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Old 10-24-2011, 09:54 AM
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Default Exhaust manifolds

Anyone have any experience using GLM performance exhaust manifolds? Aside from stock Mercruiser exhaust manifolds, anyone have recommendations for exhaust manifolds to add a little performance?
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Old 10-24-2011, 10:21 AM
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If you are making no other changes than the exhaust on a stock motor, don't waste your money. If you have a 7.4L and need new manifolds and want to ditch the heavy cast iron stockers, look for a set of 496 MAG/MAG HO aluminum take offs. Even the later cast iron manifolds would be a nice improvement at a fraction of the cost of buying new aftermarket manifolds. Both the aluminum and cast iron 496 manifolds have stainless risers.
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Old 10-24-2011, 01:03 PM
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Will the 496/8.1L manifolds interchange with older 454/502 cylinder heads???
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Old 10-25-2011, 10:40 AM
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The reason for inquiring about exhaust manifolds, I think my starboard is starting to go bad. Have 454 MPI. Considering options prior to replacement. The GLM claim to boost hp, less restrictive, and are less expensive than stock cast iron oe replacements. Just wanted to see if anyone had some advice or suggestions. If aluminum 496 take-offs would inter change that would be great. Did not think they would interchange with 454.

Last edited by MR252SS; 10-25-2011 at 10:44 AM.
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Old 10-26-2011, 05:25 PM
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Originally Posted by C_Spray
Will the 496/8.1L manifolds interchange with older 454/502 cylinder heads???
Yes they will. They just have a slight outward angle to them when bolted on a 454/502 taking up more room under the hatch.

I don't think there is any performance gain with them but they are a good bit lighter.

The glm manifolds really do not offer any performance gain either. Maybe a few hp but not much. They are simply stock replacements that happen to be aluminum so they are lighter.
I would though consider these over the 496 take offs myself. I just don't like how the 496 manifolds look when bolted on a 454.

Since it is pretty much the off season anyway, I would keep an eye on the swap shop, I saw many, many sets of gil, emi thunder, imco, etc....sell at a really good price last winter.

Last edited by Baja226sport; 10-26-2011 at 05:30 PM.
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Old 10-26-2011, 06:04 PM
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Thanks, Baja226sport. Are GLM's a good replacement as far as durability and is there any problems with fit or space under the hatch?
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Old 10-30-2011, 04:35 PM
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GLM's = poor quality, I put a set on and 6 month's after install developed a leak that led to bent push rods. If no other performance mods stick with Mercruiser or like quality.
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Old 10-31-2011, 09:32 AM
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Thanks jim66, that is good info!
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