I have a ’69 Coronet wagon. The odometer reads 67,000 miles, and the car was regularly serviced and garaged. I couldn’t leave well enough alone and began modifying the wagon shortly after I got it to make it into a cool street cruiser. First, I lowered the suspension all around, and then I added a nice vintage set of mag wheels and 235 60R-15 front tires to the front, and 275 60R-15 tires to the rear. Next, a shift kit went into the factory 904 transmission, and finally, my attention turned to the engine to get more power.
The car originally came with a 318 two-barrel, and I found a Holley double pumper 750 and an old Edelbrock Torker 340 intake. Since I was working on a tight budget, and the price on these parts was a deal, I soon had them bolted to the 318. Next, I added electronic ignition that I pieced together from OEM parts, and a new control box. This seemed to help, but the single exhaust was restrictive, so I added Hedman Hedders, and a 2½-inch exhaust system with Flowmaster mufflers. This really woke the 318 up and I was pretty happy with the improvement, but I wanted some more cam to give the engine a lope at idle. I went with an MP “Hemi Grind” cam that a buddy ran for a while in his Duster, until he switched to a solid, and added a set of 360 heads.
The little 318 now had some serious attitude, but I found the low-end to be soft. It wouldn’t even burn the tires. The car had an 8¾ rear, so I swapped the gears to 3.91’s and added a 3,000 rpm stall converter. Now it could smoke the tires, but the car just sucks down the fuel. I can’t believe that a 318 wouldn’t do better, even with the performance modifications. Cruising around, the wagon gets me an average of just around 8 mpg, which seems to be worse than a big-block. Before I messed with it the car would at least get me in the mid teens in mileage. I love the wagon, but with gas prices where they are, I can hardly afford to drive it anymore. Is it a lost cause, or can I improve the economy of the combo?
Frank, that big wagon and that combo is not going to be the best setup for fuel efficiency. I have to say that the parts selection you went with doesn’t help matters, from the double pumper carb to the single plane intake, to the deep gears and converter, and then the long duration MP cam. You pretty much have put together the anti-mileage combination. The fact that the stock 318 was fairly low compression and the big-chamber 360 heads dropped the ratio by about another full point is just the icing on the cake. If you want to keep the 318, you really have two choices right now, and that is to either try to make the best of the parts you have, or start over with a parts list that will result in a more efficient engine.
Looking at the first option, you really have to work on the tune. Those old double pumpers were notoriously heavy on the fuel use, and it will take more than a simple jet change to really dial it in. You are best off with a wide-band lambda gauge, and a good Holley tuning book. You can also expect a serious effort to dial it in. The ignition will also need work, particularly with a low-compression engine and a stock distributor. You are going to need way more advance at initial, and a much shorter mechanical advance, maybe as much as 18-28 degrees initial and 36 degrees total. You are also going to have to dial in the vacuum advance. Finally, the cam would benefit from about 6-degrees of advance, putting it in at 102-degrees intake centerline. I am confident that the tuning changes alone can net a worthwhile mileage increase.
The other option is a full rework of the combo. Since you mentioned that you were working on a tight budget, I’m not sure of how practical this would be, but I would start with a set of small chamber heads to get the compression up. An Enginequest iron head would give you a tight chamber, and flow better than the stock 360 heads. Next, a two-plane intake will be better than that ancient Torker. The standard Performer will get the job done, but even a RPM or AirGap intake is better than the single-plane. The Holley double pumper will be hard to work with for economy. As a replacement, I have found the Edelbrock AVS to be very good in efficiency when tuned. Then, we have the MP cam. A stick with 20-degrees less duration would definitely help the fuel consumption situation, but you might lose that boulevard lope. Finally, you can attack that deep gearing a few different ways to cut the rpm. You can do this with an overdrive swap, using a 500 or 518 four-speed, or by adding a Gear Vendors overdrive to your existing trans. Even if you make all of these parts changes, your results may vary, since the tune is one of the most important factors.
Valve Clearance Clarification
I have a ’73 Duster that I’ve been building into a strong street/strip machine. The car was originally Slant Six–powered. I built a 408-inch stroker combination, and the engine has stock Edelbrock heads, dished pistons for 10.0:1 compression, an Edelbrock AirGap intake manifold, old style Holley 950 HP carb, and a solid flat-tappet Crane Powermax cam, with 238/248-degrees duration at 0.050-inch, and .480/.500-inch lift. My question is about setting the valve lash. The instructions from Crane call for 0.022-inch lash on both the intake and exhaust. I have the old Direct Connection manual, and there are a couple of different procedures that I can follow for setting the lash. The one I use is called the Four Position method. There is also the Eight Position method, and either way, it tells you where to park the crankshaft and then which valves get adjusted.
I use the Four Position method because it involves less turning of the crankshaft, which is hard to get to. I hear that the Eight Position method is more accurate, so I’m wondering if my engine would like that better. What do you think is the better system?
John, either one of those systems will work with your cam, and really are just shortcuts based upon lobe positions versus crankshaft position. The key is having the cam lobe on the base circle where the lobe has no lift while it is being adjusted. The base circle comprises a very broad sweep of a given cam lobe, so it is a pretty big target. There shouldn’t be any variation in the base circle diameter, so either method will likely provide the same result. The problem with those methods is that it is tedious turning the crankshaft to the right spot, and then you have to be careful not to get mixed up on which rockers to adjust. Direct Connection and MP used to sell an under hood decal that were popular so that the valve adjustment reference was right there in front of you while you adjusted the valves.
I prefer to use another technique which is quicker, easier, accurate, and doesn’t involve all that wrenching on the crankshaft snout. The system is the exhaust opening, intake closing technique. Looking at the pair of valves for any cylinder, when the exhaust valve begins to open, the intake on that cylinder is always on the base circle, and can be adjusted. When the intake valve reaches fully open and begins to close, the exhaust valve on that cylinder is on the base circle and can be adjusted. I use a remote starter button and just bump the engine around, starting with number one, and do all the intake valves following the firing order sequence, and then go back around and do all the exhaust valves. This is the way most professionals set the lash. It saves time, and minimizes the potential for mistakes.