Quieter upgrade?

[tayto]

Yeah,I know!
That's why I asked.

look up 369 & 048 icm on Thirdgen.

short answer: get a 369 module

 

[L31MaxExpress]

To burn off more A/F before the exhaust valve opens?

Is that built into the ESC or the ECM?
The reason I ask is I'm going to use a 7427 ECM and toss the external ESC.

The startup/warmup retard is built into the PCM. The PCM simply opens the EST Bypass circuit the same way you set the timing during warmup.

 

[jdjonesdr]

Wouldn't a new stock muffler be the best bet?

 

[Erik the Awful]

Have you seen the stock exhaust? Next time you go to McDonalds, request a coffee straw for your soda.

 

[Russ B]

Have the same vehicle/engine. Just went thru this with my truck. Ended up going to local muffler shop to install the quietest muffler. Cost was $500 (used existing cat) Not sure of brand, but some thoughts to consider. Original system used 2.5 inch pipes with dual pipe out of the passenger side rear tire. My system is now a single 3 inch system from the cat back. It is dramatically quieter, however I now hear road/tire noise I could not hear before! The final result is quieter but not totally quiet. More tolerable. Another consideration is the heat transfer from the engine to the cab. I have a Silverado that should have better insulation, but I guess not. When not using the heater, I get a lot of engine heat into the cab that cooks my legs. If you do headers that will probably throw off more heat, so consider that.

 

[L31MaxExpress]

Have the same vehicle/engine. Just went thru this with my truck. Ended up going to local muffler shop to install the quietest muffler. Cost was $500 (used existing cat) Not sure of brand, but some thoughts to consider. Original system used 2.5 inch pipes with dual pipe out of the passenger side rear tire. My system is now a single 3 inch system from the cat back. It is dramatically quieter, however I now hear road/tire noise I could not hear before! The final result is quieter but not totally quiet. More tolerable. Another consideration is the heat transfer from the engine to the cab. I have a Silverado that should have better insulation, but I guess not. When not using the heater, I get a lot of engine heat into the cab that cooks my legs. If you do headers that will probably throw off more heat, so consider that.

The stock system for a L31 in a 1500 or light 2500 truck or SUV has ~2" OD pipes to the muffler and they are compression bent. They are not even 1.5" ID in the bends. As Erik stated the engine is breathing through straws. Some of the L31s came with dual 3" OD pipes to the muffler.

 

[jaybee]

Honestly, I don't think the legalities are all that hard. Unlike the coal rollers, no one is going to bust you and confiscate your 35 year old vehicle if you made an effort to keep a catalyst on it. Or two. You'll use one slightly larger one or two slightly smaller ones, so the mass won't make that much difference. Especially since you'll be replacing a very heavy, pan-style converter with a much lighter, honeycomb style. In doing so, particularly if you use 2, you can put them closer to the engine. It's an improvement, not a reduction in its function. You'll be emulating what they do with late models, and they do it that way because it reduces emissions. If it's close to anything else, put a sheetmetal heat shield between the converter and whatever it's close to...call it an inch on either side will reduce heat transfer a ton. The rest is easy. Bigger tubes. Preferably mandrel-bent. Use a big muffler. If you don't like how it sounds, cut a chunk out behind the big muffler and add a resonator in your tailpipe or tailpipes.

I lived 4 years next to a guy who had a New Edge Mustang and an S550 Mustang, neither of which had mufflers at all. In a state which has annual inspection including verification that all vehicles which require cats have them.

 

[L31MaxExpress]

Honestly, I don't think the legalities are all that hard. Unlike the coal rollers, no one is going to bust you and confiscate your 35 year old vehicle if you made an effort to keep a catalyst on it. Or two. You'll use one slightly larger one or two slightly smaller ones, so the mass won't make that much difference. Especially since you'll be replacing a very heavy, pan-style converter with a much lighter, honeycomb style. In doing so, particularly if you use 2, you can put them closer to the engine. It's an improvement, not a reduction in its function. You'll be emulating what they do with late models, and they do it that way because it reduces emissions. If it's close to anything else, put a sheetmetal heat shield between the converter and whatever it's close to...call it an inch on either side will reduce heat transfer a ton. The rest is easy. Bigger tubes. Preferably mandrel-bent. Use a big muffler. If you don't like how it sounds, cut a chunk out behind the big muffler and add a resonator in your tailpipe or tailpipe.

I lived 4 years next to a guy who had a New Edge Mustang and an S550 Mustang, neither of which had mufflers at all. In a state which has annual inspection including verification that all vehicles which require cats have them.

I have never owned a GM RWD car, truck or van built 1980 or after that did not have a heatshield running almost the whole length of the body on the OE exhaust side. Even my 83 van born without cats had the same heatshielding as a catalyst equipped van. I added dual cats to it and never had an issue passing smog after. As you say two modern cats easily fit in the OE space left behind from that almost worthless when new pellet box cat. Many of the modern replacement cats actually have an added integrated heatshield in place on them and have an airgap between the catalyst body and heatshield. They do not radiate nearly as much heat as that big old pellet box did.

My 83 ran extremely clean with no air pumps, no EGR, and dual 3 way cats added to it. Much cleaner than the stock emissions limits in the real world. That was also using an OBD1 era TBI ECM and batch fired TPI. Zero doubt the 87 will run even cleaner with sequential EFI and wideband closed loop.

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[Schurkey]

look up 369 & 048 icm on Thirdgen.

short answer: get a 369 module

Yeah, I've read all that.

I still think there's a mistake in his methodology.
1. I replaced an 048 with a 369...can't tell a bit of difference in how the truck runs.
2. The aftermarket sells the same module as a replacement for both of those numbers...and several others. If there was a real difference in ignition timing, I don't know how it would get past the EPA for either emissions compliance, or for CAFE compliance.

OTOH, I'm way too lazy to do a timing-test of the two modules of my own.

 

[tayto]

Yeah, I've read all that.

I still think there's a mistake in his methodology.
1. I replaced a 048 with a 369...can't tell a bit of difference in how the truck runs.
2. The aftermarket sells the same module as a replacement for both of those numbers...and several others. If there was a real difference in ignition timing, I don't know how it would get past the EPA for either emissions compliance, or for CAFE compliance.

OTOH, I'm way too lazy to do a timing-test of my own.

it's mainly depending on what calibration you are running. ie: if it is for a calibration for the 369 module, and you install a 048 module, the timing it pulls in the upper RPMs might be noticeable. you could do a performance tune with a 048 module you just have to add timing in the timing map where the module pulls timing.

EDIT: i guess my point was know which module you have and make sure you use the same one if you ever replace it. I tested a new acdelco 10 years ago and it indeed was a 369 variant. i qm unsure if they are all like that or if you can also get the 048 style.

048 to 369 Ign Modules? - Third Generation F-Body Message Boards

DIY PROM - 048 to 369 Ign Modules? - Ive been doing some reading of old threads and came across the one about the stock 048 Module retarding timing at higher rpm's. I did a check and I still have the old 048 module in my disty. I do notice that I get a bit of a fall of above 4000rpm. Now i...

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