modifications,where to find info

[tthibodaux]

What are the differences between the 25mod OMC and the 18hp powerhead? I would think the two powerheads are similar in design. Therefore, what's good for the 25 should be good for the 18. I think the little 25hp powerhead is popular in the 25mod class. There should be a wealth of info to be found about the 25mod OMC. Can anyone here help direct this man to an engine builder for the 25mod class?
If you stick with the stock towerhousing and transom height, Do not cut the exhaust snout off. You will lose power. The snout runs below the waterline and the passing water creates a vaccuum. Thus, "sucking" the exhaust from the motor. The power gain from this action outweighs the drag caused by the snout. Take it from me, I learned this lesson already on a stock KG-7 Merc. Unless of coarse you are able to jack the motor up on the transom. Then the lesser drag from the lower unit will FAR outweigh any powergain from that vaccuum exhaust action. I know it sounds strange, but it's true.
Best of luck to ya with your little boat! Have fun!

Depending on the year there are cubic in differances. As long as the down housing is stock, no amount of port or exhaust work is going to help. We could build a hell of a race motor for a hydro or runnabout but he's not going to be able to run it at the lake due to the elbow and horn for one thing. Those powerheads are just about maxed out stock for local lake play purposses.

[Mark75H]

. I think the little 25hp powerhead is popular in the 25mod class. There should be a wealth of info to be found about the 25mod OMC. Can anyone here help direct this man to an engine builder for the 25mod class?

It is very popular, but Mod does not allow porting the OMC in 25, just adding exhaust, I checked the rule book already and posted that higher up on this thread

[beaver]

25 hp head, carb or later mod 80& UP 75 CARB intake,exhaust from a 25. cut off exhaust on l/u and plug it up open it up right above where it was. put h2o pick up in front. look on the powercat web site go to pic and look at my 25.BEAVER TYLER

[RichardKCMo]

Of that OMC 22 ci i mean lot of nice boats tho', but there old too,well oh well.

[JohnsonM50]

What are the differences between the 25mod OMC and the 18hp powerhead? I would think the two powerheads are similar in design. Therefore, what's good for the 25 should be good for the 18. I think the little 25hp powerhead is popular in the 25mod class. There should be a wealth of info to be found about the 25mod OMC. Can anyone here help direct this man to an engine builder for the 25mod class?
If you stick with the stock towerhousing and transom height, Do not cut the exhaust snout off. You will lose power. The snout runs below the waterline and the passing water creates a vaccuum. Thus, "sucking" the exhaust from the motor. The power gain from this action outweighs the drag caused by the snout. Take it from me, I learned this lesson already on a stock KG-7 Merc. Unless of coarse you are able to jack the motor up on the transom. Then the lesser drag from the lower unit will FAR outweigh any powergain from that vaccuum exhaust action. I know it sounds strange, but it's true.
Best of luck to ya with your little boat! Have fun!

The 18s are great runners, good power & dependability but I think they are ported non radical for those charicteristics, A 25hp 22ci would bolt on and go faster but all the others that say Lower Unit are right reguardless of the powerhead 50 is optimistic at best. Ive tried a pals mini max 1nc and splashed then stuffed it, dont know if theyre alike tho.
There is a releif plate on the lower unit, remove it , copy it onto a 3/16 - 1/4 pc of alum.. drill it out then drill 1 more hole where theres room, tap a 1/2 pipe thread in and get a fitting and a tube. Fasten the tube to the transome securely and run a hose between and you now have a substitute low water pick up so you can raise the motor. You can lose alot of weight off the motor if you want too, [cowling and pan] bring it down to around 65 from 85. If you want to put a 25hp carb on just match the manifold hole to it and itll work if you look at my posts Ive written some crap on these carbs B4. A bigger one than that probly wont do it. I rebuilt a 22ci 25, enlarged the ports 1/8 then traded it to a pal who put it on a merc 1 to 1 Qwicky he did 60 in hydro [ lucky on the ports Im sure] but as is you can hope to get 7 or so mph.