GM Pistons, Vintage Air System & 1979 Chevy Malibu - Performance Q&A

Kevin McClelland Dec 1, 2008 0 Comment(s)

Messing With My Combination
I've had the pleasure of racing with the same engine and combination for 12 years now. This engine was built back in the summer of 1996 to run in my previous '57 Chevy Super Street car. Today the engine lives in my Don Davis '27 Street Roadster. Now, more than a thousand runs later, NHRA is messing with my combination.

Last weekend Daniel and I were up at Sacramento Raceway for an NHRA National Open. At the beginning of this season, NHRA mandated the use of Lower Containment Devices to prevent oil leakage on the track in case of engine failure. This affected all classes from Super Gas up. I'm all for safety; however, putting this diaper on the bottom of my engine created a whole new set of challenges.

The ambient temperature was well over 100 degrees all three days, and I ended up driving the car around the pits to warm up the engine and head over to our tech inspection. Returning to the pits to prep for our first time run, I noticed the engine wouldn't cool down like normal. My first thought was that the water pump or the electric fan was having a problem, as the Davis car does have a very small (but highly efficient) cooling system. Everything checked out OK, so I was off for our first run. As I drove up to the staging lanes, the motor was definitely running hotter than usual. After my first time run, heading back into the pits, I went through my normal routine, checking the chassis and engine and documenting the weather conditions. Interestingly, when I was going to the back of the car to connect the battery charger, I noticed tremendous heat coming up from around the diaper! After heating 10 quarts of oil up to well over 200 degrees, there is nowhere for the heat to go except up into the water jackets of the block. This big, black, heavy canvas diaper featuring an absorbent pad on the bottom made a perfect Thermos; it didn't allow the oil to cool off between runs. You have to take into consideration that this engine was designed to run on 92-octane pump unleaded; back in early 2000, California lowered its super unleaded to 91 octane. This was my first concern. Now I have superheated oil in the oil pan not doing its job of cooling the pistons.

Daniel and I ended up having a great weekend, winning several rounds. It was a lot of work, but fortunately I was able to keep the heat under control. It just goes to show you, though, that many things can affect performance. In this instance, a safety measure produced another issue, and I may still have to make adjustments to either fuel or spark to keep the engine out of detonation. Amazing, isn't it? Also, I never thought I'd be wearing a diaper at 50 years old!

Free Slugs
Q I was wondering if you could help with an identification problem. I am attending Universal Technical Institute in Exton, Pennsylvania. We found a box full of pistons, and nobody knows what they are or where they came from. They are for a 4.00-inch bore and have coated skirts and smaller rings (thinner). On the inside, under the pin, they have "GM" cast into them with the numbers 308 and 10172839. Any info you could give would be great. The sooner the better because we want to use them in our engine build to see if we can make more power than the students using stock replacements, and we need time to have them pressed onto the rods to assemble our engine. Thanks in advance.
Victor J. Miller
Exton, PA

A Now that is a real find! A box of new pistons lying around just waiting for a new home. Sometimes it's tough to find a clean 4.00-inch bore to slap new standard pistons into. They always run a little better with an extra bit of clearance. I think we've got your pistons identified.




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