V4 75 Hp

[Skoontz]

to go fast. Hugh Entrop proved that with the first Starflight series.

If ya want to play with the exhaust without speding alot of oney on that 75, cut the angled piece over the back of where the gearfoot bolts onto the midsection and weld on a 1.25" piece of aluminum channel. Angle it similarly to how the X-115 gearcase is. You could also play with an internal tuner but without seeing the inside (it's been 25 years) of the exhaust housing, the room you got may be limited....

There is no greater sound than a V-4 with open or above ater exhaust

[LIQUID NIRVANA]

Have been reading these posts re speed possible with the old V4 JohnRudes. I was very close to these V4 60's, 75, 90 & 100hp.s back in the 1960's. Now I have to say that comments like the V4 75hp "stonewalled" at 35mph is just NOT TRUE. The first ride I ever had in a boat was in 1963. It was on a 15' performance powered by a 75 Johnson swinging a 10.25" x 10" prop & I remember vividly it doing 43mph. With a 10" x 12" prop it did 47mph with a 1964 90hp.

15' Pride Starfire Runabout with a 1966 100hp Johnson. Well over 50mph


15' Pride Starfire, 1965 90hp Johnson. 47mph. Over 50mph in racing trim.

[JohnsonM50]

I don't see any prop slip in your 40 mph calculations, most props (good ones) run in the 10 to 15% slip area. I will give you 10%, which is 4 mph, 4 from 40 is 36 mph. When I worked in Engineering at OMC in 1968 through 1973 that is range that it would operate in. Granted there are some very good props that are more efficient, but none are made for your 90.

I agree, if you get 90 percent efficiency your doing good [always tryin to go faster] without an accurate measure,, gps / radar youll always feel like your goin faster than you are.

[Mark75H]

Have been reading these posts re speed possible with the old V4 JohnRudes. I was very close to these V4 60's, 75, 90 & 100hp.s back in the 1960's. Now I have to say that comments like the V4 75hp "stonewalled" at 35mph is just NOT TRUE. The first ride I ever had in a boat was in 1963. It was on a 15' performance powered by a 75 Johnson swinging a 10.25" x 10" prop & I remember vividly it doing 43mph. With a 10" x 12" prop it did 47mph with a 1964 90hp.

Those old pitot tube pressure speedometers were almost always waaaaay off. Second, there is a big difference between the 63 and 66.

To respond to Skoontz's comments ... the motors Entrop raced had special hand made fronts with big carburation or fuel injection.

Without a better lower unit and special hand made front, the tuned exhaust on the 63 V-4 isn't going anywhere but slow & noisey.

[Skoontz]

Agreed, Sam. Though that OMC gearcase looked very promising, (if you look creativley, you can see similarities to some of the quicksilver gearcases) it never went anywhere....

But, as that engine was released in 59 0r 60, many of the Merc employes who tested it on Lake X came off telling Mr. K it was far from the old fat 50.

I didn't think Entrop used fuel injectors on the 2 and 3, just alot of carb....But, I've never seen the fronts of those engines, and, knowing your impeccable detail and knowledge of history, he may very well have had an injected motor.

Even with that, I don't think any Starfilght engine turned much over 6,000 RPM. There was even a comment in that cheesy '50's style voice over on the black and white tapings after the run that said something to the effect of, "As Starflight leaves the race course with a new record under her belt, there is now proof that you don't need high RPM to make speed" or something similar.....

Now 47 with an old 90, especially if it was the early version with that disgusting carb that tanked in left turns, is pretty darn good. Put one of them bad boys on a 14' Yellow Jacket and add a whole new dimension to the speeds.....

[Droll-l6]

Those 40 miles are NOT GPS, so they might be off, but are you sure about those slip numbers ??, I got a lot higher slip numbers ......


Arne Kjetil

Checked the speedometer against GPS today, same boat/speedometer but with a different engine ( Mercury L6, 90@140hp ( 1980 90hp, ported up to 140hp spec (72)).

Speed on speedometer : 40 mph
Real GPS speed : 43 mph

Arne Kjetil

[jeff55vDSH]

I gotta agree with Ed here.

Yes, You might be able to get that V4 to go a little faster. But, you've got a lot of things working against you. But hat's off to you for your thinking and exploring options. Nothing wrong with that.

Gee, if only you had an old stick tower for your Merc powerhead...

Your V4 weighs an awful lot for a 13 ft boat (C-D version of the Mad-Cap is 13' ). Finding high pitch OMC props will be difficult. There is no point in spending $$$$ opening up the intake side of any 2 cycle engine without opening up the exhaust side. A better route to go would be to find a Merc KG9 tower & gearcase, put a 44 cube powerhead on it(a bolt-on). That combo would probably be 75 lbs less than your V4 for starters. The Merc can turn higher RPMs out of the box, no intake work necessary and you can still find relatively cheap high pitch props for the KG9, they show up on Ebay fairly often. The props will be brass 2 blades and you should be able to get them re-pitched without too much trouble. IMHO

[JohnsonM50]

I gotta agree with Ed here.

Yes, You might be able to get that V4 to go a little faster. But, you've got a lot of things working against you. But hat's off to you for your thinking and exploring options. Nothing wrong with that.

Gee, if only you had an old stick tower for your Merc powerhead...

Yeah me too.. You can go plenty fast with something relativly safe and with more realistic weight parameters. Also these OMC V4s talked about here might not be that fast and a few mods wont do it but dont forget that they are pretty big on torque. On a too small rig it can bite yer ahhhh It is good that your asking tho and at the right place.

[Skoontz]

But, the evolution of the V-4 has numerous peromance enhancing items that, if you have the time, and a little not much money, you could copy. So you are a tad off on say the bubble in the exhaust housing and you make the changes to the carbs....I'm betting you will see quite a change weather it's optimum or not. Loose the gearcase, and, find yerself one that would handle the torque of the V-4. Lighten up the tower, that V-4 powerhead is insignificant in weight, especially when you loose electric start, and he brackets that went with them.


I'm a firm beleiver in using the tools you have in the tool box especially if you are trying to save some money. There has not been an OMC made that can't be made to run circles around any Merc in their same displacement class, and I'm not referring to what APBA calls a class, I'm talking say, if a motor is 44 cubes, OK, then a 45 cubic engine would be closely paired to that....

My youth was filled with memories of my dad, and his buddies doing it over and over again, on very little money and just using the noodle.....Grind this, file that, weld this. bolt on that....Play and expaaaaa---rdiment with it, as Peter Laury would say.....I think if you hang with it, you will be surpized. No mattter what you do, document it, and share pictures!

[JohnsonM50]

Ive had 3 OMC V4s over time, a 59-75 ran good kinda flat on get up and go. It was replaced by a 72 elec.shift 85 [shift was fine]. Then a 77- 115. I thought the 85 was best. I had that on an African mahogany skiff called an American Fin, built by Askel Sundberg in Finnland [hope thats right]. What a nice boat.. even my wife liked that one! It did 38-39mph not bad for a 17ft 10in woodie huh, I had 10 coats of captains varnish on it, looked good. Wow did memory lane just kick in or what?