mufflers...to be or not to be...

[bucket]

does anyone have experence in removing the muffler and just using the converters to...well...you've got it figured out by now...hnoes

 

[vetteoz]

http://www.corvetteactioncenter.com...will-opening-up-exhaust-cause-power-loss.html

 

[bucket]

THERE IS A BALANCE BETWEEN PROPER BACK PRESSURE AND TOURQUE...
OPEN IS BETTER FOR WOT HORSEPOWER
BUT..I'M THINKIN THAT THE CONVERTERS WILL SUPPY PLENTY OF BACK PRESSURE

 

[MBDiagMan]

THERE IS A BALANCE BETWEEN PROPER BACK PRESSURE AND TOURQUE...
OPEN IS BETTER FOR WOT HORSEPOWER
BUT..I'M THINKIN THAT THE CONVERTERS WILL SUPPY PLENTY OF BACK PRESSURE

This is a MYTH! Back pressure will NOT produce power, PERIOD!

I have a post in the thread referenced in the second post of this thread that explains the origin of this widely believed MYTH! To summarize that post, many have opened up exhaust systems with no other changes only to experience power loss. This was because they did not recalibrate the carburetor to correct the leaning out effect of the open exhaust.

On Mass Air Flow systems, there's not even the need to recalibrate the carb. The MAF system automatically compensates.

NOW, all that said, if you were to remove the mufflers on an L98, the gain would most likely be unnoticable. That's because the potential gain would be at high RPM and the L98 runs out of steam at 4,500 RPM anyway. On a later car that has an intake tract that allows it to take a high RPM breath, there could be a slight power gain at high RPM.

For street drivability, where low and midrange torque is most helpful, improving exhaust flow from the cats back, does very little. The REAL gain in exhaust for the street is realized with small tube, full length headers. They provide exhaust scavenging that provide SIGNIFICANT torque gain at low and midrange RPM even with a stock exhaust system behind them. The only other mod that can offer such low and midrange torque gain is stroking.

BTW, the cats do most of the muffling anyway, so sound wise, running straight pipes from the cat back will not be TERRIBLY loud.

 

[tcxd40]

BTW, the cats do most of the muffling anyway, so sound wise, running straight pipes from the cat back will not be TERRIBLY loud.[/QUOTE]

I wouldn't say that is entirly true. My ride is a retired A/S SCCA car. And you were permitted to run altered exhaust with the approval of the officials. It had straight pipes. Extremly loud, except when at idle, anything over 1500 RPM was annoying to say the least.

tcxd40

 

[dogfish246]

From what I have researched for the past month, the LT1 and LT4 engines love to breath! For the most part, you can only gain HP by opening your exhaust. That is why drag racers use open headers!

Im sure you have heard the analogy that the engine is just a big air pump. Let air in and out easier, the more HP you will get!

Good Luck!:cool

 

[vetteoz]

That is why drag racers use open headers!

Fine when your engine idles at 1500rpm and only goes 1/4 mile at a time.
Not the same conditions as your DD

 

[bucket]

ALL IM SAYIN IS.....WHEW...EVERYBODY KNOWS THE FORMULA FOR POWER..ITS NOT ABOUT A LOT EXTREME TINKERING..BUT RATHER THE NOISE POLLUTION FACTOR AND QUALITY OF THE SOUND...I UNDERSTAND HOW SIMPLE IT WOULD BE TO DROP THE MUFFLER AND REPLACE IT WITH NICE CLEAN PIPE...BUT...WHAT WOULD IT SOUND LIKE?????
WOULD THE COPS LIKE IT??
WILL I HAVE RE-CALIBRATE ANYTGHING??

 

[MBDiagMan]

BTW, the cats do most of the muffling anyway, so sound wise, running straight pipes from the cat back will not be TERRIBLY loud.

I wouldn't say that is entirly true. My ride is a retired A/S SCCA car. And you were permitted to run altered exhaust with the approval of the officials. It had straight pipes. Extremly loud, except when at idle, anything over 1500 RPM was annoying to say the least.

tcxd40[/QUOTE]

Did that SCCA car have cats? If it had no cats, then YES, it would be EXTREMELY loud, with cats, however, a straight pipe is loud but not deafening.

 

[G Winter]

What MBDiagMan is saying is that with the L98 you can open the exhaust all you want. It will not give you noticable power increase because the intake is restricted. The system is limited to it's most restrictive air flow point, the intake. If you were to open up the intake breathing then open exhaust would give you more power. I have a very low restriction 3 in OD system from the cat back ,, seems to run just a little easier in the upper half of the rpm range. As far as an actuall increase in preformance , not noticable . I can not say it has effected low end tourge , going through two cats is plenty of restriction if that is indead needed. I tried straight pipe from cat back, plenty noisy but not real bad, nothing law informant would bother you on if you don't get wild with the throttle. I found it to annoing for longer drives , mufflers needed.

Glenn

 

[tcxd40]

I wouldn't say that is entirly true. My ride is a retired A/S SCCA car. And you were permitted to run altered exhaust with the approval of the officials. It had straight pipes. Extremly loud, except when at idle, anything over 1500 RPM was annoying to say the least.

tcxd40

Did that SCCA car have cats? If it had no cats, then YES, it would be EXTREMELY loud, with cats, however, a straight pipe is loud but not deafening.[/QUOTE]

Yes it has cats then and now. I run a complete Borla today and the difference is dramatic. Cats do not suppress the noise level at high RPM. Try it.

 

[Hib Halverson]

This is a MYTH! Back pressure will NOT produce power, PERIOD!(snip)

On Mass Air Flow systems, there's not even the need to recalibrate the carb. The MAF system automatically compensates.

As "MBDiagMan" says, the needing backpressure thing is mostly a myth but...the part about systems with MAFs not needing recalibration of the "carb"...

Well, engines with MAFs don't have carbs. In fact, a carburetor has not been used on a Corvette since 1981.

Also, when "compensation" occurs, it's not the MAF that does it. All a mass air flow sensor does is send a signal, proportionate to the mass of air flowing into the engine, to the engine controller (the computer or the ECM). The controller can, under certain circumstances and within certain limits alter the engine's fuel schedule to compensate for increases in airflow.

On a 92 that's only true when the engine is running in closed loop. It is not true at high load. When the engine is in open loop, and the need for fuel is higher than stock, the ECM calibration needs to be changed or "retuned" to get that extra fuel flow.

As for cutting the mufflers off a 92, you'll experience a slight power gain, perhaps 2-4 hp but, once the novelty of running around town with a louder exhaust wears off, you'll hate the resonance at 1500-1800 rpm on the highway.

Your best bet is a well-designe, "catback" exhaust system. Flowmaster is a good compromise between performance and price. On a 92 LT1 with a stock or near stock engine, the gain will be 5-7hp and the resonance will not be near as bad.

 

[MBDiagMan]

It is correct that the automatic compensation is only effected in closed loop mode, but unless the engine is highly modified, an exhaust change is well within the scope of the existing systems closed loop compensation capabilities.

Open loop changes would require a chip, but again, unless other SIGNIFICANT changes were made, it still would run well without any parameter changes. This is because the opened up exhaust not only improves flow, but also decreases pumping losses.

The way to take BEST advanatage of exhaust modifications would indeed be with a chip that would take full advantage of the exhaust changes. For racing advantages, this would be a must because at wide open throttle you will be in open loop mode. For most street driving, non racing situations, however, the exhaust change would be realized in closed loop mode.

 

[bucket]

im ok with it now..stock..but was cirious as to sound quality of a low buck mod...not careing about increasing performance..
thats a road this 92 and wont go down..
stock will do as performance mods are a sick drug..to what end.??
in los angeles its ludicrous...to say the least..i'll be stuck in traffic faster than you???i dont think so lol
im savin up for a c 5 or maybe even a c 6...

 

[nelson84]

Lose the mufflers and let it bark!

 

[TedC]

At WOT, the ECM runs in power mode. If the exhaust is too big, the stock ECM will run lean, and you are kissing power goodbye. Just connect a scanner and drop the rear y-pipe and mufflers and watch the results. You want a scavenging effect in the exhaust system, which is maximized when exhaust air velocity remains high with minimal back pressure. Zero back pressure reduces power below the torque peak. There is room for improvement with the stock exhaust, but the L98 is plugged up on the intake side, so don't go crazy and end up reducing low end power.

 

[MBDiagMan]

POWER MODE? That's a new one on me. The system is either running in closed loop mode or open loop mode. I will assume that you are referring to open loop mode.

There is little or no scavenging effect with a stock L98 exhaust system. Scavenging is an effect that takes place with full length headers. It is almost nil with short tubes such as the stock units.

 

[Hib Halverson]

At WOT, the ECM runs in power mode. If the exhaust is too big, the stock ECM will run lean, and you are kissing power goodbye. Just connect a scanner and drop the rear y-pipe and mufflers and watch the results. You want a scavenging effect in the exhaust system, which is maximized when exhaust air velocity remains high with minimal back pressure. Zero back pressure reduces power below the torque peak. There is room for improvement with the stock exhaust, but the L98 is plugged up on the intake side, so don't go crazy and end up reducing low end power.

All this discussion about L98 engines is irrelevant.

A 92 doesn't have an L98 engine. It's has the LT1. Additionally, the 92-96 exhaust system is completely different than whats on cars with L98s.

Also, Doc's comment above about scavenging is correct. Once you bolt an exhaust system (ie: cats, pipes and mufflers) the scavenging effect one gets under certain limited conditions on engines with headers will be extrememly limited or not present at all.

Finally, when the ECM goes into the power enrichment mode (it will also be in open loop), it is true that reducing exhaust restriction such that flow across the engine increases, the engine may run more lean. If it runs more lean to the extent that power decreases, the solution is to change the ECM calibration and give the engine more fuel.

 

[Cruzen]

Your best bet is a well-designe, "catback" exhaust system. Flowmaster is a good compromise between performance and price. On a 92 LT1 with a stock or near stock engine, the gain will be 5-7hp and the resonance will not be near as bad.

I have been wondering about the Flowmasters myself. Since they offer several different chamber designs, have you any preference or recommendations on the one two or three chamber design in relation to the stock sounding exhaust. I am thinking of just a muffler change. I would love for my 94 to have the sound of a small block 64-67. Since the 94 runs at about half the RPM of the C2 small block I am assuming it would need to be just a bit louder. I really miss that sound of that small block coming back over the rear deck of my C2 roadster and if I could recreate that in my C4 roadster I would be happy. You could hear it but it wasn't loud. Driving from Chicago to LA in a day and a half in my 65 coupe with factory side pipes permanently cured me of the need for LOUD!

The trip is short,
enjoy the ride,
Denny

 

[TedC]

I'm far from being an expert on exhaust tuning, but the comments below match very closely to what my local dyno shop has been sharing with me.

"High velocities, that don't incur pumping losses are the rule!!! Just changing backpressure is a bogus way of trying to create the "ideal" pressure in the system. The exhaust system should work like a correctly conceived header. It should extract the exhaust from the header, to minimize pumping pressures. The only way to create a system that will serve as an extractor is to properly size the tubing to allow the flow velocity to create a sort of "vacuum" behind it. Just as with headers, creating a system that will provide the best of all worlds at all throttle positions and rpm ranges is impossible. It's all going to be a trade-off. You can tune for the throttle positions and rpm ranges where you desire the greatest performance, but you'll sacrifice performance at the other end of the rpm range."