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Changing Firing Order in a Small Block Chevy?

The questions you want answers to, and the people you know will be able to give them.

Turbo Cam Timing Trip-Up

Greg Williams; 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.

Dimensionally Correct

Larry Walter; via CarCraft.com: 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.

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.

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.

More Info

Kwik Performance; Springfield, MO; 417/955-1467; KwikPerf.com

Bearing Up

Denis Garcia; 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.

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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    1 comments
    matt496
    matt496

    I have a 2500 with this 8.1 engine and I have rebuilt it with upgrades. The truck runs the quarter mile at 14.71 at 93 miles per hour and being a 6280 pound gas truck its not that bad. I also truck pull it and have took 1place 3 times and more second and third places I can remember. I also have a trailer I hull a john deere 2010 that has a high lift on, the truck trailer and tractor on weighs 15000lbs living in southwestern pa with all the hills it does just as well as a mild powerstroke or cummins just not on fuel.  This engine has a lot more in common with the old engines than this article leads you 2 believe.  The cam does have a distributor drive gear there is a dummy gear there witch runs the oil pump witch is still in the same place. Still has the same rod bearings. Same exhaust manifold flange and bolt pattern, not 2 mention it still has the old motor mount holes taped into the block and a few other things I am surely forgetting.  My truck on a rear wheel dyno made 300 at the rear wheels and that's going trough a Allison trans, that's with a cam swap tuning and true dual exhaust witch still has the factory cats. The engine is the same physical size as the old 427 truck blocks so it is big but you can get easy power out of it this article is misleading about the engine.

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