It seems gasoline prices are on a constant unstoppable climb. The rate of this climb changes, and in our current national situation these changes can be abrupt, but...it seems prices are always a bit higher than they were last year, and especially higher than they were two to five years ago. This steady-but-gradual increase in gasoline cost is making it tougher and tougher to justify building a street machine to run exclusively on premium gas--always the highest-priced option at the local pump.
We at the car magazines are guilty of showing almost nothing but higher-octane buildups and research. We typically want to produce solid power figures and are normally willing to pay the higher price at the pump when these project engines hit the road. Often, the engines built on the pages of your favorite magazines end up living in limited-use automobiles, so the commitment to premium gasoline is not a big deal.
Times are changing, so we wanted to do something different. The overwhelming majority of daily-driven vehicles remain bone-stock, as the factories built them, and live on a steady diet of cheaper 87-octane brew. What if a reader wanted to drive his hot rod more often than on sunny weekends, and wasn't willing to drop the larger dough for premium gas on a regular basis? Can a true performance engine be built to live on 87-octane?
We think so, and we've done the homework to find out how far it can be pushed. What we'll share is the bulk of the research we've accomplished toward getting this true street 87-octane engine going, and if you're considering something similar, we'll have a blueprint for you to follow. We based this buildup on the ubiquitous small-block Chevy because of its research-based existence, and the ease of parts and limited expense simply made sense in this vein. The techniques and ideas shown are quite universal, and should be on the list of "must-do" items for others pursuing the 87-octane dream regardless of engine make. We went a step further by building not one, but two small-block Chevys in both the popular 355- and 383-cube dimensions that most PHR readers favor. These tricks and tips will work just as well on any domestic V-8, and probably any piston engine, for that matter. It's bad news that 87-octane may be our future, but we're trying to make lemonade from this lemon.
THE BASICS--BLOCK, CRANK, RODS, and PISTONS
We began with '80s-era 4-bolt 350 blocks, with intentions toward stroking one up to the common 383-inch level and leaving the other at 355 (overbored .030-inch over stock.) We anticipate a hard life for these particular mills, which may include racing and nitrous use down the road. We chose a complete Lunati reciprocating assemblies for both, including the crankshaft (a good forged unit with aerodynamic counterweights and precision machining), forged connecting rods (in 6-inch lengths), and forged pistons (a flat-top design with two valve reliefs machined into their surfaces for adequate piston-to-valve clearances). Lunati offers both engine-reciprocating assemblies as internally balanced, pre-matched units.
Lunati sells these complete reciprocating assemblies in pre-balanced form, which saves time and money at the machine shop. They even ship with bearings. Their forged strength is not in question, and unlike 383s built using factory (400ci) cranks, these are internally balanced, which opens up parts selection dramatically versus the oddball, externally balanced 400-crank issues. Naturally, the 350 reciprocating assemblies are internally balanced as well. We ordered ours with 6-inch forged rods in both cases. For anyone considering a Chevy 383 or 355 at any power level, it'd be hard not to recommend checking out these impressive pre-matched kits.
To beef up our bottom end even further, we equipped the 4-bolt blocks with an ARP stud kit. It's important to remind readers how these studs must be installed prior to machining the mainline, and also how their torque figures may vary from a factory specification. We prefer ARP studs for their increased strength, improved bearing cap alignment, and increased grip length surface area (due to the finer threads in the torqued fastener nuts versus the coarsely-threaded bolts).
This type of bottom-end fortitude should support plenty of power, and probably is capable of more than we'll ever make with these low-octane mills. In this case, overkill is fine, since we intend to push limits and justified the extra durability by knowing we'd have our toes close to the line in the development and tuning of this engine. Should we push too hard, we know we've got the strength inside to survive.
Beyond strength, there's the issue of harmonics avoidance and the pursuit of smooth acceleration through balance. We've chosen to run a TCI "Rattler" balancer with its movable weight pucks inside, since we like the engineering of these pucks being able to move at will to correct any harmonic distortion instantly and at any rpm level. Unlike fluid-filled dampers, the Rattler design in unaffected by temperature and has instant response to varying harmonic interference. In a street-based car headed for the occasional racy jaunt, this type of engineering is a bonus. It doesn't suppress harmonics (like factory-type rubber-insulated dampers), it counteracts them with proper weight shift.
CYLINDER HEADS
When pushing hard against an octane barrier, detonation avoidance becomes paramount and the heads are key. In addition to limiting compression (in our case, we've chosen 9.75:1), we wanted to have an efficient chamber design to make the most of what little octane we'll have. The ports need to be sized for optimal volume and velocity in the rpm ranges the engine will be running at (2,000-6,500), and our research led us to the AFR 210 (CNC-finished) aluminum units.
We were tempted to go with the zippy 190cc intake port, and also by the known-power made by the 215cc heads, but decided on the 210 to balance the aforementioned volume and velocity issues. We preferred the tried-and-true CNC-finishing to optimize the design, since the programming is proven and the port-to-port sizing is more accurate than any human hand could ever be with a grinder.
AFR 210cc HEAD SPECS: PN 1050
Basic Package Components:
100 percent CNC Ported Combustion Chambers
100% CNC Ported Exhaust Ports
70 percent to 100 percent CNC Ported Intake Ports
3-angle Valve Job
Intake Valve, 2.080" x .050" long, AFR #7018
Exhaust Valve, 1.600" x .050" long, AFR #7057
1.550" OD Roller Valve Spring, 220 lbs. on seat, .670" maximum lift, AFR #8000
10o 4140 Chrome Moly Retainers, AFR #8510
10o Valve Locks, AFR #9005
7/16" Rocker Studs, AFR #6405
5/16" Guide Plates, AFR #6105
Valve Seals, AFR #6611
Hardened Shims, AFR #8045
Intake Valve Seats, AFR #9060
Exhaust Valve Seats, AFR #9070
Bronze Valve Guides, AFR #9050
Special orders available on request.
Specifications, Features, and Supporting Components
Head Torque 65-70 ft.-lbs.
Rocker Stud Torque 55-60 ft.-lbs.
Intake Port Gasket, 1.310" x 2.180" w/ 3/8" radius, AFR #6820
Important: Do not port match your intake manifold to this Fel-Pro gasket, as they do not exactly fit AFR heads.
Intake Gasket Option, 1.280" x 2.090" Fel Pro #1205, AFR #6810
Exhaust Port Gasket Fel Pro #1406, AFR #6835
Head Gasket 350cid Fel Pro #1003, AFR #6800
400cid Fel Pro #1014, AFR #6802
Head Bolts & Studs Standard ARP, AFR #6310 & #6305
Head Bolt Washers Manley, AFR #6320
Stud Girdle AFR #6201
Spark Plug Starting Range Autolite 3910
Combustion Chambers 76cc
Spring Pocket can be cut to 1.750, no deeper.
Valve Spacing Standard
Rocker Arms Standard
Valve Angle 23o
Angle Mill (milling available) .008" per cc
Flat Mill (milling available) .006" per cc
Pushrods 5/16" Hardened, AFR #6601 thru #6604
All detonation begins in the combustion chamber, so we were especially careful in designing the powerplant by choosing a good size chamber (at 76cc) and allowing the piston to sit "in the hole" by .012 to achieve our target 9.75:1 compression ratio figure. We then fortified the chamber with the addition of a thermal barrier coating, which will serve multiple purposes.
First, the Calico CT-2 thermal barrier coating will insulate and isolate the chamber from the rest of the head. Research has shown this to be worth power, but immediately one would think this insulating property would bring us closer to detonation. We feel it will aid in the distribution of heat across the chamber, and by engineering an efficient cooling system, we can maintain good detonation avoidance under full load. We hope to spread the heat out over the chamber and in doing so, bring additional detonation avoidance properties along. Another advantage of the Calico CT-2 thermal barrier coating is its ability to leave a smooth surface wherever it is applied. Being a ceramic type of material, the resulting surface of the coated chamber is nice and smooth. The lack of any sharp edges in the critical chamber area adds to the detonation avoidance characteristics, and will allow us to push a little further into the land of low-octane performance.
We also coated our valves and ports. The thinking behind this is twofold, as the intake charge will be insulated from heat as it enters the combustion chamber (including the heat from the intake valve), and the hot exhaust will be escorted through a similarly insulated tunnel on the way out. Header wraps and coatings make power because they keep the heat inside the header. Hot exhaust is always trying to expand, and the insulated exhaust port aids in this quest. Once the hot exhaust gases reach the header collector, they are encouraged to expand and escape, as this is where we've designed them to do so.
We chose to have the coating applied directly over the CNC-finished AFR chamber without any further prep work or smoothing. We did this so our research could be easily duplicated with out-of-the-box, unmodified heads our readers could get their hands on. Also, we felt that changing the chamber as AFR finished them would probably hurt more than it would help, since so much of their research has gone into these chambers. As a final point, the coatings are .001-.002-inch thick, and this served to virtually eliminate the already-fine CNC machine finish inside the chamber. This smoothing effect is precisely what we were hoping for in addition to the thermal barrier features the coatings bring to the party.
By insulating the exhaust valve, we hope to minimize heat going into and coming out of it. Keeping the exhaust valve cool will also aid in detonation avoidance, since the exhaust valve and its surrounding seat area is always the hottest part of the combustion chamber.