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Question And Answer - Ask Anything

If you've got questions, we've got answers.

Jeff Smith: There's nothing un-American with wanting to swap in the later-model V6, other than the mediocre power this combination will deliver. The smaller the engine, the less fuel it will demand, which might lead you to choose the little 229ci engine versus the later 262ci (4.3L) version. I drove an '88 GMC Jimmy Blazer for a while for the same economic reason, but I can tell you these V6 engines are not known for their power or economy. The '88 to '92 4.3L TBI engine was rated at 160 hp and 230 lb-ft of torque--not spectacular numbers, but the engine is limited by the stock throttle-body injection and exhaust manifolds. Edelbrock offers a non-EGR Performer, dual-plane carbureted intake for these engines (PN 2111, $205.95 Summit Racing), which would help on the induction side along with either a Q-jet or a small 600-cfm Holley vacuum-secondary carburetor. I would suggest going with the larger 262ci V6 rather than the smallish 229ci motor simply because the smaller engine was rated at only 110 hp stock when it was new, with an underwhelming 190 lb-ft of torque. When you consider that the Iron Duke four-cylinder was rated at roughly the same horsepower (yes, the torque was only 135 lb-ft), those smaller V6 engines may not really be worth the hassle. Additionally, fuel mileage in my TBI '88 S-15 Jimmy rarely hit more than 18 mpg. The early V6 engines were not as efficient as they should have been, and, frankly, while the 4.3L V6 is an "even-fire" engine with 30-degree offset rod journals, it shakes badly even with spongy engine mounts. Bolt that engine into your Camaro with typical small-block Chevy mounts, and you will notice a distinct vibration that will be difficult to eliminate, especially at idle. One advantage to the 90-degree V6 engines is that they are super plentiful and carry over many small-block engine parts as well as standard small-block-style bellhousings and starters. That will help keep the cost down on your conversion.

If the idea is to improve mileage yet still have a good-performing car, consider a small V8. The base V8 engine for the mid-'90s Caprice was called the L99 and was also referred to as the "baby LT1," because externally it looks just like a typical 350ci LT1 V8 engine. In fact, the L99 used a 3.73-inch bore and a very short 3.00-inch stroke to produce 262 ci (4.3L), but it was rated at 200 hp and 245 lb-ft of torque. This engine was also fitted with an LT1-style intake manifold, which is why it is often mistaken for its 350ci cousin. With its smaller displacement, it could easily be capable of similar (if not superior) mileage to the 4.3L V6. But more important, it would run smoother and with more power. Retaining the EFI would deliver better mileage but might require a significant investment in sensors and a wiring harness that will drive up the overall cost. But no worries, this engine could be easily converted over to a carburetor, which would also eliminate the front-mounted Opti-Spark ignition. Because these LT1-style engines were still Gen I small-blocks, they used a stub drive off the cam's distributor gear to run the oil pump. All you have to do is remove the stub drive, bolt on a typical small-block Chevy intake, and use a standard, small-block distributor--then you are in the game. While the V8 would be heavier by 70 or 80 pounds compared with the V6, it gives you the ability to use inexpensive small-block Chevy parts, including a world of intake manifold, exhaust, and distributor options. The big plus is a little more power (L99 stock torque is 245 lb-ft versus 230 for the 4.3L V6), and you have the potential to easily make more horsepower with camshaft, exhaust, and induction changes. Just remember this is a reverse-flow coolant engine, so the heads are different.

Get Your Bearings

Clayton Steffensen; Cambridge, MN: I have a question about rod and main bearings. It looks like you can get different types of bearings as far as materials and the thickness of the different materials. I have read all about bearings in the magazine, but I have not seen anything about the Clevite H-Series or P-Series rod bearings. I have a 355 small-block Chevy, and I am aiming for 450 to 475 hp with no power-adders. Which bearing is the best choice? I want the engine to last.

Jeff Smith: This is a great question, Clayton, because contrary to what many enthusiasts believe, there are some minor differences between these bearings. The small-block Chevy is a great example to use for this discussion because all these bearings are available for the venerable Mouse motor. However, if you have a nailhead Buick, you might discover there are only stock replacement bearings.

Engine bearings, especially rod bearings, are subjected to some pretty serious loads, so the material they are made from and their shape becomes critical. Clevite has created a design it calls Tri-Armor, which is a series of layers as shown in the illustration on the next page. It starts with a steel backing that creates strength, followed by an alloy layer of copper and lead, and finally by a material called Babbitt. This material was originally formulated back in the early days of the automobile and was named after its inventor. The Babbitt alloy is very soft and made out of a combination of lead, tin, antimony, and arsenic (so don't lick it), which allows the bearing to absorb or embed smaller pieces of metal or dirt. Finally, a thin layer of moly graphite is applied to make the bearing slippery and to reduce friction. This is why it's important to never use any abrasive on a bearing. You may have seen old magazine stories in which the builder would use a Scotch-Brite pad to "polish" a rod bearing. Under no circumstances should you do this on any modern bearing. It's just not a good idea for a whole bunch of reasons.

Clevite says a standard replacement bearing will work fine in a street engine that makes up to 10 to 15 percent more power than stock. Above that level, performance bearings are a better idea. According to Clevite's Bill McKnight, "Clevite's P-Series stock replacement bearing is a good choice for street-driven engines using the stock crankshaft with up to a 25 percent increase in horsepower. The P is the Clevite 77 tri-metal material, utilizing factory geometry, and is a drop-in replacement for the OE bearing. It has a long history of performing very well in a variety of applications from passenger cars to Mack trucks. You'll notice that when you remove the bearings from the box, they have a pretty, silver look to the surface. This is called 'flash tin plating,' and is a couple of millionths [of an inch]thick. It is designed to keep the bearings looking good, even if they sit on the shelf for a year or three. Savvy engine builders take a piece of newspaper and polish off the tin plating as they assemble the motor. If you've ever used the Clevite H bearings, you know they have a mottled brown surface appearance. That's what the Babbitt looks like without the tin plate. You won't get your P bearings to look like that, but polishing the tin plate with the newspaper will get you close enough."

H-Series Clevite bearings are designed for competition engines making 650 hp or more. These bearings are narrower than stock but are designed to be used for applications in which the engine builder is aware that high rpm and high loads will distort the housing bores of either the rods or the mains. These bearings have a medium amount of eccentricity and high crush along with enlarged chamfers to be used with crankshafts with larger radii to create sufficient clearance. Ultraperformance cranks often enlarge the fillet radius (where the rod journal meets the vertical part of the crank known as the cheek). Large-fillet radii improve crankshaft strength but also reduce the journal width. The H bearings are designed narrower to fit this application. These bearings probably aren't necessary for use in a street engine. You will find them in NHRA Competition Eliminator, NASCAR engines, and the like. We spoke with Kenny Duttweiler, and the Clevite H bearings are what he uses in the 347ci twin-turbocharged small-block Chevy that just ran 462 mph out the back door of the measured mile at Bonneville during a September 2011 FIA-sanctioned record attempt. The Speed Demon, driven by George Poteet, unfortunately broke several driveline pieces and wasn't able to set the record with a backup run, but we are talking about a short-deck Dart-block small-block Chevy that is making upwards of 2,200 hp. Kenny says the engine was spinning 9,000 rpm with 40 psi of boost for an excruciatingly long time. George Poteet, Ron Main, Ken Duttweiler, and the rest of the Speed Liner crew are all now Gold Card members in good standing of the Car Craft Haul of Fame. That pass, while not official, is an astonishing accomplishment when you consider that the current piston-engine record is 415.896 mph held by Tom Burkland and set in 2008!

Armed with all this information, which bearing is the best? We'd suggest going with the P bearing, since it offers strong load capacity and good crush, so if the engine detonates it won't beat up the bearings. If you've ever disassembled an engine that has been hammered with detonation, the bearings will literally fall out in your hands, which means the crush is gone. You didn't mention the rpm the engine will see, but assuming we're talking about a 6,000- to perhaps 6,500-rpm engine, the P bearing will be the best. You also didn't mention clearance, but the standard recommendation is 0.001 inch for every inch of journal diameter. For a small-block 350ci Chevy with a 2.10-inch rod journal diameter, that would be a bearing clearance of 0.0021 inch. This will work, but most street engine builders I have questioned prefer the clearance to be closer to 0.0025. If the engine is a big-block with huge 3.5-inch main-journal diameters, something closer to 0.0030 to 0.0035 is a good idea, especially on the thrust bearing to ensure plenty of oil lubes to the side of the bearing. Bearing clearance is a balancing act between load capacity, oil flow, and bearing temperature. Tighter clearance improves the load capacity to a certain point but also reduces oil flow, which in turn drastically increases the temperature. So the compromise is increasing the clearance, increasing the oil flow, and reducing the temperature at the bearing. This is where the 0.001 inch per inch of diameter figure originates. You can move these clearances around to fit your particular application. For a relatively simple engine part, this is a lot of information, and we've only just scratched the surface. If you want to learn more, check out 30 pages of bearing information in the Clevite catalog, which that you can find online at MahleClevite.com/publications/ EB-10-07.pdf.

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