Report: Project V8

Home Up Report: Project V8 GPS Speed Data


1967 Sportsman LDFV © L.Shuster

Last Updated:

22 December 2006

Progress Report on "Project V8"

Project Goals:

  1. All our boating is done between 6500 ft to 8000 ft., in the mountains above Park City, Utah. The effects of altitude on air density and engine performance are well documented. In a nutshell, a normally aspirated engine produces roughly 4 percent less power, for every 1000 ft above sea level. Effective power on my Buick V6 was down about 25 - 30 percent or about what you'd expect the inline 120-hp Chevy 4 to pull at sea level.

  2. We also typically use our boat for family water sports, including towing one and two-man tubes, knee boarding and water-skiing. I can't remember the last time the boat carried fewer than three to four passengers, and typically she's carrying six sometimes seven adults onboard. It's a tribute to space-efficient design of the open-bow Sportsman. We were constantly asking the 3.7L V6 to do more than it's fair share, and that was after we had reduced prop pitch a couple of times.

  3. The gull-wings were well constructed, but they are heavy for their size, weighing more than a lot of present-day 18-19-footers. It's a hull designed to handle moderate-to-heavy loads but it's not the most efficient hull design to push down the lake, this is especially true of the original 1964 - 1968 16-foot Evinrude/Johnson hulls.

  4. In short, I wanted to retain the boat's classic, original look and feel, but improve it's safety and reliability and restore her performance to at least the original sea level parameters of the V6. I also wanted a boat that came close to modern-day, turn-key operating and safety standards, in short, no muss or fuss.

Conversion Considerations: 

  • Last winter, I initially determined that approximately 210 to 245 (gross, crankshaft) hp would be required to meet the above objectives, using the boat speed calculator. I briefly considered rebuilding a Buick V6, even considering a larger 4.1L (252 cu in) even-fire version, or the newer supercharged 3800. While the Buick V6 engine can crank some serious power, it's not inexpensive to build-out.

  • OMC pioneered the V6 in boats and the Chevy 229/262 V6's are fairly popular in newer boats, typically powering later OMC's, MercCruiser Alphas or Volvo SX outdrives. The Chevy V6 is a shoe-in, but getting more than 210 hp would require a virtually new engine running EFI; again not an inexpensive proposition. After pricing those out and realizing how much custom transom/sterndrive build-up would be required to accommodate the Volvo, I decided to focus on staying with the tried-and-true, OMC stringer. Besides, I didn't want the "I coulda had a V-8!" syndrome to hit me later.

  • Taking careful measurements, I began to realize the fifty-year-old, Small Block Chevy (SBC) is only about 4-inches longer than the Buick V6. The Chevy V8 is actually narrower than the Buick V6 and only weighs 90 pounds more than the Buick V6. The SBC V8 spawned a entire industry of affordable, available speed parts and know-how. OMC produced 283's, 305's, 307's and 350's, all with stringer outdrives. The OMC 307 was produced in 210, 215, 225, 235 and 245 hp versions and was fairly popular from 1968 to 1975. The 350 SBC was commonly available as a 260 hp OMC model. Thus, I began searching for a suitable SBC-V8 donor,  last winter.

  • In March, I located a clean, low-hour, OMC 215-hp, 307 Chevy V8  that came out of a well-maintained 1971 Reinell 22-ft cuddy cabin. The owners had decided to depart Utah for Alaska and needed a closed-cooling (antifreeze) sealed system and opted for a used 350 Chevy-Volvo SX combination. That meant I could grab the 307 and it's long-legged stringer drive with the taller 21:16 (upper) V8 gearing, for a fairly reasonable price.

  • The Buick V6 and sterndrive found a good home: it's now repowering Brian Nelson's cool '64 OMC Deluxe 17; replacing a tired, 2-stroke, 88-hp sterndrive.

Construction Details:

The early 65-67 model Sportsman all have an easily removable, one-piece, molded, engine bulkhead/seat. Once unbolted, this makes accessing the engine area a no-brainer. I'd hate to undertake this conversion on a later model Sportsman where the engine bulkhead is molded as part of the top deck. Having free access to the engine bay area made the job a lot easier. 

Once the Buick V6 was completely removed, it was interesting to see how OMC frame-mounted engines in the early (64-67) stringers. The transom was very thin fiberglass and was not going to be strong enough to support the Bennett Trim tabs. (SelecTrim was briefly considered, but ruled out due to complexity and space considerations). Also, it was very interesting to see the obvious "off-center" offset of the sterndrive aperture. I wanted to convert the early style round aperture seal to the later "rectangular" rubber seal. One the aperture hole was re-shaped, a piece of marine-grade plywood was glassed into place. Also, four engine mounting "pads" were glassed into the floor. OMC switched over to this engine mounting system sometime in late 1967. Engine wiring was upgraded and now uses the later style, (black and yellow), round connectors. The battery was slightly relocated using a box. The V8's "long-leg" sterndrive assembly was completely refurbished by an experienced OMC stringer tech with 30 years experience.

At the same time, the steering system was changed over from the original rope-and-pulley style to OMC's mechanical TruCourse worm and gear system, which uses a sealed, push-pull cable system. Other improvements (that were easy to do while the engine was removed) are: a modern, automatic, water-sensing bilge pump and separate bilge blower.

Once everything was properly aligned and positioned the engine was bolted to it's new, floor mounting pads. I must have been living right, as the hinged motor cover just clears the flame arrestor. But the engine water pump pulley ended up just brushing the front bulkhead. A small hole was cut in the vertical bulkhead surface and provided the additional clearance. A 3-inch, stainless, clamshell vent now covers the small hole and is the only visible evidence that the V8 is tucked away under the original motor hood. (Shown below):

 DCP_0445.JPG (144227 bytes)

How does she run?

Well, better than I expected. The stock (mildly cammed) 307 idles so smoothly and quietly at 500 rpm, you have to look at the tachometer to make sure she's fired off and running. The boat's become, a "Sophisticated Lady" or maybe a "Miss Manners." It really showcases the design strengths of OMC's fully floating, nearly vibration-less, transom-isolated stringer mounting system. I thought the Buick V6 was smooth and quiet, but the small-block Chevy is just sooo… much more….. incredibly smooth and quiet. Hard to believe the difference.

As you can see in the above picture, she sits well in the water, her attitude unaffected, supporting the additional 90 pounds without looking stern-heavy. (I haven't accurately weighed her, but I'm estimating that she's a tad under 2000 pound, up from her original 1825 pounds.)

She now runs more economically, believe it or not! Starting is spot on, it's almost as well mannered as a modern fuel injected engine. I've yet to consume more than a full, 16-gallon tank in a full day (6+ hrs) of skiing. But when you lean into her throttle, the QuadraJet-fed, mouse motor has a mean-sounding V8 snarl. Cool.

Spinning a 14" x 13-inch-pitch SST prop, she pulls 4350 RPM, lightly loaded at 6100 ft ASL. She's showing 37 on the funky, original pitot-tube speedometer, when you average out, two-way WOT runs in smooth water. (See: GPS Speed Report Data). But remember my stated goals? It's not so much just about top speed. Hole shots are improved and the trim tabs lift the back end and keep the nose down until she's up on plane. What's nice is the V8 engine doesn't work nearly as hard, as the V6. I look down and am amazed to see the tach loafing at 3000 RPM, pulling a tube, along with 4 or 6 onboard. It's unusual to push her past 3500 rpm. The Buick was struggling at 4000+ rpm to try and keep up under similar loads at this altitude.

The other really wonderful, yet somewhat unexpected, surprise benefit is the OMC TruCourse steering and rudder indicator. Few, if any boats can out turn her or other OMC stringers with their 90-degree turning. The TruCourse really does add a measure of security and responsiveness, over the old cable and pulley system. The rudder indicator is especially useful when skiing and docking. I'd actually rank the steering upgrade higher than the trim tabs in overall usefulness.

Any regrets?

The only downsides to doing this conversion are measured in pounds, dollars and time. The boat gained about 90 pounds in motor weight and an additional 50 pounds (est.) for the steering and trim tab gear. That effectively reduces her rated load capacity by 10 percent. Yet, she doesn't sit noticeably lower in the water. The hit to my wallet was a little heavier, but I'm not regretting the financial aspects. In fact, I discovered an interesting fact about used boat (Blue Book) resale values: On older boats, the single variable factor that affects the boat's total resell value is the rated engine power, whether it's outboard, sterndrive, or inboard. No other improvement has such a dramatic affect on value. Doesn't even matter if the I/O hp package wasn't offered from the factory, originally.) You never do get much return on your boating dollars, but re-powering to a larger engine rating pays back a higher percentage than most boating expenditures.

I elected to have the conversion labor performed professionally, by an experienced OMC technician. I highly recommend Hansen Motors & Marine, in Salt Lake City at 801.466.4731.  It took a little longer than I would have liked, but I think the results were well worth it. Could one DIY this project? Probably, if you are the least bit handy with mechanical and electrical work and have a way of lifting the engine. It really isn't a technically challenging conversion if you stay with the old technology electric stringer drive. Converting over to a newer MercCruiser or Volvo SX would be considerably more difficult, requiring extensive fiberglass reinforcement to the Sportsman's transom and hull.

So what does the future hold? This winter I plan to upgrade the instruments and console wiring. But it's also fun to think what she'd do with a mildly warmed over 350 SBC? Nah, power corrupts, maybe I'll quit while I'm ahead.