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?

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.

Will the 496/8.1L manifolds interchange with older 454/502 cylinder heads???

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.

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.

Thanks, Baja226sport. Are GLM's a good replacement as far as durability and is there any problems with fit or space under the hatch?

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.

Thanks jim66, that is good info!