What affect preformance wise would you expect to see with a v4 lower unit on a v6 OB?
What affect preformance wise would you expect to see with a v4 lower unit on a v6 OB?
Only a guess but I would expect that you would wear the gears out before too long. Especially if you have a heavy boat or are running a high pitch prop and hammer the throttle.
I believe these lower units have slightly different gear ratios. The V-6 has a little beefier gear box and different bearings (so, I have been told). The propshaft splines are also different between the boxes.
I have a V-4 unit on my 130 hp, factory was the V-6 unit. As long as you stay with a smaller hp, it would probably be fine. I don't think I would put a V-4 unit on a 200 or 225 though.
Modified \'92 Procraft 170 Combo/\'97 Johnson 130<U></U>
Thing is I have one that had a v4 on it when I bought it. I was wondering what kind of preformance change I should expect if I were to go with the v6 lower unit. I it will be a reasonable boost in preformance than I may go ahead and start looking for one. If not I'll just wait till this one bites the dust befor I up grade. Right now I do 55 gps @ 5200 rpm WOT w/ a 21 gade, on a procraft 180 duel pro w/ a johnson 185.
If it has the correct drive shaft and shift shaft it will bolt right up.
It will use the smaller 13 spline V4 props. Some of the V6 props can be re-hubbed to work.
The gear ratio I believe is 2.0-1 vs 1.87-1 for the 6.
This will require a much larger pitch prop than what would have been on the V6 gearcase to maintain the same speed. Also if you use a V4 prop and your boat isn't a lightweight it is going to see much more slip than the V6 prop.
Now, if your boat is an Allison or Bullet super comp or something light like that you can increase your speed with the smaller case. It would have to be modified to use a V6 prop shaft and your motor would have to spin to the moon to compensate for the gear ratio.
Even the gear ratio can be changed by using gears from an inline merc case and having the case custom built. $$$$$$$$$$$$$$$$$$$$$$$$$.
If you motor is a small V6 say 150 or 175 and it is on a light but slow boat then the swap would work great. Anything else and you are asking for trouble.
You posted while I was typing.
On your boat I would think you would see a marked increase in performance.
Your 185 is actually a 200 from the year before. It actually makes 185 HP.
I'm not sure what your boat is but I am guessing it is an 18 foot procraft dual console bas boat??? Fish and Ski???
If it is a plain ole bass boat it should be in the mid 60s set up right.
Its an 18' bass boat. I dont know how its been modifed, It has a nose cone and low water intake on it, no jackplate though, and doesent look like it has ever had one. I have no idea why it has this LU on it but I had to have the prop shaft changed out and the guy that did it for me sait it was a v4.
Fred you got any v6 LU's laying around?
With a nose cone on it, it is even worse for your set up than without it. That is one of the reasons it is going so slow.
Take your prop off and count the splines on the prop shaft. 13 for a 4 and 15 for a 6.
The biggest reason for performance increases with the V-4 is the cross sectional size of the case. 25% less than the V-6, resulting in much less underwater drag. The best approach is a V-6 shaft in the V-4. This gives a wider range of props to try. You mentioned your P.S. was changed out, I was curiuos, how come? Unfortunately, with good things come sacrifices, the smaller gears in the V-4 don't like the extra torque of the larger engines. But it sure is fun while it last!!! By the way, how many V-6 cases were you looking for?
I have been in the same exact boat model with the 20 inch (V4)and the 25 inch (V6) with the same HP motor. What I saw was the hole shot of the V6 was much better but the top end of the V4 was better by only a couple MPH. I felt the V6 lower unit was better overall performance other than top end.
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Thanks for the adivese guys. I think I'll run it till it breaks then replace it with the corect LU.
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