Custom headers "Drop"
 

Hello all, I am having new exhaust made for my Donzi Classic 22 and had some questions for some of the others that have done this. I have found that my original setup only had 3 degrees of drop. I didn't have reversion then but there was a manifold with a riser being used plus I had the y pipe to the out-drive.

My question is that Mercury suggest 14 degrees of drop to be used with their engines. For me to do this I would need to drop my exhaust 2.75" from its original location. Is this something others have done? With this drop my tailpipe is going to be very close to the waterline and waves are definitely going to be rushing into and over it.

What are your thoughts?

Should I go dry or drop the exhaust and run a flapper? If I run dry I can run any cam that I want....

Thanks for any help!

Best,
Matt

Go higher on the riser/ header before the drop

I cant, I am all the way up to the hatch...

Raise it if need be. Many Nice looking custom hatches on the water. I've never if prototype gets you through season.

I find it hard to believe that you only have 3* of drop unless the transom has been altered.

Wow not much room under that hatch...just measured our cig for custom tails. It was 12.5" from the header flange to the hatch. Ended up with 10" or so of drop. Maybe a little less.

Is that 3 inch drop from the exhaust ports or high point of the risers? oh degree angle, not inches. 3 degrees is essentially dead level, which wont work. how are you measuring this? are you including the angle sitting in the water? or level on trailer?

Having the exhaust at or below the water line is not a big deal. Thousands of thru prop and countless inboard boats have exhaust at or below the water line. The issue is the amount of rise to the highest point and baffling (i.e. external rubber exhaust flappers or internal V flappers etc).

I would not go dry.

Make the elbow as high as you can, even if you have to clearance the hatch or protrude through it, and the exhaust as low as you can.

I am measuring this as the relation of the exhaust to the transom, I have not taken how the boat sits in the water into effect. I did it this way because this is what Lightning headers recommends and the boat changes angles constantly with its load. Do you think I should measure a different way?

I sounds like I should drop the exhaust 2" and have it very close to the waterline with the water introduced right at the tip. I also then plan on running a Salisbury flap. I will run a very mild cam.

When the boat is being stored on the buoy I plan to machine up a plug so no water can be introduced to the exhasut.

Thoughts?

Thanks for all the reply's!

Most boat transoms are built at about an 11* angle. That would give you the total 14* angle.
I think you are worried about problem that isn't there.

I would not get a plug and Salisbury flappers are worthless. Get some good exhaust tips with internal flappers or some Shotgun mufflers.