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Correct Spark Plugs for a 1980 Malibu and More Tech Advice

Techin’ in with Fletch

Dan Flecther Apr 10, 2015
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Sparking a Debate

Please help me with the correct spark plug choice for my engine. I have an ’80 Malibu two door. It has a 0.030-over ’99 Vortec 5.7 with a Pro Comp air-gap intake, 600-cfm Edelbrock carburetor, ACCEL HEI, and shorty headers with 2.5-inch dual exhaust with high-flow mufflers. The timing is set at 12 degrees initial and 36 total at 3,000 rpm. I run it on 87-octane fuel and use a 180-degree thermostat. The car has an M20 four-speed with a 3.73 Posi rearend and weighs 2,850 lbs. Lastly, what kind of horsepower do you think it makes?

Dave Michel
Via email

My research would indicate that your ’99 Vortec would take an ACDelco 41-993 gapped at around 0.060-inch in an original equipment application, but you don’t have an original equipment application, so that’s out the window. The retrofitted intake, ignition, etc., will dictate a different plug selection, and moreover, a different gap value. From what I’ve learned, my recommendation as a starting point would be a Bosch HR8DPX, which is a 4205 stock number. Fellow enthusiasts with similar configurations to yours seem to have had good success with that choice performance wise, and the physical characteristic of that particular plug should work out well regarding header clearances. It appears as though you’ll want to gap that plug at about 0.040-0.050 inch.

As for the horsepower prognostication, it doesn’t sound like you really upgraded much other than the exhaust, and it’s probably debatable whether the carb and intake swap helped or hindered, so I don’t see it being a heck of a lot different that it was from the factory. Certainly not much north of 300, if that, but that’s just my complimentary opinion.


Breakin’ Well

I have a 350 that has fresh rebuild. The engine is mounted on an engine test stand. I am wondering what your recommendations are for break-in of this engine while on the stand. What oil should I use? Any suggestions would be appreciated.

Thank you,
B. Blohm
Via email

I can only defer to my engine builder, Brian Tilburg, and what he uses on all his race engines. Tilburg uses Joe Gibbs Racing break-in oil exclusively. While I’m sure there are a number of other quality products that would do the job, I’d use what he uses, well, ’cause he’s the man! Here is a link to the Joe Gibbs Racing break-in oil choices as seen on Summit: summitracing.com/search/product-line/joe-gibbs-driven-br-break-in-motor-oil. As per the Joe Gibbs Racing literature: “petroleum oil provides the highest levels of zinc and phosphorus for flat-tappet engines. Additive package promotes ring seal and provides maximum protection available for cams and lifters during initial break-in. It requires no additional additives and is good for full power pulls on the dyno, one night of racing or up to 400 miles on the street.”

Additionally, here is a link from the Pace Performance site calling out their break-in procedure recommendations: paceperformance.com/p-3978-engine-start-up-procedure.html. I believe that this seems to be a perfectly appropriate and prudent course of action. Once you’ve broken the engine in properly, I humbly suggest using Peak Motor Oil for the life of the engine.


What the VIN

Fletch, I recently purchased a ’56 Chevy 150 two-door post. The VIN only has 10 digits, and it reads A56104671. The engine and driveline have been swapped out for a 350 crate engine, TH350 transmission, and a Ford 9-inch rearend assembly. What, if anything, can be learned from the VIN about the car’s beginnings?

Thanks for your help,
Jim Robinson

Jim, several things can be learned from your VIN number, but one of them won’t be at which plant your vintage Chevy was assembled. Unfortunately, you only supplied me with nine digits, omitting the plant designation code. Regardless, the fact that it doesn’t start with a “V” is a telling bit of information; your car was born as a six-cylinder unit. The “A” stipulates 1500 (150) series, and the 56 is obviously the year. Next should be a letter denoting assembly plant; for instance, “K” would indicate Kansas City, MO. The next series of numbers is simply the serial number of the vehicle.

While researching your question I came across this article from a few years back that was done by Super Chevythat provides a lot of production data regarding ’55-’57 Chebbies, and you can check it out with the following link: superchevy.com/features/sucs-1041-trifive-production-data-sheets-from-1955-1957/. An interesting little nugget of knowledge I discovered while doing my due diligence; the average new price of a six-cylinder ’56 was $1,665.


Decoding Chevy Part Numbers

Fletch, I’m hoping you can help me. I’ve gone through probably a hundred car magazines looking for information regarding a book that helps you to decode Chevrolet parts. I know I’ve seen one in the past, but I simply cannot find it, or come up with any leads on doing so. I had planned to buy it for a friend for Christmas, but now that it’s too late for that, maybe it can be his birthday present. Any help would be appreciated.

Thank you,
Richard Barber

Richard, while that sounds like a very nice gift, with the vast array of information available online these days, I’m thinking that’s almost got to be an obsolete sort of thing. However, just ’cause you asked, I poked around and found this very informative offering on Amazon: amazon.com/Chevrolet-By-Numbers-1965-69-Drivetrain/dp/0837609569. I’m guessing this is the sort of thing you were looking for?


Don’t Dump That Crank

Hello Fletch, I have a dump truck that I’m going to sell for scrap iron, and it has a 366-cubic-inch engine in it. I’m thinking that this 366-displacement piece has the same stroke as my 427 passenger car engine, and that it is a steel crank instead of a cast crank. If so, should I keep the crank for my 427?

Thanks for your response,
Georgia Mudd

Georgia, you’re correct. The 366-cubic-inch truck engine has the same 3.76-inch stroke as a 427, or for that matter a 396. Additionally, the 366 truck engines did have a forged crank, so it’s definitely a worthy piece in that regard. If you have a lot of free time, and a good bit of initiative, then have at it. With that said, I’m not really too sure I’d be inclined to pull the engine out of a dump truck that was bound for the scrap yard and tear it apart just for the approximately $200 value of the crankshaft. If you’re really cashing it in for the raw metal value, the loss of 500 pounds of material factors in to the equation as well.


Got a restoration question that’s been puzzling you? Send it to: [ m ] Super Chevy, Fletch, 1733 Alton Pkwy, Suite 100, Irvine, CA 92606. [ e ] questions4fletch@yahoo.com

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