OMC V8 setup questions

For all the V8 guros out there (DHadley and others), please go over the correct setup for the V8's - I have looked through the old posts and have seen you refernce a very different setup than that for a V6, fuel lines specifically. Please let me know how the V8 setup should differ and the correct way to do it. Thanks!

Re: OMC V8 setup questions

Welcome!!<br /><br />The V8s are great motors. You are correct about the fuel system though. There should be no restrictions in the line from the tank to the motor. No elbows, no bulkhead connectors, no primer bulb etc. All 3/8" ID hose. Use the best water seperator you can get with straight in fittings. The most popular filter is the Merc filter.<br /><br />Use the electric primer and by-pass that comes with the motor. Top rpm set up depends on which V8 you have but is either 6200 or 6700. In either case do not set it up at less than 6000. They dont like that.<br /><br />The 20" models are actually 23" and the 25" models are actually 28". Therefore its not uncommon to see 20" models on a 25" transom. It is very common to see them mounted too low and the owner complain about lack of performance.<br /><br />Tell us more about which one you have, what boat and the mounting. They're a great motor, youll love it.

Re: OMC V8 setup questions

DHadley, thanks and here’s some more info…<br /><br />The setup is on a 1985 38 scarab raider. It’s the old Miami Vice KV hull - except setup straight from the factory w/ outboards and with better colors. (I’ve heard they only made a few of the outboard 38s.) The last time it was run it had twin Johnson 275 V8s - I have come to realize one engine was a 4.0L, the other a 3.6L. The 3.6L seized up and I have purchased a dressed 4.0L block to go on top of the 3.6L mid section and lower unit. <br /><br />I’ve read from posts here that these motors like (love) to rev up to 6200 - 6700. I can’t remember what rpm range the boat turned but I think WOT was somewhere between 5400-5600 and we cruised around 4000-4500. The thinking was that this was the correct range and they would last longer it they weren’t pushed.<br /><br />I don’t know why the 3.6L seized up. The second hole up on the starboard bank is the one that locked up. I had the carbs completely redone and the correct gas line setup on that motor as you described (the 4.0L side’s elec primer was broken and we ran a pump bulb - and will now be removed.) <br /><br />For the new setup, I was planning on removing the VRO oil pumps and running premix at 50:1 with ams-oil.<br /><br />They are the 25” models and I believe they are the right depth but haven’t played around with that at all.<br /><br />The props I have are big ear chopper props, 24p. I am probably going to run it with these props and see what I have. If this thing has been maxing at 5600, dropping down a pitch or two would be a wise move….

Re: OMC V8 setup questions

Are the motors mounted to the transom or on a bracket? Should be on a bracket.<br /><br />5600 is killing the motors and robbing performance. Dropping pitch to gain rpm is a last ditch effort and usually costs efficiency.

Re: OMC V8 setup questions

They are set on brackets that are about 2 feet long. <br /><br />With the 4.0Ls, where is the desired rpm range for wot and cruising? Where else do I start looking for the rpm if the prop pitch is not the correct avenue?

Re: OMC V8 setup questions

We never had much luck using a chopper on that set up to be honest. We always ended up using the Rakers or Stilettos. With todays Turbos I'd sure try the Lightnings with the larger diameter.<br /><br />The brackets should be a bit longer than 2 feet but thats a standard mount for that rig. The top rpm is only limited by the ignition and set up. There will be a number on the power packs like 67L or 62L. Thats where the limiters are.<br /><br />At this point the motors need to come up on the brackets. That will gain rpm, speed, holeshot and fuel mileage. Most stock choppers have a horrible holeshot so keep that in mind as you go up. <br /><br />Are the gearcases stock or are there nosecones on them?

Re: OMC V8 setup questions

I will look into the Lightnings and other options as well as raising up the motors. The choppers do have a bad holeshot, but getting on plane has never been hard -hopefully I can get away with raising up the motors for now.<br /><br />Not much I am going to be able to do with the brackets this year...I will measure them - they might be a little shorter or longer. What is the optimal length?<br /><br />They are the stock gearcases - no nosecones.<br /><br />Thanks for the input!

Re: OMC V8 setup questions

The length of the brackets doesnt matter too much -- you usually need about 28-30 inches to be able to tilt the motors fully.<br /><br />Experiment with the engine height to gain rpm and performance. Dont worry too much about holeshot right now. At this point we need to see how everything responds to the increase in height. Watch the water pressure.<br /><br />Thats great about the stock gearcases.

Re: OMC V8 setup questions

The boat is still a week or two from getting into the water unfortunately - but going on your advice, it sounds like they are too deep and I will raise the motors up a little before it goes in. It was a fast boat running at 5500. If I can get it up to 6200 - and run all day at 6000 - wow!! Gonna be a fun summer!!<br /><br />Thanks man !!!

Re: OMC V8 setup questions

No problem. Those were fun rides. <br /><br />Hey, just a thought -- if its been in strage or just been sitting around with untreated fuel in it, you may want to think about cleaning the carbs. And if the fuel in the tank is untreated you may want to think about getting rid of it too.

Re: OMC V8 setup questions

I planned on redoing the carbs, that's part of the reason it is going to be another week or two before it hits the water - problably best to completely tear them down and rebuild 'em - huh?<br /><br />And on the gas - there were 40 gallons in the tank that I pulled out and put through an old car... didn't run like race gas but it ate through it!!<br /><br />Have you run a 38 KV outboard setup yourself?

Re: OMC V8 setup questions

When you do the carbs you might think about using the needle & seat from a crossflow. The inlet size is a bit larger than the looper inlet size. Its not a must but nice to do while youre there. <br /><br />Yep, I've run that set up a couple of times. Nice ride.