Exhaust system question & recommendation needed

[CamayroZ]

Hello everyone!
I have a low mileage/nearly 100% stock '88 US car.

I have been wondering what it would be like to change the OEM exhaust system, remove the catalytic converter and switch to a new system with cat delete, center resonator, and some sort of high-performance muffler.

I am hoping to get a little more "sound", and let the engine flow better? And frankly, I wonder how "clogged" my stock cat is after 35 years!

A few questions for the pros:
1) Would this change throw any idiot lights on the dash? (I did not see any sensors on my exhaust system)
2) What system is preferred these days?

Thank you in advance.


PS: This winter's project: remove the exhaust, dry ice clean the chassis, replace/paint anything that I don't like on the chassis, clean the injectors, go through the fuel system, fix the darn transmission oil drip near the tail shaft, and change(?) the exhaust, alignment, etc.

[Mick]

You will never see an idiot light because your car does not have OBD, it was exempt when imported. It's one of the most underrated features of these cars actually.

As you mentioned, you definitely want to keep something in the center. If you don't the exhaust will be quite loud, and in my opinion too raspy with high pitched overtones.

A common center section is the VSR dual cat. On a stock motor I doubt you could notice a power difference between a resonator vs high flow cats. The resonator will be louder though, as it's designed to change the tone but not really dampen. I just don't think they cut enough of that inherent high pich raspy sound these cars can have when the exhaust is open.

For my street car I was going for something similar to what I think you want. A nicer sound without being too loud. I've had a lot of different combinations on my car and settled on the VSR center section with an Eisenmann muffler. The tone is great, it's just loud enough without being "look at me" loud, and it doesn't have the low pitched drone that some combinations can develop.

Before the Eisenmann I had a Strongum muffler and while the tone was nice it was way too loud. Especially when cruising where the low pitched drone was tiring.

That's just what works for me. You'll get a lot of varying options on exhaust because it's so subjective.

[Mick]

...Also, if you're going to have the exhaust off and be working on the transmission. You should consider dropping the fuel tank to change all of the old rubber fuel lines that run above it. Once the exhaust and driveshaft are out of the way it's not that bad of a job.

[ADA///M]

No reason not to use cats with today's high flow cat technology imo.

VSR is the easy solution for center section with high flow cats. Add a supersprint street (non-race) muffler to that and you're perfect. No drone, not stupid loud. This is what I have on my car now and love it.

I had a supersprint race (straight pipe) center section with the street muffler and it was way too loud.

[CamayroZ]

Mick, thank you for the good advice!!! The exhaust is already off...I could not help myself; I pulled it off last night by myself - easy job. But that sucker is heavy, so this morning I am on Advil. I will also go ahead and remove the fuel tank and get everything cleaned up and replaced. I will have to post up the transmission leak to get some advice. I suspect the driveline will be coming off too...

ADA///M, excellent point! The only reason that I was considering Cat delete, is because I can then easily blend non-ethanol 110 leaded with non-ethanol 91. I have been doing that to my other catless cars and it seems to work well. Just that I understand, you are recommending VSR center section w/high flow cars + supersprint (non-race?)

[ADA///M]

Mick, thank you for the good advice!!! The exhaust is already off...I could not help myself; I pulled it off last night by myself - easy job. But that sucker is heavy, so this morning I am on Advil. I will also go ahead and remove the fuel tank and get everything cleaned up and replaced. I will have to post up the transmission leak to get some advice. I suspect the driveline will be coming off too...

ADA///M, excellent point! The only reason that I was considering Cat delete, is because I can then easily blend non-ethanol 110 leaded with non-ethanol 91. I have been doing that to my other catless cars and it seems to work well. Just that I understand, you are recommending VSR center section w/high flow cars + supersprint (non-race?)

Yep. VSR and supersprint (non-race)

[jimmy p.]

...Also, if you're going to have the exhaust off and be working on the transmission. You should consider dropping the fuel tank to change all of the old rubber fuel lines that run above it. Once the exhaust and driveshaft are out of the way it's not that bad of a job.

This advice is top shelf.
It then ALSO becomes an amazing time to pull the rear subframe and re-do all the rear end bushings.
A little scope creep yes, but really good scope creep.
I did it all in one winter project. It was super rewarding to take that all apart, clean, paint and refresh everything in the rear of the car.

FWIW I have the VSR non-cat center section with a stock muffler on my street car and I think its about perfect.
Its light, simple, clean looking and nothing to ever clog or wear out.

[nsubre]

Hi CamayroZ,
When you use leaded fuel it will quickly kill the oxygen sensor so the DME won't be able to set the correct air/fuel ratio. And if you have a cat the leaded fuel will kill the cat as well.

As AdaMMM wrote,there is no reason not to use a cat now. There is good information on what makes sense to increase the engine power with a system approach. Just trying random parts is is not an efficient approach and sometimes can make things no better. .

I am aware that if you don't have to pass CA smog every two years you can get away with non stock hardware. But flow is relative to what size engine you have. A 2.3 stock engine is not restricted with the stock exhaust system. When you go 2.5 or more and run non-stock cams so the engine flows more at higher RPM's than perhaps a higher flow exhaust would provide some benefit.
Larry

[CamayroZ]

jimmy p. I have always been a sucker for "...while you are in there..." syndrome. This is the truth when I say that I took apart my 1972 911S ~24 years ago to unwind the HPDE/Race crap and it turned into a 23 years long 100% nut and bolt restoration just finished a year ago! With the M3 on the lift now with the exhaust system off, I can see lots of opportunities. If I am not careful, I will have the engine and transmission removed by Monday. so...you are running catless/no-resonator and not too loud? I know that sound quality is subjective...

nsubre agreed! I forgot about O2 sensor!! I guess leaded is out. I don't have to worry about emissions testing, but I appreciate the new high flow cats are different than what I just pulled off the car which is massive.

[ADA///M]

Hi CamayroZ,
When you use leaded fuel it will quickly kill the oxygen sensor so the DME won't be able to set the correct air/fuel ratio. And if you have a cat the leaded fuel will kill the cat as well.

As AdaMMM wrote,there is no reason not to use a cat now. There is good information on what makes sense to increase the engine power with a system approach. Just trying random parts is is not an efficient approach and sometimes can make things no better. .

I am aware that if you don't have to pass CA smog every two years you can get away with non stock hardware. But flow is relative to what size engine you have. A 2.3 stock engine is not restricted with the stock exhaust system. When you go 2.5 or more and run non-stock cams so the engine flows more at higher RPM's than perhaps a higher flow exhaust would provide some benefit.
Larry

additionally I think i picked up a little low end with the VSR cats vs the SS straight pipe (i'm sure at the sacrifice of some top end) fwiw. Could also be in my head lol

[jimmy p.]

jimmy p. I have always been a sucker for "...while you are in there..." syndrome. This is the truth when I say that I took apart my 1972 911S ~24 years ago to unwind the HPDE/Race crap and it turned into a 23 years long 100% nut and bolt restoration just finished a year ago! With the M3 on the lift now with the exhaust system off, I can see lots of opportunities. If I am not careful, I will have the engine and transmission removed by Monday. so...you are running catless/no-resonator and not too loud? I know that sound quality is subjective...

I too am a sucker for "While Im In there" (I did an entire front end refresh on my street car the year before I did the rear,,, I started to do alternator bushings LOL and ended up pulling the entire front end of the car apart.

No I personally dont think catless with a good muffler is too loud, but I probably have a bit more tolerance for NVH than many of my peers. I like it my cars just a little bit rowdy and stiff.
Its so hard to give advice in that area because its so subjective. I love mine, but thats just my taste. Having said that I think the non-cat Supersprint system is "perfection", I've just always been too cheap to pony up and buy it.

[Narayan3]

CamyroZ, it was pretty easy to change all my fuel lines without dropping the tank the last time I did.

[Dave @nz]

Supersprint exhaust system with centre muffler is what I have on my M3 and it works well no drone noise and not too loud.

[CamayroZ]

Thank you, folks. Great community.

I am sitting here in my shop digesting the responses and pondering a next move! I have spent 35 years actively down the slippery slope! I have gone down as low as you can go, and came back up again! ...how far I want to take this project "...while I am in there..."

[Mick]

You have good taste in cars