Can the collective wisdom of the CF please help give me a little education on exhaust resonators and (any of) the differences of the LT1, LT4 and ZR1 model resonators.

I have a 91 ZR1 and am considering exhaust changes (see my continuing confusion in posts in the ZR1 section) but am pretty drone adverse. The 91 resonator squeezes down pretty hard internally... something like 1 5/8 inside diameter... and it chokes off lots of power.

I'm pretty settled on making a change in my 91 resonator but keeping it a factory resonator to eliminate drone. Later, I'll swap out the stock mufflers for something less restrictive and with a more aggressive sound.

From what I understand, the “later years” (after 92?), the C4s has a resonator that is way less restrictive (2 1/2 inside diameter??) than the 91 ZR1 with the “best” being a 96 LT4 (but nobody knows why).

Is there a difference in factory resonators from 93 on up from a performance perspective between the LT1, LT4 or LT5 or did Chevrolet share the resonators between all models?

Thanks!

 

If I were even considering an exhaust change and keeping the original CATS I'd get an entire LT4 exhaust and pay a shop to fabricate the inlets from the CATS to the LT4 exhaust. It's clean, uses OE hangers and be an ideal exhaust system OR find a TAKE-OFF from a '95 ZR-1 and then you wouldn't need to do anything other than bolt it on!!

***if your '91 exhaust is OE and complete I'd stand it in the corner and not modify it at all UNTIL you've accomplished something you're happy with.

 

(Thanks- I'm starting to feel that way).

So WHAT makes the 96 "the best?" I'm trying to understand the WHY of the engineer from a performance perspective? Does if flow better? Does it have tubes that go all the way through? Is the ID larger? Are the 95 ZR1 and the 96 LT4 the same resonator?

Thanks!

 

If you leave the rest of the system alone, and install an X-Pipe in place of the resonator you will have ZERO drone. I had this setup on my 94' for a while and, while still on the quiet side, sounded very good.

 

the resonator is for some resonance above 3000 rpm, but the mufflers reflect waves to cancel the terrible drone around 1900 rpm...which is where you are at when lugging the car in 6th gear on the freeway.

you don't stay over 3000 rpm for hours at a time-it is the mufflers that make or break a set of pipes on vettes. C6's don't even have midpipe resonators...

 

Sounds like you already found out a lot about the differences. If you look at an online catalog for GM, you'll see there are (at least) four difference resonators for the 91-96 model years. And, they differ from LT1 to LT4 to ZR1.

I would suspect that ZR1 would have the larger "interior" pipes but don't know that. And, as you point out, LT4's in 1996 might be it's own unicorn. Because LT4's don't generate the power of a ZR1, you'd have to think the 1996 wouldn't necessarily be "better". I'd be more inclined to think there's differences in flange/mountings and pipe diameter.

If I were looking to replace a ZR1 with stock components, opting for a 1995 makes the most sense. Or, Magnaflow makes a nice "X" muffler/resonator. It has an internal x-pipe in the muffler. Just pick one with the piping diameter of your exhaust. If it's not "exact", don't fret about it. For example, if ZR-1 uses 2.75" pipe (like the LT cars), you're not going to be hurt by a 2.5" resonator (if they don't make a 3" model). With restrictions, the length plays a factor. Shorter runs of smaller pipe don't restrict as much as longer ones.

As pointed out, the resonator isn't going to affect overall sound nearly as much as the mufflers. In fact, you SHOULD consider dropping the resonator completely just to see what you think of the sound. You might be surprised. Components and cars vary enough that it can partially be trial and error....until you find the right sound.


I should also add that a resonator is basically a mild muffler. The engineering doesn't include magic. Even with resonators, glass packs, and other "sport" mufflers, adding them in series will provide additional sound dampening. (Full blown mufflers just have more baffles, turns, and/or packing). Internal size and/or turbulence is what tends to rob horsepower. When resonators/mufflers are larger and/or less restrictive than the primary piping, there's little-to-no HP loss. In fact, you'll find Vizzard's article on how to build a lossless exhaust system (for racing) somewhat informative on this topic.

 

 

I am not aware of the differences in the resonator. I thought the '92 to '96 resonator's were the same, so it is interesting to learn there were differences. I hope more people can add more specific information.

I thought the LT1 to LT4 difference was the cross over (H pipe) on the LT4.

Also the '96 had an O2 bung welded on the driver's side pipe since the '96 had two O2 sensors per side where the '95 and earlier had one.

 

I THINK that would be due to the implementation of ODB2 in 96 (IIRC). And, the more advanced computer system added another point in the exhaust stream to measure emissions. So, 96 might not have flowed any better. Maybe it just needed another O2 sensor for the computer.

I apologize if I'm wrong. But, I thought 95 had ODB2 guts w/o being active...then GM turned it on in 96. I think that's why my friend's 96 LT4 needed extra tuning for the removal of the resonator, cats, and exhaust changes. (But I've yet to dabble in ODB2 tuning).

 

Being a holiday week, I've spent way to much time on this reading and researching. What I found out is that essentially all (guts) the resonators from 92-96 are essentially the same and have the identical inside diameter.

The differences are largely around nuanced pipe bends and bung holes.

I found this article from Marc Haibeck that pretty much says to go ahead and swap out an LT1 with the ZR1 for the same result.

http://www.zr1specialist.com/HAT%20W...rly%20Cars.pdf

 

It is definitely true that the 96 OBD2 cars had second O2 sensors behind both cats. This allows the computer to test the cats for proper working order. I don't know what that means in terms of flow, however.

The 94/95 cars had the newer style of computer and the 16-pin OBD2 connector, but without all the OBD2 functionality. Basically this is as you say. You can run a 94/95 PCM in a 96 car if you don't mind losing the extra OBD2 tests and don't need to pass a plug-in scanner emissions test. And if you keep the 96 PCM and remove the cats, you will definitely get trouble codes (and CEL) unless you can turn the cat-related tests off with tuning software.