Exhaust Holes Through Transom
 

I located a template from Hardin Marine's web site to layout and cut the 4" exhaust holes in the transom of my new 28, however, since I'm pulling the motor from my 24 I thought I'd drive to the marina and take some measurements.

The template calls for a 27.375" distance between the hole centers. I measured my existing set up at 28". Also the height above the driveshaft centerline to the center of the 4" holes was lower on the template than the actual measurment.

Does anyone have another template or am I better off using the actual measurements from the motor and exhaust that I plan on installing?

I am waiting on another template but it hasn't arrived and I want to do this work tomorrow.

Is there a standard height from the drive shaft centerline for Imco Powerflow exhaust manifolds?

Re: Exhaust Holes Through Transom
 

"GIL" powerflows :confused: I thought Powerflows were Imco.......like mine

Re: Exhaust Holes Through Transom
 

Imco is right, do you have an answer to help me?

Re: Exhaust Holes Through Transom
 

Not sure about the height but make sure you look at the drop from riser to exit. Have been told at least 14" is needed to help prevent reversion or problems from launching or when dropping down to idle. Also if present width worked and not changing motor wouldn't it work as is?
.02 cents.

Re: Exhaust Holes Through Transom
 

The rule I got was 1" of fall per foot of exhaust from end of riser to transom--also--make sure you put flappers on -- internal or external--reversion is not pretty

Re: Exhaust Holes Through Transom
 

So lower is better in this case. Then the template I pulled form the website would be better for the drop to prevent reversion. I haven't had any reversion problems on the 24 so that height or lower would probably work fine. I think the 28 will sit higher in the water also which will help.

Anyone else have info on this issue?

Thanks for the help.

Re: Exhaust Holes Through Transom
 

Poorshe is right, that is the rule I heard 1' minimum per foot. Stainless Marine makes some pretty nice inline flappers, don't use those garbage rubber Salisbury type ones...

Re: Exhaust Holes Through Transom
 

My new tips from Too Old have very nice SS flappers with rubber tips, look well made.

I'm going to wait until the template shows up. If I ever go to headers and my dimensions are wrong, I'll be screwed!

Re: Exhaust Holes Through Transom
 

I mounted engine and drive, then with a 3/8 rod and a marker taped to the end I transfered the mark as I drew the rod around the end of the exhaust.Use the center of that to drill. Also you will need a drum sander to enlarge the hole to match the angle of the flange on the tips.