Intake & Exhaust

[Frog2Spider]

I have a FI '81, and I'd like to 'liven it up' a bit. I tried replacing the Cat with a Test Pipe, but I did not like the sound! Is there a 'Flow Thru' muffler, to replace the Cat, that will provide better exhaust breathing and keep a nice rich sound? I have a Danny McDonnel stainless steel rear muffler. The car doesn't have to go through any EPA testing.

Also, I presently have a K & N filter in a stock box. I plan to replace that with a open style K & N.
Any suggestions for improving the fuel supply?

Thanks
Dave

[TimpanogosSlim]

The term you're looking for is "resonator".

Find an exhaust shop in your area - they can replace the cat with a zero-restriction resonator. It shouldn't cost more than a couple hundred bucks. It's what it sounds like - an acoustic device that uses resonance to cancel out or alter the frequency of the sound.

Really, the resonator itself is less than a hundred bucks, and they might charge a hundred bucks an hour to weld it. Which is not entirely unreasonable. But shop around. This is not hard work - anyone who can cut tubing and weld sheet metal can do it.

I should plug my friend's exhaust parts business - Aero Exhaust - while I'm here. But i don't specifically know if he has anything that is appropriate for our cars. Mostly race parts and diesel performance parts, at the moment. Dinan uses his mufflers on their race cars, for example.

As for the intake, Rather than switching to a cone filter you might look into working the plumbing so that you have ram air from that square hole in the front of the car. Plastic drain pipe parts are a perfectly reasonable material to build an air duct out of. Ram air is a real thing, that most new cars have from the factory these days (carefully hidden behind the grille work), and you can do it yourself. I believe there have been some discussions here on this forum about just this sort of modification.

I'm not convinced that a naturally aspirated engine like ours is going to benefit much from an upgraded filter. Really, the only aftermarket filters that actually impress me are donaldson / volant PowerCore filters, which use a folded ruffle design to provide many times the surface area of cone or panel filters. I have a Volant intake with PowerCore filter on my 2007 VW GTI and like it. As for cone filters, they often have less surface area than the panel filter they replaced, but they have less restriction because they don't filter as well.

[Frog2Spider]

Thanks TimpanogosSlim,

Any thoughts about how the sound of a resonator is different from the sound of a test pipe? Hopefully, it wouldn't cause an significant increase in the exhaust sound. I'd hate to pay for everything, and not like what I hear, but then I guess that might be the chance I'll need to consider taking.

I like your idea of Ram Air, I'll look closely and see if there is a 'path' that would allow the plumbing without a lot of cutting. Are you suggesting to plumb from the box and leaving the K & N in it?

The '81 is fuel injected, not naturally aspirated. Any thoughts on simple mods to improve the performance there?

Thanks again,
Dave.

[RRoller123]

I have the fully stock CatConv to Resonator to Muffler setup, and just very recently replaced the CatConv with the Test Pipe and noticed no change in the volume of sound, and it actually sounds a little better. More hum, smoother tone overall. My ears aren't the best, but they aren't that bad. I guess I am surprised that others have reported that the Test Pipe was much too loud. More power too with the Test Pipe versus CatConv.

[TimpanogosSlim]

Typically a resonator takes the rasp out of it and lowers the overall tone.

I understand your concern though - when i bought my GTI a previous owner had installed a chinese ebay 3" downpipe (no catalyst), deleted the resonator, and replaced the "suitcase" muffler with an anonymous high flow muffler.

I spent a couple hundred bucks having a new resonator added. It took away the raspiness of the exhaust note, and the next day my neighbor asked me what I had done because it sounded so much more powerful.

[Frog2Spider]

Thanks again Slim,
I think I'll try it. A little more volume, but a low tone is what I'd like.

Thanks also RRoller,
I think the Test Pipe used with a Resonator and Muffler setup, must take away the loud, harsh, high pitch noise I experienced.

Replacing the Cat with a Resonator sounds it's worth a try.

Thanks !
Dave

[Dawgme85]

My experience is as follows:
When I bought my '77 it was basically a stock California car, 54k documented miles, but with the smog pump removed. After a few months I decided to have the head rebuilt, port matched, and the exhaust manifold replaced with a ceramic coated 4-2-1 manifold (early model). When it went back together, the original cat became "lost", so was not reinstalled. I also had a new generic muffler installed, as the original had broken loose from the center section. At this point, the car was too loud, so I chose to have a low-restriction cat installed a week later, which mellowed the sound just enough, but didn't noticeably affect the performance (which was significantly better than before). There's no more flat spot at 4000 RPM, and it will easily pull to 7500 in the first 3 (maybe 4) gears. I've also had a K&N filter installed for the past couple of years, but recently swapped it out for a paper filter, with no adverse effects to performance. All in all, I'm quite happy with the performance of the 1756, though I'm thinking about building a nice performance 2L sometime down the road. Next up will probably be a performance exhaust system, such as the one sold by Csaba at AR.
If you're looking to make your Spider a bit more "lively" (for the street), I would heartily recommend an 1800 head, port-matched, with a good 4-2-1 exhaust manifold, exiting to either a low restriction cat or a resonator, with a performance exhaust system from there back. Good luck.
LeRoy

[TimpanogosSlim]

Yeah I'm torn on the issue of catalysts for cars that aren't driven daily.

On one hand, i have some respiratory issues that run in my family and i am acutely aware that NOx emissions are a respiratory irritant.

I spent about $250 having a high-flow magnaflow catalytic converter welded into my '07 GTI's chinese downpipe - not because it wouldn't pass emissions (I know where the lazy inspectors are), but because i felt like a dick driving it 400 miles a week catless. If i spend too much time at WOT with the performance tune turned on the computer throws a catalyst efficiency code, even with a spacer. But I'm pretty sure it's running rich at WOT because the valves need cleaning.

On the other hand, I'm not going to be driving my classic cars all that much, and they all have small engines. And in Utah, with Vintage plates, there is no inspection of any kind.

My '77 was non-catalyst from the factory. The '80 i just picked up has a cat, but my plans there include an all new exhaust of at least 2.25" diameter. Right at the moment my '84 turbo diesel jetta coupe has no exhaust system to speak of. Hot side of the turbo vents directly to the engine bay. Really need to have someone fab me a downpipe.