Ideally, you'd like the intake manifold to rest at the same temperature as the rest of the engine. This leads to more consistent atomization of the fuel. V8 engines don't have this problem because the intake is nestled in the engine, but an inline six's intake is perched off the side of the engine, resting at a temperature much lower than the block. This can lead to driveability issues as the engine comes up to operating temperature.

The factory setup mitigated this by bolting the exhaust and intake manifolds together. As mentioned earlier, aftermarket manifolds have provisions to run coolant underneath them (or to adapt something).

 

That would suggest that cheap glasspacks are equivalent to flowmasters.
Or, that would also suggest that having absolutely no exhaust would be equivalent.
Unless you are running nitro funniez..
but yes. let her breeeeeath.

Doing the same K!. Rebuilt 300 is about to go in, going with EFI's, H pipe, flowmasters, dumps. No emissions here so all that trash is going. going, gone.

 

X2 with the myth. It is an old wives' tale that keeps resurfacing. 20% gain, however, sounds rather much. But if that means 20% more than the stock log set up I certainly agree. I would be cautious if quoting info from the Clifford Performance site.

Because of limited space I've been considering a muffler from Summit that has the X inside the muffler. Dynomax Ultra Flo X mufflers, $123.97. It is expensive, but an X pipe alone is $70, and would take labor and hardware to install. It seems to be, with a nice throaty tone, just what I'm looking for.

It is my understanding that cool air delivered into the engine produces the best performance, hence cold air intakes.

 

That is also not a myth. Years of SCCA and drag, timeslips and trophies says so


There seems to be a disconnect, for whatever reason here. Back pressure is a real thing, but that doesn't mean that you just should have it, or need it or even should want it. There are a LOT of calculations that go into tuning intake/exhaust to achieve maximum HP/TQ out of what you have. Heads, power curve, fuel mixture, what you seek and what the goal is. Then applying these techniques to your particular setup and seeing the results (time slips or not). Tuning for a power curve is real. To suggest that just having open headers vs a matching proper breathing system, is the same.. well.. that’s just not reality. To toss out blanket statements as “it’s not real” / “it’s a myth”, doesn't really hold up too well on the track. We all have different setups (even same engines wont be the same) , plus our output goals are going to be different for our applications. Doesn’t mean that you need to worry about it or should have it or that it would even make any difference for your setup. Plus nobody from the internets can just tell you wether you need it or not, or how much there should be of it. There is no right or wrong answer. This takes many dynos, testing and a goal. The reason why “this keeps popping up”, is probably because it’s from someone who has gone through this process.

All the same though, you guys know way more about trucks than I ever dream of. Full respect and I need you. Hold me. xo

 

This dude is local to me. He's done a few. Hope to get mine rol'n soon.
Cool tips here.

Upgrading a 300 carb Straight Six. (Pics) - FSB Forums