Jeff Smith: In a way, you're both right. Several decades ago, drag racers were obsessed with windage and thought restricting oil to the top end of the engine would decrease the amount of oil draining back. This would mean with less oil hitting the crank, horsepower would improve. All those experiments proved was it's easy to kill valvesprings by eliminating oil to the top of the engine since the oil keeps springs cool. Too much is not good, but too little is worse.
I had a conversation with Kurt Urban of Urban Performance regarding this point and he told me the GM LS-series engines are particularly susceptible to pumping the pan dry because the crank-driven gerotor oil pump is very efficient. This may be accentuated by the fact that these engines are purposefully designed to only drain oil back in the corners of the engine rather than down over the top of the camshaft like Gen I small-block Chevys and most engines built in the '60s. To combat this situation, we discovered that Comp Cams builds oil-restricting pushrods with half-size 0.050-inch lube holes that reduce the volume of oil to the top of the engine. These Comp pushrods are available in 5/16-inch diameter in various lengths for GM LS-series engines. This lesson apparently evolved out of GM's Corvette road race experience.
Older engines are less likely to experience this situation since they have excellent drain-back capabilities, but these engines can also experience a flooded top end if the engine is equipped with a high-volume oil pump. While there may be a need for a high-volume pump in certain situations, virtually all popular street engines we deal with have no need for high-volume pumps. You may recall we just did an oil pump evaluation ("The Great Oil Pump Test") in the Nov. '09 issue and found that the standard small-block Chevy oil pump came out on top in terms of power and was worth 8 hp peak and almost 5 average horsepower over a high-volume version of the same pump. So those are very good reasons to invest your money somewhere else instead of buying some trick oil pump that really isn't necessary-at least for a small-block Chevy. While this is off the subject somewhat, the 351C and 429/460 Ford engines feed the mains and rods through the lifters, so with these engines, higher pressure and perhaps a higher-volume pump would be of some benefit.
Kurt Urban Performance
Commerce, MI; 248/345-8169
Simi Valley, CA
With the advance mechanism removed, it's easy to see how the two small pins (arrows) move
Advancing the Spark
Joe Pacheco, via CarCraft.com: I seem to have a timing problem I just can't figure out, so I thought I would ask your opinion. About two years ago I bought a new Mallory 85-series street HEI distributor. I have an '82 Trans Am with a 327 small-block and a World Class T5 trans. When I was setting the timing, I noticed only 8 degrees of mechanical advance at 3,600 rpm. The car is currently running 18 degrees base timing, so if you add 8 degrees mechanical, I am only getting 26 degrees of total advance. I did some research on these particular distributors and found the amount of total advance built into these units is 36 degrees. The distributor came with a spring set to adjust the mechanical or centrifugal advance, so I tried the lightest springs in hopes that they would increase the amount of total advance. No luck-the advance just came in sooner. I have pulled the cap and checked the rotor for binding and found nothing. When I turn the rotor by hand, it looked like I have about 1/2 inch of advance, so the weights are not binding. I am stumped. Do you know if these distributors had issues with the advance? Once in a while, the car will run really well with a lot more pull, but most of the time it is not running to its potential, which leads me to believe I am getting the correct advance. Please help.
Jeff Smith: I spoke with the Mallory people and they say the 85-series HEI is the standard replacement version of the HEI. It sounds like the advance mechanism might have a small burr or some obstruction left over from the stamping process that might be preventing it from advancing the timing. We've included a photo of the stock-type HEI advance system for reference. In the photo, we've removed the rotor, the weights and springs, and even the inner tab that fits over the posts so you can see the advance slots. Note that an HEI distributor uses two slots as opposed to a single one used with the older GM point-type distributors. It's possible that there is a small burr or obstruction in this slot or perhaps somewhere on the top of this mechanism where the weights move across. I know you mentioned the rotor seemed to move easily, but that may be with your assistance, and the system may bind when left on its own. This also fits in with your statement that lighter springs only brought the minimum advance in quicker. Plus, you state that every once in a while the car seems to run much better. This could be the result of the weights actually advancing as they should-but something is holding them back from doing that consistently.
It would be worth the effort to remove the distributor and take it to a shop with a distributor machine so you can watch the weights move with the rotor removed. Also check the relationship of the center piece to the two centrifugal weights. This might be the best way to determine exactly how much advance the distributor is delivering. If the advance mechanism indeed binds, then you've discovered your problem and can now fix it. Carefully disassemble the entire advance system and smooth any sharp edges or stamping flash that may exist on the weights, plates, or in the slots. If you can see a sharp edge in one of the advance slots, you will have to drive out the roll pin that positions the distributor gear on the shaft. Once the gear is off, the shaft can be removed, which will allow easier access to the two slots. This will also give you access to the plate underneath, as that might be part of the problem as well. Once everything moves freely, lightly lube the area with Lubriplate and reassemble the distributor.
The distance the pins move inside the slots determines the amount of mechanical advance available with this distributor. That 36 degrees sounds excessive, and if so, you will need to limit the travel so you can add some initial timing. Some HEIs may come with bushings over these pins that limit the amount of available travel. These bushings can be exchanged for smaller (more advance) or larger (less advance) bushings to custom-tailor the total advance. You mentioned you currently have 18 degrees of initial timing. After repairing the distributor, you should shoot for total centrifugal advance of something like 22 to 24 degrees. This will allow you to set the initial at 12 degrees, and with 24 degrees centrifugal, this will create a total of 36 degrees. Remember to always disconnect the vacuum advance hose from the distributor while you're checking the centrifugal and initial timing.
A substantial amount of combustion chamber cooling can be accomplished by directing a stream of oil at the bottom of the piston. Look closely and you can see the oil squirters just above the main bearing cap in this aluminum Ford GT engine block. These 5.4L engines are the ultimate version of the Mod motor. Look for more Mod stuff coming next month.
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Car Craft Mag
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