Elkview, WV: Hey, guys. I'm a longtime reader who loves the magazine. If there is no replacement for displacement, why haven't I seen anything in the magazine about the Chevy 8.1L engine? Is this an engine that can be built? Are parts available? What is the configuration? Also, an unrelated question: What's the deal with the camshaft that changes the firing order in the small block Chevy? I have heard very little about this type of cam and wanted to ask someone with a large information and experience base.
Jeff Smith: The main reason you have not seen very much on the GM 8.1L seventh-gen Vortec engine is-how do we say this without malice?-because, at best, this engine is a bastardized branch of the big-block family tree. It looks like a Rat, sounds like a Rat, but weighs more than a Rat and certainly doesn't make power like a real Rat, and it really isn't what we think of as a big-block Chevy. Perhaps its only redeeming value is its displacement. At 8.1 liters, the engine sports a 4.25-inch bore and a 4.37-inch stroke for 496 ci, but that's about where any similarity with a Rat motor ends. The firing order and head-bolt pattern have changed, all threads are now metric, the heads sport a tiny 2.19-inch intake valve along with a nonadjustable net- valve-lash system, and the EFI induction system sucks. Stock horsepower in trucks was dismal at 225 hp. This engine was widely used in big trucks, like the GM Kodiak, and in marine applications. We've heard the engine was discontinued in December 2009.
With all that working against it, why would Dart suddenly introduce two brand-new performance iron-blocks, rectangle-port heads, and even a carbureted intake manifold for this miserable beast? The story is that the natural gas and oil fields in Texas prefer max- displacement, big-block Chevy engines that operate at wide-open throttle (WOT) at 1,800 rpm to twist pumps. The bigger the engine, the more power it makes, so the 8.1L motors are popular for their torque. When GM dumped the engine, Dart saw an opportunity and jumped in with two new castings. The first block could be used on the street, with a max bore size of 4.350 inches. Even with a mild 4.250-inch stroke, that's 505 ci. The second is intended for monster-inch applications, with siamesed bores that can accept up to a 4.600-inch bore and up to a 4.750-inch stroke. You big-block junkies probably already know that computes to 632 cubes! Dart's Jack McInnes tells me Dart built a 638ci oil-field version that makes 800 lb-ft at 1,800 rpm (!) and peaks with numbers of 566 hp at an off-idle 3,900 rpm with 854 lb-ft of torque at 2,800 rpm using the dual-plane intake. For a gasoline engine, those are some bad-boy grunt numbers. Just for fun, I plugged those numbers into the Quarter Pro dragstrip simulation program. With a 3,600-pound car, shifting at 5,000 rpm with a Powerglide and a 3.55:1 rear gear, the engine would run 10.73 at 127 mph going through the lights at barely 5,000 rpm with a 32-inch-tall tire. Dart's iron, rec-port, 8.1L castings come with a 306cc intake port and 108cc chambers, and they are machined for 2.19/1.88-inch valves. The heads are only sold as bare castings, so you have to assemble them. McInnes also mentioned that the stock crank, rods, and especially the cast pistons are not up to contemporary performance standards. If you want to build an rpm motor, Dart will soon be offering a stroker crank and rod combination along with a piston recommendation. The heads will run $688.41 each for bare castings, and the intake manifold lists for $575.66 on Dart's website. This means you will easily have $2,800 invested in complete heads, an intake, and some kind of performance roller cam and valvetrain. This would still be a cast piston and crank engine, which sounds like it won't respond well to lots of rpm. Plus, the stock cam does not have a distributor-drive gear, as the original engine is EFI/DIS, but cam companies like Comp make performance hydraulic roller cams for this engine and could probably whip up a cam with a distributor drive if you asked nicely. But taking in the big picture, it appears it would still be less expensive to build an old-school big-block with a stroker crank if you had your heart set on 496 cubes.
As to your question about the different-firing-order small-block Chevy camshafts, according to retired GM Engineer Don Webb, this has to do with crankshaft torsional vibration. Webb was one of the development engineers on the original LS engine design, and here is what he said about changing the firing order from the small-block's original 1-8-4-3-6-5-7-2 to its current 1-8-7-2-6-5-4-3.
"It all has to do with minimizing crankshaft torsionals. There are 16 possible firing orders with right bank forward or left bank forward (eight each way)....Actually, right bank forward is slightly better than left bank forward, but marketing asked us to maintain the essence of the old small-block (SB) where we could....Because it would be a radical departure from the SB design to switch banks, we decided to use the best firing order with left bank forward, which is almost as good....At the time the SB was developed in the early '50s, they were aware of the crankshaft torsionals but were only able to do rudimentary calculations to determine the best firing order....We, on the other hand, were able to simulate all 16 and let the computers...resolve the issue...while we slept....If memory serves, the old SB firing order was third best with left bank forward.
"Why was minimizing the torsionals important on the LS engine?...Because the spark/injector timing is derived from the reluctor wheel, it is located as close as possible to the neutral spot on the crankshaft, which exhibits no torsionals whatsoever....This happens to be just ahead of the centerline of...the No. 7 cylinder....All torsionals forward of that point...go in one direction, while to the rear of it, they are in opposition. This is one reason the Opti-Spark distributor in the Gen II SB (LT1) is not as accurate as hoped, because the crankshaft and the cam are constantly feeding torsionals into the reluctor, causing it to dance around and vary the spark timing by several degrees....In spite of the torsionals, it was...still a major step forward from the old post-style distributors....The crank-mounted reluctor wheel design gives you several unique advantages:... 1) almost perfect timing,...2) almost instant starting in any weather, 3) a lower idle speed while still running smoothly,...4)...increased efficiency,...and 5)...decreased noise.
"Many of the engineering changes we made away from the SB design were undetectable in and of themselves but were directionally correct with sound engineering analysis behind every decision, and when taken as a system, the Gen III was the result, a decidedly better engine....NVH (noise, vibration, and harshness) were the deciding factors in this instance, and the drag-racing crowd would be the wrong folks to chase the question....NVH are among the least of their concerns."
Thanks to Don for taking the time to illustrate some of the finer points of engine design.
Dart Machinery; Troy, MI; 248/362-1188; DartHeads.com
A Question of Efficiency
Mexico, ME: I'm 69 years young...and I've built cars since I was 15....I bought an LQ 9 6.0 377ci with trans and everything to go with it to put in my '56 Chevy two-door Delray. Now I'm told it will only get 13/16 mpg. If this is true, what can I do to get 20-plus mpg like the 5.3 gets, or should I just keep the 350 that's in it now? I really wanted to go to EFI because not many people in Maine dare to do it. They are all old-school types. I love Car Craft. I'm sure you hear that all the time, but I do. Thanks.
Jeff Smith: There are some basic physics that are revealed by fuel mileage numbers. In-town mileage is really based on the size of the vehicle and the displacement of the engine. Heavy cars or trucks (even with a small engine) require quite a bit of power to accelerate up to even a slow speed of 25 or 30 mph. Do that a few hundred times in traffic and you'll use a lot of fuel. On the highway, the vehicle accelerates up to speed once (unless you live in Los Angeles, where the traffic sucks) and then uses a minimum of power (roughly 20 hp) to maintain that speed. Weight isn't as much of an issue once the vehicle is up to speed, but aerodynamic load plays a big part. Let's assume your LQ9 6.0L engine was originally used in a Chevy 3500-series, two-wheel-drive, extra-cab pickup. These trucks can come with a 4.10:1 rear gear and giant tires. Curb weight (found on Motor Trend's website) looks like somewhere in the neighborhood of 5,200 pounds. Combine that tonnage with the massive frontal area of a big Chevy truck punching a mountain-sized hole through the air at 60 or 70 mph and it's no wonder the fuel mileage numbers are enough to put you on your gas station's Christmas card list. Now let's look at your '56 Chevy. It probably weighs around 3,200 pounds with a frontal area that might be 25 percent smaller than a 3500- series truck. You are using the same electronic overdrive trans, but more than likely your rear gear ratio is quite a bit taller, say 3.50:1. With an overdrive ratio of 0.70, the rear axle ratio is effectively changed from a 3.50:1 to 2.45:1 in overdrive. Let's assume a set of 27-inch-tall tires on the back of your '56. That means in Overdrive with the lockup converter engaged, your engine speed at 70 mph is around 2,100 rpm. That's pretty low, which helps the fuel mileage. On the freeway, with your car spinning around 2,200 rpm in Overdrive, it's not unrealistic to expect the engine to deliver 20 mpg or better. Since your '56 doesn't weigh nearly as much as a 3500-series Chevy pickup, the in-town mileage should also be better, perhaps between 15 and 17 mpg. These are not pie-in-the-sky 50-mpg numbers the Obama administration would like all pedestrian, drone Americans to achieve, but they are not bad numbers. Of course, if you want better mileage, the 5.3L LS engine would be a better choice, but just know it won't deliver nearly as much torque. A big component of fuel mileage depends on how you drive. At 69 years young, my guess is you're not smoking the tires at every intersection, so your mileage will probably be better than your lead-footed, 16-year-old grandson. Not too surprisingly-as this is Car Craft, not Green Scene magazine-my suggestion would be to stuff that LQ9 into your '56 and show those kids how it's done. You won't get any better mileage out of a typical small-block Chevy because the LS engines are far better. Go with the 6.0L LS, and you'll be glad you did.
Aloha, OR: We just completed installation and debugging of a hydroboost into a '62 Toyota Land Cruiser. Your story in Junkyard Builder (May '11) was very similar to ones we'd read previously but your suggestions led to some problems that have now been resolved. Your readers might appreciate our experience.
We bought a hydroboost kit from a California company that said the kit consisted of parts intended for a Chevy 4WD pickup. We had a Saginaw power steering box and a GM pump (canned hamûshaped) from a '68 K10 Chevy that was rebuilt locally. Our initial installation was as you described, but it resulted in a gradual self-application of the brakes after only a few miles of driving.
Further research on the Internet revealed our experience was not that unusual. The fixes we applied consisted of: 1) routing the drain line from the hydroboost directly into the pump reservoir, 2) installing a small power steering cooler after the power steering box but before the filter, and returning to the power steering pump return fitting, and finally 3) cutting 1/8 inch off the plunger rod connecting the hydroboost to the brake booster. This last fix came about as a result of loosening the bolts holding the hydroboost to the master immediately after experiencing the self-application of the brakes and seeing the master pushed away from the hydroboost by the plunger. Hope this might help those who try to implement the suggestions in your article.
Jeff Smith: Thanks for your installation details, Scott. We've run into self-application of brake in the past and discovered, as you did, that there must be some clearance between the pushrod and the master cylinder piston to compensate for temperature changes, as everything heats up and expands, especially if the master cylinder is aluminum.
Opening and closing points can be confusing, which is why this illustration from Comp Cams
Turbo Cam Timing Trip-Up
Wabasha, MN: I enjoyed the camshaft and turbo's article ("The Truth About Camshafts," June '11). On page 26, Urban claims that with opening the exhaust valve sooner with either a tighter LSA or long exhaust duration, the engine generally responds better....I get the longer exhaust duration, but I always thought (with all other things being equal) a wider LSA would open the exhaust earlier....Maybe I have been reading my degree wheel incorrectly all these years!...
Jeff Smith: Occasionally I get caught moving too quickly. Perhaps I went into valve float when this error made its way into the magazine. Yes, Greg, you are correct that when the lobe-separation angle (LSA) is widened, it opens and closes the exhaust valve earlier. Just to add to the clarification, it works the opposite for the intake lobe, where widening the LSA means delaying the opening and closing of the intake valve.
: I have a 350ci Chevy with a short water pump in a '60 Studebaker Lark convertible. I am currently using an engine-driven fan that just fits behind the radiator....I cannot move the radiator forward because the A/C condenser just fits behind the grille. I want to upgrade to an LS-series engine using the stock EFI. I am not concerned about the electronics, as I have installed EFI engines into Studebakers in the past. However, the engine and cooling fan (electric or engine-driven) must fit into the same space as the current engine. Are the LS engines with accessory drives longer than engines with short water pumps and V-belt accessory drives like the alternator, power steering, and A/C?... Thanks for your help. I love the mag, especially the tech articles.
This illustration shows the basic dimensions of the LS engine. According to Will Handzel’s
Jeff Smith: According to a set of illustrations we got from our friends at Kwik Performance, it appears that all the different LS engine configurations are slightly shorter than a typical small-block Chevy (SBC) with a short water pump. The main source of possible confusion will depend on which LS engine you choose. Our previous research into the LS engine accessory drives revealed that there are three different depths, depending on the application. The truck engines use a balancer that extends farther forward than the early LS F-car balancer, while the LS1/LS6 Corvette application is the shallowest. Each of these drives requires its own specific components, like balancers, water pumps, pulleys, power steering, and A/C components. Our pal Wayne Powell at Kwik Performance also informed us that the '10/'11 Camaro accessory drive has changed and now has basically the same depth (harmonic balancer spacing) as the truck systems.
In terms of overall length, the LS engine block from the bellhousing flange to the front of the block that mounts the water pump is about 1 inch shorter than the same points on the Gen I SBC. If the depth of the accessory drive is the primary concern, you should go with the Corvette style. Finding used parts will be difficult because they are in such demand. The brackets and power steering pump are actually quite affordable, but the alternator is specific to the Corvette system with its unique mounting lug spacing and is a big-dollar hit. The best price we've found on a new one is through Auto Zone at just under $300. As an alternative, the LS engines used in the '98 to '02 Camaros employed an accessory drive package that is only about 1 inch deeper at the harmonic balancer but configures the alternator down low on the driver side underneath the power steering pump. Sometimes this can place the alternator either near the crossmember or possibly by the steering box on a front-steer application. We've also learned that the truck and early LS Camaro/Firebird alternators will interchange, making them far less expensive and easier to find than the Corvette stuff.
Kwik Performance sells a conversion kit for $287.00 that converts a truck accessory drive
Comparing the LS engine dimensions with the SBC, the LS-block is about an inch shorter. All the LS water pumps end up being roughly the same length, excluding the small protrusion on the end of the pulley. That puts the overall length of the LS engine at 25-3/4 inches. A short-water-pump small-block Chevy ends up with a dimension of 27-3/8 inches from the bellhousing flange to the flat portion of the water pump pulley flange. It would appear from these dimensions that you have gained approximately 1-5/8 inches, which means the engine should fit in your '56 engine compartment with no problem. We even looked at the distance from the bellhousing flange to the end of the crank pulley, and the Corvette LS engine measures 24-1/2 inches, while the SBC appears to be around 25-3/4 inches or roughly 1-1/4 inches longer.
Another point worth mentioning is that the small-block Chevy includes a shelf or protrusion that extends beyond the back of the heads and creates the bellhousing flange. The LS eliminated this extension and places the crank flange flush with bellhousing flange. This effectively shortens the LS engine but places the cylinder heads farther rearward in the engine compartment. The limiting factor then becomes the clearance between the passenger-side cylinder head and the firewall.
There are some truck engines (yours may be one) that use an engine-driven fan on the water pump. These fans are rather deep and may not allow the engine to fit within the confines of your engine compartment. For something much more compact, go with an electric fan. A large, single, electric fan can be around 4.5 to 5 inches in depth. But what often happens is interference between the deepest part of the electric fan and the water pump. By using two smaller fans, you can stagger their positions and gain as much as 2 inches, as the fan and shroud assembly can be as much as 2-1/2 inches shallower.
Kwik Performance; Springfield, MO; 417/955-1467; KwikPerf.com
Germany: I'm a young guy from Germany with a big love for old cars, like my '65 4-4-2 Olds convertible and my '69 Ford Taunus 20M. I'm sorry about my English. It's terrible, I know. I need two weeks to translate your magazine into German-that's what I call addiction.
I'm rebuilding a Ford...2.8L, 171ci V6 engine, and I have a problem with the measurements from the installed rod bearings. I have measured the runout in all six, but I don't know if I'm doing it properly. The rods were resized after I installed a new set of ARP bolts, and I use Clevite 77 bearings (CLE-CB723P10). Bolts are stretched to the ARP specs and the rods are not overheated.
I read the following on the instruction site from Clevite/Mahle: "When measuring a bearing ID or wall thickness, avoid measuring at the parting line. To determine bearing wall eccentricity or assembled bearing ID ovality, measure at a point at least 3/8 inch away from the parting line." I measured all six assembled rods at the "incorrect" assembled bearing ID,...3/4 inch (or more) away from the parting line, not 3/8 inch away. In another words, I measured rod No. 2 (max example) approximately 0.00275 inch out of tolerance at 3/4 inch (or more) away from the parting line. Can it be possible? UFF (?). I need really your help! Best regards from Germany.
Always measure bearing clearance in the true vertical as indicated with this dial bore gau
Jeff Smith: Wow, Denis, it takes you two weeks to translate each issue of Car Craft into German? That's dedication. Don't worry about your English-it's far better than my German, that's for sure. I think we can help you. The Clevite manual talks about measuring for ovality-or looking at the additional clearance provided by the taper built into the bearings near the parting line. They are certainly correct in stating that all bearing inserts increase the clearance as the bearing approaches the parting line of the bearing. This is done because all bearings are designed to be "crushed" into place when the two bearing halves meet at the parting line. This crush tends to push the bearing insert inward, toward the crankshaft journal. To prevent this, the bearings are tapered to increase the clearance and prevent journal contact at this junction. That is why you should always measure bearing clearance in the pure vertical position. That means measuring the inside diameter of the bearing perpendicular (90 degrees) to the parting line. This is where you will find the smallest inside diameter of the bearing. This is true for both main and connecting rod bearings. As a simple example, if the crankshaft main journal on No. 1 measures 2.9975 inches and the inside diameter of the No. 1 housing bore with the bearing in place is 3.000, the actual bearing clearance will be 0.0025 inch. If you attempt to measure the bearing clearance anywhere except absolute vertical, the clearance will be much greater.
It's also important to note that variances in bearing clearance are almost always caused by either changes in journal diameter or in the housing bore diameter, such as the inside diameter of the connecting rod without the bearing. If the inside housing diameter is slightly tight and the crankshaft journal diameter ends up slightly larger, it can drastically affect the overall bearing clearance. In my experience, the actual bearing thickness changes very little between inserts. One trick that sometimes works is that after measuring all six or eight connecting rod clearances, if you find a couple of tight clearances and perhaps two or three loose ones, try swapping the bearing inserts between the tight and loose rods. Often the crush exerted on the bearings can affect clearance and just swapping bearings can result in clearances that are more even throughout all the connecting rods.
As for bearing clearances, I would try to put your clearances exactly in the middle of the published factory range. The published Clevite rod-bearing clearances for your engine are a crazy range of 0.0004 inch all the way up to 0.003 inch. That puts the ideal bearing clearance at 0.0020 inch. The main journal clearance range is a similar 0.0006 to 0.0032 for the 2.43-inch main journal crankshaft. Here's where we'd suggest a clearance of 0.0022 to 0.0025. A rough rule of thumb is 0.001 inch for every 1.0 inch of journal diameter. So for a 3.00-inch Olds big-block main journal diameter, you would shoot for 0.003 inch of bearing clearance. Tighter clearances will support higher loads but will cost in terms of reduced oil volume and therefore higher localized oil temperature. Wider clearances are the opposite in terms of reduced load capacity, but they will result in higher oil flow and lower oil temperatures.
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