Jeff's Performance IMCA Modified Engine - Horsepower IMCA Style

One of the great things about IMCA Modified racing is the no-nonsense approach the sanctioning body has taken to teching its race cars. When it comes to engines, the IMCA has one of the thinnest rule books you will find in stock car racing. Instead of a bunch of limitations on which parts you can use, the sanctioning body depends on a relatively cheap claimer rule and market forces to keep costs in line. The idea is that you can do just about whatever you like, but you could be claimed.That means the challenge is to build as much horsepower as possible as cheaply as possible. And for an enterprising engine builder, that can be a lot of fun. The key is to understand which components in the engine will give you the greatest bang for your buck and which components you should save a few bucks on. Jeff Hill, the owner of Jeff's Performance in Sherman, Texas, has been a significant player in the IMCA Modified engine game for years, and he says he is constantly finding new ways to make more power for less money.

To find out how far we could get building an IMCA-style small-block on a real-world budget, Circle Track recently began an engine-building project with Hill. The idea wasn't to simply build your run-of-the-mill IMCA Mod engine, but to try a few new things we had seen on the market recently that intrigued us. Our plan was to consult with Hill on the different components we wanted to try, and then leave him alone to figure out how to put it all together.

The first thing we wanted to try was EQ Cylinder Heads' new performance heads for the Chevy small-block. The key feature of these cylinder heads is the ultra-small 50cc combustion chambers. With standard 23-degree cylinder heads, the stock chamber size is usually around 74 cc. And because of the valve angles and minimum deck thickness, you can usually cut the chambers down to approximately 60 cc before either the deck gets too thin or you start cutting too close to the valve seats. Fifty cc is the smallest chamber size we've seen for non-Vortec, as-cast cylinder heads, which can give engine builders the opportunity to get compression ratios that have not been possible before-especially if your rule book mandates flat-top pistons.

In addition to the small chambers, EQ Cylinder Heads has also included just about everything else necessary for a cast-iron racing head. Several different runner sizes are available, and all have good flow numbers for as-cast ports. For this build, we chose a 200cc intake runner. Other features include hardened exhaust seat inserts as well as bronze valveguides and angled plugs. The heads also arrived with a three-angle valve job, and the valves were sized at 2.050 inches for the intake and 1.600 inches for the exhaust.

To make the most of these small combustion chambers, Hill worked with KB Performance Pistons to design a set of pistons with his specific needs in mind. For years, KB Performance Pistons has specialized in producing hypereutectic performance pistons, but the company recently began selling forged pistons as well. We are using the new KB-forged line of pistons here. These pistons have a lightweight design combo with a small slipper skirt and narrow wristpin to cut weight. Altogether, the piston weighs just 447 grams. This is a brand-new piston created expressly for this build, but KB Performance says it can produce copies for anyone wishing to reproduce this engine package.

Hill also worked with Crane Cams to come up with the best valvetrain combination for this engine. The camshaft is the most unique component in the valvetrain combination. It is a solid flat-tappet with 0.374-inch lobe lift on the intake and 0.381 inch on the exhaust. Combined with the Crane 1.5:1 ratio roller-tip aluminum rockers, total valve lift comes out to 0.561 and 0.572 inch, respectively. The cam is degreed at 103 degrees, and the advertised duration is 283 degrees for the intake and 287 degrees for the exhaust. At 0.050-inch lobe lift, the duration is 258 and 262 degrees. This cam is unique in that it's quite aggressive with lots of lift, considering it is mated to stock diameter flat-tappet lifters. Hill says this is also one of the first times he has used a cam on an engine of this style with more lift and duration on the exhaust than the intake. Springs are double-nested with an installed height of 1.900 inches. On the seat, they are rated at 130 pounds.

The block is a core that was sourced from Enginequest, which is part of the EQ Cylinder Heads family of companies. The bores were cut 0.060 inch over for a total diameter of 4.060 inches. Combined with Jeff's Performance's own crankshaft with 3.750-inch stroke, total displacement is 383 ci. Hill also used his own rods for this build. The forged rods utilize the stock Chevy journal size of 2.100 inches but are 6.00 inches from center to center for an improved rod/stroke ratio. Both the crank and rods are available through Jeff's Performance.

Hill says this engine was designed to run on alcohol, but he prefers to always break in all of his engines on gasoline. This is because the gasoline allows extra heat into the engine sooner compared with alcohol, which means the rings seal more quickly and reliably. If you break in an engine on alcohol, you run the risk of milking the oil before the rings seal up, which jeopardizes the bearings. Interestingly, Hill says the only difference between his alcohol engines and his gas engines is the carburetor. The same camshaft will make peak power with both. Thanks to the small combustion chamber and the domed pistons, this engine produced 14:1 compression, making running it on gasoline-even race gas-a little dicey. Still, it produced 508 lb-ft of torque and 510 hp with a Holley HP 750 carburetor. Once the alcohol carburetor was switched over, the engine knocked off 558.3 lb-ft of torque at 4,500 rpm and 530.4 hp at 5,900 rpm. These are impressive numbers on their own, but they become astounding when you consider Hill says he will sell this engine for just $6,595.