Likes Likes:  0
Results 1 to 2 of 2

Thread: Help tuning a V4 85hp

  1. #1
    Team Member
    Join Date
    Jun 2017
    Post Thanks / Like

    Default Help tuning a V4 85hp

    Hi all been lurking in the forum for a while now so i thought i would take the plunge and ask how i can mod my V4 85. I was going to turn her into a 140 but i was unsure of the outcome but now its has come time to decide on what to do with my motor a Johnson 85hp crossflow 1980 (so 85hp at flywheel) and a collection of bits
    I have the following
    1 bubble exhaust and manifold plus stuufers from a 140
    1 set of reed stuffers from a 140
    1 set of 1 5/16th carbs from a 140 (Jets are 76c) also have a set of 58c I have taken out the choke plates as i will be using the choke primer.
    1 set of 1978 High Comp Heads from a 140.
    1 set of CCR sport reeds
    I was toying with adding these to my 85 block and porting the block to 140 spec.
    I know i have to cut the lower rib out to fit the bubble exhaust
    I was going to get the porting done at the same time.
    Now i dont know if the porting will be on par with the factory spec.
    I dont have the money just to buy a 140, they are also pretty hard to come by (i live in Scotland)
    So i will just add the bubble exhaust and other parts and run it as a tuned 85 Will this work ????
    Will i get just as much power with the exhaust left off???
    I would like to try and get around 85 at the prop more if i can.
    I have probally asked this question in other forums but now is the crunch time
    Does anyone know of a way to get more power out of an 85 ????
    Some folks on here must know of a way to build a reliable fast V4 85 motor
    Thanks Dan M thanked for this post

  2. #2
    DaBull Dabull1919's Avatar
    Join Date
    May 2005
    Post Thanks / Like


    Of course the best hop up is a higher hp V-4 but you say that can`t happen so hears something to think about.
    These things you mention will help performance but I wouldn`t port it to 140 specs. Your 85 has a smaller bore than a 140 and would suffer in low end torque. The 1977 115 V-4 was a runner for sure so maybe look at copying those ports instead.
    Also there is a mod that most people like to do to cross flows that will give you top end but kills low end. They cut a half moon in the piston skirt just like OMC did to their race motors but keep in mind that those motors were intended for closed course racing where low end didn`t really play a part so don`t get talked into that mod.


Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. 300xp tuning advice
    By Cash to Burn in forum Technical Discussion
    Replies: 0
    Last Post: 06-29-2015, 06:01 AM
  2. propeller 85hp yamaha racing
    By velocity85 in forum Technical Discussion
    Replies: 2
    Last Post: 05-25-2013, 03:48 PM
  3. Tuning a -1986 Yamaha 15hp
    By vStrandell in forum Technical Discussion
    Replies: 7
    Last Post: 12-12-2012, 03:58 AM
  4. Crossflow Engine Tuning
    By doppler491 in forum Technical Discussion
    Replies: 2
    Last Post: 07-08-2010, 08:31 PM
  5. OMC tuning!!
    By inshoreracing in forum Technical Discussion
    Replies: 3
    Last Post: 03-17-2007, 04:03 PM


Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts