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Just my imagination

Hey, there is a good foundry here in Oregon......maybe they will cast me the cover pieces......couldn't cost much, right????? Does the car with side pipes get the resonance that seems to be a common complaint?

No resonance to speak of. I don't know what I'm gonna have on my hands when I get through with my engine build-up though. ;)

_ken :w
Let me see if I can answer a couple of different questions here: First, Graham asked

“I have a 92 with true duals, no y-pipe. Now I've been looking at 2 options. 1 is to go with a Corsa cat-back and the other is to just replace those big LT1 mufflers with Magnaflows. I beleive I have a 2.5" exhaust system and have no intentions of increasing hte pipe diameter.
Now if I follow what you are saying going with either of these solutions will not get me any increase in hp/tq. Because the biggest offender is the cats. Correct ???
So if that were the case then would I get a better gain by replacing the cats with ones from say Random Tech that are more free flowing while still meeting emmissions ???”
What you do depends somewhat on your budget. First , I don’t know how free-flowing the Random Tech cats are in relation to the standard cats. Their website shows an LS-1 Camaro getting a 16 HP increase with a cat change, but your LT-1 engine is not quite as sensitive to backpressure as an LS-1, so your results might not be quite that good. In any event, your improvement is not going to be near as good as if you simply eliminated the cats. How often do you get emissions tested?
I’m not at all a believer in “cat-back” exhaust systems unless of course you need new tubing anyway. The tube material is another issue: some materials are much better than others, but that's a subject for a whole 'nother post!

I don’t know what replacement converters cost, but a more cost-effective approach might be to go with low-restriction mufflers, just using the stock piping. Your mufflers are fairly restrictive, so with a good muffler the power improvement should be greater than with free-flowing cats. IF cost is no object, and you must have catalytic converters, then go replace the cats also. You will see a further improvement, but it might be quite small. Look at the power curves that Random Tech puts on their website: with this small amount of improvement, you only get a significant benefit at high RPM, above say 4500 RPM.
Then Louie asked:

“So, could I conclude from this discussion that the best bet would be to put a Walker Y-Pipe with PowerEffects tunable exhaust system?”
“The one goal that I must achieve is the elimination/significant reduction of the resonance (1200 to 1800 rpm) that currently kills the joy of long cruises in our '90, L-98 coupe. “

I would certainly think the Walker ‘Y’-pipe would fix the resonance problem. That resonance noise is caused by two things: the pipe lengths in the exhaust system have a resonance excited by engine firing at around 1200 RPM (80 Hz), and the cabin has an acoustic standing wave whose frequency coincides with that same engine firing frequency. That is, the cabin has an interior dimension (probably length) that is equal to half the wavelength of 80 Hz sound. The only fix is to change pipe length (impractical) or to put a connector between the pipes at the correct location. The Walker part does that.
I can't render an opinion on the Power Effects mufflers; I don't know how they work. If they reduce noise simply by increasing restriction, though, like a SuperTrap does, by the time you get it reasonably quiet you'll have a huge amount of backpressure. The SuperTrap, for example, has low restriction when it's noisy, but if you make it quiet, you've got the same thing as sticking a potato in your pipe.
ok so, now 2 q's

1. What are the better/best materials for the exhaust?

2. where is the optimum plce to put and X pipe in a '92?? (to minimize the resonance)


Thanks for the feedback. Oh and I forgot, Welcome! Good to have you onboard.

To answer your question on the emmissions testing. Every year. It's actually the biggest part of the inspection. The rest appears to be cursory. So removal of the cats would be bad. I'll skip the Random Tech cats for now. They are about $250ea.

I asked about the LT1 mufflers because I have an inexpensive option that was presented to me. A local muffler shop has a pair of the stainless steel Magnaflows with a nice 4" polished tip already welded on from the factory. He got stiffed because the guy that ordered them never showed up for the work. So he will sell them to me at cost and install them dirt cheap. These are a straight through design. I know of a couple of people who use these and they say the car has a nice deep rumble and turns heads when they get on it. Neither of the two have any complaints about resonance.

Hey Mike,
Just be careful with an X or H pipe too far in the rear. You may not be able to drop the spare tire cover to get at your spare in an emergency :eek

I had a Hooker header set up with 3 inch Flowmaster exhaust with Randon Flow Cats on my '85 for many years. The performance was good, but the reasonance was deafening. I would say that you need to take Ken's feedback with a grain of salt because it is a side exit exhaust. If you go with a side exhaust you will eliminate most of the reasonance that comes up through the rear hatch area (literally like an audio speaker cabinet). Maybe I am getting old, but headaches from driving are not fun.

I removed everything but the cats, and went to a 2 1/2 with Flowmasters. It is still 2 to 3 times louder than my GTS Coupe. If I were to do this today, I would go with a 3 inch Corsa system because of their sound cancellation technology. It might not yield maximum flow, but the differences with the competition is not even negligible (unless you are building a dyno queen). I drove my C4 for 156,000 miles and sound makes a difference over that many miles.

That's my $.02...

Graham--thanks. I will make sure to double check the spare tire clearance before install. I was borrowing a friends car last night and ended up having to change a tire in a Home Depot parking lot while it was snowing. brrrr.

Brad--- I am a little younger, and I can tell you that I don't mind the noise outside, but the resonance inside gets me. I too would sacrifice a bit of the hp for a quiet interior.

Exhausting Subject !

Hello, and Welcome to CAC Graham ! :w
I would like to ask your opinion of a Dynomax muffler P/N #17221 ? I have a '96 LT-4 'vette, and I am thinking of installing a pair of these in replacement of the stock mufflers. I am not afraid of installing the smaller dia. pipe all the way through, however, I am more concerned at the moment with getting my car to sound like it has a 300 + hp engine under the hood. I will make occasional trips to the drag strip, however, I don't want the buzz of two chamber Flowmasters. I live in a state that does not currently have vehicle inspections, so deleting the cats would not present a problem ! Thanks in advance for all of your advice and knowledge!

I have the 2 chambered racing Flowmasters and they reosnate like heck. Outside they sound very aggressive.

Thank's Brad !

I appreciate the "feedback" that is why I don't want anything close to that on my car. I plan to use this car more "socially" than racing at the track, however I feel that there is an acceptable balance between power and sound out there ! I have 2 chamber Flowmasters, with Hooker Super Comp. headers on my '69 Cougar, and when I feel like dragging my knuckles and waking the dead, I just fire that baby up, and look for smooth sections of asphalt to tear up !

Exhaust Materials; X-over placement

Mike had a couple questions:
"1. What are the better/best materials for the exhaust?

2. where is the optimum plce to put and X pipe in a '92?? (to minimize the resonance)?"

First, I'm basing my materials selection criteria on use in North America, where you get a significant amount of salt exposure, and a significant amount of sulphur in the fuels. In increasing order of desirability:
1) carbon steel - totally undesirable; rusts badly in days, perforates within a year of average use.
2) aluminized carbon steel - good for a daily driver, perhaps, since the aluminum coating provides a reasonable amount of protection against salt corrosion, unless it has been welded or the coating has been otherwise damaged. Then, in the presence of ANY salt, the steel substrate "sacrifices" to protect the aluminum! Thus producing rapid pitting leading to perforation. Lives maybe two to four years in average service.
3) 409 "stainless" - Not a true "stainless" steel, since it doesn't have any nickel in the alloy, but it does have good elevated temperature strength; carbon steel is like silly putty above 1000F. The 409 develops a rusty surface fairly quickly, although it will take a high polish if buffed. In Texas or Arizona, for example, this material might last just about forever unless the car is used only for short trips. In Detroit, this stuff will last probably 4 - 7 winters.
4) Then comes aluminized 409 (AL 409) - The aluminum coating here gives excellent salt corrosion resistance; due to the lesser activity of the 409, the aluminum coating if damaged will sacrifice to protect the steel substrate. The appearance will be far superior to uncoated steels, since no red surface rust will apear until every little bit of the aluminum is gone. This would be a "lifetime" exhaust system on cars that aren't exposed to enormous amounts of salt, and if not welded.

Sometimes, depending on the exact alloy content, a condition known as "intergranular corrosion" can cause 409 or aluminized 409 to fail in weld areas, where the heat of welding has 'sensitized' the alloy to intersticial salt corrosion. The solution to this is:

5) 439-Ti or 18 Cr-Cb, two alloys having both higher levels of chromium (18%) than 409 (11%), and either titanium or Columbium (Niobium if you're un-American) or a combination of the two to prevent chromium-carbide precipitation, and intergranular corrosion. The higher chromium content also provides greater high-temp strength. This material will still develop cosmetic surface corrosion. I'm just guessing, but in daily use this might be a 6 - 10 year system. Much longer without salt exposure. These ferritic stainless steels will also take a high polish.
6) Finally, the ultimate material for automotive exhaust (IMNSHO) is aluminized 439-Ti (AL 439-Ti or equivalent. The coating provides cosmetic corrosion protection, while the substrate provides temperature resistance and intergranular corrosion resistance. Nobody knows for sure, but the best guesses are that this will exceed ten year life in the most severe environments, such as places using calcium chloride road salt.
PS: I didn't mention any of the austenitic stainless steels like 304 because of the intergranular corrosion issue. The first exposure to salt, even just near the beach, will cause weld areas to crack like a glass rod.

As for the cross-over pipe for a '92: I'd say put it just behind where the left and right pipes begin to 'Y' apart, near the differential. Checking of course for clearances! Then you might want the 3-chamber Flowmaster muffs. Those sound fine on my son's '96 C*bra!
It's important to note that "quiet" and "horsepower" are not mutually exclusive. See the C5 for proof; its' total exhaust backpressure is less than half that of the C4.
:w jkd

Are you sure the exhaust is free from the cat. conv? You may be running targas' like my 85.
redbob--thanks for the detailed response. I like to get things to last. (hate repeating the same jobs over and over) Since this is my daily driver, it will see all conditions.

thanks agian
Hi. Not sure if you were aiming at me or redbob on the Dynomax question. I had Dynomax on the 84 I had for a while. Made it sound good but idling in the garage it was pretty noisey. Also low rpm, high gear, with a load and they were really annoying. Sounded like you were in old truck. The resonance was too much. And they also had a little on the highway. Not terrible, but not great. If you want NO resonance then you need to look at Corsa.

I'm pretty sure I'm going to try the Magnaflows really soon so I'll let you guys know how that goes.

Thanks for the awesome explanations. I'm afraid your metalurgy skills are way beyond me. For a test of the Magnaflows I'll just leave my stock exhaust pipes alone. They've been on there since 92 and still look pretty darn good. All those other exotic sounding minerals like Columbium I've never heard of... Can I get them at the drug store when I get my prescriptions and then just rub it on my exhaust pipes ;)

Your Right !!!

Hello Vms4evr !:w
Yes Sir, you are correct ! I was meaning to address that post to RedBob ! I just purchased a set of DynoMax Ultra Flow mufflers with 3" in/out opening's, and I am still not sure if it would be worth my time/money to downsize the rest of the exhaust system as RedBob was stating ! I may, however I am not wanting to have a full race exhaust on my car. I am kind of discouraged now,:( if those are the same mufflers which you had on your car ! Well, I guess I will know for sure after a trip to the muffler shop ! RedBob, if you read this, what are your thoughts on my goal for the exhaust on my car ? Thanks All,

Hey Steve,
I'd be surprised if they are the same, but you never know. When I got the car they were on it so I didn't choose them. Not that they are a bad muffler. These were also on an 84 which is a different setup. Just not my taste. And that is the biggest point here. My idea of too loud or too much resonance probably is not the same as yours. So go ahead and try them. If they are 3" inlet/outlet and a straight-through design then they will be louder than your factory mufflers for sure. Don't be too discouraged. Try them and let us all know what you think. We all play guinea pig with our changes and can share them with each other. I just did that with my gear change. If I was unhappy that would have been a $1,000 oops! Fortunately I'm very happy with them :D
I know several people who just put muffler eliminators on their LT1s for all of $200 installed! Many of them are really happy. To each his own. I'll still try the Magnaflows and report back. Ain't this fun being part of the grand experiment :s
Grand Experiment Redux..... !!!!!!

Hello Graham !
Yes, It is great to be part of the Grand Experiment ! I will definitely post my results with these mufflers in about a week ! I will also be adding an air foil, as well as a K&N air filter at the same time as the muffler install ! I don't really have a feel for what the total HP gain will be with these parts, however I'm sure that I will get a little seat of the pants improvement ! Thanks,

to P-ColaVette:
Sorry I didn't see your question sooner; I think you'd be doing fine if you went down to 2.25" dia. pipes on your car. I've done it on a ZR-1 and on the early '90's LT-1, and all we got was MORE HP, because as I mentioned earlier in that thread, there's less flow disturbance at the muffler and resonator connections.
I'm not sure I'd do this for the Backpressure reduction alone, but if you had to replace pipes anyway, it'd be something to consider.
The weight reduction is appreciable.
Regarding the Walker mufflers: having had them on a M*stang GT, I think I can safely say you're going to be disappointed in how they sound - unless maybe you're 17 and only want them for cruising the drive-in.:)
Like Graham said, they sound like an old truck at low RPM; probably set off burglar alarms cruising around looking for a parking place at the mall. They ARE low-restriction, but whether or not they are mufflers is the question!
Happy New Year,
- R
Well I whimped out on the Magnaflows. Went down to the muffler shop and looked at the pair he had. 2.5" straight through design with a big but short 4" round outlet. They would look silly on the Vette. One of his friends was there and had a set of the same ones on a V8 Ford truck. Now not to compare a Ford truck to a Vette but those mufflers are loud as he**. Now way. The Vette would resonate just like those mufflers I had on the 84. Like Redbob said. If you're 17 and just want a lot of noise they would be great. The guy told me he puts them on imports for teenagers and they love them...
So I'm saving the $300 I would have spent on the Magnaflows + $300 I would have spent on that silly hatchback louver idea... So I figure I'm $600 closer to a Corsa catback system. Which was the system I wanted all along. Just wasn't keen on parting with $900 for 2 mufflers, resonator, and pipes... but the Corsa has almost 0 resonance, straight through design, and has a sound that I personally like. Oh and it's rated to flow 42% more than stock.
I know this is for the C5, but since we're on the subject of exhaust:

1. Is the titanium exhaust on the Z06 really as great as everyone says it is?

2. It took 7 years for the development of the C5 exhaust?

3. Are the C5 stock exhaust systems pretty much "optimized" in terms of flow? What I'm really trying to say is, besides for tone, would putting an aftermarket exhaust on a C5 really be that cost beneficial?


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