Manifolds/Risers

[sogood]

Still getting familiar with my new boat and it's engine in particular. It's a 5.7 Mercruiser, circa 1990 with an Alpha Gen 1 outdrive. I have come across a pair of used manifolds/risers, apparently clean and crack free, for a very good price. But, I believe there are two types used, as in 3" and 4". Mine appear to be 4" as they are bolted down with the long bolts as opposed to the 3" version using studs. Am I correct in this?
​My question is, are they interchangeable? What's the difference and what exactly do they do? Be gentle with me.......................

Thanks in advance.

 

[Bt Doctur]

the manifold can accept both types 3 inch exaust with studs or 4 inch with bolts main difference is in the size of the Y pipe and the rubber couplings

 

[sogood]

So, given that the manifolds and risers are advertised as having "come off a Mercruiser 5.7 V8" then they would do for me and my Mercruiser 5.7 V8? I just think, if they'll do, they'd be useful spares to have.

 

[Bt Doctur]

The 5.7 used both the 3 inch and 4 inch versions

 

[Scott Danforth]

Using old manifolds lis like buying used underwear

 

[sogood]

I don't care to go "Commando".

 

[Bondo]

Using old manifolds lis like buying used underwear

Ayuh,..... Long Johns,..??

I buy used GI poly-pros at the Soldier's exchange over by the Army base All the time,....

As for used manifolds,....
In freshwater,... manifolds die from freezin' fulla water, not rust or corrosion,....

They don't "Wear Out",....

 

[Scott Danforth]

I buy used GI poly-pros at the Soldier's exchange over by the Army base All the time,....

..

Ewwwwww