Mercury Verado 400 IL 6 to Mercury Verado 300 V-8 Fourstroke

Mercury 300 v-8 fourstroke engines
Re-Power from Mercury 400 IL6 to Mercury 300 v-8 four stroke Verado. I used my 36ft Yellowfin for testing.

First off, Thanks Lee Murray, Scott, David and the crew at Murray Marine for knocking this job out and doing some creative rigging to get me going.. Murray Marine Inc 

Here are some notes if you are changing from the IL 6 to the V-8s.. 

  • Make sure you have extension 14 pin harnesses. The coupler on the V8 is in the back of the motor about 3 ft extra will be needed.. 
  • The water in fuel alarm is now on the motor on the FWS canister. 
  • Triple and twin applications should have some plugs for inside top holes to improve water pressure.. Many Deep Vees will have the motor dry there sucking air, these gear cases seem to care. 

My set Up.. 1:85 GR 20.5 XP Eco Enertia Props. Same bolt holes as my 400s. 150 gallons fuel. 

Out of the box testing….

  • Hole shot was INSANE! More than I expected.. Tossed my 36 on top like a toy.. 
  • Low mid range Super strong.. 32 mph fuel economy was 1.8 this will be great in the slop in winter.. 
  • Mid Range fuel at 40 was 1.7 
  • 53 mph Fuel was 1.25.. still very strong.. 5000 rpm
  • Top end.. sprints to 60 and hit 62.3 on the rev limiters.. I could go one more inch in pitch. 
  • I am a little light on water pressure at cruise but strong at the top. Will be adjusting this..

Run Characteristics.. 

I never thought that 210 lbs less weight would make my boat run so flat. But it might be the gear ratio or the gear case design.. But it runs REALLY flat on no trim.. Super responsive to trim.. she comes right up. the balance is perfect. I think the new motors will improve my already great ride in the 36.. 

Update June 6 2021 – Absolutely incredible motors. Top end speed is about 63 mph on my set up right on the rev limiters. Seems like these motors do not care about load. Super steady.

Acceleration is ungodly. The transient spark technology TST in these motors snap to when you stab the throttle between 3500 and 4500.. Hand On!… No lag.. Just instant Power.. sick! super impressed stronger than 400s. 

Thats all I have at the moment.. Just wanted to quench some thirsts… Check back for more updates..

Experiences With These New Motors

September 18 2020 – I fished the V-8s on my 36 ft Yellowfin for the first time this week. See My post on September Yellowtail and Groupers.

June 10 2021 – Fuel economy over the course of the year has been steady at 1.58. Oil changes are showing little to no wear in the oil over the 100 hour interval. I have 375 hours on the motors.

Capt. Steven..

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