After digging into the inner workings of several big-inch engines over the past several years, we thought it was time to see what Harley-Davidson has to offer. Along with the standard 223.52cm (88inch) Twin-Cam engine that equips most of their 2005 motorcycles, you can have a big-bore of 241.3cm (95inch) or the insane 261.62cm (103inch) stroker engine.
Having said this, we must explain that there are a few rabbit trails that you have to follow to get a big engine from Harley-Davidson.
First, if you want a 241.3cm (95inch) motor, it is only available through the Genuine Parts channel, as parts kit or as separate parts to convert an 223.52cm (88inch) Twin Cam engine. A few years ago, Harley offered these engines in special edition CVO bikes, but as of June 2005, there isn't a production bike available with the big-bore engine.
The engine's increased displacement is arrived at by increased its bore from 3 3/4inches to 3 7/8inches. This can be done by either having your stock cylinder bored out at your local bike shop (which is direct a problem in Thailand) or buying a set of big-bore cylinders from your Harley dealer.
Most dealers will not have stock of this but most will take orders with deposit payments, Harley has a number of pistons and high-performance cylinder heads to support this size engine. And we advice you to be sure that what you order is what you need, the local Thai knowledge of big-bore engines and replacement parts is a lot less then what you are used to in the west.
As for the 261.62cm (103inch) stroker engine, you can get one of these several ways; buy the parts out of either of the aforementioned Harley-Davidson catalogs and convert your Twin Cam, buy the complete engine from your Harley-Davidson dealer, or pick up one of Harley's current CVO bikes.
Last year they offered two CVO models that are fitted with the 103inch engine; the Screamin Eagle Fat Boy and the Screamin Eagle Electra Glide 2.
Harley arrives at the 261.62cm (103inch) size by combining the big-bore cylinders with a stroker flywheel assembly. The stroker wheels bump the stroke to 4 3/8inches from the stock 4inche. You can use the stock cylinders to build this engine, as they will need to be bored out, but you must use Harley Screamin'Eagle stroker pistons.
It is also highly recommended that you use a set of high-performance heads; the stock Twin Cam heads can't breathe well enough for an engine this size.