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MG MGB Technical - exhaust manifold

hi guy need to start looking for a new exhaust an i am not sure on weather it is worth changig to a tubular manifold system or not. car is a 76 gt with hif4 carbs. going to go for a rear silencer only because of speed bump hitting the center box on a regular basis but on a standard engine will the tubular manifold have ant real benifits.
thanks
john
jr williamson

John,
I think it's generally agreed the stock exhaust manifold is as good or better than most replacement headers.

I have that setup with just the rearmost muffler on my '77 B (converted to twin HIF) and it's a great setup. Sounds good and good power.
David
David Steverson

The only real benefit of the tubular manifold is that you don't have those six pesky nuts and bolts to deal with. However to get it in (or out) you have to raise the *back* of the car if you can't raise the whole car.
Paul Hunt

John,

most tubular manifolds have a very poor fit. The 4 year old (still new) PECO header in my garage was welded that bad, i fitted my old modified carst one again.

Big Bore tubular systems have their merits at 5000+ rpm depending upon the cam used, but as long as your engine is not past stage two, there are no real benefits but the 6 lousy nuts as allready mentioned by Paul.

Ralph
Ralph

ive just had my carbs and tubular manifolds off for the third time, can any one tell me the size of the studs , im going for those nord lock washers .they should do the trick .
daz

John-
On an otherwise standard engine a tubular steel exhaust manifold will not increase power output at all. Tubular steel exhaust manifolds have much thinner walls that can resonate under the fluctuating pressures inside of the exhaust system and thus are much, much noisier. At certain parts of the powerband, they can actually resonate into an annoying ringing sound. In addition, tubular exhaust manifolds are welded assemblies, and their welds have been known to crack under the repeated stresses of heating and cooling. Further potential problems of misalignment of the exhaust runners with the exhaust ports, and mounting flanges not being on the same plane, all contribute to making the purchase of a tubular exhaust manifold into something of a gamble. The Original Equipment cast iron exhaust manifold has none of these problems. Because of the lesser heat conductivity, the cast iron exhaust manifold will radiate less heat into the engine compartment. Its greater mass will also have the side benefit of reducing noise to a level notably less than that attainable with any tubular steel exhaust manifold. If you want better exhaust system performance, the Peco gray system will fit the Original Equipment 1 ¾” diameter pre-1975 exhaust manifolds without modification. Often a performance exhaust will sound good at idle and while accelerating, but then turns into a howling monster while cruising on the highway and literally drives you out of the car, ears ringing. This might be acceptable in a racecar, but not in a street machine. At highway speeds, the Peco system is actually quieter than an Original Equipment system, emitting a rich baritone sound rather than the ear-pounding basso profundo or the rasping tenor of some other systems, proving that a good performance exhaust system need not be noisy enough to break down the structure of your internal organs.

Daz-
5/16-24 UNF.
Steve S.

Tubular manifold Daz? AFAIK they just use a standard U-clamp to connect to the remainder of the exhaust system. It's cast manifolds that have the six studs and nuts.
Paul Hunt

This thread was discussed between 21/10/2008 and 22/10/2008

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