GREGGPENN

I'm on the 2nd engine and 6th iteration of exhaust setup for my 89. Yup, that's right, been to the exhaust shop 6 times....all for mods.

Except today.

The first iteration was stock -- which was too quiet.
The second iteration was (350) cats, glass packs, and resonated tips. (This was pretty sweet..slightly euro sounding).
Third I added sidepipes to the 350. It had a big more bark because it was missing resonators. (They have internal glass packs).

With the 383, I was worried about extra sound -- having also converted to headers. I went with Magnaflow spun cats, a SpinTech muffler, and the internal glass packs of the sidepipes. The drone in 6th was annoying...though TOO quiet at higher rpms. It sounded a bit too similar to the 350 with sidepipes -- except more hwy drone.

So, I tried a Magnaflow center cat in place of the SpinTech. I hoped it would be a tad bit quieter...and I'd noticed the ONLY thing SpinTech is good for is accentuating the lowest frequencies. Since removing it, I decided I don't like their mufflers. The pull too much of the high frequency "bark" and create drone at lower rpms. This was confirmed two ways....

With the Magnaflow in, I got ride of the hwy drone...plus I noticed a bit less carbon on my sidepipe tips. That meant cleaning them less often -- which was part of my goal. But, that cat only lasted about 3 months! The brick came loose last week. I need call (or find out) if a gold-colored heat shield tells me if it was too lean or too rich. (Anyone know?)

The shop said the thought my 383 was just too much for that converter.

So, my choice was a smaller 2.5" glass pack in it's place...or 3" straight pipe. I was worried about overall sound of the straight pipe, but started it up after cutting out the converter. I was pleasantly surprised. It barked like an SOB but didn't seem to drone as much as I thought.

So, I put in the 3" straight pipe. That means I'm running Magnaflow pre-cats (spun metallic) with the sidepipe glass packs on a 383 with headers. I'm surprised, but there's no drone! That means straight pipe is better than the stupid SpinTech I tried! So, my advice it to stay away from SpinTech mufflers.

I gained more top-end too. It's not choking out at 4500rpms anymore. I'll have to run it a few more times to decide for sure -- because I let off (shifted) passed by 5k rpms. It get's there quicker too.

The best part is how loud it barks on quick acceleration. Much more impressive sounding 383 now. Plus, I don't have the hwy drone anymore. Needless to say, I'm a happy camper!

This makes me think anyone can get by with pre-cats and glass packs as a reasonably sounding setup! Not too loud, barks like crazy, and no drone.

Try it.

mcm95403

inb4allthebutt-o-meter-haterswhocan'ttellifachangemakesanimprov ement

JrRifleCoach

notsureiunderstandwhatyoursayingabouthte butt-o-meterthing

mcm95403

Reference to the "exhaust" thread where there was a certain amount of back and forth about being able to tell if an exhaust change could be felt/noticed.

TA

Wow, very touchy aren't we?

I can't speak for Aklim, but I can tell you my issue was your claim that there was a "significant" (your words) gain from switching from L98 exhaust manifolds to LT1 manifolds. You compounded it by saying you could feel the difference (hence the butt-o-meter comments). We asked how you possibly felt a likely 5 hp gain which obviously got your panties in a bunch.

Maybe we have different definitions of "significant". I still believe that if you tested your car (dyno or track) with the only change being your exhaust manifolds you would see only 5 hp or so. 5 hp is not "significant" in my book and I can't believe you would feel a 5 hp change.

Sorry for the hi-jack Gregg. Glad you got your exhaust worked out.

TorchRedlt4man

Thanks for the info on the exhaust systems, Gregg.

Amazing what the absence of some parts can do for an engine.

IBTL!

GREGGPENN

No problem.

This thread was more about the sound changes…and how I was surprised. I did mention something about performance but it wasn’t the focus of my point. When people are making exhaust changes, there’s usually an equal amount of concern for power and sound….though power probably has the edge in desirable outcome.

For curiosity, I went looking for the thread in question. I went looking for the threadwherewordsruntogetherafterdiscussi onofexhaustchanges. The contents wasn’t exactly what I expected, but there are reasonable points about what can be felt. In general, I think it takes something like a 5-10% change to really notice the result of a modification. I’ve talked about this subject (with others) for about 15 years and some would say it takes about 20hp to notice a difference. For our 250-300 (stock) hp engines, that means less than 10% might be felt.

Starting out, I think it’s easy for the novice to be fooled by changes in sound. I, myself, went through a learning process about sound. I’ve changed my exhaust several times and sound-insulated my car. I’ve gone louder, to softer, and back. I think I’m getting better separating sound from performance. Mostly, that comes from observing where (in town) WOT burst break tires loose – and in what gears. I also notice how easily they break loose and normally focus on upper gears. With a stick, I have control over gear selection and like to focus on the performance of 3rd gear. I’m right on the edge of getting 3rd to break loose – because it does under specific conditions. So, it provides a good measure of changes in power.

If others use a fairly measured and calculated approach, I think it’s possible to recognize fairly small changes in power. OTOH, it’s also reasonable to qualify the change accordingly. I would tend to think a manifold change wouldn’t be night and day – but I’ve never done it. I would think the resonator change (which seems more the issue of that other thread) would be more likely a perceptual versus actual change in performance. Someone clearly posted the small (negligible) affect of an LT1 resonator. That seemed more the issue of the other thread – and how it may/may not be perceived.

In my thread, the issue is a muffler versus converter versus straight-pipe.

After talking to Magnaflow a while back, I’m fairly confident in knowing that a 94009 universal converter flows in the 400cfm range. Compared to straight pipe, it’s a significant drop and shows why many are aching to drop even performance converter in lieu of straight pipe. There SHOULD be a noticeable gain in power. The difference would be a variable – depending on the power of a car. Higher powered cars are going to be more affected by the addition/removal of a converter.

To be clear, pre cats (bullet) cats aren’t as dramatic in their effect. That’s because they’re placed in dual pipes where your overall flow stays up in the 700-800 cfm range. (Simply add the flow of the two converters together).

On mine, I went from a dual-in/single-out muffler to a main (center) converter. It helped hwy drone but didn’t seem to compromise power. I could break tires loose in 2nd and third gear as easily as before. Even though the car got a bit quieter, it didn’t seem slower. (BTW…when I sound-proofed my car, I definitely noticed the quieter-seems-slower phenomenon.) Because I couldn’t feel any drop in power – going from a muffler to a converter, I had to assume the converter didn’t hurt as much as people sometimes think –OR—the muffler isn’t as good as the seller would claim.

One of the things that bothers me about SpinTech is they claim much better results than Magnaflow and Flowmaster – but refuse to use the same level of flow testing as the standard performance community. IIRC, 28” of water is normally the standard for measuring flow of things like heads, intakes, throttle-bodies, etc… I’ve also heard/read ratings for mufflers, straight-pipe, and converters.

IMO, SpinTech blows hot-air up consumers hiney by measuring their own stuff using something like 10” of water. Plus, they haven’t (or won’t admit) to comparable measurements on other speed equipment. They only “claim” better performance.

I’ve bought their products twice – due to the advantage of custom-building the inlets, case-size, and outlets. They have someone more flexibility in design – but I question the results. They say they’re better – but I don’t believe it any more. Compared to a performance converter, I felt zero difference. Actually, it possible the converter was slightly better.

Now that both items are removed from the car, it seems more obvious what a single muffler or converter can do in a center-cut location. Swapping from muffler to converter to straight-pipe shows the disadvantage of that brand of muffler -- both in terms of sound and power. Neither was a plus.

Often, this forum debates and searches for the best solution between big (expensive) brands like Magnaflow, Corsa, Borla, Flowmaster, etc…. This post is to encourage people to stick with less expensive options like glass-packs and bullet-cats. I like the use of cats to keep cars from overtly polluting the atmosphere. I also like them for their reduction in sound. I like the use of glass-pack (resonators) for cost, ease of installation, and simplicity.

People like Vizzard have shown glass packs and other types of mufflers to be more restrictive to flow – than properly chambered mufflers. SpinTech is supposed to be one of those brands. But, when considering drone, street performance, and power consequences, I don’t think the cost justifies the outcome. What little (if any) improvement in power is negligible – compared to the infinitely better sound quality without those canister mufflers.

What I’m saying is I think those large-body case mufflers are the biggest part of the drone problem with our C4’s. They provide a chamber to form the resonate frequency that doesn’t “agree” with the shape of our car. I saw one recent poster who’d filled up the air space around his gas tank. There may be something to that. But, I also think a simpler solution of bullet converters and straight-thru resonators is an equally effective solution in combating the resonance problem we often see complained about in C4 Corvettes.

Of the six iterations of exhaust systems on my C4, the two that focused exclusively on converters and glass-packs produced the best result. I think there’s something to be learned from that.

ch@0s

I would have agreed with you Mark if you had not used the word "significant". I went from L98 to LT1 exhaust before you did and noticed the difference in size of the exhaust. I couldn't tell you if there was any difference because of the different heads although I'm sure there was.

mcm95403

Yes, but my comments related to the manifolds, not the exhaust system itself. Maybe "substantial" would have been a better word choice, but I think it's splitting hairs. Also, since I did one side and then the other side a few weeks later and could tell a difference each time, I rate that as "significant". After both were on I was surprised at how much easier it was to pass on the freeway more than I was at the extended upper RPM capabilities.

Hopefully in the next couple of weeks I'll be putting mine on the dyno so I'll finally have some real numbers of what it's doing with the new engine.

ch@0s

Dont you have different heads now? That really won't count for anything. I have no doubt they are better flowing but I would agree with everyone else here prob just 5 HP if your lucky unless you change the whole exhaust don't you think?

mcm95403

Don't forget that exhaust systems don't flow air - they flow exhaust, so airflow ratings of exhaust components aren't a relevant test measurement.

The whole "airflow" thing came from the early 80's when the Cyclone Sonic Turbo mufflers were introduced. The marketing people made the correlation that your mufflers should flow as much air as your carb. Of course the problem there is that (4 barrel) carbs are measured at a 4" pressure drop (2 barrel carbs are measured at 1.5" pressure drop which is why a Mopar Six Pack is 1350 "advertised" CFM, but is really about 930 "4 barrel" CFM).

The problem with the airflow thing is that exhaust flows in pulses rather than a steady state. The exhaust pulses are very similar to the ram tuning done in our CFI, TPI and LTx engines.

When an exhaust pulse exits the chamber past the valve it's very hot, moving at very high speed and has "two components". One is a high-pressure wave clinging to the walls of the (header/manifold) pipe and that high-pressure wave is pulling the physical by-products of combustion in a low-pressure zone slightly behind it. Maintaining the velocity as much as possible if one of the main goals of the exhaust system. Keeping the velocity up insures that the exhaust doesn't slow down and "stall" in an oversized pipe. Stalling would them become a restriction to the engine. The basic misunderstanding of this is where the "you need back pressure" idea comes from. An engine doesn't need backpressure, it needs a properly sized system. Of course for some of us, pipe sizes and things like single converters are something we're stuck with for smog compliance.

That high-pressure wave clinging to the pipe walls are what glass packs are designed to disperse. The louvers are supposed to direct that high-pressure wave into the packing leaving the combustion by-products on their own to get out of the pipe. Their inertia will only carry them so far, so of course the exhaust coming down the pipes has to work to push those by-products the rest of the way out of the system.

I won't turn this into a dissertation on how Flowmasters use that pulse energy to help evacuate exhaust from the engine, attenuate sound waves, etc. I will say that when you use the correct Flowmaster for the application, it will be quieter both inside and outside the car while making the most power possible. When I worked there we had countless race cars that we worked with who were amazed that the right parts could reduce sound levels to meet track requirements and still make either no or very little difference in power. It wasn't unusual for a willing racer to change his engine package to work with a better exhaust system and end up with an increase in power with a reduction in sound output.

mcm95403

I am the first one to say that my butt can't feel 5 hp but I think the problem here is that everyone is talking about a peak hp difference when what I've described repeatedly is a torque and "willingness to rev" improvement.

aklim

Maybe if you had a NUMBER concerning how many HP your butt dyno was sensitive to it would be a better choice. Perhaps you should say "My butt dyno can sense a difference of X HP.". Feel free to tell us what X is anytime.

Without a "Before and After" you have nothing. Obviously you failed your scientific process part of your science class or should have failed it.

aklim

So you are saying LT1 manifolds ALONE picked up what? 50HP?

aklim

I believe someone was running 550 HP with the Random Tech setup. Thought I read it somewhere. Anyone know for sure? I put it on my car because it got too loud for the wife to drive around in.

I tossed mine from from the get go because of TPIS LT headers and hollowed out the cat. Made too much noise for the wife so it went and replaced it with Random Tech. Maybe I should get something to replace the Borla Stingers if it bothers the wife that much.

Tom400CFI

Not in the cars that we're dealing with here.

You're right in your extensive post about the exhaust pulses, but that is gone in any stock or stock-like system by the cats. THERE IS NO "TUNNING" after the cats. After stock manifolds, after the resonator. By the time you get to the mufflers, you are really are looking at "air" flow...or put another way, the flow of gaseous substance.

mcm95403

Once again, I never said 50HP. Rather than jacking another thread, you're welcome to call me any time to discuss it. My number is on my website.

aklim

Not wasting my battery unless you have some specifics to discuss. You can't feel 5HP by your own admission but it isn't 50HP. Thanks but no thanks. You want to "dance in the fog" so nobody knows what you are doing. You don't have the stones to tell me how accurate your butt dyno really is because you know I can call you out on it if there is sufficient money involved.

As to hijacking, well, see post 2.

mcm95403

I don't know about you but I have 32 years of "car guy" experience which includes working in automotive machine shops, multiple speed shops totaling almost 5 years, 2 1/2 years as lead tech advisor at Flowmaster mufflers, and have had several dozen muscle cars like my 68 Charger, 69 Road Runner, 71 Charger R/T, 70 Super Bee 440+6, 70 Superbird 440+6 4-speed, a 76 Aspen R/T (The Aspen from Hell), 2 Slant Six Demons that both ran low 14's at 96-96 mph, a 300 hp 2.5 Turbo Dodge Spirit and many others.

In cars like ours that run in the 14 -13 second range, 10-15 crank hp usually equates to 1 tenth in the 1/4, which is also about 1 car length. I don't know about you, but I can feel that kind of a change.

In my Super Bee there was so much power it was more difficult to tell small changes. The best indicator I had of when it was really running "right" was to wind it up to about 20 in first gear and stab the gas. If the window washers would squirt on the window from the snap, then I knew I could race anyone and not worry about losing.

Before the 440 Six Pack went into the Bee it had the original 383. When my friend Steve and I ran at Baylands (he had a 70 Road Runner 383 Six Pack with a Crane Fireball cam, otherwise we were equal) he would pull me by 2 lengths and stay ahead. When I swapped on the Weiand 8008 intake and the 750 AVS off of my friends 69 Coronet R/T I could immediately tell a more than "significant" improvement. Sure enough, the next time we ran at Baylands, I pulled him by 2 lengths and pulled ahead slightly in the top end.

I've made changes before that were questionable - ignition upgrades, headers on the Aspen (it still had to run through a single 2 1/4" cat so the headers didn't do much) and things like that.

As for the LT-1 manifold swap as I've said repeatedly - the improvement was mostly felt in mid-range torque and much more willingness to rev and pull harder at higher RPM's.

I doubt many people here are able to afford to go to a dyno every time they make a change to their car - me included. I don't know if it would have made a difference if I still had a stock intake on it and/or stock mufflers. When I did the manifold swap I had already done the Accel intake and Flowmasters.

If you can't tell the difference in your car between a night with nice cool, dense air and a 110 degree day, or the difference between sea level and a few thousand feet of altitude (which KILLED the Super Bee when I moved to Reno!) then I don't know what to tell you.

Believe what you what, but I know when I feel a difference and when I don't. I have no reason to make anything up or lie about it. If it works, then great, if it doesn't I have no problem stating that. As I've said before, with 4 failed marriages I'm the first one to admit that I make mistakes. I'm not dancing in the fog (whatever that means), and I have no problem discussing whatever you like. I don't hide behind a keyboard slinging mud. I relate my personal experiences and knowledge. If that doesn't jive with yours, well that's life. You don't have to accept it - after all it's the Internets.

My battery has plenty of juice, so my offer still stands - feel free to call me any time you'd like to discuss any of this. I'm a very open person and will discuss pretty much anything - mistakes as well as good things in life.

cudamax

Hey MCM Im with you Even slight HP Changes can be felt and its real good to know that their is other MoPar Lovers Here. Ive been running them since way back in the late 70s. In my 2800lb 1969 GTS 340-4sp with the 68 8 3/4 Banjo running the 323s Even swapping out from a 750 to an 850 on my Dominator single plane manifold u could feel a 10 to 15 hp change and on my 70 440-6 pac Cuda 4spd swapping out the end carbs with the lightest Yellow vacum springs made the end carbs open fully their 1050cfm that could be heard 2 blocks away. Just that mod alone made those babies open as soon as about 2500rpm and that could be felt also.
Heck I can remember taking out my back seat and spare tire and jack and taking off my hood on the GTS COULD BE FELT.

I would and I could adjust my 850 Holley double pumper from 2 full turns out to 2 1/2 or 3 full turns out and feel by a floored pull in 2nd gear how rich it should be best for the nights temp by how much or how fast it would smoke the rears at 35mph and how hard it would pull