bb manifolds
 

What is the most economical bb aluminum manifold on the market. currently have original cast iron manifolds on my twin 454 420hp trs setup. Please advise, i don't want to reinstall originals.....too many water ingestion issues!

The 454 420HP TRS had a single plane alum manifold. If yours is cast iron, was likely a 330HP. The 370HP TRS had a GM dual plane alum intake.

I think he is referring to the exhaust manifolds. I imagine you have the Mercruiser performance manifolds that came on the 420's. They have 6 bolts that mount the huge riser to the manifold and stainless tails?

Look into revolution marine manifolds, 1000 bucks a set. Would be a big weight savings off the back.

Revolution Marine and Dana would be a close second. They are just a little more. I think Stainless Marine has a set that is just a little more.

yea, I really like those dana manifolds, they look great, the price is right, and I hear they dyno well.

I have those old iron 420 manifolds. They are huge, individual runners in the manifold, 4 1/2 exhaust opening, and i have the rare 4 1/2 tails that bolt to them. They were known for leaks, due to the wet joint at the riser. The problem with these suckers is they are extremly heavy. If the standard merc 4" manifolds weigh 65lbs, I would bet these are every bit of 85-95 lbs each. I almost broke my back installing them. If my boat dont sell, they have to go. Im would love to save 250-300 lbs off the back of the boat.

Stainless marine on mine 5 years now, still great...

can a guy get a set of manifolds
 

thanks for the input guys. i've had a lot of trouble getting a hold of two pair of manifolds. revolution marine i looked into but they would never call either myself or my mechanic back who is a performance boat dealer. dana marine didn't have a riser that they thought would 100% work with my trs setup. stainless marine was three weeks lead time for "custom" trs style risers. But good ol' teague had two sets of imco's with trs style risers in stock. Yeah i had to spend some more money than i wanted but i think i made the right choice seeing as the manifolds arrived to my mechanic today. Now, question is....what kind of performance gain should i see? Any thought?

If you are only changing manifolds and everything else is stock. Then you'll most likly see no gain or very minimal. If you've done other performance mods like cam, intake and carb, then you may see 200 more rpms.

did you change the exhaust?

The exhaust manifolds that came on the Merc 420hp engine is actually a decent exhaust manifold when it comes to breathing and performance. They're better than all the other cast iron exhaust manifold designs that Merc has produced for their other engines----even so, the 420hp manifolds are still very heavy and leak internally.

As Payton mentioned....you may see very little gain if any on top (WOT) if you're only adding the aftermarket exhaust to a bone stock engine. If you upgrade to a larger cam then the engine will increase in RPM depending on the cam being used. If you plan on upgrading to a cam....then install some hydraulic roller cams if your wallet will allow you to and add do some light bowl/pocket port work on the heads with some short side radius work on the exhaust side and you should see a a kick in the pants difference then. Have fun.