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Hates: Liver. Loves: Diesel
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6,306 Posts
Do you mean the exhaust crossover?

There really is no "better" in this case so I'll give you some pros and cons.

Cold fuel makes a cooler intake charge which makes it denser, which in turn makes more power. Hot fuel (as long as its not evaporating in the lines) costs some power, but is more capable of fully atomizing which means better fuel economy, a touch better drivability, and lower polluting emissions. If you have a catalytic converter it may also increase its life since you aren't dumping as many HC emissions into it.

The crossover works similarly. If you leave it open, the engine will warm up faster, probably get a bit better mileage, and take advantage of the benefits of hot intake charges, but again the heat spreads the molecules out which reduces power.

I have a 454 that I built for mild performance (400 hp) and I blocked the passage. It probably wouldn't have made more than a couple HP difference, but it was a decision. I built a low-po 350 for a panel truck and I left it open. Its a 4-speed manual and I like how quickly it heats up and gets off fast idle. Easier to drive that way. I also need all the help I can get in the MPG department :)
 

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Yes, it will change the sound. Mine had a sick sounding cough at idle before I put the h pipe on. I have seen the same thing on some videos posted at other forums. My guess is that without the connection between the cylinder banks, you get the sound of a pair of odd firing 4 cylinder engines.
 
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