Difference between single, double can exhaust and tubi?

This is *not* my opinion, but here's what the Lotus guys are saying about Tubi:

http://www.hsv.org.uk/topic.asp?f=17&h=28&t=153608

 

Interesting questions. I have a "4 can" exhaust on my TR....a Borla system. It is very light weight compared to stock, and runs so cool that I removed the stock ugly heat sheild. The system bolts directly to each of the 4 headers, with 4 straight-thru mufflers, and 4 tail pipes. It's surprisingly mellow in tone. But at full throttle it howls quite nicely yes indeedy!!

 

Heat isn't being created by the muffler -- it's in the cat. I'm no chemistry dude, but here goes: When unburnt hydrocarbons get slammed into platinum or palladium, it basically gets the leftover carbon monoxide and hydrocarbons to burn up. Voila! Heat! The better CFM of the cat (like HyperFlow), the faster those burnt up gasses get tossed out the back of the car.

In the muffler, there is no catalyst, so it's just the existing hot fumes that flow through it, muffling the noise. I suppose the more restrive the muffler, the longer those hot gasses would stay in there. Longer time in the muffler = more backpressure = less heat released.

techs... did I get this all wrong?


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If I may hitchhike on your thought....
How about a single can off a 355 put on a 348. It has a bypass system-some kinda vacuum operated valve-that bypasses the cats-and maybe a chamber or two in the muffler? That's what that inlet in the top center of the 355 muffs is. It's a single can, and definitely lighter than the doubles on 348s. I can lift the single, but probably not both doubles at once, so it's a few pounds lighter. The cutout pipe if fed by a pipe beginning at a split in the exhaust manifold. So, a cat modified with another pipe beginning about where the oxy sensor is-feeding the cutout (sounds so 50s) would surely produce good sounds, lower backpressure, and more horsepower.
Total cost? 355 muffler on ebay about $200
Cat modification at local muffler shop $200?
Cutout valve off 355 from junkyard ?
Vacuum hose $1

Ferrari has used exhaust modification to get extra horsepower for years.
I'll call it Frankenferrari!

 

I just happen to have a 355 muffler laying around if you want to try it out. And I will honor your "quoted ebay price of $200" plus shipping costs.

 

Would you need two cutout valves with that concept...and no new cats or track pipes?

 

Looks like you could bolt a plate over it with a gasket if you didn't want to use it. I think the cats would have to be modified slightly-cheap job at the muffler shop-to hook up to the new inlets on the 355 muff. I think 355 stuff would have to be modified as well, since the header pipe is split to accomodate the bypass pipe and the cat, so I would see no advantage to buying 355 cats or track pipes.
It definitely bolts up to the springmounted muffler hangers on the 348.
There's only 1 of the bypass valves on a 355, bolted to the single inlet at the top center of the muffler, so without looking I'm guessing that the bypass pipe on the 355 is a y-pipe.