new to mr N/A, i swear, this car is faster than it should be..

[4W4K3]

A lot of MKI N/A's in good condition are lucky to register above 100WHP on the dyno. Most are in the high 80's to low 90's. Torque is even lower. If your car were stock and in PERFECT condition, you still wouldn't be making 120WHP. As LordNikon said they put down 112HP at the CRANK stock, to the wheels even less.

In your first post you mentioned a bunch of upgrades you wanted to do. I hope you realize doing all of that won't make your car significantly faster. Most of it is just maintenance.

Upgrading your muffler does nada for you. If it's too much larger than stock it will actually hurt performance. Getting a FULL exhaust from the headers back might help a tad, but it's not going to give you 30WHP or anything. Maybe 10? If you build up your engine you benefit more from exhaust, stock power doesn't need much more if anything.

[te51levin]

Originally Posted by 4W4K3

Upgrading your muffler does nada for you. If it's too much larger than stock it will actually hurt performance.

I'm going to disagree with this. A local friend (unfortunately, not someone on this board) and I spent a day with his stock '85, comparing exhaust systems. We used Streetdyno to test the results and found that replacing the stock muffler and cat with a test pipe and SC muffler gained five peak horsepower and eight at redline. A much louder setup with a small glasspack was worth seven peak horsepower and eleven at redline compared to the stock cat and muffler. So there are definately tangible power gains to be had by making intelligent changes to a naturally aspirated AW11!

One important note to add is that we found NO LOSS in low-end or midrange power with either setup. That is solid evidence against the old muffler-shop myth that you need backpressure to make torque. It's not the backpressure you need; it's reasonably sized header tubing. Big headers will kill velocity at low RPM, and that hurts torque. Small headers that provide good velocity at low engine speeds will add backpressure at high speeds and kill horsepower. Everything's a compromise.

For those who don't know what Streetdyno is, please read up before attacking. It's not a real dyno, but it does the same thing in much the same way by recording acceleration via the ignition signal and calculating that into a full-spectrum horsepower and torque plot.

[4W4K3]

Originally Posted by te51levin

I'm going to disagree with this. A local friend (unfortunately, not someone on this board) and I spent a day with his stock '85, comparing exhaust systems. We used Streetdyno to test the results and found that replacing the stock muffler and cat with a test pipe and SC muffler gained five peak horsepower and eight at redline. A much louder setup with a small glasspack was worth seven peak horsepower and eleven at redline compared to the stock cat and muffler. So there are definately tangible power gains to be had by making intelligent changes to a naturally aspirated AW11!

One important note to add is that we found NO LOSS in low-end or midrange power with either setup. That is solid evidence against the old muffler-shop myth that you need back pressure to make torque. It's not the back pressure you need; it's reasonably sized header tubing. Big headers will kill velocity at low RPM, and that hurts torque. Small headers that provide good velocity at low engine speeds will add back pressure at high speeds and kill horsepower. Every thing's a compromise.

For those who don't know what Streetdyno is, please read up before attacking. It's not a real dyno, but it does the same thing in much the same way by recording acceleration via the ignition signal and calculating that into a full-spectrum horsepower and torque plot.

I remember reading your posts about this on another forum. I don't disagree with your findings.

I just doubt the thread started has a "test pipe" in his system. I assumed by "larger muffler" that a shop just welded on a fart can and he's probably still running stock cat and pipes. I wouldn't expect any performance out of that.

[Recklesss]

Originally Posted by te51levin

I'm going to disagree with this. A local friend (unfortunately, not someone on this board) and I spent a day with his stock '85, comparing exhaust systems. We used Streetdyno to test the results and found that replacing the stock muffler and cat with a test pipe and SC muffler gained five peak horsepower and eight at redline. A much louder setup with a small glasspack was worth seven peak horsepower and eleven at redline compared to the stock cat and muffler. So there are definately tangible power gains to be had by making intelligent changes to a naturally aspirated AW11!

One important note to add is that we found NO LOSS in low-end or midrange power with either setup. That is solidevidence against the old muffler-shop myth that you need backpressure to make torque. It's not the backpressure you need; it's reasonably sized header tubing. Big headers will kill velocity at low RPM, and that hurts torque. Small headers that provide good velocity at low engine speeds will add backpressure at high speeds and kill horsepower. Everything's a compromise.

For those who don't know what Streetdyno is, please read up before attacking. It's not a real dyno, but it does the same thing in much the same way by recording acceleration via the ignition signal and calculating that into a full-spectrum horsepower and torque plot.

if you read the guy's post, he said "maybe ten hp". you said 11. not that much of a difference in ten or even 15 hp, thats quite a gain in my opinion for a 1.6 liter (as opposed to gaining maybe 30 on a 5.0 for instance)

just clearing things up, i think you both were saying the same thing

[te51levin]

Originally Posted by Recklesss

if you read the guy's post, he said "maybe ten hp". you said 11. not that much of a difference in ten or even 15 hp, thats quite a gain in my opinion for a 1.6 liter (as opposed to gaining maybe 30 on a 5.0 for instance)

just clearing things up, i think you both were saying the same thing

We may be making the same point, but approaching it from a different angle.

My real concern is that so many people in the MR2 world, especially the MkI world, simply repeat what they hear whether it is true or not. A prime example is when people say that there are no gains to be had by changing the exhaust on a MkI. My friend and I proved that that was not true. I want people to be aware that there definately is potential for substantial improvement so they don't continue blindly repeating the same old "it won't help" mantra they have been chanting for years.

[4W4K3]

Fair enough, I'm hardly an "expert" when it comes to the MKI MR2 and do a lot of posting based on what I have read and not actual experience. I wouldn't want to lead someone in the wrong direction.

[lsgheero]

to add to te51levin's comment about the exhaust...

I cant vouch for added hp but the power curve changed on my mk1 na stock when I took off the glass pack the previous owner had installed and went back to the original muffler I have a more steady power curve through the rpms


just my 2 cents....

[E T Haggis]

what do you think a straight pipe right from the headers does for you?

[curvesrgood]

I'm sticking with my previous post and honest butt dyno results... cold air intake (large one, preferably K&N) matched to a good exhaust (I picked HKS but when I saw the size/weight I was not exactly pleased). The COMBINATION of these two things with nothing else made a noticeable increase in horsepower and I noted no real losses in the low rpm range (and the car idles quiet but sounds Wicked Mean from 4,300 rpms and up... I can link you to a video where you can hear the car wind out as my camera man videos from out the sunroof if you'd like... with mk2's falling behind as I pull away). Top end definately winds out better and I rarely cruise under 4000 rpm. These 4ag motors were made to rev high, they seem to prefer it actually. Of course doing just exhaust will do nothing because the motor is still restricted at the other end (duh)... do both (without going overboard on the exhaust end), and you'll notice an increase.

Just running a header and downpipe would be a hefty loss in power more than likely due to the extreme loss of backpressure... gotta have some backpressure in these small, lightly modded motors folks!

Oh, and here's the

video

where you can hear the N/A... sorry for the bouncy camera work, a broken strut and hard driving with someone hanging out the sunroof trying to film is tougher than it looks! I also couldn't see behind me out of anything other than side mirrors so I had no clue I was screwing up the video pulling away from the other cars. You can hear the N/A really good from about the halfway point on when I get in front of the pack and lead for a bit.

[te51levin]

Originally Posted by curvesrgood

... gotta have some backpressure in these small, lightly modded motors folks!

NO NO NO NO NO NO NO NO NO! That is absolutely, fundamentally incorrect!

Backpressure is an unfortunately byproduct of a modestly sized and/or poorly engineered exhaust system, or sometimes of a grossly oversized header that kills velocity. It is absolutely not something that is designed into a properly built performance exhaust system. There are exceptions, but they are so rare and so specialized that they need not be discussed here.

One more time for those who missed it:
BACKPRESSURE IS NOT YOUR FRIEND.

If one more person declares that backpressure is necessary or beneficial I am going to split my skull and let the *&%ing demons out!

[curvesrgood]

Please explain why these glass pack to stock exhaust causing the smoother power band (I've heard others say similar things when changing exhausts on mk1 n/a cars, that they gained some butt dyno power going back stock from some... not all... crazy rediculous high flow exhausts)? Is the factory tuning that spot on that the computer is confused with too much airflow? Or do people just not do the obvious combinations of a functional conical short filter or a true cold air intake setup when they've done these exhaust swaps? I had read somewhere online that these things needed some backpressure, suppose that site had poor information as seems common with these motors. The 85 with a trd header, and supertrap muffler (no cat of course) and adjusted timing was rediculous fast I drove last week... that muffler did nothing whatsoever on that car other than perhaps amplify the sound a bit... that car had no real backpressure and clearly needed none. My bad, I'll stick to 4ag info from trusted sites from now on, lol.

[te51levin]

Your grammar is a little tough to follow and I'm not sure what you mean about glass packs. But basically, I refuse to admit butt dyno observations. The human ass is a fine piece of engineering as far as seating is concerned. However, it is so poorly calibrated as a performance measuring device as to be unuseable. Almost every time I made a change to my car that resulted in improved performance, the difference was not discernable by butt dyno. Those little changes that I couldn't feel, or thought I felt, or that felt like losses, added up to almost 30 horsepower! If I relied on SOTP rather than actually measuring the results I would still be right where I started.

And really, unless you've actually measured the mean (average) backpressure as well as backpressure at different points throughout crankshaft rotation, you won't know how much more or less backpresure there is in the system after the collector, or at the exhaust valve throughout its opening and closing cycle. There's just no way to know until you test. Even then, there is no guarantee that you can simply apply a pressure reading to your power output and construct a reliable conclusion based on those two figures.

I don't know why the car you drove last week was faster, or felt faster, than whatever you are used to. You are comparing two entirely different cars with several different modification all applied at the same time. The only way to say for sure what made what difference is to test each mod, one at a time, on the same car, and see which ones help and which ones hinder. Anything less than that is, at best, guesswork.

There is so much more to the science of exhaust and induction than simply whether you have more or less backpressure. I can't even begin to pretend that I understand it all, but I know the basics, and one thing I do know for damn sure is that backpressure is not a goal to shoot for.

[E T Haggis]

so having no back pressure u need not to worry. because you really don't need it. So i shouldnt be concerned about the straight pipe hurting my power at all?

[curvesrgood]

Well that was the other thing I was going to mention... we are talking about butt dyno here which has no bearing whatsoever on reality. I was talking about the fellow who had posted earlier (just above my post with the video) who was running a glasspack setup (oldschool musclecar deal generally that more or less amplifies sound and creates no backpressure) and some guy above in this same thread had talked about removing that setup that someone had put on his and going back to a stock exhaust and his car ran smoother/better (I noted he didn't say faster though). I was just curious why swapping from something super high-flow (said glasspack for example) back to stock would cause a noted improvement in the power curve unless the computer was confused or something like that when the other muffler was on. (also I'm 90% more sober and 60% less confused than I was when I posted yesterday).

Oh, and E T Haggis: My S/C seems happy with a borderline straight pipe (have a massive exhaust leak at the flex pipe I haven't fixed yet and have been enjoying frightening other drivers and small children with how rediculous the car sounds right now).

[E T Haggis]

yup thats straight pipe.. fart can on crack

[te51levin]

Originally Posted by E T Haggis

so having no back pressure u need not to worry. because you really don't need it. So i shouldnt be concerned about the straight pipe hurting my power at all?

As I stated above:

Originally Posted by te51levin

There is so much more to the science of exhaust and induction than simply whether you have more or less backpressure.

That means that you absolutely CAN NOT determine whether an exhaust system makes more power, or more favorable power delivery, simply by looking at "backpressure".
I can go into detail, but nobody seems interested in reading detail, so let's just skip it. I mean, we haven't even talked about where in the system this backpressure is supposedly taking place, whether it occurs across the RPM range or only at certain points, etc etc. I understand that you guys want simple answers, but there is no simple answer unless you build something and dyno test it against a known baseline. If you want to go into harmonics and fluid dynamics, I suggest you set aside a lot of time and money for an education so that you can understand the research required to really get a result. That is an entirely different procedure than going to Kragen, picking up a Cherry Bomb and decreeing that it has no backpressure and will therefor produce a given result.

Originally Posted by curvesrgood

I was just curious why swapping from something super high-flow (said glasspack for example) back to stock would cause a noted improvement in the power curve.

First off, let's establish one thing: that glasspack may not flow better than the stock muffler. Many glasspacks have louvered cores that stick out into the exhaust stream like rows of teeth in a shark's mouth.
You may have a glasspack with a 2" slip fit bushing on each end, but only 1.25" open space through the middle. If you get a big piece of styrofoam, put it on a lathe and turn it into a 2" diameter cylinder, then try to shove it through the glasspack, what's going to come out the other end? A 1.25" diameter cylinder and a whole lot of little chunks of styrofoam. Same thing happens with the air as it passes through one of those louvered cores. "High flow" indeed.

Your uncle Skeeter (the one hasn't worn a shirt since 1992) is going to tell you that you can turn that glaspack around so that the air flows over the louvers and not into them. This just destroys any silencing ability that muffler ever had. It does not improve flow. Uncle Skeeter doesn't know &^% from apple butter about fluid dynamics. And his '84 Trans Am is not "makin' five hunnerd horse" no matter how many vacuum lines he has removed. Oh no - another redneck power myth debunked. Vacuum lines do not cost horsepower!

Let's revisit the glasspack and assume for the moment that it does actually flow more air than the stock muffler. We'll assume that it is properly sized and that it has a perforated core rather than a louvered one. Can we tell by looking that it will outflow the stock muffler? Absolutely not. So we'll assume we've put them both on a flowbench and confirmed that it does. We'll also pretend that the butt dyno has been set aside and that the car has actually been to a dyno and confirmed that the car ran smoother and/or made more power on the stock exhaust system than it did on this glasspack. Why?

So many possibilities:
1) The glasspack setup included tubing that was poorly bent, crushing the pipes and reducing flow.
2) The glasspack setup included tubing of the wrong diameter, producing a mismatch between pipe and muffler.
3) The glasspack was welded in so poorly that welding slag hung into the exhaust stream, disrupting flow.
4) The glasspack system was poorly built and created exhaust leaks, disrupting flow.
5) The glasspack system created a different resonance than the stock muffler due to physical length or design, thus affecting the exhaust flow through it at certain speeds.

And of course we still have the possibility that the stock muffler just plain outflowed the glasspack.

Long story short (since most people aren't going to bother reading most of this anyway):
You won't know about the straight pipe's effect on power unless you DYNO TEST it. But if you are going to do that, be prepared to spend hundreds of dollars in dyno time testing pipes of different diameter, length, etc until you find what works for your exact combination. Also know that if you ever change your combination, the exhaust pipe will need to be changed for optimum results. You can rest assured that there are better ways to make power on a 4AGE than by chopping off the muffler. Most of them will also not mark you as an arrogant, inconsiderate punk as quickly as running around with no muffler will. It does annoy other people (to the point that they may seek revenge) and it does not make enough power, if any, to justify being an ***hole. So don't do it.

[E T Haggis]

You can rest assured that there are better ways to make power on a 4AGE than by chopping off the muffler. Most of them will also not mark you as an arrogant, inconsiderate punk as quickly as running around with no muffler will. It does annoy other people (to the point that they may seek revenge) and it does not make enough power, if any, to justify being an ***hole. So don't do it.

Im sorry what do you recommend or did you already state it above and i missed it.

Long story short (since most people aren't going to bother reading most of this anyway):

btw i read all your text dont feel like your wasting time.

[curvesrgood]

No, you weren't wasting your time, I'm looking into the Hendrick's motorsports program they've just set up locally at the community college here actually for this next year, so I'm always trying to figure things out, why they work like they do, how to make everything more efficient, etc, so you didn't waste your time, and the post was helpful.

And thankfully the S/C doesn't have a crazy huge hole in the flex pipe... a good bit of exhaust is flowing through the system still and through the stock cat and newer stock S/C muffler, so it is "moderately reasonable" sound wise (friends say it sounds like a mean street bike winding out)... as opposed to my dad's S/C which has 2.75 or 3 inch pipe run from the flex pipe back (no cat)... that is rediculous loud and everyone and their brother tries to race him. I told him that was gonna be too loud for something he drives around a lot!

[te51levin]

Sorry guys, I guess I was just venting a little bit there. I don't mean to come off like a jackass...sometimes I just feel like I'm repeating myself is all. At any rate there are a few choices out there. if you have an NA, a new SC muffler is a good upgrade for a reasonable price, and fits with minimal mods. If you have an SC you may need to look into something custom to get any more performance.

if you guys are interseted in learning more, pick up a few books. I like Four Stroke Performance Tuning by A. Graham Bell and a very old but still relevant one, The Scientific Design of Exhaust and Intake Systems by Smith & Morrison. Both are often available at Half.com (my favorite place to shop for books).

[4W4K3]

What's a book?