High Performance Head Swap

No fatigue or breakage problems with this type of mounting, as basically it replicates the original mounting of the european style twin downpipe muffler setup.

The steel strap extension with two holes bolts directly to the lower engine mount (late type lower mount with the extension arm for muffler mount) and on the side of the muffler you will notice a flat plate welded on, this has two captive nuts welded to it's underside and is used to attach the original gearbox exhaust mount. The entire system is sprung with the engine/trans.

The muffler setup shown is for a left side rear outlet X19 (here in Australia we had exits on left or right depending on year model)

Downpipes come down and pass under the rear chassis crossmember, don't follow the "around the houses" route of the stock cat front pipe, it will get too tight and restrictive.

I'm not sure about the "headers by ed" collector sizing, that might be more appropriate for the join from 4 into 2, which in our case happens inside the exhaust manifold. If you were fabricating custom headers, then sure 1.5 primaries into 1.75 secondaries, but we are talking secondaries into tertiarys... which acts like more of an expansion chamber. Best book on the subject ever written is "the scientific design of intake and exhast systems" by Smith and Morrison... have a read of that and I think you'll find 2.25 is well sized (taking into account available length) for an expansion chamber to suit engines of our size.

Muffler used is also 2.25 internals, quite a few mufflers that are 2.25 inlet/outlet nipple shrink down to 2.0 or 1.75 internal pipes...

The 1500's I install this system onto are usually around 10 to 10.5: CR and you can stand several meters back and still feel a very strong tailpipe pulse. Several have dynoed at near 100hp at the rear wheels, so I know this works and works well.

SteveC
 
Exhaust System

Hi Steve,

Thanks for the additional comments. My copy of the book is on it's way from Amazon.

I like the rigid construction bolted to the motor approach, and the Euro Twin-pipe certainly backs this up. One of my main gripes with the Bertone's system is the irritating bunch of noises it creates. Between the screech of the coupler & the squeaks of the many springs, it sounds like Saturday night in a questionable motel....

As the Bertone exhaust exits on the right, I went looking for a right side bracket mounting location on the motor. Lo and behold, there are four stout tapped holes where the A/C compressor fell off. A bracket from there through the hole where the single pipe originally went should do the trick.

I like your 2.25" muffler, as further reading has stated that collector efficiency is degraded by restriction after it. I guess our only point of difference concerns the diameter of the pipe out of the main 2 into 1 collector. By using a tuned length for the 1.5" secondaries, and the 1.75" collector output, I expect there to be scavenging from the valves in one downpipe to the valves in the other. One slight tweak is that the secondary from cylinders 2&3 must be a bit longer than that of the cylinders 1&4, so that the valve to collector distance is the same for all cylinders.

Brian, "in da UP"
 
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