ddahlgren

I would think long cam duration making less torque at 1500-2000 rpm would have less cylinder pressure and lower amplitude.

aklim

I have the T-top that I ditched for the fiberglass one because I didn't care for the sun. That said, it seems like it didn't make any difference with acrylic, fiberglass or topless going down the road.

Tom400CFI

Maybe, but wouldn't you then open the throttle more to get back that same cylinder pressure to make the same power to maintain the same speed?

If your cyclinder pressure was down...car would slow down.

ddahlgren

Yeah you are right 25 hp at a given rpm = some cylinder pressure and if rpm is held to the same in all tests th cylinder pressure is the same in all tests.

ddahlgren

Somewhere in this thread a Magnafow X muffler ( think that was how it was referred to) was mentioned as a very low drone muffler. I looked at the Magnaflow website and found nothing. They did not even mention a replacement muffler for their cat back system. Any ideas on part numbers or cost. The closest they had listed that looked like a C4 muffler was either 230 or 260 each and a bit rich for me.

Tom400CFI

IDK about Magnaflow, but DynoMax makes an Ultra Flo X-flow muff.



.

GREGGPENN

same/similar design

In the Magnaflow lineup:
https://www.magnaflow.com/products?partNumber=12599 (dual 3")
https://www.magnaflow.com/products?partNumber=12568 (dual 2.5")

billschroeder5842

Maybe it was me(this thread is SO long it it tough to keep up with the conversation)

I put a MF Resonator on my ZR1 and kept the facotry mufflers.

The MF X resonators flowed much better and pro research showed the factory mufflers "aren't that bad on restriction, zero drone but are very quiet (mix and match to taste is guess).

I like them, the only downside is that they are bigger and hang a bit lower. Need to be super careful over speed bumps.

GREGGPENN

Did your shop mount as high as possible? Or maybe graft to existing pipes w/o considering if higher was needed?

I don't remember LT4Obsesses commenting on this....or others in threads approving of it.

Edit....Found a thread that says Maghaflow parts 12468/12469 might be better? Summit shows they are shorter...but same height.

Ahhh....Part 11386 has a shallower 4"x9"x14" case (vs 5"x8"x18" cases of the two parts above OR...5"x8"x22" of the parts I listed in post #207 above).

I bet the 11386 is the one C4 owners have been happier with...though it may only be available in a 2.5" dual inlet/outlet version?

Their line is called "Tru-x Mufflers". They sell in the $110-$180 range depending on size/case finish.

Video of the 11386 (on a C5) in this thread.

ddahlgren

Ran into this if of any interest
https://www.performancetrucks.net/fo...ne-fix-424169/

GREGGPENN

Looks like you can find some vids of this muffler on YouTube.

ddahlgren

Found this at Jegs for 110 and free shipping. I have no problem removing the cat to install it where the cat was as after 25 years CT has no smog don't even have to show up. I assume with a L98 I need to cut the Y-pipe and add tubing an cut the Borla cat back system and add tubing there, Problem is I can't weld and need to see if a muffler shop will install it being emissions exempt now. Possibly bringing the CT statute saying it is exempt due to age would not hurt there and obviously will stop by first and chat with them as it might take several shops to get it done. I do have one shop in mind and the guy that owns it gave me my first ride in a 59 injected vert. It did not have GM injection had hilborns so an old time hot rod guy and probably not real concerned about smog on a 25 year old car. My other few questions are

Is it ok to leave the Borla mufflers
Is the car going to stink up the garage or while running with no cats as there are none in the current y-pipe? It will still have O2 and run closed loop when warm.
Do I need any sort of heat shield to fit in the tunnel where the cat currently is?

There might be more but need to get brakes fixed first too. Any ideas appreciated too.

aklim

Why? All you need is a welding shop. Don't have to ask them anything other than what you need done and how much.

Why can't you leave the Borlas there?

Why? When I drive the car, I start it up and move it out. Nobody says you have to sit there and breath in the exhaust for 5 minutes. Start, put it in gear and go.

I doubt it. It might feel a little warm if you didn't have the shields and you were in 100 degree heat and the car was idling there for a long while.

ddahlgren

We get a lot of idling time where I live small town that it is there is one main road in and out with a draw bridge that opens at lest every hour and if a commercial boat needs to get through it can open anytime. 100 degrees 2 weeks out of the year is quite possible or very close to it. They make a mat but says can not touch the exhaust so a matter of how much room there is in a 1991 tunnel where the cat lives no it seems like the 9 1/2 inches is going to be the first challenge.

GREGGPENN

Mufflers don't build heat like a converter. As long as you have say....1/2" clearance between muffler and floorpan, I think you'll be fine.

Choose to leave/omit the Borlas based on how loud you want it.

Never hurts to quiz shops before you go. Most they can do is say no.

As for the lack of cats, plenty have been happy...others haven't. I think it's your personal tolerance. From my perspective, I'd think you'd be OK...because I'm running with outlets just under my door handle! LOL

Of course, I have cats...but I can still smell the exhaust occasionally. Seems like it would be less for you.


If you've removed both pre/mid cats AND are running the Magnaflow with Borlas, you might still have a moderate amount of sound/drone at hwy speeds. I'm not sure you'd be happy with ONLY the Dynomax x-muffler....unless you like LOUD.

ddahlgren

From what you are saying it sounds like I am just trding the muffler for the cat without much gain

1972bluelt1

Had Dynomax turbo mufflers and "Y" pipe. Mind numbing drone. Put stock hack on.

MatthewMiller

I think if your cat is a good one you probably won't gain a lot of power. To me, the big advantage of going without cats is never having to worry that running rich or with a miss for a short time will ruin a perfectly good cat. Otherwise it's completely possible to use cats that cause very little or no detriment to power.

ddahlgren

Other than the Borla cat back system that I bought because the original owner mad a mess trying to 'fix' things the engine is bone stock. Just trying to make the more durable exhaust tolerable as far as noise goes. I certainly did not notice any power changes and did not expect any.

GREGGPENN

gain?

In terms of power, true....no perceivable gain.

In terms of sound, you'd probably like it better.