motor? Have you done multiple dyno runs to prove this? Sounds like a pretty reputable grape vine...

 

good topic. anyone else to chime in????

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LudeBehavi0r &raquo;</TD></TR><TR><TD CLASS="quote">As well as everyone else who said 2.5 was adequate for most all motor set ups.....

What makes you say 2.5 is more than enough for all motor? Have you done multiple dyno runs to prove this? Sounds like a pretty reputable grape vine...</TD></TR></TABLE>

This is what I was saying. Most people just assume that 2.5 inch is ideal, when in actuallity, it could be 2.75, 2.83, 3.19, 3.60, 4.2 inches that's ideal for one's setup. ****, people make more power with open header all the time.
I'm thinking the argument here is: scavenging vs. flow and at what point, having more of one makes more power.

smaller exhaust = more scavenging, less flow
larger exhaust = less scavenging, more flow

2.5 inch can't be the sweet spot for every all motor honda.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92TypeR &raquo;</TD></TR><TR><TD CLASS="quote">Switched from the T1R 65mm to the new T1R 70mm and picked up 4.5hp. No tuning done.


</TD></TR></TABLE>

Was that the 1st gen T1R exhaust?

About 4 years ago on SGT's B20 he had my B20VTEC header, test pipe, 22" resonator (10436) and a 4x9x14 Magnaflow muffler. He made 231whp with the exhaust and 232whp open.

Last week I dyno'd a car that lost hp across the board when we ran it open, so things are dependent on set up.

One problem with going to 3" for an Integra or Civic is that you are limited in what you can run for a resonator. I have a 3" resonator with a 4" body but it's only 12". Most other companies' 3" resonators are 6" round which is just too big for a DC2/EG/EK/etc. so the sound levels go way up there for the 3" systems.

But I think if you are approaching 235-240whp it would probably be beneficial to go up to 3". But this won't always be the case. At least for some of my headers it also depends on whether it's a 4-1 or 4-2-1, and how that header is sized.

Again, there is no easy answer or program to determine all specs a given set up will need. It boils down to the fact that you won't know until you try it.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SMSP &raquo;</TD></TR><TR><TD CLASS="quote">Was that the 1st gen T1R exhaust?

About 4 years ago on SGT's B20 he had my B20VTEC header, test pipe, 22" resonator (10436) and a 4x9x14 Magnaflow muffler. He made 231whp with the exhaust and 232whp open.

Last week I dyno'd a car that lost hp across the board when we ran it open, so things are dependent on set up.

One problem with going to 3" for an Integra or Civic is that you are limited in what you can run for a resonator. I have a 3" resonator with a 4" body but it's only 12". Most other companies' 3" resonators are 6" round which is just too big for a DC2/EG/EK/etc. so the sound levels go way up there for the 3" systems.

But I think if you are approaching 235-240whp it would probably be beneficial to go up to 3". But this won't always be the case. At least for some of my headers it also depends on whether it's a 4-1 or 4-2-1, and how that header is sized.

Again, there is no easy answer or program to determine all specs a given set up will need. It boils down to the fact that you won't know until you try it.</TD></TR></TABLE>

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SMSP &raquo;</TD></TR><TR><TD CLASS="quote">Was that the 1st gen T1R exhaust?</TD></TR></TABLE>

The 65mm was the first batch of their new style. I'm assuming by 1st gen you are refferring to the large Ti canister.

ID of the 65mm was 61.1mm (2.41") and the ID of the 70mm is 65.6mm (2.58")

The new T1R 70mm is the latest gen style with 70mm piping.

 

Well I ask because the 1st gen system, which was actually 63.5mm (2-1/2" OD/2-3/8" ID), had 2-1/4" ID flanges at the B pipe and after the resonator. PLus the B pipe and/or axle back were made to bolt up to the stock systems so there was a big bottleneck at the joint along side the gas tank. If you had the first system like I describe, your gains are probably more due to the loss of the bottlenecks vs the size of tubing.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SMSP &raquo;</TD></TR><TR><TD CLASS="quote">Well I ask because the 1st gen system, which was actually 63.5mm (2-1/2" OD/2-3/8" ID), had 2-1/4" ID flanges at the B pipe and after the resonator. PLus the B pipe and/or axle back were made to bolt up to the stock systems so there was a big bottleneck at the joint along side the gas tank. If you had the first system like I describe, your gains are probably more due to the loss of the bottlenecks vs the size of tubing.</TD></TR></TABLE>

Ah yes, there are no bottlenecks on my 65mm system. It is my understanding they started producing catback systems w/o bottlenecks, but offered separate Bpipe and Axleback pieces with reduced flanges to bolt to stock piping.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LudeBehavi0r &raquo;</TD></TR><TR><TD CLASS="quote">As well as everyone else who said 2.5 was adequate for most all motor set ups.....

What makes you say 2.5 is more than enough for all motor? Have you done multiple dyno runs to prove this? Sounds like a pretty reputable grape vine...</TD></TR></TABLE>

my motor is at 240 - 164tq and running 2.5 inch. which to me is more than enough. i have never tested a 3 inch on it, but i have several friends in the 220 to 245 range that run a 2.5 inch. but as the posted dyno shows a gain of 4 hp, but to me the extra money isnt worth the experiment to see the changes.

 

Haha, I was thinking this exact same thing a week ago. for a good question and waiting answer or more proof

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by diesel32 &raquo;</TD></TR><TR><TD CLASS="quote">my motor is at 240 - 164tq and running 2.5 inch. which to me is more than enough. i have never tested a 3 inch on it, but i have several friends in the 220 to 245 range that run a 2.5 inch. but as the posted dyno shows a gain of 4 hp, but to me the extra money isnt worth the experiment to see the changes. </TD></TR></TABLE>

Fair enough. Glad you didnt take my inquisition as an attack

 

FYI-

se93 just replaced his crush bent 2-1/2" with a 2-1/2" mandrel bent system from me and went to 224whp.

Here's his previous graph. https://honda-tech.com/zerothread?id=1785784

 

I wonder what gains if any if he went to a 3 inch collector and piping?????

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bambam &raquo;</TD></TR><TR><TD CLASS="quote">But who the hell decided 2.5 was the best for ALL allmotor applications? It seems to be the general consensus...but just questioning why. Is it something we've all just come to accept and haven't put any real thought into it? </TD></TR></TABLE>

Seems like there is a general consensus and "no real thought" put into anything for most of this site, that's where myths come from. Start with the stock throat size. Honda picked that size i guess. I stepped my stock throat size out to 3" to mate to a 3" exhaust. What does a bigger throat size change between a 2.5", 2.75", and 3" throat? was that your question?