2018 NEWS


2-Stroke Services


Porting is a metal machining operation designed to enhance the powerband characteristics of an engine, especially with aftermarket bolt-on accessories like exhaust and intake products, stroker crankshafts, big bore kits, and ignitions.

Eric Gorr Racing offers all-inclusive porting packages for all types of 2-stroke and 4-stroke engines used in dirt bikes, ATVs, snowmobiles, and shifter karts. Eric Gorr does all the porting himself and has worked with porting tools since the early 1970s and ported over 50,000 cylinders. More than all the other popular hop-up shops combined.

Eric is well trained in the use of the latest software programs that the motorcycle manufacturers and racing teams use, like the ones available from Professor Gordon Blair. these programs are the standard in state-of-the-art design of championship winning motorcycle engines and recognized by the Society of Automotive Engines and used by the world’s top universities. Eric Gorr Racing is a Gold sponsor of the University of Wisconsin (Madison) Formula SAE Team.

Eric uses modern computer design software to do the number crunching needed to reconfigure cylinder ports to enhance the powerband to the way you want it to be. Eric is the only tuner in motorcycle racing with two US Patents US4261306US4457267, a published SAE technical paper, and six motorcycle books to his credit.

Eric made his reputation on porting and does all the work himself, no illegal aliens, space aliens, or third world slave labor. It’s just middle-aged fart-knocker labor from one of the oldest and most experienced tuners in the world, whom still actually rides motocross, dirt track, trials, and supermoto.

Cylinder porting can improve the reliability and ride-ability of your bike, and all the top end parts need to be modified as a set like in these package deals.


All 2-stroke porting packages include complete porting, not the fake fluffy crap that most In and Out Porting and big time SoCal hop up shops offer. All of these porting packages include the following; disassembly and cleaning of all the top end components, complete porting and polishing, cylinder head machining, base machining, diamond honing, baking soda blasting, powervalve service or epoxy-filling, powervalve assembly and timing of applicable models.

50cc AUTO BIKES $75

Cobra, KTM, Polini; cylinder porting with head mods to push the limit for advanced riders.

65-112cc MINIS $160

Your choice of porting for powerbands that work best for beginner and trail riders as well as national caliber experts in Supermini classes.

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Stock YZ125 on left and ported YZ on the right.

125-200cc BIG BIKES $160

Three powerband choices of more low to mid-range, more mid to top end or a smoother broader powerband, plus all of the services listed above.

250-550cc BIG BIKES $200

Three powerband choices of more low to mid-range, more mid to top end or a smoother broader powerband, plus all of the services listed above.


This service includes cylinder porting and race-ready honing to a new OEM cylinder. You can supply your cylinder for porting or we can sell you a brand new ported cylinder for $600. The porting powerband choices include stadium (low&mid hit) and outdoor (mid-top). Head mods and powervalve service included.


In the glory years of the 500cc Grand Prixs in Europe throughout the mid-1980s and 90s, Eric’s CR500 tuned Hondas were the boss ride. Legends like Jorgen Nilsson and Leif Persson of Sweden, Rob Herring and Mark Eastwood of England, Jacky Vimond of France, and Peter Dirkx of Belgium owned the first turn at the GPs and turned the ultra-expensive HRC Factory bikes into insignificant bridesmaids. At the 1992 USGP at Glen Helen, Swedish champion Jorgen Nilsson holeshot the field in both motos.

 In modern days the Service Honda CR500AF’s have reveled in the praise of American dirt bike magazines for the last 12 years. Eric offers porting through Service Honda and in 2006 Dirt Rider magazine ran an Internet Bike Shootout and www.dirtrider.net teamed with Service Honda. DR’s test riders demanded that a manual clutch be installed on the bike because the powerband was so smooth they thought the Rekluse auto clutch was slipping. The testers praised the porting and powerband with the smooth powerband with extra revs on top. You can choose the type of powerband and fuel type. Eric builds a lot of CR500s for mx, enduro, desert, hill-climb, dirt track, and ice-supermoto and oval racing.

 The porting package on the CR500 includes cylinder porting, base machining, head work, manifold matching and polishing, epoxy porting, soda-blast cleaning, and diamond honing to the next oversize if needed for $225 additional. Parts options include your choice of pistons from Wiseco Pro-Lite, Vertex cast&coated, Pro-X, and Wossner piston kits—$175, Cometic stainless steel gaskets—$30, and top end bearings—$20. The CR500 porting package with top end parts is $425.


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Vintage porting $185; vintage big bores $550; Custom Powder Coating in vintage colors.

Eric raced motocross since 4-strokes were popular the first time (1970) with his Ducati 250 Scrambler. Working as a mechanic and tuner since 1971, Eric has accumulated porting specs from all sorts of sources like factory racing directives, practical experience, and the use of modeling software. You might say he’s a bit of a vintage freak and sympathetic to vintage meisters like yourselves.

 Eric is particularly skilled at Maicos and Yamahas, and works on all brands of Japanese and European motocross bikes. If you are a vintage freak and have historical specifications that you would like machined to a cylinder, Eric will cater to your needs. He has also ported cylinders to exact historical factory specifications from Harley Davidson Racing directives from Dick O’Brien to Team Green to Yamaha Wrench Report and even Swedish-language blue-prints from Husqvarna. If you have an antique cylinder with a cast-iron sleeve and you want to preserve the bore size, we can have the cylinder bore nickel-composite plated for an additional $225.

YAMAHA YZ465, 490, & WR500 $185

Starting with the first YZ250A in 1974, Eric tuned and raced YZs. In 1980 he teamed with Troy Bradshaw and hit the nationals. Troy pulled some awesome starts and great placings in the Trans-Am series and soon Team Keystone Yamaha’s sported Eric’s Flow-Ported YZ cylinders. In 1981 Keystone’s Jeff Hicks placed second to Danny "Magoo" Chandler in the Trans Am series. That series launched Jeff Hick’s career as a factory sponsored Team Yamaha rider.

In 1984 Troy Bradshaw made history at Loretta Lynn’s by winning the Open Class championship besting the factory sponsored riders from Yamaha and Kawasaki. The porting, cylinder head and carb tuning specs developed in that era can help your YZ run much better and be less sensitive to fuel quality and jetting.

Services include center-mandrel machining of all the gasket surfaces of the cylinder and head, complete porting and polishing of the exhaust port, epoxy-filling of casting flaws on applicable models, intake boost-ports bored and polished, head modifications, diamond-honing to next oversized Wiseco piston $185. Wiseco piston kits $195 extra.


What a sick twisted form of racing! G-Forces that will give you kidney failure and the ability to cut lap times faster than an Indy car! Eric offers a wide range of services ranging from cloning old cylinders to setting up specs for mx class and IC engines and even clay-oval outlaw racing. Eric specializes in CR125s and also handles all the IC engines like the Pavesi, TM, and CRC.

Eric performs cylinder porting and matching head mods, along with diamond honing of the bore for only $185.


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Tools of the porting trade

Racers are a superstitious bunch and if you have a cylinder that is trashed and you need a new one cloned to the old one for good luck sake, Eric can fulfill your wish. Send the old cylinder and a new one. Blueprints or drawings are OK too if the old cylinder is destroyed.




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Cylinder base and head machining

Cylinder head and cylinder bases can be turned and machined to produce a powerband that is better for beginners and trail-riders. The technical reasoning is that this modification serves to retard the port timing and increase the squish velocity produced in the cylinder head. If you just want more low end and don’t want to spend a fortune, this is the best mod that will give you the biggest bang for your buck! 
$75: 50-112cc $100: 125cc-550cc


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Head mods for pump or race gas, big bores and strokers $35.

This service includes all machining modifications per situation and application. Services include gasket surfacing, turning, clearance-machining for big bores and or strokers, flat-top piston conversions as well as hemi and conical dome shaping, lowering compression for low octane pump gas with ethanol, raising compression for high altitude, TIG-welding, o-ring groove cutting, plug-hole turning and threading. 


Powervalves are built into the cylinder around the exhaust port. They’re supposed to make the exhaust port bigger when you twist the throttle open. Powervalves are complicated mechanisms prone to failure. We offer a service to clean, inspect, and adjust the powervalves. This service comes standard with all porting and big bore packages.


Crankcases can be improved with porting and a set of new ceramic bearings and Teflon seals. Crankcases can be ported for smooth transitions to the transfer ports, clearance mods for big bores and stroker cranks, re-surfacing or even welding or epoxy repairs. Send a set of bare cases or with your cylinder.

CYLINDER PLATING (aluminum cylinders) $180 for 50-150cc and $250 for 175-550cc

Most modern dirt bikes use hard coatings applied directly to the aluminum cylinder bore. Nickel-composite plating is the hardest low friction coating available. We can plate a cylinder back to original size or to a big bore size for no extra charge. Our work is covered by a 1-Year warranty. This service includes cylinder head resurfacing, stud removal and thread repair, and powervalve service and assembly on applicable models.

CYLINDER PLATING (iron cylinders) $275

This service is especially great for vintage cylinders with cast iron sleeved bores and CR500s. It is designed to preserve the bore at a particular size. We use a nickel-composite coating that is very hard and longwearing and comes with a 1-year warranty.

BORING and HONING for iron-lined cylinders $65

This service includes cleaning, boring, diamond-honing, port chamfering, exhaust bridge relieving and polishing. We offer Wiseco, Pro-X, JE, Athena, Magnum, and Vertex piston kits as well as generic gaskets and bearings.

Cylinder Resleeving with Port Matching $275

Most dirt bikes made before 1990 were manufactured with iron sleeves that eventually wear out. Resleeving is a popular repair for late model bikes too. If your bike’s cylinder needs resleeving we can port match the new sleeve to the cylinder, resurface the head and base gasket surfaces, and hone the cylinder to the original bore size. We stock aftermarket sleeves from LA Sleeve and Advanced Sleeve and piston kits like Wiseco, Wossner, and Vertex. Parts are extra.

Crankcase Welding and Resurfacing $100+

Crankcases need repair when the chain comes off the front sprocket, the connecting rod breaks, or when the engine is cased on a rock. We offer a service to save you the major cost of replacing the crankcases. We start by bead-blasting clean the cases, TIG weld the damage, regrind and shape the weldment, and surface grind the case halves. Prices start at $100 for a set of bare cases.

Diamond Honing $65

Cylinders that are plated with nickel composite plating can sometimes be repaired from minor seizures with diamond honing. All of Eric Gorr Racing\\\'s big bore kits include free diamond honing and porting updates for one year.



Crankshaft rebuilding for 2 and 4 stroke engines.


We’ll clean and inspect the crank, press it apart, polish the pin bores, press a new rod kit of your choice; HOT-RODS, PRO-X, OEM then we’ll true the crank to factory recommended specs $84.95


Special consideration is given to 4-stroke cranks, like checking the journal surfaces and polishing, deburring cam gears, flushing oil passages, pressing and truing with new parts, and pin welding for safety $84.95