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MG MGB GT V8 Factory Originals Technical - Exhaust Systems

In an exhaust system what does the resonator really do? I was thinking that with my V8 conversion I could run dual pipes with just a muffler and tail pipe for each pipe instead of the resonator/muffler system that now exists.
Bruce Mills

I agree with you. I plan to use RV8 headers off the engine. Then 2 1/4" aluminized pipes all the way back with two Flowmaster mufflers (and a centralized gastank) Who cares about the resonator? Even though my car is a '68 and doesn't need to go through emitions, I'm sure if it had to it would pass.
Wally Jonker

In an exhaust system the "resonator" is in fact an expansion chamber. It is designed to cause a low pressure wave to be reflected back to the exhaust port at around TDC to assist in scavenging the last of the exhaust during the period of valve overlap. Now you know!
I have fitted my roadster with a dual system using RV8 style headers and pipes straight through to absorbtion type silencers at the rear. However after some trials we fitted a balance pipe between the two sides just behind the bell housing.This gives some "interference" between cylinders and results in much smoother running. This car a 3.5 litre with modified heads 390 double pumper Holley and a cam gave 210 hp at the flywheel 5300 rpm.and is extremely fast.
My "factory" GTV8 3.9 with RV8 headers, 600 Holley,similar heads and a single exhaust system gives 215 hp AT THE WHEELS and it's hardly run in with only about 2000 miles on it
Whatever you do, make sure you fit a high pressure fuel pump.We monitored fuel pressure with the standard SU type and it dropped to vittually zero at high rpm. We fitted a Facit unit which gave 5lbs/sqin
which is what a Holley needs.
robert pulleyblank

So the resonator has nothing to do with the emissions?
Wally Jonker

The first time I can recall resonators appearing was on those large American V8's of the late 50's with factory dual exhausts (Oldsmobile, Chrysler, Mercury, etc.). I always understood their purpose to be to quiet certain frequencies in the exhaust noise reulting from the much larger volume and reduced restriction of the dual system. Hard to see how, with all those cylinders dumping into them through log-type manifolds and many bends of pipe, they could create any type of reflected-wave-scavenging effect back at the valve. I remember some of my hot-rod friends would replace the resonators with a straight piece of pipe, and this yielded a definite "rap" in the exhaust note, even with the original factory silencer/muffler still in place.

I believe the only effect they have is auditory - plus a little more backpressure - and any impact on emissions would be happenstance.

I agree the resonator would create more back pressure. Would the removal of the resonator then cause the car to backfire going down a hill.
Bruce Mills

Answer is a definite "maybe". If the engine was already on the verge of running lean at idle (closed throttle plates) the slight reduction in backpressure caused by removal of a resonator could conceivably further lean out the mixture, and give an intermittent popping in the exhaust on the overrun. If so, it would indicate that a carb adjustment is needed. Bear in mind that removal of the resonator may just make an already-present "backfiring" more audible.

This thread was discussed between 24/01/2000 and 26/01/2000

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