Like the block, some prep...
Like the block, some prep on the cylinder heads will require machine-shop level expertise. Here, Kevin Troutman of KT Engine Development opens up the pushrod holes on the Dart Iron Eagle cylinder heads to gain clearance required by the larger lobes on our Comp Cams racing camshaft.
In the first two installments of Circle Track's Limited Late Model engine build we prepared the foundation for a race engine that makes the most bang for the buck. In the previous two installments, we finished prepping the block and installed the crank, rods, and pistons. This time around, it's time to get busy with the cylinder heads and valvetrain. Although it has already been installed, the heart of the valvetrain for this project is a custom-ground cam from Comp Cams, designed specifically to make the most from this engine package.
Right about now you're probably saying to yourself something along the lines of, Custom cam! I thought this was supposed to be a real-world budget build. The beauty is anyone can get a custom cam for his engine since Comp does not charge extra for this service. You can get an off-the-shelf cam if that suits your needs, or you can choose from any of the hundreds of grinds available from Comp's catalog. Cam spec help is also free by calling Comp's tech line.
Finally, before we get started, there are a couple small points that probably should have been pointed out earlier. Good engine building practices require fastidiousness when it comes to cleanliness.
Here's a comparison of the...
Here's a comparison of the work done to open up the pushrod holes. This was done on a milling machine, but you can do it by hand if you want. This not only creates room for larger pushrods, but it also cuts a little weight off the top of the engine. Just be careful not to break into the intake ports.
This means making sure your assembly area is clean and as free of dust and dirt as possible. Building your engine will also most likely take place over several days, or even weeks, so make sure to keep the engine covered between work sessions. Large garbage bags are cheap and work well for this. They will also catch oil that drips off the assembly and keep it off of your shop floor. Finally, every part that goes onto your engine should be cleaned before it's installed. This includes brand-new components that are straight out of the box.
We won't bore you with photographs of all the individual parts on this build being cleaned, but be assured that it's happening. A large parts washer is great for this, but make sure it's relatively clean. Lots of race teams have a parts washer they use for cleaning the gunk off of gears, hubs, or whatever else needs to be cleaned, and no one is really sure when anyone last changed the solvent. If this describes your parts washer, don't use it (at least until you flush and replace all the solvent). If you don't have a parts washer handy, you can get by with a gallon of lacquer thinner and plenty of shop rags. Let's get to it.
Even with new heads, you may need to have the valve seats cut. We are using larger 2.020 intake and 1.600 exhaust valves (the maximum allowed by most tracks), so new seats had to be cut to enlarge the Iron Eagle's 1.94/1.50 sizes. Also, if you're running stock heads, they usually come with only a one-angle valve job. Investing in a three-angle valve job (30/45/60) is usually money well spent because it will greatly improve airflow through the port.
Most rulebooks have a minimum cc rule for the combustion chambers-usually 62 cc's-so to maximize compression, you'll need to get your heads decked to bring the chamber to the minimum size. Here, Kevin Troutman measures the chambers before cutting.
The Spec Sheet
Want more details? No problem. Here are the specs for our mechanical flat tappet cam from Comp Cams. Our cam was installed at the suggested 104-degree intake centerline.
| ||Intake ||Exhaust |
|Grind # ||5682 ||5683 |
|Valve Lash ||0.018 ||0.020 |
|Gross Valve Lift ||0.481 ||0.481 |
|Duration @ 0.020 ||274 ||278 |
|Duration @ 0.050 ||248 ||252 |
|Lobe Lift ||0.3101 ||0.3010 |
|Lobe Separation ||108 || |
|Intake Centerline ||104 || |