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Rebuilding Hot Rod Honda Engines
By Dave Emanuel
Traditionally, hot rodding has been as American as apple pie, baseball, hot dogs and Chevrolet. Certainly, imported vehicles have been "hopped up," but serious hot rodding has always been dominated by enthusiasts who believe that engines have eight cylinders, pushrods and 16 valves.
For the past 40 years, machine shops catering to devotees of high performance have assembled countless big block and small block V8s manufactured by General Motors, Ford and Chrysler. Until a few years ago, incorporation of performance-increasing equipment and modifications in a rebuild of an import engine was a practice requested almost exclusively by customers who road raced or autocrossed. Not any more.
Hot rod imports now abound in virtually all regions of the country, and the demand for high performance import engine rebuilds is increasing at a dramatic rate. Surprisingly, the most popular vehicles among import hot rodders are those produced by Honda. Civics, Accords, Preludes and Acura
Integras are regularly modified for improved street performance, and many of these make regular appearances at drag strips.
Racers with terminal cases of Hot Rod Hondaitis combine turbocharging and nitrous oxide injection as a means of coaxing more than 450hp from 1.8L engines. Hot rod Hondas can also be found in oval track competition. Many tracks have classes exclusively for imports and/or domestic cars with four-cylinder engines and front wheel drive.
Obviously, most high performance Honda customers don’t get carried away to the point that they’re looking for more than 400hp. Like their V8-oriented counterparts, they’re simply looking for a reasonable power increase along with equally reasonable reliability. For rebuilders, that means employing many of the same proven techniques they’ve been using for years - but with a few new twists.
Like most overhead cam engines, Honda powerplants are very efficient in terms of the amount of horsepower produced per liter of displacement. As such, the cylinder heads typically have excellent air flow characteristics and are capable of meeting an engine’s air flow demands at higher rpm levels.
Even the most sedate Honda engines produce peak power at or above 6000 rpm and some don’t reach peak power until the tach needle is nudging 7500 rpm. Obviously, the stock ports have excellent air flow characteristics. However, since they reside in standard production castings, they can benefit significantly from some cleanup.
Considering the relatively small displacement of Honda engines, extremely large ports aren’t required. In fact, they can be detrimental because a dramatic increase in port volume will reduce velocity, taking low speed torque with it.
Finesse, rather than brute force, should be exercised when reworking Honda ports. Blending the valve bowl area and applying a three- four- or five-angle valve job will pay the biggest power dividends.
Another relatively easy means of increasing power is to increase compression ratio by milling the cylinder head. Most Honda engines have between 9.0 and 9.6:1 compression ratio. Removing a few thousandths of an inch from the surface can bump the ratio by half a point. This slight increase is especially useful when an engine is equipped with a high performance camshaft.
Cylinder pressure (cranking compression) is controlled by static compression ratio and valve timing. An increase in cam duration, with no increase in static compression ratio, translates to a drop in cylinder pressure and a corresponding loss of power. Although such losses are relatively small, they are significant in small displacement engines.
With a large displacement V8, such losses can be tolerated because an engine will still have an abundance of torque. But in an engine of just over 100 cubic inches, preservation of torque is of prime importance.
One point to keep in mind when rebuilding a Honda high performance engine is that milling the head will retard cam timing, requiring the installation of adjustable cam gears to reestablish stock phasing. On dual overhead cam engines, some engine builders advance only the intake cam (back to the stock position). This effectively alters lobe separation and widens the power curve. Be advised that the slots in some cam gears aren’t of sufficient length to accommodate the required amount of cam timing adjustment.
Also keep in mind that a variety of valvetrain configurations exist. Honda has produced both single and dual overhead cam engines, some of which are of the VTEC persuasion. VTEC stands for Variable (valve) Timing Electronic Control. This system employs a third "high speed" cam lobe and rocker arm for each pair of intake and exhaust valves. At low engine speeds, the lobes positioned directly above the valves control the opening and closing cycles.
At higher engine speeds, oil pressure, under electronic control, is applied to a sliding piston that locks all three rockers together. When this occurs, the middle or third cam lobe takes over and extends cam lobe duration and lift. This arrangement significantly broadens the engine’s power band, enabling it to produce strong low speed torque and top-end horsepower.
Major increases in power output shouldn’t present much of a problem for the lower end because Honda engines are typically blessed with generously proportioned main bearing webs. Some engines, such as the later VTEC models, contain a reinforcing girdle that ties the three main bearing caps together.
Factory block machining tends to be very accurate and many high performance Honda specialists note that align honing is rarely required unless a block has been damaged. Of course, it never hurts to check, but don’t be surprised if all the bearing saddles are properly aligned.
Another unique aspect of machining Honda blocks is the honing procedure. With typical high performance rebuilds, final honing without torque plates attached would be absolutely unthinkable for anyone not machine tool challenged. However, torque plate honing may well be somewhere between optional and not required on these engines.
The cylinder bores in Honda engines are siamesed together, but do not contact the main block structure anywhere but at the bottom of the cylinders. The water jacket completely separates the cylinders from the surrounding block material.
As such, when the head bolts are tightened, little if any force is transmitted to the cylinder walls. The block outer walls may distort when head bolt torque is applied, but the cylinder walls are virtually unaffected. Obviously, opinions vary as to the amount of cylinder wall distortion caused by head bolt tightening, but the fact is that many successful hot rod Honda engines have been built with cylinders that were honed without torque plates.
The free-standing bores do present a potential problem in super high performance applications. With 20-plus lbs. of turbo boost complemented by a shot of nitrous oxide, cylinder pressures escalate right into the Twilight Zone. In this type of environment, stresses are such that movement at the tops of the bores leads to power loss, and ultimately engine loss.
As a means of increasing bore stability, some shops add a plate that fills the water jacket at the deck surface, thereby tying the cylinders to the outer block walls. However, this type of modification is only required with maximum output engines used strictly for drag racing.
Much more typical of a Honda performance rebuild is an overbore to clean up the cylinders and decking the block to either reduce deck clearance or resquare the block. Following these operations, the tops of the bores are usually given a slight radius, as is found in new Honda engines (to ease piston installation).
Except for full-tilt race engines, stock crankshafts and connecting rods are adequate, as are standard replacement pistons. These components are perfectly capable of handling the type of power increases achieved through a high performance rebuild. Obviously, custom pistons are required to achieve a significant increase - or decrease - in compression ratio. (Stock compression ratios range from 8.8:1 to 10:1 depending on year and model.) That type of adjustment is usually required only if an engine is to be turbocharged or supercharged, if an extreme change in compression ratio is necessary, or if stroke is altered.
Considering that imports constitute one of the fastest growing segments of the high performance market, and that Hondas and Acuras are the most popular imports in this segment, high performance rebuilding of Honda engines represents an area of significant potential growth. It’s one your shop may be able to mine for added profits.