Port Height

Hi Randy,I have a 20' Hydrostream with the xt bottom and a 225 omc ,about a 92 model,183 ci, wanting to boost it up a bit, planning on finger ports, better reeds, and wanting to raise the ports. I am looking for some suggestions on port height (exhaust and finger ports). I know this boat is a little heavier, It has 10" jackplate and low water p/u. Are there any sites dedicated to the high performance OMC's? How much compression is safe to run on pump Gas?

                               Thanks, This  is a great site
                                Chuck....20 Vantage


Chuck and Katrina, 

I didn't know there were so many Vantage's out there. Here's my skinny on the 3 liter loopers. The ones I've been around work pretty good with a few easy mods. The first common one is to run the 2.7 liter heads on the 3 liter block. This is only for the non closed deck block. The 2.7's and the 3 liter's had finger ports already so no need to worry about that. The problem with porting one is you only make more power at a higher rpm. The 35 amp charging system and the heavy flywheel are bad things to have if you go this route. The OMC also has a closed exhaust system so it is difficult to make all the neat porting work to your advantage. I'm not saying it is impossible, just very expensive. By comparison you can mod several Mercs or Yamaha's for the money to do an OMC the right way. I said the right way because I won't even do the OMC unless I job out the porting job. Monty racing and Wayne Taylor are a couple of guy's that do OMC's. 

Now the other part of the coin. The Vantage is a big boat. It needs a motor with grunt and low end power. If you port your 3 liter you'll have a high rpm temperamental bitch for a motor. I wouldn't do it. I'd work on set up, propping and balance. Solid mounts if you don't have them. 

Just for reference I'd call Alan Stoker at John's Custom Marine and ask what they do to customer's engines on the Stoker Sport Tunnel's they sell. Your boat has similar needs so if they have run mild mods on 3 liter's on their boats, copy them. I definitely think that would be the best package. A ported motor on the Vantage is like a Ferrari motor in my pickup, it'll work but it's not the best combo. 

In closing I don't want to come across as picking apart your plans, I just want to tell you what I would do if I owned your boat and wanted more performance. I've got friends that have ported up the OMC 3 liters and the results are kind of depressing. OMC's run pretty low compression compared to Merc and such, but we have run 130 psi with pump gas. Just be mellow with the timing. 

Hope some of this helps,



Please submit whatever questions you have to IHRTechTalk@yahoo.com.  All questions and answers selected will be displayed on this page as they come in.  Note: though all boaters are welcome, priority may be given to I.H.R. members.  Randy can not be held responsible for any advice given.  Though his information and expertise is second to none, he has no control over what you do with your boat.  It is up to you to boat safely and act responsibly, and his advice is only to be used as a guidance for your high performance boat/motor of which you are the one responsible for the risks involved.

Mark C.


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