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Old 06-20-2009, 07:51 AM   #1 (permalink)
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pumping losses- exhaust valve lift

Hello; I have been lurking on and off ,and have a question about exhaust valve lift in my 97 s-10 5-speed 3.73 rear truck. I bought it for 400 and rebuilt engine, I cut intake and exhaust gaskets to fit and smoothed intake runners and cleaned up cast iron exhaust manifold for higher flow. I would like to learn about using higher or lower ratio rocker arms to increase millage or power or move curves around, I am using stock cam and all stock parts on 2.2 liter except I instaled electric fan. I also have 3.42 posi-track rear to drop rpms . I have instaled the largest diameter stock tires 235-75-15's. thanks mac.

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Old 06-20-2009, 11:39 AM   #2 (permalink)
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Hi, not sure how much runner reworking you did, but it is advantageous to leave (or create if it doesn't have one) an antireversion step to suppress the airflow from going backwards in the ports.

Removing huge casting marks is good, getting the surface too smooth is not. Especially in the intake manifold and ports, you want to keep the boundary layer relatively thick to avoid separation along with fuel accumulation in the bad areas of the port. Also keeping a little turbulence downstream of the injectors is a benefit. Sometimes adding creative turbulence inducing protrusions can help. Otherwise, a 120 grit cartridge roll is generally a good texture.

I stress caution as for shifting the torque curve around much since it is a fuel injected, but changing the rocker arm ratio probably means increasing/decreasing power inversely to fuel mileage
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Old 06-20-2009, 03:23 PM   #3 (permalink)
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Just curious: why do auto manufacturers use a metal for the exhaust manifold that rusts so quickly and easily?
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Old 06-20-2009, 06:00 PM   #4 (permalink)
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The alternatives are much more expensive. Cast iron can take a lot of heat and is cheap to make. Stainless steel is more expensive a material and has to be welded right or it can crack. The rust on the manifold usually takes a while to penetrate. The cast iron sections of the exhaust on my Subaru have outlasted some of the stainless steel, though all of it is original as of this moment.
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Old 06-20-2009, 09:15 PM   #5 (permalink)
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Hi mac and Welcome to the place.
Enjoy your stay ,

Cheers , Pete.

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