E-mail your tech questions to us at carcraft@primedia.com (include the words "What's Your Problem?" in the subject line) or fax them to 323/782-2223. All correspondence must be signed with the sender's real name (not a nickname or a screen name) and include the sender's hometown and state or province. While mail cannot be answered personally, Car Craft will publish as many letters and replies as space permits. Photos are welcome, but no materials will be returned.
Where's the Boss?Why doesn't the ZZ502 crate motor from GM have the fuel-pump boss machined into the block? The 454 H.O. has the boss, and from what I can gather it's also a Gen VI block like the 502. What's the deal?Gary CooperRancho Cucamonga, CA
We spoke with Kevin McClelland of Flowmaster, who was involved in the development testing of the Gen V and Gen VI Chevrolet big-block engines. He explained that the 454 and the 502 are each unique castings, not differently machined versions of the same casting. When the Gen V was introduced (for 1991), neither the 454 nor the 502 had fuel-pump bosses. These engines were intended for then-current applications, which all used electric fuel pumps. At the time, the older Mark IV engines were still being serviced with new Mark IV blocks. However when the Gen VI was developed, the fuel-pump boss returned to the 454, as you've observed. This was done because the Gen VI 454 also had to serve as a service-replacement block for all previous 454-equipped vehicles, many of which had carburetors with mechanical fuel pumps. Since the 502 was never intended for production use, the boss was left off.
Misguided RockerI've been reading a lot in your magazine and others about GM Vortec cylinder heads and the performance advantage they offer over other GM heads. I may be able to get my hands on a set that came off a low-mileage engine that was replaced under warranty. However, I'm confused about one issue. I understand that a specific intake manifold is needed, but what's the deal with the rocker arms? Most articles written on the subject say that later "guided" rocker arms are needed, but why? All of the small-block Chevy engines I've worked on operate without guided rockers or any sort of pushrod guideplates, so why the sudden need? Couldn't I just transfer the original rockers from the '76 350 in my '68 Chevelle to the Vortec heads? I don't plan on running a big cam or turning high rpm, so what's the problem?George WestfieldBoulder, CO
Actually, the small-block Chevys you worked on did have pushrod guides, just not the type you're accustomed to seeing. True, there aren't bolt-on guideplates on stock small-blocks, but the holes in the heads that the pushrods pass through act as guides. Take a closer look at an older set of heads and you'll see that the holes are not round, but slightly oval with flat sides. In later years, engineers decided to make the pushrod holes round and larger so as not to interfere with the pushrods at all. To replace the guiding function, the rocker arms were redesigned with a grooved tip. The grooved, or guided, rockers look nearly identical to earlier unguided examples except for the tip. You will definitely need them if you upgrade to Vortecs, but a set of 16 brand-new arms, complete with new fulcrum balls and locknuts costs only around $40 from GM. If you're really scrounging, check late-'80s/early-'90s small-blocks in the local boneyard or machinist shop core pile, as some of these also used the guided arms.
Spare Parts, Part OneI am currently in the process of rebuilding a '77 350 for my '64 Impala SS. When I was comparing '68 327 rods and pistons to those of the 350, I found them to be exactly the same. Is it possible to use these 327 rods and pistons in a 350? Would there be any problems?Matt CroxtonValley Head, AL
Take a closer look. A measuring caliper will show that the distance between the center of the piston wristpin bore and the piston deck, usually referred to as compression height, is shorter on the 350 slugs. The actual compression-height measurements of the factory pistons are listed as 1.675 inches for the 327 and 1.56 inches for the 350. As you undoubtedly know, both engines share a 4-inch bore, but the 350 has a longer stroke-3.48 inches compared to the 327's 3.25 inches. Since both engines use a 5.7-inch connecting rod and a block with the same deck height, the increased stroke of the 350 crank requires that the wristpin be located higher in the piston. Putting the 327 pistons and rods in the 350 would create a situation where, at top dead center, the pistons would protrude above the deck of the block.
Spare Parts, Mopar StyleI'm looking to replace the stock 318 in my '69 Coronet 500 with a larger small-block Mopar. I have a '71 360 block, as well as a set of '69 340 full-floating rods lying around, plus a set of 10.5:1 stock 340 aftermarket pistons. Is it possible to bore the 360 0.040-inch over and use the 340 pistons and rods in the 360?J.R. KorenCooperstown, NY
As you know, the 340, though smaller in displacement, actually has a larger bore than the 360 (4.040 inches versus the 360's 4.000 inches). The 340 has the same 3.31-inch stroke as the 273 and 318, so the 360 obviously gets its increased displacement from a significantly longer stroke (3.58 inches). Both the 340 and 360 share the same length connecting rod, so the problem with the combination you suggest lies with the compression height of the piston-the wristpin bore is closer to the piston deck on 360 pistons (see Spare Parts, Part One). Installing standard-bore 340 pistons into an overbored 360 will result in pistons traveling up beyond the top of their bores at top dead center.
We ran your proposal past contributor Steve Dulcich, who has assembled a number of Mopar small-blocks, and he noted that if you actually have a set of low-compression 340 pistons ('72-'73), you could assemble the engine your way. However, he points out that you'd still have to machine the tops of the pistons to shave off a little more compression height, and basically, that's not worth doing. The 340 rods are the same as those used in 360s, but they're bushed on the small end for full-floating pins. You could get a set of aftermarket 360 pistons set up for full-floating pins and retain your 340 rods, but there really isn't that much of an advantage to full-floating pins on a street motor. We mention this because it's likely that the wrist pin bushings in your 340 rods are worn out, and replacing them is somewhat costly-between the cost of the bushings and the labor to install and size them. If you want a 360, you're probably better off simply rebuilding one using 360 guts.
Environmentally Compatible?I've heard a lot of talk about which headers are emissions legal and which are not. I have several questions on the subject.
1. What kind of headers are compatible with a catalytic converter: short-tube or long-tube?
2. If long-tube headers are compatible, would they make more horsepower than short-tube headers?
3. Would catalytic converters be less restrictive if placed closer to the headers?Bob AdamsOcean City, NJ
First of all, the only headers that are truly 50-state smog-legal are those certified by the California Air Resources Board (CARB), and CARB's exemptions are only granted for specific applications on a case-by-case basis. Laws vary from state to state, and they're fairly stringent in New Jersey. Many states have adopted California standards, and simply installing a catalytic converter does not ensure smog compliance. Full-length headers generally allow too much heat to escape from the exhaust gasses before they reach the cats. This prevents the cats from "lighting off"-the term used to describe the point at which the exhaust-scrubbing chemical reaction begins.
As far as header configuration goes, generally speaking, a long-tube design will make more power than a shorty, though we've had good results with some recent 31/44-length designs, such as those from Hedman.
Finally, the general rule for converter placement is that the farther a restriction in the exhaust system is from the exhaust port, the less impact it will have on engine performance. Therefore, placing the cats closer to the headers will make them more restrictive. Of course, to go back to the original point, converters must be close to the engine to function properly, which is why you'll find them either as part of the manifold or right after it on most late-model production cars.
Advance DebateI hope you can settle a little dispute for me. Friends of mine (Ford, GM, and Mopar owners) have asked me to help tune their cars; most are 11- to 12-second rides. We seem to constantly have a problem getting the vehicles to idle without the mechanical advance coming in. I keep telling them to lock out the mechanical advance, install a start retard, set the timing, and be done with it. Since these cars leave the line above 2,000-3,000 rpm anyway, with the advance already in, I don't see the need for functional advance mechanisms. They feel that not having a working mechanical-advance distributor just isn't right, and that the distributor has got to have the lightest springs possible. They also believe that if you set the timing at a constant 30 to 40 degrees, some type of major engine damage will result.Don GundersonWaterford, Michigan
Your method of locking out the advance mechanism is a common practice among drag racers and has been for decades. Before there were start-retard functions in ignition systems, most guys would rig up an ignition kill button so they could crank the engine without spark to get it spinning and then release the button to fire it.
You didn't tell us much about the vehicles in question. Are they race-only or street/strip? This is important, because race-only cars can make due with fixed timing settings and so forth, but street-driven cars were designed with advance curves for a reason: To cope with the varying engine load conditions a road-going passenger car regularly faces.
To answer your question, yes, you could lock out the distributor and have the performance you're looking for assuming that these cars do, in fact, maintain higher rpm from launch all the way down the track. It isn't the most sophisticated approach, but it could work. Of course, even with the start retard, there may be detonation issues on the street under part-throttle loads-this is probably what your buddies are concerned about. Detonation can indeed cause engine damage in the form of blown head gaskets and broken or burned pistons.
You mentioned that your friends want to run the lightest springs possible. This is really the obvious flaw in the tune-up. If you don't want the advance to come in too early, you can't use the lightest springs. It's that simple. Heavier springs exist to help you tune the advance to come in when you want it.
Our advice: Leave the locked-out distributors at the drags and experiment with springs and weights to produce the advance curve you want. If you really want to get high tech, have the distributors curved at a shop that has and knows how to use a distributor machine.
Poncho PressureI have a question for you concerning my Pontiac 400 motor. I am concerned about a very low oil-pressure reading. When in drive, at idle (870 rpm), and at operating temperature, the gauge reads 13 psi. At highway speeds (70 mph at 3,800 rpm) it reads 40 psi. Are these readings too low for safe operation?Fred AligDenver, CO
Pontiac V-8s are notorious for low oil pressure at idle, but it isn't necessarily a problem. With the engine at normal operating temperature, the old standard of 10 psi per 1,000 rpm still holds true, which would put you safely in the black. We've seen plenty of seasoned Pontiac mills allow the gauge to drop almost to zero at idle in Drive when coolant temperatures are hovering around 200 degrees, and many of them performed flawlessly. Pontiac engine builders often take steps to improve the situation, typically by keeping critical tolerances on the low side (for street engines) and upgrading oil pumps.
Evidently, the Pontiac engineers weren't too concerned with oil pressure at idle in their V-8 engines, as the factory spec provided is given at 2,600 rpm, at which point they feel you should see 30-40 psi in standard V-8s and 55-60 psi in performance V-8s.
Trick TriggerPlease educate us on the advantages and disadvantages of the crank trigger used in the "672hp Pontiac 350" article (July '02). I assume it provides a more accurate timing of the spark since it would eliminate timing-chain stretch. How is it connected to the distributor? Is it a good street item? It certainly looks trick.Conrad A. Carter Jr., P.E.via e-mail
Your assumption about the increased accuracy of the crank trigger is correct, and this is the main reason racers prefer these units. Normally, once the crank trigger is installed, the distributor is locked out, meaning the advance mechanisms are disabled and fixed in one position. Drag racers often set the distributor for maximum advance and leave it there, but for the street, this isn't really a feasible approach.
There are a few ways to use the MSD crank trigger. The first involves simply mounting the trigger unit and plugging it into a typical MSD ignition box, such as a 6AL. However, this arrangement provides no timing curve. The next option is to use MSD's Timing Computer (PN 8980), which has a preprogrammed, nonadjustable timing curve. To use this, you would lock out the distributor's advance mechanisms and set the distributor for the desired total timing. The control unit will then retard the initial timing by 20 degrees during cranking, and hold it there until the engine exceeds 1,000 rpm. From there, the control gradually advances the timing and reaches the total mechanical setting (at the distributor) by 3,000 rpm.
MSD also offers a Programmable Timing Computer (PN 8981), which allows some tuning through rotary switches for idle timing, including the points at which the advance curve begins and ends. There is also a Multi-Function Ignition Controller (PN 8979) that is digitally programmed either with a hand-held control module or a laptop computer. This offers broad tunability but is also the most complex option.
How Hot Is Too Hot?My 455 Buick had not been driven for 16 years. I installed a new radiator, clutch fan, 160-degree thermostat, and fan shroud, and I used a 50/50 coolant mix with the original recovery bottle. The engine ran at 205 degrees F on a 95-degree F day. It doesn't seem to boil over, but does this constitute an overheating problem, or am I worrying about nothing?Scott HolmanPittsburg, CA
First off, your 455 is not overheating. Although most of us consider anything over 200 degrees F on the gauge to be too hot, OE manufacturers don't recognize an overheating condition until the coolant hits about 230 degrees F. This is pushing it, and would probably require the presence of electric cooling fans to keep the heat from getting out of hand while idling in traffic. The primary reason carmakers allow operating temperatures to approach these levels seems to be to reap the benefits of the cleaner exhaust emissions that result.
There are, however, a few things to check out. First, you didn't say what type of gauge you're using, or whether this gauge was in use 16 years ago when the car last ran. Obviously, the accuracy of the gauge could be questioned, but the real question is whether or not the 205-degree-F operating temperature is higher than it was the last time the car was on the road. An appreciable change in operating temp might signal a problem, but if the car ran just as hot back then, it's probably nothing to be concerned about.
Here's another area to investigate: The fan clutch. Did you replace the whole assembly, including the actual fan, or just the clutch? If you changed the whole fan, there's a good chance that you didn't use an exact duplicate of the original, so make sure the new one is up to the task. The tips of the fan should fit closely to the opening in the shroud, and the fan blades should be positioned about halfway in. If you only changed the clutch, make sure the new one is working properly. A number of experienced mechanics we've dealt with have warned against cheap aftermarket clutch fans, claiming they often don't function like originals and have excessive slippage. With a big engine like the 455, there's going to be lots of heat and not much rpm at idle, so fan clutch engagement is essential. With the engine running warm, try the old trick of placing a piece of paper in front of the radiator. If it doesn't immediately get sucked flat against the fins, your clutch is probably not doing its job.
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Balance JobI understand that most Chevy 383 stroker kits incorporate external balancing by using a Chevy 400-style damper and flexplate. Even kits that are sold as balanced rotating assemblies frequently use the 400 damper and flexplate. Some kits, however claim to be "neutrally balanced." I have been lead to believe the GM Performance Parts HT383 crate truck motor is internally balanced like a standard 350. If this is true, can you clarify the differences and advise which is better, assuming a new crank is required?Robert l KeelingLouisville, KY
When balancing an engine, the mass of the components hung on the rod journals of the crankshaft must be brought into balance by offsetting weight on the counterweights of the crankshaft. The balance factor takes into account the motion of the components, factoring 100 percent of the reciprocating weight and typically 50 percent of the rotating mass. Unfortunately, the standard GM 400 crankshaft traditionally used in these engines does not have enough counterweight mass to bring the assembly in balance. While the crank's counterweights themselves lack the required mass, GM's clever powertrain engineers simply hung the required weight at each end of the crank with eccentrically balanced dampers and flywheels/flexplates, creating "externally" balanced engines.
The GMPP HT383, similar to the traditional 350/400 production-based strokers, is externally balanced, but the balance factor is different from either a 350 or a 400. GM lists a specific damper, PN 12498008, for the new HT383 application, while at the output end a PN 14088765 flexplate, common to '86-and-later one-piece rear-main-seal small-blocks, is specified. Follow the directions from GM and proper balance will be taken care of.
Production-based custom strokers typically used the eccentrically weighted production 400 dampers and flexplates to achieve balance, often employing way too much eccentric weight. Better too much than not enough, though, since the assembly can be brought into balance more easily by removing weight than by adding it. Expensive custom balancing can be one of the hidden costs of a pieced-together stroker. Some aftermarket stroker cranks have a "split balance," combining an externally balanced 400-style flywheel with a neutrally balanced harmonic damper to achieve overall balance.
While external balance is the norm for 383s, internal balance may be achieved by the use of dense Mallory metal inserted into the crank's counterweights, rather than using the eccentrically weighted, external-balance dampers, flywheels, or flexplates. What's the difference? Externally balanced engines make up the deficiency in counterweight at each end of the crank, which serves the purpose of bringing the total rotating assembly in balance. However, this arrangement is not without compromise. With the eccentric weight hung at the extremities of the crank rather than at the counterweight directly in line with the piston and rod weight they are charged with offsetting, a bending movement is imparted to the crank. With a low-rpm slug like a production 400 small-block, the magnitude of this force is negligible, making an externally balanced assembly an effective approach to bringing the engine into balance. In very-high-rpm applications, however, an internally balanced engine will hold an advantage in minimizing these bending motions, which become more significant as rpm escalates. As a consolation, high-rpm race engines are more likely to hang much lighter components at the crank journal, making internal balance much more viable. On the other hand, in a typical street/strip rpm range, we'd hang our hat with the Detroit engineers and simply externally balance it and not get too hung up about it.
