Bigger Exhaust = Better Mileage

Just to share my experience.

I upgraded my exhaust system from a stock 2.25" which went down to 1 7/8 by the tail pipe, to a complete 3" mandrel bend system. I also upgraded the swing valve to 3" from 2.25". My mileage went from about 26MPG to 30-32MPG.

This is on a 1988 Chrysler 2.2 Intercooled Turbo.

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Bigger Exhaust = Better Mileage

simarcom's picture

Thank you for sharing this very interesting experience. Can you tell aproximately how much you had to invest for those modifications?

I've heard that bigger exhaust pipe was helping a lot on big trucks as well so it make a lot of sense. Did you notice any more power from the engine also?

thanks again,

simarcom

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Bigger Exhaust = Better Mileage

ssheen's picture

I am embarassed to say how much I spent on it. Nothing went my way when I did it. You should be able to find a local exhaust shop that can weld up mandrel bend pipe for about 300$. Big truck places seem to be cheaper for some reason. My cost was about 325 for the complete 3" mandrel bend pipe and 135$ for the muffler, that was USD. Plus there was shipping and customs. The install was not smooth as the first place said they could do it, changed their minds half way through. So the install cost me twice what it should of.

Yes, I noticed more power. People say, for my engine, the 3" can be good for around 50hp over stock. I have no idea if that is true or not. My last dyno run was 198whp. Stock is 175hp and probably about 140whp (20% for losses) So I am up about 60whp. That was with the car detuned as well, 8 degrees of timing instead of the stock 12.

That 60whp is cummulitive with the exhaust, bigger swing valve, underdrive pulley, slightly ported head, and probably other things I am forgetting.

My car site http://www.sheenconsulting.com/car

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Bigger Exhaust = Better Mileage

E=mc2's picture

Big exhausts work on turbos, but not espec with non-turbos?

http://www.hondalife.com/modules.php?name=Sections&op=viewarticle&artid=...

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Bigger Exhaust = Better Mileage

ssheen's picture

Since engines are air pumps, I would think helping them breath better would good thing. Regardless of if they are turboed or not. That said, I have no experience with larger exhaust on a N/A vehicle.

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exhaust

iburnh2o's picture

I've opened up the flow on virtually everything I have ever driven and never lost mileage and always increased it. In the old days of carbs I did witness leaning out of mixtures, which back then mean fattening up the jets for more power.

Certainly there is a limit to how far one should go.

ie: I'm fairly confident that the common 'tuner honda's' have reached if not exceeded the limit with Cummins sized exhaust pipes.

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Bigger Exhaust = Better Mileage

mpgman's picture

The engineering train of thought is that exhaust velocity helps to evacuate the cylinders. The small diameter exhaust pipe will do a nice job of keeping the velocity high at lower engine speeds, but at higher engine speeds the larger pipe will be able to flow better (giving the exhaust gasses a way out) while still maintaining good velocity.

On turbo cars, the turbine (exhaust side blade) will difuse the exiting gasses pretty much eliminating the velocity aspect of the exhaust pipe. In this case, the less back pressure (larger the exhaust pipe diameter) the better, even at low rpms.

On naturally aspirated engines, the exhaust gasses constitute a mass (just like wind) in motion. The faster that mass gets moving (higher velocity) the harder it is to get it to slow down and stop. So if the mass keeps moving even after the piston reaches TDC becaust it's moving so incredibly fast, then there will hypothetically be a vacuum created inside the cylinder by the time the exhaust valve closes. This creates 2 benefits for power and economy:
1) There would be almost no exhaust gasses left in the cylinder to dilute the next intake charge.
2) With a vacuum inside the cylinder, once the intake valve opens the intake charge will start filling the cylinder even before the piston starts to move down in the intake stroke.

Obviously the exhaust pipe diameter is a compromise. On turbo cars, the pipe must fit between the body and gas tank, suspension, fenders, etc. On naturally aspirated engines, too small of pipe diameter means great mileage at engine speeds that are rediculously low (1800 rpms and 45 mph). Too big exhaust and no low end torque, lousy mileage, possibly great power at red line (and possibly not).

So where did your eyes glass over and you decided to move on? :?

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Bigger Exhaust = Better Mileage

diamondlarry's picture

On naturally aspirated engines, too small of pipe diameter means great mileage at engine speeds that are rediculously low (1800 rpms and 45 mph).

Quote:

I'm not sure how this post is going to look when it's done(first time using quote) but here we go. The above may explain what I saw on my uncle's rented Metro a long time ago. He was a salesman and had rented a car while he was in town. When he stopped by my grandpa's, we naturally wanted to look under the hood since at the time Metro's were new. The two things I noticed right away were: it only had 3 cylinders and the exhaust tubes on the manifold were so tiny. His car was an automatic with air and he said that the car was running around 44mpg. He also noted that when he went to step on the pedal, the car seemed to be saying, "Oh, you want to go. Ok, here we go." :)

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Bigger Exhaust = Better Mileage

E=mc2's picture

I've been interested in the use of swirlers to increase the flow rate out of an exhaust....

JCWhitney has sold exhaust tips that are supposed to do this kind of thing...I use SS flex pipe for my exhausts (cat back) and it would be fairly easy to insert 3-4 of these in this tube every 1.5 feet or so...if they were effective. Or cut open a bullet type glass pack and insert a swirler?

http://www.vortexexhausts.com.au/

...improve your fuel economy by up to 25%!!!

http://www.spiralmax.com/tet.htm

They also sell the Turbolator...

http://www.jcwhitney.com/autoparts/Product/tf-Browse/s-10101/Pr-p_Produc...

...has anyone tried one of these?

I've mentioned this device other places and gotten the usual "snake oil" response...something going on here.....

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Bigger Exhaust = Better Mileage

ssheen's picture

You could try water injection into the exhaust down pipe right after the exhaust manifold or turbo. The water mist will cool the exhaust gases, causing them to contract, lowering the back pressure. I have not tried this, just have read about in one of George Wiseman's books.

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WI exhaust

iburnh2o's picture

Scott

What you describe is how water injection is used on 2 strokes.

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Bigger Exhaust = Better Mileage

E=mc2's picture

I'm currently beginning the process of making my own spiral muffler similar to the....

http://www.spiralturbobaffles.com/semiinfo.html

Supposed to have a good sound and not much more backpressure than a straight pipe. Increases HP...torque...and mpg....we hope.

Will post pics when finished.

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spiral mufflers

iburnh2o's picture

E=mc2

Please keep us posted with this. If possible maybe you could photograph the process and consider writing a short article? While it's nice to buy things off the shelf it's even better to build them yourself for much less $$$.
Especially when you're expirementing.

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Bigger Exhaust = Better Mileage

Typrus's picture

What is really needed is something to aid the gasses to flow more smoothely around sharp curves, as in where it goes over the rear axle in RWD'ers. Taking these corners creates turbulence, and in turn creates backpressure.
The cooler air gains density, and in doing so gains weight. With how rapidly gasses expand with temp, I'd say that you could easily double or triple the weight of the air moving through the exhaust. Sure, it takes up less room, but it also has more mass, and therefore creates backpressure by forcing the engine to work harder.
At least thats what makes sense to me.

We have a 4 inch mandrel-bent straight pipe (cat and mufflerless) on our 02 7.3L Powerstroke diesel. It came factory no cat btw, for those wondering. We went to that from the factory non-mandrel 3 inch pipe with muffler. Throttle response was increased intensly, and mileage hopped up about 1.5 points. Considering the Excursion weighs around 7800lbs, thats significant. Let alone from a 7.3L V-8. Of course, when the warm-up valve closes on cold mornings, the turbo revs way up and it sounds like a 747 is taxiing in the driveway. I enjoy it. Our neighbors hate it. I can't imagine why.... lol.
I have a friend with an Audi 80, 2.3L Inline 5. We removed both factory mufflers and replaced them with a single Cherry Bomb glasspack on the tip. She both growls like a mini-V8 and gets about the same mileage. Which is great considering my buddies driving RPM went up 1000 since the change (makes more noise lol)

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Bigger Exhaust = Better Mileage

BDKR's picture

E=mc2 wrote:

I'm currently beginning the process of making my own spiral muffler similar to the....

http://www.spiralturbobaffles.com/semiinfo.html

Supposed to have a good sound and not much more backpressure than a straight pipe. Increases HP...torque...and mpg....we hope.

Will post pics when finished.

I know I'm coming to the game late here, but what is described here looks a lot like the Morosso Spiral flow Bullet mufflers. I have a 3 inch version. Straight through core with a spiral path going around it.

http://www.ronsraceshop.com/products.asp?ID=989

Cheers,
BDKR

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Bigger Exhaust = Better Mileage

mpgmike's picture

BDKR wrote:

E=mc2 wrote:
I'm currently beginning the process of making my own spiral muffler similar to the....

http://www.spiralturbobaffles.com/semiinfo.html

Supposed to have a good sound and not much more backpressure than a straight pipe. Increases HP...torque...and mpg....we hope.

Will post pics when finished.

I know I'm coming to the game late here, but what is described here looks a lot like the Morosso Spiral flow Bullet mufflers. I have a 3 inch version. Straight through core with a spiral path going around it.

http://www.ronsraceshop.com/products.asp?ID=989

Cheers,
BDKR

Very reasonably priced at $50 as well!

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Bigger Exhaust = Better Mileage

ssheen's picture

How do like that muffler? Full 3" exhaust? Is it quiet or does it drone? How was the HP increase with it?

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Bigger Exhaust = Better Mileage

paulorr1's picture

3" cat back comming soon to a Dakota near you! Just ordered 3" pipe, muffler and U-weld-it tailpipe kit from Jeg's along with MSD 5 ignitiom box. I've hit 25.6mpg on winter gas and would like to see 27 with the 3.9 Dakota. The exhaust manifolds and Y pipe will remain stock size for velocity. The CAT will become flanged as will the tailpipe, That way some tests of other components can be run.
Backpressure is not our friend. Back in the carb days a little backpressure helped to regulate the fuel curve so the carb didn't wander too far out of calibration. That is absolutely not the case any more. Any and everything you do to decrease backpressure in your exhaust will help performance from off idle on up. You do still need to maintain primary pipe velocities but after that you can dump to the atmosphere. Not practical, but you get the idea. Look forward to this and plan to use 4" right at the end of the tail for looks and a more bassy big block sound. Got to have a little fun with your mpg, right?

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Bigger Exhaust = Better Mileage

ssheen's picture

Watch that big sound. Mine is too loud, my wife will not ride in my car anymore.

I have been thinking of 4" from my SV to a cut out and the 3" system.

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Bigger Exhaust = Better Mileage

fltcoils's picture

make a muffler. Doesn't have to have turns and twists or fiberglass inside. don't need to restrict. just expand inside and then exit. typically 18-24" long, at least 3 times pipe diameter.

To visualize this...imagine a museum with a large central gathering area and dis play areas stretching out like spokes from main chamber. Down one tunnel a group is making lots of noises. How likely is it that someone in one of the other tunnels will hear them? not very. This is because the sound from the group reaches the central room and quiets as it spreads out. Then only a little bit of that softened spread out sound reaches down the other tunnel. This is how mufflers work. They aren't about pressure, just sound waves, a different physics phenomena.

great NACA papers on all this dating back to the 1920s...
http://naca.central.cranfield.ac.uk/reports/1920/naca-report-55.pdf
http://naca.central.cranfield.ac.uk/reports/1954/naca-report-1192.pdf
http://naca.central.cranfield.ac.uk/reports/1953/naca-tn-2943.pdf

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Bigger Exhaust = Better Mileage

paulorr1's picture

Too late. All ready ordered. At low cruise RPM there should be near zero backpressure in the system. My goal in this is not the N'th degree of mpg change with exhaust but again something practical that anyone could duplicate (for cheap).

I have NO PROBLEM with anyone willing to spend big bucks for improvements in mpg or power but I'm cheap and have a family and house to pay for as do many others. I always concentrate on low buck, practical things that a reasonably skilled person could duplicate. Maybe their efforts won't come out so pretty but they could still be very effective.

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Bigger Exhaust = Better Mileage

RoadWarrior's picture

I'm of the opinion that free flowing mufflers are good, and can help MPG, but on N/A engines the header and downpipes should not be too large in diameter or volume. I figure about where the pipe passes the firewall on most vehicles is where you can start to open it up. If you've kept the velocity high and helped the scavenging at the head end, you don't want it running into a brick wall at the muffler, so good breathing there is helpful.

I was watching one of those oversimplified car modding shows the other day on speed channel, and they actually did a useful test that confirmed my suspicions about the majority of bolt on performance headers. For N/A street use and MPG they would appear to get too wide too soon. They were testing on an engine dyno, and comparing the curves. Several headers were significantly down on torque in the sub 4000 rpm range, and although peak torque was increased by a couple of percent, it was shifted into higher RPM. Max power was up on all of them. Only one of the ones tested managed to keep torque near stock at low RPM and increase it somewhere useful (midrange) while boosting top end.

So as far as exhaust mods for N/A go, you've probably got only a 20% chance of seeing any small MPG or driveability improvement out of a new header, with a 80% chance of seeing it get worse. IMO then, headers only seem to be worthwhile considering if you need the last few MPH on the back straight. Of course if you have the patience and $$$ to dyno a bunch, you can pick the one that proves me wrong. They might be a better buy when you've got such an extreme porting job and cam that "uncorking" it will release 30% more top end rather than 4 or 5% but most recentish N/A vehicles in hot street tune will probably drive a lot better on the stock header.

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Bigger Exhaust = Better Mileage

paulorr1's picture

Agreed! The typical blackjack cheap speed shop headers we used on our V8 cars would probably be far superior to the shorty rams horn headers that predominate today.
They weren't equal length but tended toward 36-40 inch long primaries and reasonable primary diameter. Even at that THEY ARE A PAIN IN THE B#*^T. That's why I'm sticking with the cast iron manifold and stock Y pipe. No hassles. The proof can be seen on the track with all the factory+CAT back systems that work great at improving acceleration and mileage. Almost a no brainer, even for me!

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Bigger Exhaust = Better Mileage

fltcoils's picture

http://e30m3performance.com/tech_articles/engine-tech/x-pipe/x-pipe.htm

""What does an X-Pipe do?" ... as individual exhaust pulses move down the exhaust tract, they leave behind them a negative pressure wake. If the exhaust pathways come together at just the right places, then these negative pressure wakes can help "suck" on neighboring cylinders in such a way that those cylinders achieve much higher filling then they would on their own. "

:)

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Bigger Exhaust = Better Mileage

paulorr1's picture

I have looked at the X pipes before and I think they have good potential but not for my single 3" system. Think about the explanation above. Those pressure pulses act exactly like in an intake system (or audio). The best utilization comes from defining where your torque peak RPM is and then calculating the total pipe length to the X to gain maximum benefit from the pressure waves traveling from and back to the engine. For MPG the best place would be at a distance relative to normal cruise RPM rather than peak torque.

Good stuff fltcoils.

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Bigger Exhaust = Better Mileage

katman's picture

Spend the $40.00 on PipeMax. Enter your engine data and it will tell you what size of pipes and lengths to use.

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Bigger Exhaust = Better Mileage

paulorr1's picture

Forgot to mention the sweat equity part of my home fab 3" exhaust. The chosen muffler, although inexpensive, is basically a flowmaster type design along the lines of a single chamber (LOUD). The psuedo catalytic converter will be gutted, filled with steel pot scrubbers toward the outside. The center will be perferated screen rolled to 3" and welded to 3" nipples. The perf/nipple pipe inserted thru the cat body to form a high flow premuffler. Then the purchased muffler followed by the tail Flowmaster 3" tailpipe kit. The tailpipe bends will be slit from the outside thru the radius of the bend to insert flow guides or vanes if you will. Bends are the greatest enemy of flow and big contributors to back pressure. The mass of gas flowing thru the system wants to go straight (ahh, the immutable laws of physics). Every bend causes turbulence as the mass is forced to make the turns. Flow guides are used frequently in high efficiency air handling systems that are confined to close quarters and tight bends. They really work. Really. No kidding. Fer sure.

If this is not clear, don't worry. Pics to follow. This can be done in any exhaust system. I will probably use only one per bend but ideally 2 or 3 would be most efficient.

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Bigger Exhaust = Better Mileage

wadak1234's picture

Paul,

I'm running a full 3in. exhaust all the way back on my 92 Dakota with a 318, the truck was 3in. out thru the convertor and then reduced down to 2.5 inches after cat. I ended replacing the cat. with a newe high flow and flow master 70 series big block muffler 3 in. all the way and it made a very big bifference in performnce and helped gas mileage. I a bit louder than stock, but my wife dosen't like it too loud for her.

My son is driving a Chevy S10 and he had to replace his muffler and cat and the shop he took it to didint have 2.25in pipe. S the put an entirely new 2.5 inch exhaust system high flow magnaflow cat and muffler. he getting 30+ mpg oon the highway. He lost a little bit of low end but gained that back with the additio of a MSD ignition system and K&N air filter. the truck has gained considerable top end also. This truck is a 2.5 liter 4 with a 5 speed.

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Bigger Exhaust = Better Mileage

paulorr1's picture

The system is installed and works great with the high flow cat modification(LOL)! The only time it is noticeably louder is at cold start up when the engine runs rich. Once warmed up it is barely louder than stock with some increase in sound climbing hills but dead quiet coasting down the other side. Very happy with this system so far. Have not installed the tailpipe guide vanes yet nor the 4 1/2" final tailpipe. Everything is flanged for easy service and modification.

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Bigger Exhaust = Better Mileage

paulorr1's picture

Finally finished and installed the exhaust tip. It's 4 1/2" electrical conduit wrapped in stainless with a stasinless rolled liner. Rolled the outer liner over the leading edge of the opening and welded to the inner liner. Sorry for the obvious dirt on the tip in the pic but it's been raining here incessantly. Took longer than expected as I,ve been laid up with an injured knee.

Definitely get that low exhaust note now and it's hard not to push the pedal too far.

Pic won't upload here so check the garage section.

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Bigger Exhaust = Better Mileage

markweatherill's picture

I just discovered this thread! Interesting reading.

My Nissan has an exhaust of about 1" diameter with a huge rear silencer.

I've obtained a 'performance' exhaust designed for a Nissan Pulsar GtiR and intend to bolt this on in place of the rear half of my exhaust system.

I'm hoping this is far enough away from the engine not to affect the exhaust scavenging etc.

That rear silencer must weigh a ton though. The weight saving alone will be worth it, I hope.

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Bigger Exhaust = Better Mileage

mpgmike's picture

Interestingly enough, some cars respond very well to larger exhaust, but a few don't. The theories on less restrictive exhaust have been formed from the successes, which far out number the failures. I think you're on the right track, but don't go overboard.

Mike

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Bigger Exhaust = Better Mileage

qsiguy's picture

For most vehicles you can get good results by just putting a less restrictive muffler on it, leaving the pipe diameter alone. Just need to change the most restrictive component(s) to make a difference. High flow cat would be good as well. You can move quite a bit of air through a pipe of various sizes but it's where it runs into restrictions and sharp bends that it slows down your flow.

What I'm getting at is that you don't need to spend big money on a large diameter system to get results. Just a DIY muffler, cherry bomb, or whatever, will help for a small investment. I will probably do this on my Toyota p/u sometime soon.

My focus at the time being is on a non mpg project. Well, it might be mpg related but most likely will result in a reduction in mpg :) I'm installing a rear mounted turbo system on my '94 Infiniti Q45. I will post a complete write up of the project when it's done or close to it as the same process could be used for mpg improvement but for this car it's not for that. This is my toy and I'm going for hp, performance, and FUN!! :(X)

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Bigger Exhaust = Better Mileage

markweatherill's picture

A rear mounted turbo, as in literally in the exhaust pipe at the rear of the car...?

Now that's worth a try, I suppose. I can picture some benefits over a front mounted turbo. And some less good points too...

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Bigger Exhaust = Better Mileage

manilow's picture

I've seen it done here. They used a variable vane turbo to reduce the lag, keep the turbo spooling at optimum speed.

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Bigger Exhaust = Better Mileage

LSR's picture

I'm still at fewer than five posts so I'm not permitted to post links, but if you can decipher the following secret code, :wink: sts turbo . com you'll find both model-specific and universal kits utilizing rear-mounted turbos.

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Bigger Exhaust = Better Mileage

qsiguy's picture

The turbo can be mounted anywhere in the exhaust system. Typically people will place it where the OEM muffler is and remove the muffler. In my vehicle it will be mounted on the drivers side rear of the vehicle since that is where my muffler currently is and has the most room for the turbo. The compressor plumbing gets ran back up to the engine. The air filter will now be under the vehicle or wherever you want to run it to from the turbo compressor inlet.

The design works great as long it is sized properly. The primary difference is that the turbine a/r will be smaller to account for the cooler exhaust air taking up less space. When sized correctly there is no more turbo lag than any other setup. You can get lag from any turbo install if the turbo isn't sized correctly. The PSI loss from the long compressor pipe isn't any more than you will get from an intercooler.

The advantages I like about this setup are that it is cheaper, easier installation, less heat under hood, less heat in turbo, less heat in intake air (no need for an intercooler unless you are running high boost), and the sound is amazing with the turbo so close to the tailpipe. There are a bunch of videos around and many on the STS web site.

Here are a few links to read through if you want more info.

Squires Turbo Systems. My nephew had one of their systems on his Dodge Hemi truck. STS used it for their booth at SEMA and it was in a bunch of magazines. It was incredibly fast and would smoke the tires on demand.
http://www.ststurbo.com

This forum is huge and several guys who have actually installed a DIY rear turbo on their vehicles discuss the ins and outs of the install. They have comparison 1/4mile times and dyno numbers to verify results. It's a long one so be prepared to read for a while. The night I found it I spend quite a few hours reading through the whole thing and there has been 389 post on that thread!
http://www.thirdgen.org/techboard/power-adder/238864-another-remote-mount-turbo.html

Here are photos of a really nice install on a Porsche 928 of the STS turbo kit.
http://www.clearimageautomotive.com/Porsche%20928%20Rear%20Turbo.htm

I will be starting a separate thread showing my installation when I get further along. I should have the turbo, wastegate, and BOV next week and I already have a bunch of parts.

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Results

markweatherill's picture

I've replaced the rear silencer on my car with a length of pipe. I ended up not fitting the 'performance' exhaust after all

It's not too noisy at idle or at cruising speeds, but a little too much when accelerating to speed. So I think I need to find a suitable 'insert' to put in the tailpipe to quiet things down without causing any more restriction than the old silencer did.

The good part is my mpg hasn't got any *worse* on my drive to work. I'm wondering if the overall mpg has changed either...

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Bigger Exhaust = Better Mileage

markweatherill's picture

Another update:

I've managed to reduce the noise to acceptable levels with inserts in the tailpipe, however mpg is worse.

I realise I can't replicate the silencing ability of a baffled silencer by using a partly blocked piece of pipe!

As the Mrs said, you've done your experiment, now PUT THAT SILENCER BACK ON THE CAR.

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Bigger Exhaust = Better Mileage

paulorr1's picture

Hi all,
Been really busy with work and family. My truck had its annual inspection in January. I chickened out on the modified CAT before the inspection and installed a Magnaflow 3" CAT. It actually sounds way better at startup and climbing hills. Power did not decrease. I'm glad I changed it as my mechanic told me the truck is running fairly rich. Probably would have failed emissions.

Now that's pretty interesting as my mileage is still good (just started checking again this week with the Summer gas). What could possibly happen when I ever finish building my EFIE? No excuses here. I have everything to finish the project and have just not done it!

God bless
Paul

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Exhaust dyno tests

NaphthaMPG's picture

http://www.pontiacstreetperformance.com/psp/exhaust.html

Good information about performance and exhaust combinations.

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Emissions reduction, and better mileage

Sabertec's picture

there is a new product avaiulable which has been tested in a california emmissions lab using EPA standards which has shown to reduce all major emissions as well as increase fuel economy by 6% - I have this product on my car and have increased my mileage by 14% the product is called the (deleted by iburnh2o)- you can get moire information on this from there web site as well as the testing result numbers.

if you care about mileage and/or the environment, this is for you

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Bigger Exhaust = Better Mileage

qsiguy's picture

First you should get setup as a vendor prior to posting something like this, it's easy.

Hmm at $149 I'd like some better details on how it works, how it's installed, and why it works before I drop that much money. Interesting tho, definitely due more research.

Are there any photos of it on a vehicle and can you give us some better technical info. On this side we thrive on the data, not fluff and promises.

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Bigger Exhaust = Better Mileage

Sabertec's picture

The testing has shown a combined fuel economy of 6% in lab conditions at a EPA certified lab in Ontario California. as well as 57% reduction in HC, 14% in Co, 34% in NOx, 6% Co2, 33% Ch4, and 88% in NMHC - It is easy to install, it clamps onto the end of the tailpipe using a U-Bolt which is attached to the Blade.

How do I set up a vender profile?

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Bigger Exhaust = Better Mileage

qsiguy's picture

Check out the stickies here:

http://mpgresearch.com/viewforum.php?f=17

Then you need to contact one of the moderators.

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Bigger Exhaust = Better Mileage

markweatherill's picture

The 'product' (which doesn't take much detective work to track down) has some impressive claims. I'd assume the only way a device that bolts on to your tailpipe can have any mpg effect is by increasing back pressure. And the result may or may not be an improvement.

It must be more clever than that! Looking forward to reading more about this.

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