Exhaust - why so loud.

My exhaust journey:

Question: are there 2 or 3 generations of Comptech mufflers? I thought I read three, but a buddy insists it is two. If three, what is the difference?

Started life with a stock 99. Very quiet. swapped out the muffler for a latest gen Comptech. Loved the throatiness. My son said 'now it sounds as good as it looks'. That's my boy....

So then I bought a 91 CTSC, 7lb boost, DC headers, earlier gen Comptech muffler expecting similar sounds to my 99. Nope, a LOT louder and a nasty resonance around 3500rpm, right at 82 on the highway which is what a lot of drivers do on I95...

I have two theories:

1) It's the headers, so not much to be done
2) Maybe the cats are gutted. Would test pipes quieten this down some if they are in fact gutted? Any easy way to tell short of pulling them off?

Any other ideas? I am considering swapping the mufflers over to see what the difference is, if any

Thanks!

Does your 91 still have the stock cats? Or test pipe?
Gutted cat would be similar to Test pipe which will make it lounder..

The loudness your hearing with the same exhaust would most likely come from the headers. I installed dc headers on my car and it was way louder then just an aftermarket exhaust with cast manifolds.

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But there are also older ctsc kits that constantly blew out mufflers. That may be it as well. Just some things to consider.

BTL3.0 said:

Does your 91 still have the stock cats? Or test pipe?
Gutted cat would be similar to Test pipe which will make it lounder..

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91 has cats, but I don't know if they are gutted or not.

Jinks, what do you mean by "blew out mufflers" exactly? Do you have more details on this? This is definitely an older CTSC kit, pre-2007 I think.

You can start by removing 3 of the cat bolts and peaking inside with a flashlight. Headers are an absolute necessity on a 91. If cats are good, I'd lean towards the muffler. Headers will make slight difference, but again, I'd lean towards the muffler. I think what Jinks means is, mufflers are pack with a glass packing that will eventually deteriorate and leave the muffler.

You should be able to smell if there are cats in there or not. Its a really distinctive smell.

Bernhard

Your muffler on 91 is shot.

The Comptech exhaust had basically 3 versions, but only 2 are really recognized.

Version 1 of the Comptech was a single "UltraFlo" stamped muffler with dual straight tips. These are pretty rare.


Version "1.5" (aka version 1 or Gen 1) of the Comptech was a single Stainless Steel muffler with no stamps on it, with dual double thickness "slashed" tips - this is the most common one seen today.


Version 2 of the Comptech has two separate mufflers that are welded together.

boca rat said:

Started life with a stock 99.

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What year is your car, a 91 or a 99?

boca rat said:

So then I bought a 91 CTSC, 10lb boost, DC headers, earlier gen Comptech muffler expecting similar sounds to my 99.

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I thought that the CTSC for a 91 is different than one for a 99? If you installed headers and Comptech muffler for a 91 did you get Cats with this whole Supercharger / exhaust purchase?

If your car is a 99 do you want to sell the COMPLETE 99 exhaust system from engine heads to tip of exhaust?

If your previous Comptech exhaust fits a early NSX, reinstall it and I think that you will like the sound again. The other one is blown out.

I believe he have both an 99 and 91.
99 being stock with only comptech exhaust
91 is his new daily with the 10lb ctsc plus other mods.

BTL3.0 said:

I believe he have both an 99 and 91.
99 being stock with only comptech exhaust
91 is his new daily with the 10lb ctsc plus other mods.

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Exactly, waiting for the summer to sell the 99. I will swap the v2 for the v1 and see what it does and I still have the stock 99 muffler. Thanks for all the feedback guys. I'll post back with what I discover.

I'm betting your ctsc eventually heated and blew out the packing of the mufflers. There's a few threads around here about that. Search and the truth shall be revealed.

Oneway to lower your cabin noise and temperature is to wrap your header. That's if your cats and exhaust are not blown

chrisfrom619 said:

Oneway to lower your cabin noise and temperature is to wrap your header. That's if your cats and exhaust are not blown

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OK, update on this.

I swapped the v2 onto the 91, reverted the 99 back to stock, sold the old blown out v1, sold the 99.

This is still really loud in the cabin when highway cruising above 3500rpm (although WOT is actually a great snarl...!), and I have Dynamat everywhere including under the headliner, in the doors etc. The v2 is better than the worn out v1 and the drone is gone, but still way louder than I would like and WAY louder than the 99 was with the exact same muffler. So back to:

1) The headers make a difference.
2) The CTSC/intercooler setup makes a difference
3) The cats are blown out. No bad smell, so I think they are (partially?) functional.

So, I have these three options remaining:

a) wrap the headers per [MENTION=25983]chrisfrom619[/MENTION]. What does this entail? Effort and cost? Will this reduce engine bay temps as well?
b) swap the cats for a different set to see if that is the issue?
c) swap the headers for something else?

Has anyone compared DC to say Comptech headers? Or anything else?

Thanks!

Tubular steel headers will make a difference, especially compared to the '91 cast manifolds and probably relative to the later OEM manifolds. I speculate that the later OEM manifolds still probably have a greater wall thickness than the aftermarket headers. Wrapping the headers may help slightly with the ringing; however, most of the wraps are thermal barriers, not acoustic barriers. Don't expect a huge improvement. Good luck trying to wrap the headers if they are on the car, particularly the front one.

The supercharger will make a difference. About 60 - 70% of the energy released from the combustion of the gasoline / air mix goes out the tailpipe as a combinations of heat, pressurized exhaust gasses and sonic energy. Burn more gasoline / air mix than before and you are going to get more sonic energy.

A partially functioning converter can sometimes generate odd smells. If the core of the converter is totally missing, I don't think that you will get any odd smells, particularly if your ECU is functioning correctly and controlling fuel mix to 14.7:1. I have a 1971 pre catalytic car that has been retrofitted with digital FI, runs pretty close to 14.7 at idle and does not generate any odd smells. If the cores in your cats have gone missing (somebody intentionally removed them?), only visual inspection will confirm that.

Finally, the dynomat stick on viscoelastic pads are primarily vibration dampeners. Not so good at sound absorbing. If you want to absorb / block sound, you need something like 3M acoustic (the stuff that a lot of car manufactures now use for sound control - good luck getting it unless you want to buy a couple thousand square feet!) or use mass loaded vinyl backed by an isolator pad. The dynomat doesn't hurt, its just that piling on multiple layers results in little improvement.

Thx OldGuy. I am going to Nsxcapades next weekend so may try and compare to other rides and see how I do. I may also look for a set of cats to swap in and see what that does for me.

The flex pipe on your DC headers might be busted.

lazyboyz69 said:

The flex pipe on your DC headers might be busted.

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I don't have a flex pipe....!