Meet The Twins: A 1,320 Horsepower Twin LS7 Powered Offshore Boat

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We’ve covered a few LS-swapped boat stories in the past, like Jeff Jost’s LQ4 6.0 liter truck motor swapped jet boat and this video documenting an LSA 6.2 liter swapped into a customer’s boat by the experts at Michigan Motorz, but none like this one. This my friends, is a badass, 1,320 horsepower racing boat powered by two LS7 7.0 liter C6 Z06 Corvette enginesBuilders Dave Kutscher and Pat Weismann are no strangers to LS engines and everything it takes to stuff one (or should we say two?) into a jet boat. Weismann is well-known in the offshore racing community; “We have never known Weismann to do anything normal, and we expect nothing less!”

Both Kutscher and Weismann are the owners of Traction Products Inc/Weismann Marine LLC, based in Costa Mesa, California. For over 51 years now, they’ve dedicated their expertise to becoming a world leader in innovating everything watercraft, marine, and road racing related, specializing in transmissions and custom designed watercraft parts. It’s obvious the passion they have for their business has bled over into their own boat.

K&N Filters was enlisted to build custom air intakes for the paired LS7 powerplants.

K&N Filters was enlisted to build custom air intakes for the paired LS7 powerplants.

The Penalty for Success

Our semi-automatic transmissions were banned in 1997, after we went 11 for 11… – Pat Weismann

If you’re not familiar with boat racing events, they have a lot of parallels to automotive racing, with many events sanctioned by the American Power Boat Association (or APBA). Like road racing, the APBA divides competition into classes, defined by what kind of equipment is permitted, in order to keep a level playing field. When we inquired which class they race in, Weismann said “We are not allowed to race this package in the top classes. Our semi-automatic transmissions were banned in 1997, after we went 11 for 11, winning the class 1 title in APBA and SBI (Super Boat International). Our drives were banned in 2001. We race the boat in the Performance class which is just a MPH restriction.”

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We couldn’t have put it better ourselves.

The transmission he is referring to is the one they’ve engineered and manufactured for use in trophy trucks and a supercharged LS7 swapped Ferrari 360 (among others), that has a history with the Indianapolis 500 that dates back to 1963. Designed to fit within the confines of tight spaces, this unit provides some serious torque handling capabilities for any application, not just road vehicles.

“The WBD [6-speed automatic transmission] was engineered as a unit,” Weismann explains. “The internals can be coupled with the WHT differential section, and be made into a transaxle. It can also be made into a 4-wheel drive system with the addition of a drop-box. We made a special case so the trans would bolt to the drive on our boat. As you can see, it’s been designed for versatility.” We think it’s safe to assume, you can now add ‘twin LS7-powered boat’ to the list of compatible platforms. Details on all of the transmissions Weismann offers can be viewed on their website.

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Integration to Prevent Disintegration

Dry sump tanks increase oil capacity and keep the engines fed during long stretches of acceleration.

Dry sump tanks increase oil capacity and keep the engines fed during long stretches of acceleration.

So how does all of this translate to use on their boat? Per Weisman, “We used an aftermarket dry sump tank to increase the oil capacity for the long straights at wide open throttle. Initially, we used a MEFI-4 controller [GM’s marine EFI system] with a UMI cable throttle-body. It was OK, but when we shifted, we needed throttle-by-wire to control the engine better during those shifts, so we went with an MSD Atomic LS EFI system to help the driver. We’re able to shift the transmissions with our own TCU and without a clutch. We control the engine during the shift by either raising the revs for a down shift, or dropping the revs for an upshift.”

The engines are installed flywheel-to-flywheel, with offset gearboxes transferring power to twin driveshafts, then to the six speed transmissions and drive units.

The offshore racing environment puts the entire drivetrain through stresses never experienced on dry land, meaning that even minor details can become major issues. “The serpentine belts needed raised, edge-type pulleys to keep from kicking the belts in the rough water,” Weismann adds. “There are no engine isolation mounts to help dampen the impact in a race boat application like ours. Both LS7 engines are in-line flywheel to flywheel, and include two FNR offset boxes, and two WSD’s (Weismann Surface Drives).”

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The inline layout has several advantages over a typical side-by-side marine installation; it allows for a slimmer hull and fewer issues with header clearance, and putting the engines back-to-back means one of them doesn’t have to be set up to run “backwards” (turning counter-clockwise when looking at the crankshaft from the front of the engine) or have an additional gearset to counter-rotate the props. It also makes it easy to place the outdrives closer to the center of the boat to improve handling.

We are the first to make this combination, but now they are starting to be used by the bigger companies… – Pat Weismann

Light Makes Right

With an understanding on why they chose their own transmission, we asked, ‘Why twin LS7s?’ Weismann explained, “Power to weight. We looked at a supercharged LS2 6.0 liter in the beginning, but opted for the simplicity of naturally-aspirated motors. The 7,400 RPM redline was very appealing. Fuel economy was highly considered for weight savings as well. We used 50 gallons during a race, compared to 200 gallons from our supercharged big block we had originally. The difference in fuel weight savings was 350 pounds versus 1,400 pounds. We are the first to make this combination, but now they are starting to be used by the bigger companies. The engines themselves are not stock, either.”

Custom water-cooled headers carry away exhaust gas - like many other components on this boat, they're designed specifically for this application.

Custom water-cooled headers carry away exhaust gas – like many other components on this boat, they’re designed specifically for this application.

Weismann goes on to add that both motors are fitted with LS9 rods, LS9 cranks, forged pistons, Chevrolet Performance DA camshafts, ceramic ball hydraulic lifters, and other supporting valve-train parts. Weismann says that combination is good for 660 horsepower and 547 pound-feet of torque, per LS7.

“The popular motor to use is an LS2 6.0 liter that has been supercharged, or a typical big block swap with a supercharger or turbocharger is the other way to go,” Weismann admits. “With a supercharged or turbocharged engine, you’ll need an intercooler, good fuel, and to utilize an LSx iron block. Our old supercharged big block setup weighed in at 1,400 pounds [per engine], while our new one is only 536 pounds.” Though the weight advantage is clear, we can’t help but think to ourselves that it’s expensive enough building one LS7 with quality OEM and aftermarket parts, but two?

Initial installation of the twin LS7 engines.

Initial installation of the twin LS7 engines.

Nothing Worth Doing is Ever Easy

After deciding against forced induction and in favor of natural aspiration, there were still some complications Weismann and his partners had to overcome during this build. “There were no marine parts available, like water cooled headers, water pumps, serpentine belt brackets, closed-circuit cooling systems, engine mounts, or a self contained engine harness.” That’s when he realized he was really going to have to improvise and call in some favors. Companies like Racepak and MSD lent support to their project, providing the proper electronics and their Atomic LS EFI to handle the boat’s engine management needs. The boat also sports custom air intakes provided by K&N.

However, what wasn’t available off the shelf or couldn’t be modified from an existing part had to be fabricated at their shop. We asked Weismann after the two years it took for them to complete their build, if they could do it all over again, what would they have done differently and why? “We would have run air to water radiators with fans for a closed-circuit cooling system, and dry headers with ceramic coating to reduce more weight and water drag, by eliminating the raw water pickups. Changes like these just make things run smoother, and efficiency is what we’re all about.”

In line with common offshore racing practice, one man handles steering while the other controls the throttle, but the boat's cockpit is laid out so that it's possible to drive solo. Separate controls adjust the angle of the drive units and the trim tabs. Keeping the boat trimmed out for minimum contact with the water while still maintaining the nose pointed at the right angle is the key to maximum speed.

Weismann has been involved in lots of different marine projects in the past, from flat-bottomed boats to Deep-Vs. He has plans to take the boat this fall to Super Boat International (SBI) in Key West, Florida this November to race in the P class for the 35th Annual Key West World Championships. “We also plan on doing a few endurance runs as well.” If it hasn’t sunk in, Weismann is always in search of improvement, and let on that there’s a new hull in the works for this amazing dual-LS offshore boat. We have no doubt that whatever’s next will show the same attention to detail and world-class engineering, but when they hit the water with their next-gen race boat, we’re going to shamelessly beg for a ride…

Kutscher and Weismann share billing on the long, long bow of the offshore boat.

Kutscher and Weismann share billing on the long, long bow of the offshore boat.

About the author

Harrison Noble

Living in San Diego for most of his life, Harrison was exposed to a variety of cars at an early age. His passion for anything that is fast, or has a V8, brought him to Power Automedia.
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