I've got an '86 Donzi Hornet III with a 502, running stock manifolds,

Any suggestions as to replacement manifolds? Not sure what the weight savings could be, or the performance improvements...

Any help or comments would be appreciated,

Why are you looking to replace your manifolds? Are you looking for performance gains or just replacement?

Are you salt water or fresh?

How much are you looking to spend?

These are a few deciding factors.

If just looking to replace, there's not much performance gain from just swapping exhaust system alone. So stock type manifolds would be cheapest.

I say stock type manifolds because there are aluminum manifolds available that would save you weight. Possibly around 20 lbs or more per manifold. So a 40 lb or better weight reduction in the rear is always a good thing.

Which brings me to what type of water? If salt water, aluminum is not going to last very long without some regular maintenance. So the cast iron manifolds might be best for longevity and cost.

If you're looking to boost engine performance at the same time, or in the future, an aftermarket exhaust would be ideal to take advantage of those gains. Obviously very costly. You have every option available to you at different price points in this area. Stainless headers, aluminum manifolds, steel headers, used exhaust options , etc...

More details would help with making suggestions.

Yes, good point, I'm in fresh water, weight savings was my biggest factor, $$ is a factor, the season here is 2 months, I take it out on a few Donzi weekends, or up to a friends cottage...performance gains would be nice, but not the main factor...

I had cast manifolds on my 32' Fountain. Previous owner was not big on maintenance and both sets had signs of rust/ leaks at all the riser joints when I got it. One took down an engine. Wet riser joint is a horrible design if you ask me but I'm no engineer. I replaced them with Stainless Marine. If you Google you will be very hard pressed to find any threads of failures. They fit like a glove, zero modifications and zero worry of it ever happening again due to the design. Just that change alone raised the back of the boat 1". As to performance I cannot comment as I had to rebuild both engines and modified them both at the same time, but I have read that 1mph is common on a stock setup. They also look way cooler too so there is that.

Stainless Marine manifolds will typcially fail with an exterior leak, vs an internal exh runner leak getting into the engine.

They weigh quite a bit less than the cast iron BBC.