Lunati's 343 hp 305 Build-up
Using traditional hop-up techniques, Lunati's goal was to achieve maximum performance at an affordable price from the 305 small-block in a non-emission-controlled environment. The engine should be capable of running on the street, with decent idle characteristics and low-end torque. For longevity and practicality, the engine ought to develop peak power at around 5500-6000 rpm. finally, the package needs to be reasonably priced because the high-buckers would just as soon spring for the larger displacement small-blocks.
All 305 blocks have two-bolt main caps and use cast cranks. The Lunati 305 rotating assembly consists of a standard 3.48-inch stroke cast crank turned 0.010- or 0.020-inch under, indexed and balanced. Reconditioned stock rods are fitted with Mr.Gasket SPS bolts. Both crank and rods are supported by Michigan77 bearings, and are kept oiled by a Melling standard M55 oil pump.
Silv-O-Lite Keith Black Signature Series pistons (PN 144) were chosen. Manufactured from high-silicon alloys, they combine light weight with superior detonation resistance and (compared to forged pistons) permit tighter wall clearances for improved oil control and quieter operation. On under-4.100-inch bore engines, Silv-O-Lite piston skirt clearances can be set as tight as 0.0015 to 0.0020 inch; yet their rigid skirt design and high-silicon alloy permits running the piston "looser" than a traditional casting if desired--as high as 0.0045 inch. These pistons yielded a 10.26:1 compression ratio, used with a 0.038-inch-thick head gasket, 0.010 piston (down) deck, and a 60 cc combustion chamber.
Silv-O-Lite pistons come machined for Spirolock piston pin retainers. Usually, floating the pin requires bushing the rod. But to keep costs down while retaining the floating pin feature that allows the homebuilder to assemble the rods onto the pistons himself, Lunati runs the floating pins "steel-on-steel," with no bushing. If that worries you, remember that Chevy did the same thing on the '69 Z28 302's and warranteed them for 50,000 miles. The key is maintaining 0.0003 to 0.0005 inch of pin-to-rod clearance, not to mention drilling the rod for pin oiling.
Another depature when using the Silv-O-Lite pistons is piston ring end-gap. These pistons make more horsepower by reflecting heat energy back into the combustion chamber. As a result, the top ring runs hotter and requires more clearance than usual. According to Silv-O-Lite, increasing the ring end-gap does not affect performance or oil control because normal end-gaps are realized at operating temperature. Conversely, failure to provide sufficient end-gap can cause a portion of the top piston land to break, as the ring ends butt and lock tight in the cylinder. Silv-O-Lite provides a "recommended ring gap" chart with its pistons for varying applications that recommends multiplying the bore diameter by approximately 0.0065 to get the recommended ring end-gap on a normally aspirated non-computer street engine. On Lunati's 0.030-over 305 (total bore= 3.766"), the end-gap with the chosen Speed-Pro plasma-moly "file-fit" 5/64-5/64-3/16 ringset ended up at 0.025 inch for the top ring and 0.014 for the second.
Lunati used "generic" 305 iron cylinder heads (casting number=14014416, used on LG4 and HO engines), replacing the 1.84-inch stock valves with larger 1.94-inch valves, but kept the stock 1.50-inch exhaust valve size, treating both to a "good' standard valve job. They also ended up gasket-matching the heads and doing a little bowl work before installing Lunati high-performance springs, retainers, locks, screw-in studs, and pushrod guideplates.
Lunati installed one of its Streetmaster hydraulic non-roller-tappet grinds that offers reasonable idle quality with just a touch of that performance "rump-rump" so dear to our hearts. At least that's how it behaves in a benchmark 350; the cam is a tad more radical in a smaller displacement motor. To compensate for the engine's small displacement, the cam was installed 4 degrees advanced, and uses 1.5:1 ratio long-slot rockers.
Why not use a smaller cam? Lunati says it's hard to move air through a small-bore motor with a restricted valve area like the 305. You need a bigger cam to make this small cylinder work, but there are limits due to the small displacement. Fortunately, the relatively long stroke for this displacement engine helps low-end torque, so the engine isn't all that cam sensitive.
Edelbrock's Performer RPM intake was used. This manifold pulls through 7000 rpm, but it's divided plenum also makes it work at low rpm. It has exhaust heat passages, but no EGR provisions or divorced choke stove pad. Edelbrock says the manifold is not 50-state smog-legal on most emission-controlled applications. The tall plenum won't clear the stock hood on late-model Camaros, either. Holley's model 0-4776 600 cfm double-pumper carb was used.
Lunati used a pre-computer ACCEL Blueprint HEI distributor with conventional mechanical and vacuum advance, along with ACCEL's in-cap, high-intensity coil and spiral-wound 8.8 wires. The ACCEL unit comes with extra mechanical advance weights and springs, and the vacuum advance is fully adjustable. For the full-throttle dyno test, the unit was run as delivered.
Lunati's engine was tested on Dynotech's SuperFlow dyno using a generic set of 1 5/8-inch primary tube headers. The best results were obtained with the stock jetting and 38 degrees total timing, where a peak of 343 corrected horsepower at 6250 rpm was observed. The peak torque output of 356.2 lb-ft occurred at 4250 rpm. The engine made over 1 hp/cubic inch from 4500 through 6500 rpm, the highest rpm tested. It made over 300 lb-ft of torque from 3000 rpm (the lowest test point) through 5750 rpm.
Through all the tests, the engine idled smoothly at 750 rpm. Dynotech's technicians believe the engine would have more potential with less restrictive heads. They also think that the engine would perform better with a 650- or even 700-cfm carb, albeit at the cost of additional bottom-end sogginess.
Racing gas with a 108-octane level was used for all tests. This gas is not generally available for street cars. Assuming the use of 92- or 93-octane unleaded, you could get by with a true 9:1 to 9.5:1 compression ratio street motor when using cast-iron heads. The generally accepted rule of thumb is that you lose 12 to 15 hp for each point drop in compression-- so an otherwise identical 9¼:1 engine would be down about 15 hp from the results reported here. This lost power could be easily regained by using aluminum heads fitted with bore-clearing 1.94/1.50 or 1.55 valves, such as those offered by GM or Air Flow Research. Not only do the heads flow much better than 305 iron castings, but aluminum's superior heat-rejection characteristics allow 10:1 street engines on available unleaded premium pump gas. In any event, the end result is a 305 that will surprise quite a few late-model 350 owners.
|Dyno Test Results|
|Lunati's engine was tested on Dynotech's SuperFlow engine dyno, using the 200 rpm/second acceleration test schedule. All values are corrected to 29.92 inches Hg, 60°F dry air.Test fuel was 108 octane race gas. Peak amounts shown in bold.|
This article was copied from the October 1993 issue of Car Craft Magazine, and is used without their permission. Results cannot be guaranteed, and keep in mind that technology has brought about many improvements, so these results can be surpassed.(I wanna go home-let me out of the house)