S&S-Based Harley-Davidson Evolution V-Twin Engine - Engine Builder Magazine

S&S-Based Harley-Davidson Evolution V-Twin Engine

A customer in Toronto recently turned to Gregg Dahl and GMS Racing Engines for a Fast Bracket Racing drag bike engine. Dahl answered the call as those engines are his specialty. The result was this 200 hp S&S-based Harley-Davidson Evolution V-Twin engine.

We first met Gregg Dahl of GMS Racing Engines at the 2016 PRI Show. He stopped by the Engine Builder booth to offer his knowledge and writing prowess for the 2017 editorial year. We took him up on the offer as his Uniontown, PA-based engine and machine shop specializes in V-twin builds, performance work, dyno-tuned race engines and custom-built cylinder heads.

Stacey Bortz, drag bike racer and Gregg Dahl’s girlfriend. Photo by Steve Parsons Photography.

We knew his work was good too, because his girlfriend, Stacey Bortz, puts those engines to the test on the track, and most recently set an American Motorcycle Racing Association (AMRA) National ET record in the Outlaw Street class with an 8.25-second quarter-mile time.

Those engine-building chops that allow Stacey and her bike to set records and that help Dahl contribute great pieces to Engine Builder – like the February 2017 cover story V-Twin Validation, and an upcoming piece on motorcycle heads and components for August – are what he puts into every engine he builds.

Gregg Dahl of GMS Racing Engines – GMS stands for Gregg’s Machine Shop. Photo by Ed Hinchey, Thunder Roads

The engine highlighted in this week’s Engine of the Week was built for a customer up around the Toronto, Canada area. The engine is a S&S-based Harley-Davidson Evolution V-Twin, and is going to be in a Fast Bracket Race drag bike.

“The engine is built to stay together for a long time and provide a lot of runs,” Dahl says. “The engine isn’t built full tilt. The compression is only 13.8:1. We built a big engine slightly to the mild side to allow us to run the number without having to lean on anything too hard. It’s a sweet combination. The engine makes around 200 hp at 190-200 lb.-ft. of torque on the rear wheel. Honestly, it’s a simple, basic, great big engine. The customer is shooting to run 8.90s at the track.”

Photo by Evan Sanders

To start, Dahl used basic cases from the S&S 145 tribute motor from about 10 years ago. “We had to do some work inside the case to get the big stroke to clear so the rods would clear,” he says. “All of the parts are all hand massaged to fit together. In the heads we put a 2.300 and a 1.800 exhaust valve. Being that the RPMs of the engine will be shifted around 6,800 – 7,000, if that far, we don’t have to run killer valve springs because of the real stiff valve train parts we have. Valve spring pressure will be around 275-300 on the seat and about 800 open.”

Photo by Ed Hinchey, Thunder Roads

GMS Racing Engines did a lot of machining on the heads since those came from S&S as unfinished castings. This is also a flattop piston engine because of the 151 cu. in. size.

“It’s such a big engine we didn’t have to put domes in it,” Dahl says. “We were able to mill the heads down to get the correct cc to get the compression up to about 13.8:1. At the same time, milling the heads down that far also unshrouds the valve on such a big bore. When we milled the heads down we actually see the flow bench result a little bit, especially in the low lifts because the valve is hanging down out from underneath the head a little more.”

When GMS gets the cylinders for the engine from Axtell, those are also not finished. Dahl finishes those here at the shop.

“We have our own torque plates that we made up and we use the actual fasteners in the torque plate that will go in the motor, and we use gaskets with them,” he says.

That’s not all he does on this engine. There’s some breather timing that Dahl does where he machines or grinds the window that the rotary breather gear runs in to get the breather timing correct. He also degrees the cam and scoots the drive gear around on the cam to get the timing where he wants it before welding the timing gear to the cam so it doesn’t move. He also trues up the flywheels.

“We also had to do some work for valve clearance,” he says. “Being that we are trying to achieve this compression with a flat piston, there was a lot of piston machining. We had to make the valve reliefs a little bigger but not deeper. We had to cut the rear piston for the front piston to go through it at the bottom of the stroke. The pistons are gas ported and we run light-tension rings.”

Photo by Ed Hinchey, Thunder Roads

This Evo engine has a 4-3/8″ bore and a 5-inch stroke, and has a laundry list of top-quality parts involved. The Red Shift 715 cam closes the intake at 71 degrees at .053” lift. It has S&S special application engine cases. It has a S&S billet HVHP (high volume high pressure) oil pump. It has a set of GMS’s own proprietary lifters, which are modified from Hylift Johnson. The cylinders are finless ductile iron from Axtell. The pistons are from JE. The heads are S&S B2’s that GMS custom finishes. The shop used Pac springs and the engine also has Victory 1 valves and all the valve train hardware is Victory 1.

Photo by Ed Hinchey, Thunder Roads

“We use Smith Brothers push rods, which are really cool because they are adjustable and are 7/16″ tapered down to 3/8″,” Dahl says. “They’ve got to be real stiff because they are 12-inches long. We use S&S billet rocker boxes and our own GMS 4.140 chrome moly rocker stands. We use rocker arms from either S&S or R&R Cycle. We send all the valve train out to Hekimian Racing Engines for cryogenics.”

GMS uses Cometic gaskets on all its engine builds, and this Evo is no different featuring Cometic on the head and base gaskets.

“For the head gasket sometimes we use MLS and sometimes we use soft copper depending on the application,” he says. “If a certain engine is going to see a lot of teardown time, we tend to use the copper gaskets because it requires a little service, but because the motor is apart all the time you can leave the head gasket stuck to the cylinder and just pull the head and do what you have to do, and put it back together. If it’s an engine that’s going to stay together long term we use the MLS gasket because it’s a good, permanent gasket.”

Photo by Evan Sanders.

The Evo got MLS gaskets and has ARP fasteners throughout. The engine has S&S 5-inch stroke flywheels in it and S&S 8.5-inch aluminum connecting rods. It also has a single S&S Super D carburetor on it.

This Evo V-twin engine is very similar to the ones Dahl and GMS build for their drag bikes, which boast a 15:1 compression ratio and 260hp at the rear wheel. It should be one heck of a bike engine!

Engine of the Week is sponsored by Cometic Gasket

To see one of your engines highlighted in this special feature and newsletter, please email Engine Builder managing editor, Greg Jones at [email protected]

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