Very Low Tech Exhaust Question

rarely is a cat straight enough so you can poke a straight pipe through it. the only reason to do that is to look legal. often a cat is so restrictive that you can remove the muffler and just run cats be legal and still not too loud. sometimes not. you got to try it. manufactuers seem to leave power on the table perhaps because of emmissions of smog and noise and vibrations. There is some compromise is max performance, max quiet,minimum smog, max ride comfort. You change any part and you effect this. In general small gains in power/torque are gained without cats and with muffler changes if you can figure out the compromises. more can be gained by getting more air in freer flowing intakes, freer flowing exhausts and ecu tuning to take advantage of all that but by then you have upped your smog output, upped your noise output, decreased ride comfort.

 

I have not heard of anyone going thru the trouble of inserting a pipe but I can tell you my experience with the cat delete that I installed. Mine actually look like functional cats and was pretty disappointed that they sound almost exactly the same on song but a little louder at idle. Power on the other hand was noticable (seat of the pants) mostly from a throttle response perspective

 

Bob- Even with cats on, some exhausts are so loud they are illegal and, to some, annoying. Had one of those on my car. Like FBB said, best to experiment to see what you get, realizing it is illegal to remove the cats and will ensure you do not pass emissions tests if your state has them. Some catalyst beds extend all the way across the cat can, so there would be no way to push a pipe through the beds

 

So I will say that currently my F355 is too loud. I did delete the cats and I am running a magnaflow stainless steel muffler

http://www.summitracing.com/parts/mpe-14386/overview/

This is not a small muffler but it is much lighter than stock. I am also running a set of Doug's electronic exhaust bypasses on a custom exhaust I designed.

http://www.summitracing.com/parts/dou-dec250a/overview/

I have ditched the factory bypass, factory cats, and factory SDECU's and replaced it with a Aerospace Logic Unit.

Automotive :: Ferrari Catalytic Converter Instrument and ECU Controller - Aerospace Logic Inc.

So this should give you an idea of what I am running with regard to the exhaust... It flows very freely, and with the cutouts open, the normal exhaust path is where the dumps are located. I used the upper path to feed the muffler. Unfortunately, the muffler is not sufficient at quelling the exhaust sound to a point that I feel I would like.

I want the car to be pretty quiet at cruise with the exhaust cutouts closed. I can still talk to the girlfriend with the current exhaust, but it's a bit loud. With the dumps open, really, it's not that much louder. It sounds amazing at WOT, but I think I do have a solution that will incorporate a little surgery on the muffler. I have a TIG welder, so a little open heart surgery on the muffler is not a problem.

Noise and flow are firmly coupled, related, but not linear. My goal from the cat delete was to stop the car from eating it's headers and running the entire engine bay cooler. It is my belief that the cats the Ferrari specified for the job are perfect for emissions, but inadequate for the motor at full song. The whole second path is proof of that, Ferrari would not have added complexity without it being needed.

Mark

 

That really depends on the particular car. On the Ferrari, I would suspect the muffler in this case, since there are two paths for the exhaust above 4,000 RPM which should be more than sufficient to handle the flow, I could be wrong. Scientific approach would be to measure the flow capacity of each.

The right answer is that both need to be addressed to achieve the best balance of sound and flow.

Mark

 

I eliminated the cats on my 88 TR, did not make much of a difference at all. I then used a Flowmaster muffler, big difference in sound. Not obnoxious, just throaty.

Whatever you do, don't forget that opening up the exhaust leans out the mixture, usually outside the correction range of the closed-loop O2 system, so you will have to compensate. Plenty of F-Chat threads on this for each car model

 

That's surprising since the closed loop O2 usually can manage a pretty significant correction. I don't doubt that it can lean out the mixture, but I would be curious as to the exact cause. This is also more likely a problem with cars that use speed density and not mass airflow.

Mark

 

You are right, some can compensate more than others. The correction range depends on the fuel injection used and more importantly the year. OBDII vehicles will throw a fault code if out of the range limits as it is sensing a fault (e.g. it may think you have a vacuum leak).

 

Ya, agreed. I am not an expert on the specific limits of authority that the Motronic system allows. Some mass air OBD-II systems are not as code happy as others. Mazda's Denso ECU, for instance, allowed for quite a bit of this nonsense and was rather forgiving, even in my 1999 Miata with a turbocharger, right up until I overvoltaged the MAF sensor under boost (~240 RWHP) LOL. FWIW, I used to tune and build a lot of forced induction setups for Miata's and other 4 cylinder cars. Eventually the customers would always rip out the factory ECU because it was holding them back and get rid of whatever piggyback ECU they wanted to use.

The eventual solution for smog purposes was to run the factory ECU in parallel, give it the inputs we wanted and allow it to think it had a MAF. O2, and RPM that made sense while giving all the real authority to the stand alone ECU. Sometimes we would just run a larger MAF when going over 250 HP or so. No codes, plug in the OBD-II and everything was just peachy at the smog shop. Provided you tuned it well, it would pass every time... as long as they didn't get too picky about the visual inspection (in CA). Having a CARB E.O. number for the "kit" helped.

Stand alone ECU's are really the way to go if you are planning on serious modifications, getting the base tune to where the factory was is tricky with an engine like this and under all settings. You can get close initially, but to really optimize HP/TQ, fuel consumption, A:F ratios, EGT's, stability at idle, emissions, etc, etc takes hours of work. It's also a lot of fun, especially if you have some trick parts and high octane fuel (like E85 for instance). You can run a snot load of timing on 100+ octane, and my guess, is that the F355 motor would eat it up and then some.

Mark