Free-flowing Intake and Exhaust for Fuel Economy
 

Oh my goodness, here it is again...

But really, I just read a bunch of sites saying performance intakes and exhaust are good for fuel economy and blah blah blah. It makes sense to me, it really does, but 400 on an exhaust and having the result suck would really really suck.

And it just doesn't make sense, because from a honda perspective, the cars with the best gas mileage has the smallest intake manifolds. And that's not just the cheap cars, it's the cars like the VX that had an *** load of engineering put into them to get great gas mileage, so honda wouldn't have just gotten cheap on that part.

Has anyone tried this? I might just get some really huge tubing and a cone filter and try it. Or else, mehbe I'll block off half my intake opening for a tank or two and see how it feels. I just dunno.

I think free flowing exause
 

I think free flowing exause is bad for city milage (not enough backpressure for low rpms). I am not sure about
the highway. I also think low backpressure makes warm up time longer because all the heat is going out the pipe.


The usually ricer cat back is 2.5" piping. I think that is too big for most fuel efficient 4 bangers.

The performance exaust people all claim more hp/mpg/tq. It WILL help mpg if your driving a 6,000 rpm all day copared to a stock setup driving at 6,000 rpm all day.

for a 4 banger I think
 

for a 4 banger I think 2.00-2.25 is the max for both power and economy. For my car I've been told to go a max of 2.5 because I had nitrous. My exaust is still stock cause I took the nitrous off.

What ricers don't understand is that you can put an electric cutout right after the header that opens and closes at any rpm you want. You don't even have to press a button. They can keep their stock exaust system and have power when they mash on the gas.

Like if I were to get it for my car I would program it to open 3000-6200rpm. So until 3000 rpm it's closed. Not only it would give a unbeliavable top end but at smog nobody is going to say anything because your exaust system is fully stock. It's also cheaper than getting a header and a complete catback.

Quote:What ricers don't
 

They do actually understand this but most opt out of it because they know the importance of running a cat for legal or nice person reasons.

The people that I've seen run like this generally have the switches for only when they see the track.

Re: Quote:What ricers don't
 

If I had this system I would not drive over 3000rpm on the street. Going in that rpm burns a lot of fuel and gets you in trouble with the cops. For a honda I'd set it at 4000rpm.

It does burn a lot of fuel,
 

It does burn a lot of fuel, haha. And if you try to launch that high you get crazy wheel hop (or at least I did on my mom's camry, I was freakin scared).

When I take my car to the track it'll be the same condition as street but mehbe with a different tune on it.

Re: Free-flowing Intake and Exhaust for Fuel Economy
 

Crap - it's back. The exhaust thread. Honestly, I wish there were some real answers out there, especially for the Honda design -- because I really need to replace mine. I think only a Honda engineer can answer the questions we have. Otherwise, we're going to need an experiment to get the answers we want.

RH77

Me too, I'm planning on
 

Me too, I'm planning on interning at honda in the shop for a while but I'm doubting they'll know anything about it either. :(

Re: Me too, I'm planning on
 

That's cool; but yeah, I think the exhaust diameter, backpressure, exhaust flow, and header style vs. fuel economy are advanced design issues, that someone high-up in the ranks knows every detail. The team that designed the exhaust system for the VX for example. The thing is, at Honda, the whole team works together as one unit instead of divisions that have their own responsibilities and meet once in a while to put the pieces together (but still, each system has an expert and apprentices). Unfortunately, I don't speak Japanese. Maybe we should write to them, I don't know. They're pretty cool with the advancement of environmental causes and their brands. My folks live pretty close to where they make the Civics and Accords in Ohio -- drove by the plant once -- very clean looking.

RH77

If we wanted to write a
 

If we wanted to write a letter as a site I have a friend that could translate it into japanese for us, or at least clean up my sloppy japanese. Mehbe I'll talk to her father since he used to be head of jamsat and he can call honda for us.

Went to the site
 

I went to the Honda North America Website, and they don't have an e-mail link, so we'll have to draft a letter as a collective site, or even better, use your connections if you can work them.

One problem -- they'll want you to buy OEM equipment because that's what they designed for the vehicle, and the dealer repair/parts network is important to the organization -- so it might get political.

RH77

exhost
 

Well guys it works in a couple of ways - there are equations that calculate the length of the pipe to give proper tuning as a function of the cylinder displacement and pipe diameter to get proper extraction effect. Valve timing can really affect how it performs because back pressure with intake and exhost overlap vs no back pressure and valve overlap can cause different amounts of discharge gases remaining and different amounts of fresh charge getting into the cylinder thus affecting efficiency. Best to have very little restriction and the valves set to not allow intake charge from getting out the exhost before it goes through a power cycle and gets burnt. Big thing is to have the length and diameter correct so that you get an extraction effect from the prior exhost pulse helping the next exhost cycle pull the gasses out of the cylinder. Of course at low throttle this does not matter as much Oh and you can tune it for RPM so pick your operating speed!

I think we could just
 

I think we could just inquire about the design choice and tie it into their environmental commitment and say we love your design, but we were wondering about a civic ex exhaust on our civic vx.

Re: exhost
 

Right, but I don't plan on replacing the cams with the exhaust -- and Honda engines tend to have quite a bit of valve overlap -- especially with VTEC systems. That's why the some intakes are super-loud and require a silencer for the average user. So, do you just play it safe and stay stock? Is there an equation for the above? Hopefully SVOboy can get us hooked up. And for the non-Honda folks here, sorry, but they're really particular when it comes to emissions and efficiency.

RH77

Valve timing is a sticky
 

Valve timing is a sticky wicket.

Unfortuneately I can't do much on the front of calculating exhaust unless were talking about turbos, however, I can find us something out about cam timing. I have actually been thinking about that a lot lately and that's my next area of research, so we'll see.

Re: Valve timing is a sticky
 

That I didn't consider -- you can adjust the cam timing. I've never done it, but it doesn't sound easy. I'll have to consult the Haynes manual...

RH77

VTEC
 

AS I recall the VTEC opens valves more and with different timing at higher RPM so just quit reving it (yeah like that will happen) and you should be able to get good economy. Make sure your header pipes are the same length for each cylinder and are free flowing and pick your muffler to suit your noise lever. My firent with the F150 also has a Honda and used to work for Honda so I will ask him about exhosts. He has the VTEC in his Prelude.

You've got the concept of
 

You've got the concept of vtec pretty well. rh77 doesn't have it, :p, neither do I, though I will soon!

I'm excited, vtec is the shizzle, y0.

Re: VTEC
 

Well, the exhaust system I need is for the non-VTEC in the garage. The VTEC V-6 sucks the fuel down when on the agressive cam, so I tend to stay away from that area of the RPM band, but it will haul when prompted (I do need a CAT for that one). It's the old-school VTEC where it it kicks-in at like 4500 RPM; the new i-VTEC varies the timing/lift based on a whole shload of conditions.

So my it's for the DOHC 1.8L Non-VTEC(B18B1) engine (Integra). So, there's the piping from the header, a CAT (which is still good -- gets to stay), a resonator, muffler, more piping. Smaller/larger diameter, replace the header (what style), muffler type??? I'd hate to spend the money on something that kills my gas mileage, because once it's installed, its in there until it breaks.

RH77

Re: You've got the concept of
 

I believe the proper response is W00T? :-P My '99 Si taught me a lot about VTEC -- the modified intake was louder than the exhaust, and what a rush. But putting a free-flow exhaust on there (Greddy Evo) actually increased fuel consumption -- was it psyhological? Maybe. Was it mechanical? Possibly. Was there too little backpressure? Perhaps. Am I starting to sound like Donald Rumsfeld? Likely.

RH77

I share your questions about
 

I share your questions about the exhaust SVOBoy, and considering the restrictive nature of the VX/HF/CX/HX (all fuel economy cars) intakes and exhaust, I can only assume that Honda did it this way for a reason.

if you want to write a collective letter to Honda, let's do it. IMHO there is no reason to translate it to Japanese, as English is the international langauge now. I have no doubt that the Honda HQ has fluent english speakers available in their engineering department.

I'll even put the letter together and I'll send it off.

Me = doesn't like the whole
 

Me = doesn't like the whole global language thing. Lemme try and get in touch with the guy who used to run jamsat, he prolly knows someone.

I think I may be able to
 

I think I may be able to shed a little light on this subject. First, we have to remember that auto manufactures make compromises when producing a vehicle, sometimes big ones, sometimes small. Material cost, R&D cost, labor cost, customer needs, environmental requirements, sound requirements, etc, will all effect the design and construction of a car. This is why systems like VTEC were invented in the first place, it allows less compromises to take place.

If a car was designed to travel at 55 mph, at 2,000 rpm, on a flat surface, in a straight line and no one cared what it looked like, sounded like or put into our air, I'm sure we would already have the best example of what would yield us the greatest MPG. Unfortunately, few or none of those points are true. So we are stuck with the problem of engineering our own solution from what we know.

Let's start with the intake system. Most air boxes and intakes are designed with a resonator (or 2 or 3) built in, limiting the amount of "growl" that's produced when you step on the throttle aggressively. This probably disrupts the laminar air flow in the intake and causes greater pumping losses, so ditch the resonator(s).

Intake pipe size. This is going to be along the same lines as exhaust pipe size, just imagine your intake manifold is a header (the plenum is the collector), well the intake piping connected to your throttle body is also going to dictate pumping restriction and port velocity into intake manifold itself. I think out of all areas, this one (the intake piping) will have the least greatest effect on mileage.

Now as for the intake manifold itself, the runner length, runner cross section and plenum volume will all greatly effect the volumetric efficiency (VE) of the engine. For instance, as the intake valve opens the air begins to move into the cylinder, and acting like water, air has inertia that will build and have kinetic energy. Now that air inside the runner literally bounces back and forth between the back of the closed valve and the plenum. If the runner is tuned to the correct length and has the right cross section for that RPM (!!!), that pulse of air will be timed to force its way into the cylinder the next time the valve opens. Unfortunately, this is only true for a fairly small RPM range, which is why some engines are designed with 2 stage intake manifolds (i.e. Integra GS-R) This is one of the things that allows an engine to achieve greater that 100% VE without external supercharging.

This is why you see intake manifolds with small long runners on engines like the CRX Hf and Civic VX.

The exhaust manifold (or header) is much the same. Its job is to match up the exhaust pulses, which have a high pressure head, and low pressure tail, so that these 2 ends equal each other out and make for nice even flow. The low pressure "tails" of these pulses can actually suck the exhaust out of another cylinder, this is referred to as exhaust scavenging. Again, exhaust manifolds are only most efficient within a certain RPM band.

Still with me?? As far as exhaust piping goes, you want to try to maintain a similar exhaust velocity as the collector of the header, but again, this will only be true for a certain rpm band as well. Smaller pipe will be a great benefit at lower RPM.

In a perfect world, we would have solenoid actuated valves, no TB or plenum (don't need them with solenoid actuated valves anyways), a material that could change shape instantly to form smaller longer runners at idle and get progressively wider and shorter as RPM increased, same goes for exhaust manifold and pipe. And while we're at it, variable rod / stroke ratio and compression ratio too! =)

Starting from a Honda platform, I would probably take a VX motor, and tighten down its operational RPM band even more. Tune every part of it for 2,000 RPM.

I hope this gives you somewhat of a clearer picture of how everything fits together. This is just the very tip of the iceberg really, we haven't taken into account heat, air density, altitude, etc.

I hope I didn't ramble! =)

Old Pontiac
 

I had a 6 cylinder Pontiac Tempest in the '70s. I used to drive between Boston and Albany regularly, at about 80 mph. I put a set of Clifford headers on it. It went from about 12 to over 15 mpg. It made me a true believer in headers. Of course, the original Pontiac exhaust manifold was a cast, high-restriction POS, but the experiment proved the theory in my book.

I'm not sure how much help headers are for late model cars, since the newer intake and exhaust manifolds are a lot more free-flowing.

Great info Bunger!
 

Bunger - awesome info. What I'm stuck with is a '98 Integra LS, Automatic (B18B1). I tend to cruise at 57 mph actual (62 registered on the speedometer) which is around 2300-2500 RPMs if I remember correctly. I do most of my driving on the highway at highway speeds, so around 2000-3000 RPMs. So, should I build a system that's tuned specifically for that range? From stock, what would that entail? I assume a smaller diameter exhaust pipe and a more restrictive intake. From there, would a different intake bolt-on from another Honda engine that's more restrictive? Now your article didn't mention anything about a muffler -- should I go with a free-flow or one with restriction? The exhaust system is literally falling apart, os I need to act soon. I have a leak that is pretty potent at idle (the CAT is fine, so I plan on leaving it). Bottom line is I'd hate to invest in an intake/exhaust system on my fuel-economy experiment car, and have it reduce economy. Thanks again for your expertise...

RH77

RH77, Thanks for the
 

RH77,

Thanks for the kudos, glad you got something from it.

As far as replacing your exhaust with something thats going to be better for mileage, the biggest difference would probably come from a header, which unfortunetly, unless you pay someone (or are able to weld it up yourself) to make you a hand built one, your best bet is to stick with the stock piece.

Now for your exhaust system, you may find a mileage increase from smaller piping, or possibly a smoothly tappering piece right after the manifold collector to act as a venturi, helping to increase velocity without causing too much backpressure. For a muffler, the more free flowing the better, within your tolerance of noise level.

I'm going to be experimenting with some titanium tubing later on, as it seems I can source it for around $1.50 an inch, which isn't too bad considering the weight savings. If I can talk my friend who has an engine dyno into it, I could run some tests to see what changes have the greatest effect. (his setup can meter fuel flow also!)

Sorry I don't have a better answer, I'll keep thinking about it and let you know what I come up with.

You're very clever, I have
 

You're very clever, I have learned something from this but realize now I am more confused.

Why's this?

Woot!

Re: You're very clever, I have
 

With most mufflers designs, the exhaust velocity is going to go to crap anyways, so at very least, don't create a bottleneck. The good part is, that far back in the system, the exhaust gases have had some time to cool and condense, so flow requirements decrease.

In a perfect world you would probably have a total straight tube that very slowly decreased in diameter to maintain the port velocity with a tip that was designed in such a way that the passing fresh air would create a vacuum, and thus lower pumping losses even more.

So I can get a nice sounding
 

So I can get a nice sounding muffler for the crx and have it not kill my mileage/possibly help?

Any suggestions?

Re: So I can get a nice sounding
 

define "nice sounding." I've seen too many hondas/crxs in the area drive by...

WWWWRRAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAHWW
WRaAAAAAAAAAAAAAAAAAAAAAAAAAAAAAHW!!!

Nice sounding is kinda deep
 

Nice sounding is kinda deep but not enough to hear from inside another car as anything more than just hmmm.

I'm thinking sorta like a diesel, :p

Re: Nice sounding is kinda deep
 

I've heard that the RS-R ExMag is a good choice -- slightly louder than stock. I had a Greddy Evo on my '99 Si and it was a bit louder than I liked, but the sound quality was deep and mellow. As far as air resistance goes, I'm told that the Dynomax muffler allows more flow and sound deadening.

Bunger -- this has been a tough discussion that's been going on for a while. That's cool that you're willing to test some piping -- maybe we can get somewhere on this. It's complicated, but I think we can tackle it...

RH77

not sure about latter crx's
 

not sure about latter crx's but my '85 crx-hf has a full stock exaust on it, came from honda welded as one piece, 9 feet long, bolts under the oil pan, and goes all the way back to the exaust pipe tipe, suposedly has a life time warenty on it as well, anyway, it's a small pipe, a few steps in it I think making it smaller as it goes back, and I personaly think it's to loud, because it sounds like what I think you are basicly looking for, rummbly a little corse, but it's fully stock so I suspect it's about as quite as I'll get, if you want it a little louder I supose drilling a few small holes in the muffler.
As far as I can tell what has been said about small pipe and exaust gas volisity is true, to big a pipe and it's like blowing in to a sewwer pipe, you loose all your momentum, and after market headers, altho they alow a smoother flow, they are simply to big for proper flow.

Anyone here know vector
 

Anyone here know vector calculus? If so, good stuff might happen, if not, we'll just have to wait for me to pick a little bit of it up.

Re: Anyone here know vector
 

Well crap, how long is that going to take? Sheesh, my exhaust might fall off in the meantime ;-) Geez, calm down, I'm JK.

Actually I was thinking about Vectors during the airspeed indicator thread. Since most of the time the wind isn't going to be entirely coming from the front or the back, it would attack the vehicle at a vector angle -- suggesting that FE decreases during crosswinds (since the side of the car was mentioned to not be very aerodynamic). But depending on the speed, the crosswind may hit the car at a vector angle that hits an aerodyamic piece, like the bumper, but still forces the vehicle laterally. Anyways, I gave up on Calc/Physics long ago, so we're all counting on you!

RH77

Well, vector calculus is a
 

Well, vector calculus is a little different than that. It uses gradients and what not to split up things like flow into the seperate dimensions and find speed and concentration and forces and ****. Good for magnetism I think. I've only had one class on it so far so I dunno, I just finished gradients.

Anyway, we might need to have 3 airspeed indicators and do lots of quick mental math, or get three that are electronic and build a controller, *shrug*

Re: Well, vector calculus is a
 

Not saying I'm great at it, but I'm familiar with vector calculus of multiple variables (although more than three variables can be tough **** to do by hand). MATLAB is very capable of handling this though.

Aren't you still in HS SVO? What high school level class is teaching vector calculus? We didn't cover it until the second year calc class @ GT, and it's one of the top engineering schools in the USA.

Quote:MATLAB is very capable
 

Can I run this **** in mathematica? It would give me a reason to try the trial version. Can't wait to get it when I go off to dartmouth.

Yep, I'm in high school. I am taking multivariable and discrete math now (two courses) and my multivariable teacher (who also went to dartmouth) has been teaching us vector calculus since we just finished doing multiple integrals. I'm trying to get in a solid foundation because I'm trying to skip the intro math **** and take multivariable the first trimester, which is what my teacher did.

Re: Quote:MATLAB is very capable
 

I don't know if you can run MATLAB in mathematica. I've never used that program.

Damn, I guess that's what I get for going to the lowest scoring high school in one of the lowest scoring counties in one of the lowest scoring states. Good luck with your college adventures. :)

I meant the math shit in
 

I meant the math **** in mathematica, it's like matlab but better.

Thanks for the luck. There never was a math class for me and my 4 friends, but we skipped two years and forced the school to make it. Only 3 of us in each class and I'm the only that is doubling up. :)