It's a 20"

nice now you just need a good prop. is it a 20 or 25 inch shaft?

Jason it's just an 85hp, so I don't expect too much. Not only that, there is no vertical adjustment on the motor. That being said, based on comments here and thinking about it more, I ordered a manual jackplate yesterday. It wasn't much money and I think it will be well worth the investment. Thanks all,
Chris

I was using a small hub prop on my 150 johnson and it was horrible!!!!! Bad cavition and blow out . changed it up and it was a different boat. the motor your putting on, what hp? With out a jake plate and at least a five inch set back i would set your motor to its highest setting and work your way down, but it could be good. before i changed my motor up i was running a yamaha 115 v4 without a jackplate and setback mounted to the transom and i ran on the hightest setting and the boat felt great just could not get more than 65 mph . you should for sure invest in a 24-26 pitch prop to start out maybe a 19 if your pulling anyone. good luck let me know what happens . Jason

do you have a water pressure gauge ?
i would recommend u get one if you want to raise it high or you may cook your motor

Well, currently I have probably the worst possible prop for it. It's a factory 3 blade (can't remember the pitch, but WAY to small). My parents had it on a bowrider in the 90s and it had an amazing hole shot! Not really sure what I'm going to use. I guess I'll start with it and try different ones from there. I think I rememeber reading that the 850's (it's a mid/late 70s) had a lower gear then most which makes my small prop even worse!

well worth it. one inch above sounds good with your set up, but trials will be the only way to tell . what prop are you planning on running?

No, I don't have a LWP. However, I did consider getting a jackplate to make any adjustments/future engine changes easier. I'm just trying not to spend a whole lot of money on this project. It may be worth $150 though.

do you have a low water pick up? you can pick up a 5 inch set back jackplate for about 150$ is well worth it

Regarding motor height.... I'm getting ready to mount my Mercury 850 (manual trim, [20" shaft]) on my Viper. Is there a good rule of thumb for height? I'm thinking about the anti-cav plate about an inch above the bottom of the pad. Sound OK? It won't have a jack plate either, so I'll use a hardwood block to raise the motor up on the transom (if needed) and then bolt the motor to the transom. I know I'm not exactly creating a high-speed Viper here, but it's what I have. What do you all think?