Performance headers for my Donzi 28 ZX
 

Hi all
my name is Mike and I live in Bournemouth in the UK, I came out to Springfield Ilanois in 2012 to buy beloved 2006 Donzi 28 ZX and shipped it back to home in UK.
I love the boat and during my ownership have kept it right up together and done a few mods such as had the ECU,s remapped.
my mechanic has advised me that I need to change the manifolds/headers as there are over manufacture time for replacing, so I thought if I am going to spend out, I may as well go for a performance set instead of the stock 350 mag mercruisers.
can you advise me on what's the best type for my boat, I am the only Donzi owner here in Christchurch, Bournemouth so there's no one to talk to about it.
hope you can help.
all the best
mike

Cmi is full headers. Stainless marine is manifolds. Both make small block stuff. You won't really see any gains over the stock exhaust without more work like heads/cam. If you don't plan on doing those things just going back to stock is the cheapest easiest solution.

Small blocks will not give you much if any additional gains with headers, but they will set you back $$$. If you like the look of them and have the money....buy the headers, but it will only give the boat a better look (hatch up). All other instances, buy stock manifolds/risers. Much cheaper and the performance will be the same. Stainless Marine makes some good manifolds that are considerably less than CMI headers, and they free up some weight in the back of the boat compared to the cast-iron stock manifolds, but that's an expensive upgrade for minor performance gain.

Headers
 

Thanks guys 👍
What other mods can I do without breaking the bank to get more out of her
as I said I had the ECU,s remapped which certainly does feel better through the power band I am running 23 in mirage props and trimmed out balls out I am hitting just over 70

Stainless marine manifolds or headers will lighten the stern of the boat a bit, negligible performance gain IMO. I don't have your current setup in my 28, but I do believe those are the correct props for you. I think the only way you'll see noticeable gains in performance would be with ProChargers or Whipples and that isn't a cheap upgrade. Not many mods on SBC's will give you a performance gain...sorry. I'd stay away from the superchargers too if you're looking for reliability and don't want the hassle of 91 octane, IMO.

Heads and cam. Best gains. Superchargers are very reliable when tuned right. Just look how many supercharged motors merc built. Look how many auto manufactures uses superchargers and turbos. It's really in tuning.

If you want reliability go with Stainless Marine you won't have to worry about them leaking.

is your mechanic saying the manifolds are due for replacing because of salt water ?
does your boat have thru hull exhaust ?

if yes to both, cmi makes a stainless steel header type exhaust for the small block called e tops
they are direct replacement, do not need tails and cmi will drill and install bungs for any sensors your
existing exhaust may have.

look them up on various websites from cmi and their distributors, cmi, cp performance, teague, hardin, etc.

My 99 still has the original ones
are you sure you need to replace them

I'll echo this, if your cast iron manifolds need to be replaced because they're rotted off from saltwater, then stainless headers are your only option. The Stainless Marine manifolds are aluminum and will rot off in saltwater too. If you don't use the boat in saltwater and/or you adequately flush the motors after each use, the stock manifolds should be fine. They're giant chunks of cast iron, they don't just "wear out"...