Chevy "492" castings with straight spark plugs were originally installed on the '70 LT1/Z2
Straight Talk on Angle Plugs
What is the difference between a small-block Chevy angle-plug and straight-plug head as far as performance goes? Is it worth spending the extra money on expensive headers just to use angle-plug heads (especially if you already have two sets of straights)?
On small-block Chevy angle-plug combustion chambers, engineers moved the plug tips closer to the roofs of the chambers, supposedly to improve combustion efficiency and gain power. The first heads to feature the angle-plug configuration were a special parts-counter-only version of the conventional production straight-plug, 64cc chamber, "492" casting. Other than the angled plug location, the casting was identical and carried the same "492" casting number; hence, it offers a useful yardstick for comparing just the effects of altering spark plug location. The consensus was that original angle-plug heads were worth 10-12 hp on high-compression engines using high-dome pistons because they reposition the plug higher in the chamber so the flame front is no longer blocked by the piston dome. In fact, angle plugs made practical the use of even higher domes (with correspondingly higher compression ratios); previously, really big domes on small-blocks often proved counterproductive because of the flame-front blockage problem.
Because the angled plug's firing tip also ends up more centered in the chamber and oriented slightly toward the exhaust valve, the hottest part of the mixture is ignited first. With the plug located closer to the chamber's quench area, maximum turbulence is directed toward the plug, thereby improving combustion speed and pressure rise. In theory, this improves combustion efficiency even on engines without domed pistons, but on a street engine any power gain that results from changing spark plug location in an otherwise identical head is so slight it's not worth the hassle of conversion.
The angle-plug version of the 492 heads is no longer available, having long ago been superseded by modern GM and aftermarket angle-plug, off-road heads with redesigned intake and exhaust runners and higher-efficiency chamber shapes. In the modern era, Chevy also installed angle-plug heads on production L98 and LT1 aluminum-head engines. Whether off-road or production, these heads feature many improvements besides a revised spark plug location, so comparing today's modern high-efficiency angle-plug castings with old-style straight-plug castings is like comparing apples and oranges. Although, as we've seen, spark plug location alterations aren't that important for a flat-top piston engine, the modern-tech heads' other refinements can definitely offer a significant performance enhancement on a serious performance engine.
I transplanted a TH350 in place of my original Powerglide trans. My problem is that the original solid linkage interferes with the speedo cable. The new trans is correctly geared for my 3.42:1 rearend, so I just need a 1.0:1 speedo box to offset the speedo cable input. I've been to several local trans shops and no one sells one. If you could point me in the right direction I'd really appreciate it.
James Lee Garrison
A miniature 90-degree offset 1.0:1 speedo adapter box requiring only 1 1/2 inches of clearance is available from Lance Martin Automotive. The 90-degree leg can be reclocked in relation to the other leg as needed. One drawback is that miniaturization makes the unit more costly; it'll set you back about $80. Alternatively, you could always install an aftermarket floor shifter with cable linkage.
Lance Martin Automotive:
815 Hilbert Rd:
Fallbrook, CA 92028-1608:
Boil, Boil, Toil, and Trouble
I've just put together a 406ci (0.030-over 400) small-block Chevy with a supercharger. It dyno'd at 460 hp and 524 lb-ft of torque. The problem is that the fuel in the carb boils when the outside temperature is above 85 degrees. It usually happens when I decelerate after pushing it kind of hard. I've made it better by installing a heat shield under the carb, replacing the mechanical fuel pump with an electric fuel pump, moving the fuel lines away from the block, messing with the timing (it's never knocked), and mixing in some aviation fuel with premium gas. What's next?
There should be no less than 3/8-inch clearance (and preferably 1 inch clearance) between
Try the following:
(1) Check the clearance between the underside of the air cleaner lid and the carburetor's vent tubes (see illustration A). Run the car without the air cleaner; if the problem disappears, you've found the culprit.
(2) Install at least a 1/2-inch phenolic (plastic) spacer under the carb to prevent heat transfer from the engine to the carb (these plastic spacers are much more effective than a simple aluminum plate).
(3) Recheck the fuel line routing. You said you routed the fuel lines away from the engine, but what about the exhaust system? Sometimes exhaust heat transfers through the frame to the lines even if there's no direct contact between fuel lines and exhaust pipes.
(4) Pushing fuel is better than pulling-is the electric fuel pump installed back near the fuel tank at or below the tank's fuel level?
A standard Holley fuel pressure regulator can be used as a bypass valve by plumbing it as
(5) Install a 5/16- or 3/8-inch fuel return line. Recirculating the fuel in a constant loop back to the tank ensures a fresh supply of cool fuel, even under low-demand (deceleration, cruise, and/or idle) conditions. Manage the return rate by installing a check-valve in the system's return side. You can use a standard Holley fuel pressure regulator for this purpose (PN 12-803, 3/8-NPT ports, 0.220-inch restriction; or PN 12-704, 1/2-NPT ports, 0.4375-inch restriction; see illustration B for correct hookup). BG Products offers a single-stage diaphragm-valve bypass (PN 171021).
(6) Metallic fuel lines and steel/braided "racing" hose retain more heat than plain polyester-braid hose or Nomex-braid hose. However, cheap parts-store rubber fuel-line hose doesn't hold up and is not sufficiently fire resistant. Aeroquip's FC300 AQP braided polyester hose and StarLite Nomex hose are now NHRA-legal for plumbing the entire fuel system. Other similar hoses may also be acceptable; contact the National Hot Rod Association for the latest rules.
(7) If your car has been upgraded with a performance dual-exhaust system, check its routing where it passes the fuel tank. Often, routing is tight and the exhaust temperature heats up the fuel inside the tank.
1695 Indian Wood Cir.
Maumee, OH 43537-0700
BG Fuel Systems
1450 McDonald Rd.
Dahlonega, GA 30533-2424
Holley Performance Products
P.O. Box 10360
Bowling Green, KY 42102-7360
National Hot Rod Association
2035 Financial Way
Glendora, CA 91740-0950
I have some questions regarding solid-lifter cams. First, why do manufacturers give solid cam specs at zero clearance when the cam is not run at zero clearance? This is really misleading when buying a solid cam and looking for a certain lift and duration.
Second, wouldn't the duration figure given at 0.050-inch lift be different if you figure in the lash clearance of the cam? Just how much does the lash clearance change the duration anyway?
This illustration shows the differences between hydraulic and solid lifter profiles of sim
It is confusing, but big numbers sell product! Putting the best face on this issue, remember that the installer can vary the lash-setting on a mechanical cam, which of course affects lift; so, it could be said that most aftermarket companies publish theoretical valve lift figures and leave it to the tuner to figure out the "real" lift (theoretical valve lift minus the lash setting).
And even assuming zero lash, the official published valve-lift figure is somewhat arbitrary-invariably, there's some valvetrain deflection, and stock-type rocker arms may not really yield their advertised ratio. Hydraulic profiles generally don't achieve their theoretical published valve lift figure either; they lag a bit because the pushrods slightly compress the lifter.
As for duration-whether advertised, seat, or 0.050-it's always calculated at the tappet, not at the valve, so even with "zero" lash, the actual working duration is somewhat higher due to the rocker arm's multiplier effect. A gross rule of thumb is that measured working duration increases about 2 degrees for each tenth of a point increase in rocker arm ratio. But the actual increase in total area under the curve makes the cam act as if duration increases about 4 degrees for each tenth of a ratio increase. Professional racers often decrease duration (as measured at the tappet) as much as 10 degrees when moving up from 1.6:1 to 1.8:1 rocker arms; this maintains the same horsepower, but increases torque.
Nevertheless, due to the considerable lag induced by the necessary lash clearance setting, a mechanical cam needs to have about 8-10 degrees more duration than a comparable hydraulic cam to achieve an equivalent powerband when both cams are installed in the same engine.
The Bucks Stop Here
I'm looking to build a 400 or 383 small-block Chevy blower motor. I would like to make 400 hp (with an 8.0:1 or 8.5:1 compression ratio) on just the motor, no blower. With the base motor at this power level, I'm gonna bolt on an ATI ProCharger for some real fun! All the local machine shops say it can't be done without major dollars invested. I was wondering if you could help.
The key to keeping costs reasonable is staying under 10-psi boost and investing in a good set of heads-like Air Flow Research's $1,250, 195cc intake runner offerings. Cam selection won't be critical under 10 psi; you can get by with a single-pattern 292 Isky MegaCam or equivalent hydraulic flat-tappet grind at this level.
In contrast, achieving maximum performance potential under higher boost conditions requires a custom dual-pattern blower cam with wider lobe separation than the Isky cam's 108-degree LDA; such dedicated "blower" grinds generally aren't best for unblown running. High boost levels also cause head gasket sealing problems on a 400 due to the block's thin deck and thin siamesed cylinder walls. If you must have a 4 1/8-inch-bore engine and high boost, it's time for a pricey Bow Tie block with its beefy siamesed cylinder walls and extra-thick deck. High boost also mandates an aftermarket forged crank with a bigger big-block-style front snout-serious boosters have been known to rip the snout right off the crank.
An alternative is to forgo the 400 and build a 383. Boost builds torque, so a 383 will get the job done fine without any head gasket-sealing problems. KB Pistons offers hypereutectic 383 pistons (PN KB121) that produce about 8.8:1 compression with 64cc combustion chambers. With the AFR heads, above-recommended cam profile, reasonably competent machining, and prepped stock 5.7-inch rods, you can achieve 400 hp with the 383 in an unblown configuration with no sweat. When you bolt-on the supercharger install an 850-cfm Holley double-pumper, minimum.
If you shop around for good-guy parts deals, assemble the engine yourself, and only farm-out necessary machine work, you ought to be able to put an engine like this together for around $4,000.
Air Flow Research
10490 Ilex Ave.
Pacoima, CA 91331-3137
Isky Racing Cams
16020 S. Broadway St.
Gardena, CA 90247-0803
Check Engine or Checkmate?
I have an '86 Buick Grand National. When I step on the gas pedal the car stalls or stutters. It does not happen when the car is cold, just when the temperature is at or about 160 degrees. It has nothing to do with the transmission. I changed the spark plugs, the wires, the coil pack, and also the temperature sensor. I also checked the fuel rail and it is getting sufficient fuel pressure. I noticed that the "check engine" light would come on, and it returned a code which translated to the "boost control solenoid." I changed it for an AC-Delco unit and it still continues to do the same thing. The "check engine" light still comes on only when I drive on the highway, when the turbo is building up boost. Could it be the module? Why is the "check engine" light continuing to return the same code?
First, a rule of thumb: When a code is set, it's not always the device itself that's faulty-the hoses, electrical connectors, and wires that comprise the entire circuit controlling the device could be the actual culprit. For example, there are lots of vacuum hoses on a turbo car, and with age they eventually crack.
A bad solenoid, or leaky vacuum hoses from the turbo wastegate to the solenoid, would cause an overboost condition, in turn resulting in momentary detonation-then the car falls on its face. But that does not sound like the symptom you describe.
So, chances are the primary performance problem is not caused by the code your diagnostic scan is reporting. There is a MAP sensor that monitors boost pressure and also displays boost on the cluster. This sensor doesn't set codes when faulted, but can cause trouble when it does. Possibly it is skewed and feeding the ECM the wrong boost data.
If the stutter is only a transient problem (just a second or so) the TPS (Throttle Position Switch) could be the culprit. It may be slightly out of adjustment, but not enough to throw a code. On a digital voltmeter, the '86 turbo Buick V-6 TPS should read between 0.35-0.45v throughout the entire throttle range, with a 0.40v plus-or-minus 0.05v curb idle adjustment spec.
If the TPS is OK, check the fuel pressure again under a load. It should increase by about 1 psi for each pound increase in boost.
Inspect the EGR valve. It does not deploy until 160 degrees F, which is why you may not have a problem until the vehicle warms up. Once again, a slight EGR valve malfunction may not necessarily throw a code. For example, a diaphragm spring going "soft" could cause premature valve opening, resulting in a tip-in stumble. Disconnect the hose going to the EGR and see if the problem goes away. There is also a serviceable EGR valve filter; it can't hurt to replace it.
If a scan tool is available, check the O2, coolant temperature, and Mass Airflow sensor outputs. Also recheck the coolant sensor (ECT); that circuit may still have a problem. If the O2 sensor is sending a false rich readout the ECM will continue to lean-out the fuel curve when in closed loop. Disconnecting the O2 sensor can disable closed loop long enough to see if the problem takes a hike. If a scan tool isn't available, disconnecting the ECT or MAS sensor will send the system into back-up mode, possibly rectifying the condition temporarily.
If the above doesn't cure the problems, then yes, it's probably a bad module.