OMC tuning engine..help!!

[inshoreracing]

Hi ,
I am a french driver, and I will race with 3l OMCon a racing midlle section like F1.

for carbs, I have the choice between 2 bore, 38mm or 47 for the venturis.
The max speed is 180/190km/h at 7300/7500 rpm.(the boat is a light cat)

for you what is the better choice a little or a big venturis.

the race is during 24 hours, and time to time, the night, we have ice on the carbs....

I need help, because I am not sure to have the good solution?
what do you tinnk about that?
thanks by advance

[Mark Poole]

Several people on this forum might be able to help with that question with a little more info on your set up. Porting (wild or mild), head cc, etc. For what it' worth, colder conditions could favor the big carbs. High temp and low air density would not favor the big carbs. It is important to keep track of air density when racing carbureted engines. Fuel injection compensates automatically.

[jphii1]

You want to run mid bores. I can't remember the part # but I know the last 3 are 743. I'll get the number when I go to the shop on Tues. I'd stay away from the big bores if you're only gonna turn it 7500. Can you work the carbs or do they have to be stock?

[Zonker1]

Using the airbox. You would remove the obstructions from the inlets, making the airflow as smooth as possible. Then space the cover of the box out about as much as you can, without interfering with the motor cover. This should allow the carbs enough air, but shouldn't incur any icing problems associated with humidity, and air density, because you are drawing air in, but allowing it to mix in the box. This acts as a common plenium for the carbs.
Just my thoughts.
Zonker