Chevy Tech Q&A - June 2014

Kevin McClelland Apr 9, 2014 0 Comment(s)
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Q I have an '80 Malibu Wagon that I am turning into a "ProSleeper" (you heard it here first). It's a cross between Pro Touring and a sleeper. It's running a Hotchkis TVS system, Wilwood replacement front calipers, and a ZZ383 crate engine with a 350 Turbo and 2,000-stall. I have added a 650 mechanical secondary double-pumper carb from a previous project. The jets are 68 and 72. I'm using a Holley 12-834 mechanical pump, rated at 80 gph. My objective is great throttle response for street driving and occasional drag racing (for test and tune). Am I leaving power on the table with a "little" 650-cfm? Back when I bought it 10 years ago, the 650 seemed to be very popular and in keeping with the "smaller is better" concept so widely promoted. I am also running an HEI, which I have locked out the mechanical advance to 36 degrees and ditched the vacuum advance, along with a spring weight swap.

Also related to the above is my rearend. It has a stock 7.5-inch posi with 3.08 gears. I'm going to try it as is until budget allows an upgrade. Besides, I'm real curious about the top-end capability and fuel economy with this "highway" gearing. The car weighs in at around 3,200 pounds, so I'm hoping I can keep decent acceleration and highway ability with this gearing. But if I have to, I'll bump it up to 3.42-ish. People tell me this rearend will grenade very quickly. I'm only running a 245 street tire, so traction will be limited. Is it worth investing any money into an aftermarket posi and axles? (Still way cheaper and lighter than a 9-inch swap.) Will the 7-5/8-inch ring-and-pinion fit the 7.5-inch (from a Monte Carlo SS)? What's the breakaway torque rating on this unit before service? Thanks!

Tom Silver
NL Canada

A ProSleeper, is it new? Surely someone has uttered these words at one of the Hot Rod Power Tours. Now, since you're from Canada, it's the first time in the great North! We like it! Especially since you've converted your wagon into one.

The 650-cfm carburetor is plenty of air for your ZZ383. If anything, you're giving up a few ponies at red line. All the rest of the time driving your package you're building the best torque curve to move your wagon. Locking out your advance in your distributor will give you great throttle response and part-throttle snap. With only 2,000 rpm of stall speed you'll be able to put too much load on the engine at slower speeds (2,000-2,800 rpm) with the advance locked at 36 degrees. Be careful and pay close attention to spark knock and detonation. Also, having the spark locked at 36 degrees isn't going to give you the best fuel economy. At part-throttle cruise, driving down the freeway your combination will probably be around 44 degrees total timing. This is where the vacuum advance comes into play to increase fuel economy. You may want to rethink your advance package and reinstall your mechanical advance weights and springs. Limit the mechanical advance to around 8-10 degrees total in the distributor, which will be 16-20 degrees at the crank. This advance should be all in by the 3,000-rpm range, and you will want to set the initial spark timing at 14-18 degrees, based on how much advance you set up your distributor to have. This will put you in the 34-degree total range, and then throw around 10 degrees of vacuum advance. This will give you a well-rounded advance curve and the best fuel economy you're going to achieve with the ZZ383.

As for the 7.5-inch diff, yes, the 7-5/8-inch gearset will fit into that housing. We agree with your buddies' opinion of the 7.5-inch diff. You can spend a bunch of cash hopping it up, and it would probably live, but it's still a 7.5! We would ditch that rearend and look for an 8.5-inch unit out of a Buick GN Regal or a Hurst Olds. The SS Monte Carlos still have the 7.5-inch diff. Don't know why GM cheaped out on the SS Monte. You can still find the 8.5-inch diffs out in wrecking yards. This is a direct bolt-in into your '80 Malibu wagon. You can find a complete selection of gears and posi-tractions to choose from. The production 8.5-inch would live behind your ZZ383 without a problem. We've got a Buick GN rearend in our Malibu wagon race car. It's filled with Strange gears, axles and spool, ARP studs on the caps, and an Unlimited aluminum rear cover with load pins and back brace. This rearend has given us six years of service without a whimper. We're even throwing 600-plus horses at it and it's gone as quick as a 1.41 60-foot. The 8.5-inch would be a much cheaper way to go than the 9-inch route. Also, it's all GM and it's a bolt-in.

Have fun with your ProSleeper! To each their own, and we love wagons. They make very cool performance cars, and you always have a bedroom!

New Idea for Clearance

Q I read some articles in your magazine about the SBC 434. I have a new Dart SHP block and a new Callies CompStar 4-inch-stroke crank. I have read many articles, and each one seems to use a different rod and has a different view on how they fit. I don't want to have to grind a bunch on the block. The Callies Ultra XD rods are supposed to be the best fitting, but they are $1,500. Do you have any real-world ideas on which 6-inch-stroker-friendly rod to use? Thanks!

Dave Snyder
Via email

A Thanks for the question. It gave us the opportunity to look into these Ultra XD connecting rods, and the really trick application of canting the rod parting line. Callies has a patent pending for this technology. Let's look at how it picked up clearance between the block and camshaft in stroker applications.

Stuffing inches of stroke into any engine has been a popular performance option since the internal combustion engine was invented. When the GM engine designers laid out the crankcase, they never imaged we'd be stuffing 4 inches of stroke into a Gen I small-block. The placement of the pan rails, camshaft, and cylinder walls assumed a max stroke limit. When the Gen I small-block was conceived, it started as a 3-inch stroke engine, then pushed to 3.25 inches for the 327, and then to 3.48 inches for the 350. We believe this is where the original designers had given the engine its limits. Then along came the 400s with their 3.75-inch stroke. GM had to go back to the drawing board and shorten the connecting rod to 5.565 inches, shorten the rod bolts to clear the camshaft, and to keep the wristpin in a production-happy location. Also, they needed to increase the main journal diameters from 2.45 to 2.65 inches to ensure production integrity of the crankshaft. When you extend the stroke out to 3.75 inches, you lose pin overlap between the rod and main journal. This is where the two journals share common material and you're not relying on the counterweight material to transfer all the forces down the crankshaft to the flange. All of these changes were put in place to stroke an engine properly.

As we have written, small-blocks have ballooned in displacement to unbelievable levels. The performance of these engines is incredible with the selection of cylinder heads on the market. However, with any stretch of design there are compromises. Dart has accommodated many of these compromises in its SHP small-block castings. This block has been relieved for cylinder wall and pan rail clearance to fit a 3.75-inch stroke without any clearance issues. Even with this block you still have to be mindful of connecting rod clearance to camshaft. Going another 1/4 inch further on stroke will require grinding of the pan rail and cylinder walls. To minimize this—and to gain the needed camshaft clearance—the Callies solution is right on point, with the slightly rotated connecting rod parting line to rotate the bolt area away from the block and camshaft side of the connecting rod. This not only alleviates camshaft clearance issues, but it also gives you more clearance between the block.

Another major benefit of the Callies XD Ultra design is that you can use a standard base circle camshaft. When you reduce the base circle of the camshaft to gain connecting rod clearance, you lose rigidity of the camshaft. With the camshaft lobe designs, and the spring pressures required to control the valvetrain at engine speeds of today, the reduced base circle camshaft turns into a wet noodle in operation. No one ever talks about the performance loss of camshaft flexes, which creates cam timing variations and lift losses. Now, this is why we use raised camshaft locations in stroker applications, and large camshaft journals to increase the base circle in all-out racing applications.

In our opinion, you'll be dollars ahead using the Callies-innovated design. Sure, cost a few bucks, but the benefits out weigh the cost. There's the XD Ultra design in 5.7-6.25 inches for small-block Chevy applications. The two rods that you should be looking at are the 5.85-inch (PN U14130) and the 6.0-inch (PN U14135). Give Callies a call for more information at 419.435.2711.

Finally, you mentioned using 6.0-inch rods in your application. This will leave you with a compression height of 1.00 inch for your wristpin placement in the piston. You didn't mention what power level you plan on for this build, but that's rather tight. If we were building this package we'd go with the 5.85-inch rod to give you a 1.150-inch compression height. Your piston and ring manufacturer will love you, and with a 4-inch stroke that rod ratio is so blown up that the additional 0.150 inch of rod length isn't going to be the difference. The 6.0-inch rod combo gives you a rod stroke ratio of 1.5, and the 5.85-inch rod comes in at 1.46. As stated above, stroking engines is all about compromise. Picking the right ones is the difference between a good packaging, and well you know. Good luck.



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