The New Tillotson Racing Blocks designed by EC Carburetors

We have been the primary Tillotson importer and distributor for kart racing for over 35 years. Not only are we master blueprinters that can get the most from a Tillotson carburetor that dominate the limited and open races across the country, but we have also designed many different base models for Tillotson in that time. Tillotson trusts our knowledge and expertise. That's why they came to us to help them develop their engine programs. 


Nearly four years ago we met with the Tillotson Team at the SKUSA Supernationals. Tillotson had shown interest in the box stock classes. At this point, we had already designed the PK-1A, and now they wanted a complete competitive engine. We named the project 196R. While we were meeting, we at EC brought two other suggestions for engines. We watched the market peak with the current box stock 196cc engines and didn't feel it was the only market in karting. The karting market had started to move to the 212cc engines due to engine cost and Local Option 206 with more racers interested sprint racing.  We viewed these two engines as the growing markets in karting. Tillotson took all of our suggestions into consideration but wanted more time to decide on the other engine programs. For the 196R, we designed the PK-1B and the JT-207 Head, and we specified the rest of the components from the best manufacturers.


While we were designing the 196R and 212R components, we started on the block, piston, and rod, having foreseen the need for these parts. Luckily, we were right, and Tillotson came wanting a 4cycle spec sprint engine we named 225RS. The engine components minus the carburetor are all but finished. Tillotson's engineers will do the finite analysis to make sure the designs we created will work in manufacturing and determine if changes needed to be made. 


We want to use the existing Predator/GX200 Clone architecture since it is the most popular design and would allow for it to go into the market with an already large aftermarket. It would not be considered a radically different block for box stock classes, allowing the karting rule committees to approve the block design so that we can make a 68mm and 70mm bore versions. This has not yet been decided but would offer a more durable block for those classes. The 225RS falls in line with some of the Local Option 206 philosophy of a low-cost alternative to 2-cycle and even competitive box stock racing, but our block design for those kinds of racing to some extent is overkill. We did this because while spec racing and box stock have its place in karting, that's not where we at EC find our niche. We rely on innovation and performance, our carbs dominated limited, open, and rwyb racing classes. We wanted a block that fits with our philosophy. 


We're going to breakdown each side of the new Tillotson block to thoroughly cover all the design features and compare them to the average clone/predator block.

                       Tillotson Block Front


Tillotson-EC Racing Block – Front

Let us start with the front or leading part of the block. This doesn't seem too exciting at first, but you will see ribbing and a couple of gussets that add strength and rigidity to the block. On the right, you will see a band where we made the crankcase side thicker. There are very few blocks that have ribbing and very few, usually racing designated, blocks with gussets. No other block we have seen have added a band to make the crankcase cover area stronger.

                        Tillotson Block Crankcase Side

Tillotson-EC Racing Block – Crankcase side

The band that starts in the front makes its way around the edge of the block on the crankcase side. This is done for strength and benefits guys who can't afford a billet side cover or racers in stock appearing classes where the billet side cover is not allowed. This should help in areas that may crack with regular Predator/GX200 Clone blocks. A typical brace is usually welded to the inside left part of the block by the side cover, we hope that by adding this band will resolve that problem. 


As you can see with stock blocks, that band is very narrow. This is usually the reason for issues with cracks or fractures in those areas. This block will use the clone or Honda billet side cover in case you need to know what to buy. Look for our new EC billet side covers in the future. 


Tillotson-EC Racing Block – Inside

While we're looking at the crankcase side cover side, let's look inside the crankcase for some of the small changes. Firstly, there are no mounts for oil sensors; this is a block for racing after all. You may find there is a little less webbing in areas where we added more material. The webbing that remains is also made thicker. The bottom dowel also runs the width of the block; this helps add a little more strength. By the top of the block by the bore has a bit more room for crankshaft clearance, this makes a useful reference when the block is sleeved to where you need to clearance the bore. The bearing location has more material around it and a larger chamfer to guide oil to the bearing. This should help some with the stress fracture that can happen at the bottom of the bearing location. The block will use a clone or Honda camshaft, not the non-hemi predator. Any predator 212 or Honda/clone 196cc crankshaft will work in this block, just make sure your flywheel matches the taper of the crankshaft you use.  


                        Tillotson Block Top

Tillotson-EC Racing Block – Top

This is an almost complete redesigned area for the Predator/GX200 Clone blocks. We designed the blocks to have them with or without tank mounts. This means most top plates or linkage kits will not work, but in the 225RS class or any class that doesn't require a stock carburetor, this isn't an issue as you don't use them for more than mounting a fuel pump. This cleans up the looks and aesthetics of the engine. We will have a top plate made for mounting fuel pumps soon. We left the areas to add a governor system this is to allow any future use of the engine in case such as the predator 212 box stock classes where the governor is required. We will touch on the jug separately, but you can see from the top view that there is bracing on the top of the jug with the Tillotson logo.  


                     Tillotson Block Bottom

Tillotson-EC Racing Block – Bottom

We try to leave no stone unturned, and that includes the bottom of the block. The base of this block is not like any Honda or Clone but instead borrows some elements of another manufacturer's racing block. While it's not a very common concern for most, one thing that may go unnoticed is the engine mounting areas. The Predator/GX200 Clone will have 4 pedestals that the block stands on which is unlike our block. The bottom of our block mounts directly to the engine mounts or plate. The engine mounts, therefore, become an extension of the block, making it more rigid and stronger. The bottom is also squared on the outside, unlike the clone block that angles and curves around the mounting bolt holes. 


As you can see, the regular clone has bosses for the fan shroud by adding material and making ours solid across the block, this makes ours stronger and seals the fan shroud guiding air into vents in the bottom of the block.  The next thing that may go unnoticed is the oil drains are made much thicker, and the webbing is thicker and wider as well. We reduced some of the webbings by making the bottom more solid and by doing so allows us to create channels that will guide air under the block for better cooling. The channels help cool the air and act like ribs to strengthen the bottom of the block. 


                        Tillotson Flywheel Side

Tillotson-EC Racing Block – Flywheel Side

Other than the jug, this is where you'll quickly see significant differences in the Tillotson blocks and the regular clone blocks. Let's start with what's most apparent, the bracing from the jug to the bottom-back of the block that continues from the bottom-front to the top of the jug. This bracing has a band on the outside adding more strength helping seal the fan shroud so we can direct it under the block and around the jug where cooling is more critical. There are a few areas that are filled in and where webbing was removed. This is a bit of a tradeoff, but overall this has added strength while cleaning up the looks of the block. The fins and the remaining webbing is made thicker, therefore stronger. Its a little hard to tell but there is more material added overall but specifically around the bore of the jug. You can kind of see this around the lower bolt where it meets the bore. We did this to allow larger bore sizes. 


                       Tillotson Block Jug

Tillotson-EC Racing Block – Jug & Back

Now we're getting into the more exciting block features. The back side of the block is much like the front where we have added ribbing and gussets for strength. The bottom of the jug, as well as the top of the jug, have bracing added to the fins much like welded block reinforcements that attach the jug fins to the crankcase itself. While there have been some blocks to include variations of this type of bracing most do not cover both sides of the jug or connects with bracing on the side of the block. The fins we mentioned before are thicker, and the backside is made longer to connect to the bracing and reinforcement made on the back and sides of the block. The added material and longer fins act like a heat sink. EC was famous in the '60s and '70s for adding much larger fins to his engines to help them cool better, increase the performance and longevity of his engines. The bracing also creates a channel that guides the air produced by the flywheel around the jug for better cooling. 


Another point that was mentioned before is material added around the bore. Before we knew we could get the blocks without a sleeve, we wanted to make sure we had enough material to make a 3" block. It was lucky that we could get the bore without a sleeve; it made it easier on machine shops to prep a block for a 3" sleeve or nikasil. 


                       Tillotson Block Bore

Tillotson-EC Racing Block – Bore & Deck

I saved the best for last, and that's the bore and deck area. Off the bat, we have more displacement that the 212 and 196 engines. We made this block in two versions a 72mm or 2.835" iron bore or a 75.95mm or 2.99" aluminum bore. The aluminum bore is a first of any Honda or clone block. This allows the bore to be nikasil coated rather than being sleeved.  


Here are some values that will help you see how much displacement you can gain.

72mm bore

196cc Crankshaft 54mm Stroke = 219.86cc or 13.4ci

212cc Crankshaft 55mm Stroke = 223.93cc or 13.66ci

Aftermarket Crankshaft 56mm Stroke = 228cc or 13.9ci

ARC Billet Crankshaft 2.300” Stroke = 237.85cc or 14.51ci


76mm bore (3.00”)

196cc Crankshaft 54mm Stroke = 244.96cc or 14.94ci

212cc Crankshaft 55mm Stroke = 249.5cc or 15.22ci

Aftermarket Crankshaft 56mm Stroke = 254.04cc or 15.5ci

ARC Billet Crankshaft 2.300” Stroke = 265.01cc or 16.17ci


On the Tillotson blocks, we moved the dowels to the bottom of the bore. This gives more room at the top to seal the engine with a head gasket or o-ring. We also added more material in the push rod oil galley, Untouched this adds rigidity to the bore and more sealing area for the head gaskets. This also allows even bigger bores if you want to go beyond 3 inches. The oil galley on the side looks to be as large or even more substantial on this block but it actually been moved out so you can continue to use the oil galley rather than welding it closed or near-closed. 


Tillotson-EC Racing Block – Wrap Up

The Tillotson block we designed here at EC's was created for the new Tillotson 225RS Race Spec engine individually but also as a replacement block for current Tillotson engines if needed. Since we're in charge of the design, we over-engineered it to suit our needs and our customer's needs as well. Our goal is to provide a better block with more strength and better cooling-both, giving an opportunity for more power, reliability, and innovations. We want this block to inspire builders and even hobbyist to go beyond the limitations of other blocks and engines. This block wouldn't be possible without our hard work and sacrifice to make this a priority. Blood, sweat, and months of frustration have gone into designing this block to sell it at an affordable price for the average racer and hobbyist. We have delayed projects to have this block built and are close to wrapping those up soon. 


Look forward to our new billet heads, carburetors and engine components coming this summer. We are the leaders in small engine innovations, and performance, and this block is our testament to our 50 plus years of knowledge and experience.  


EC's keeps ya puttin'.


Quick links to parts in this article below.


Tillotson 225RS 72mm Block


Tillotson 76mm Block


Tillotson 225RS Parts