1989 3485 Avanti exhaust manifolds 454-gctid815336

[jgregdds]

Does anyone know what exhaust manifolds and risers will fit 454 cu. in. 1989 3485 Avanti. I know many will fit the engine but I am concerned about the height of the manifold and riser. The stock ones are VERY close to the floor and engine hatch. The originals are no longer available.

[yachtman]

I am installing sierra brand mercruiser 454 style exhaust manifolds. They are nearly the exact height of the original thermocon develvo manifolds that you probably have???

If you go to those you will need to get new longer 4 inch exhaust hose stubs and relocate the oil filter and the fuel filter filter mounts. With the manifold and riser no spacers were needed.

If you want I can post the part #s

[jgregdds]

If you could post those part numbers that would be great. Thanks for the help.

Greg

[yachtman]

"jgregdds" post=815357 wrote:
If you could post those part numbers that would be great. Thanks for the help.

Greg

I can later today I have to get some time to collect the info.

[yachtman]

I'll post the information pretty much in picture form.

The manifold siera part # 18-1957-2

You can see the part #'s on the boxes.




Riser # 18-1976-2

[yachtman]

The original exhaust manifold literally weighs about 100 lbs. I lashed a rope around the manifold and with a come along I winched the manifold out. It was all I could do to through it over the side of the boat. You will see I the pictures that You need to have new exhaust hose. Probably each about 25 inches +. Also you will need to rehose the cooling system. Not really a big deal. You will need to remount the oil filter I plan on mounting mine on the front of the engine opposite the fuel filter.

You will need to make a small mounting bracket for the fuel filter and oil filter as the can no longer be bolted to the manifold.

You will be able to see the manifold is about an inch below the cockpit sole. . I believe it will work better because the riser is taller than the original. The water entry is much higher. Also the center riser manifold produces more power and torque than the original.



You can see the space the manifold has to the floor in this picture nearly touching it.

[yachtman]

See the 2 bolts holding the lifting bracket? Use those to make a new bracket for fuel filter mount. Do the same thing for the oil filter.

[yachtman]

[yachtman]

The space of the original manifold.....

[yachtman]

The crusader manifold is also a option but they are more expensive and harder to come by. I decided to use mercruiser style because if I ever need new parts they are easy to get.

I have more pictures but couldn't get some of them to post.

I think no matter what style you chose there will be an amount of fabrication because the mounting is different. That's just the way it is.

[kiwi55]

Hi their I changed to after market ones by an Aussie company they have agents all around the world they are hi Tek marine they are stainless steel saving in weight increases np an better economy win win situation have a look won't hurt

[jgregdds]

Thank you so much. That information will save me a lot of time trying to figure out what will work. And yes, the old manifolds are massive. I plan on having some help removing them.

Thanks again,

Greg

[yachtman]

"kiwi55" post=815451 wrote:
Hi their I changed to after market ones by an Aussie company they have agents all around the world they are hi Tek marine they are stainless steel saving in weight increases np an better economy win win situation have a look won't hurt

I looked into those and at nearly $4000 an engine that would be $8000 for the boat plus labor probably close to $10,000.

Exhaust alone would total my boat.

You can get the sierra ones for about $600 and engine for a complete kit.

The sierra manifolds.also.do come with the bolts and gaskets. If you want.the closed cooling you will need.to purchase block off plates to the risers.

[attachment]38446 wrote:
Screenshot_20170629-045006.png[/attachment]

I believe that is an each price

[jgregdds]

Yeah that's a little rich for my blood. The boat is almost 30 years old so I think the Sierra is the way to go.

But thanks for the info!!!

Greg