live2ridenmi

I have searched for information about exhaust without finding the facts I need to make decisions for my 454 mag build. Here is my dilema and questions that I would greatly appreciate any help or opinions with. Thanks in advance ! So I have a 454 mag at my engine builder that has very low time on that was sunk and started, no real damage, but was turned in as a core and I have spoken for it to build in place of my spun bearing 330hp 454. He will be rebuilding this engine. I am trying to use all resources to fund this build. It has the center rise manifolds. What are the stock manifolds capable of flowing for hp ? I think I found it would be at about a 425hp limit ? Are some better, 90 deg. risers worth buying for under $400 ? I dont't ever see spending the money on the high end exhaust. Are the 496ho manifolds worth the purchase for my build ? I have decided that a flat tappet cam is ok to use since I wont need the capabilities of roller to push the lift limits for an under 500hp build. I may be able to use the stock cam but don't know that at this time. I also like the idea of just purchasing another flat tappet cam with newer technology. Also, would it be wort asking Bob Madura to help with a cam grind ? My exhaust decision will decide on my cam !

Knot 4 Me

A set of take-off 496 manifolds and risers would be a nice upgrade from the stock cast iron manifolds/risers. Early 496 manifolds are aluminum. They made the switch to cast iron around 2004-2005. The manifolds on my 496 built 9/03 are aluminum. All the risers are stainless. Also, there is no difference between 496 MAG and 496 MAG HO exhaust. Sets usually go in the $400 - $500 range.

dereknkathy

The aftermarket riser that fits stock center dumps is pretty. That is its only improvement over the stock iron riser. No real extra dry length, no improvement on breathing. AND it is about 800 a set. The stock manifolds are maybe good to 400 hp or so. Get the best exhaust you can. It is difficult to get exhaust that is too big for your needs...

BajaDan

iTrader: (2)

I don't believe that the 496 manifolds will work on the pre Gen 7 engines. Different port and stud size and spacing.

Dan

apollard

I have 496 manifolds on a Mark IV w/ 781 heads. No issues, had to change some brackets, different bolts & such, but fit the heads just fine. Ports match great. Nice upgrade over stock for not much money.

BajaDan

iTrader: (2)

Good to know. Thanks for the correction and information.

apollard

Forgot to add the risers do not line up with old style Merc manifold riser locations, so changes to the exhaust might be necessary. I had enough room the 1" or so of extra height could be taken up by the exhaust hose. But this is a potential issue with any exhaust change.

Budman II

iTrader: (1)

Not sure if the 496 manifolds make much of an improvement on performance, but the fact that they went to a dry riser / manifold joint should make them less prone to internal leakage and more reliable. Thousands of engines have been ruined when the stock Merc wet joint manifolds start leaking water back into the engine internally. Hot exhaust valves definitely do not like being quenched with cold lake water!

dereknkathy

Wasnt that gil manifold also used on 454-420 hp engines? Anybody know how much power they support?

live2ridenmi

Thanks to all that replied ! I think I have been on the right page after all I have tried to learn and decide on for my build. So,what do the 496 manifolds and risers support for hp ? I have also seen sets on ebay of different popular brand for under a $1000. anything in particular to look for ? Any flat tappet cam recommendations ?