Aftermarket Exhaust Vs stock muffler

[72boughitnew]

I have always said, you never get a free lunch when an engine is modified. Power increases equals reduction in service life. A car manufacture has to warranty their product without regard to the ham fisted driver that operates the equipment. As a result considerable amount of reserve is engineered into the product. Changing exhaust, compression ratios, valve timing or induction independent of each other usually causes performance, reliability and service life issues.

With respect to back pressure in an exhaust system, it is only effects performance when it impedes exhaust scavenging (later part of the exhaust stroke). The main problem with back pressure is the effect it has on cylinder head temperature and exhaust valves.

I had considerable experience with Wright R3350 turbo compound radial engine. It had 3 power recovery turbines (PRT) that were coupled to the crankshaft by gear reduction units and fluid couplings. These were blowdown turbines not pressure turbines like a turbo charger. A blowdown turbine is like a water wheel it absorbs energy but does not impede the flow. The advantage of the turbo compound was that you could achieve higher torque at a lower break mean effective pressure, thus less stress on the engine components. At max power the PRTs added about 550 shaft horspower. Wright claimed that the PRT did not affect engine performance and they were correct. The monometer tests showed that the backpressure was roughly equal to a well designed jet stack system, during the area where exhaust scavenging affected performance. What they failed to mention was that the high pressures and high temperatures that occurred when the exhaust valve opened and the energy was absorbed by the PRT resulted in dropped valve seats burned exhaust valves and shortened service life of the PRTs. Eventually improved metals resolved the valve problems. By then the jet engines had taken over and the turbo compound became history.

[aeromech]

The 3350 is one bad assed engine. Back in 1981 we had a full size cutaway with an electric motor to rotate it. Not sure if LSD was involved but designing that engine took some original thinking.


Link

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Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[otiswesty]

I have the Ernst muffler and I had it ceramic coated prior to installation. I used to have some POS performance muffler that lasted 4 years, followed by an OEM VW muffler from a junkyard when busses were still in junkyards. I rattled the used muffler with high temp silver and it lasted almost 10 years. The Ernst has been on there 5 years and should go the duration. Never have to think about it.

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1978 Sage Green P22 Westfalia
1989 T3 Syncro Single cab

Just a regular guy

[raygreenwood]