Compression TrapI read your response to Earl Trapp regarding the application of 2.02 (x-heads) versus 318 swirl port heads. I am working on a '70 318, which has 84,000 miles. I intend to rebuild the engine with stock bearings and rings, and keep the stock pistons. I'm planning to install a Crower hydraulic cam with .444/.467-inch lift and 288/298-degrees of duration (at .050-inch). I am installing an Edelbrock Torker with a 600-cfm Holley carb. I have also acquired '69 340 exhaust manifolds.
I have been trying to find some "X" heads to install (they are hard to find and very expensive), but am intrigued by some friends' and your comments on the smaller valve swirl port heads. A friend of mine has said he thinks '88 and '89 318s had these heads.
Please give me your opinion on which model years had these swirl port heads so I can go to my local salvage yard to find some. Also, if I could find "X" heads would my compression lower, or was your response intended for newer even lower compression engines than my '70?
Also, I am told by Crower that I am border line on my selection of my cam, but can have a stock torque converter and have adequate vacuum for by power brakes while sitting at a traffic light. What is your opinion?
I am not trying to build a racer, just a daily driver with a little extra pop out of an already respectable engine.Mark PasquaNeedville, Tx
You are looking to save some money by freshening up your 318 with the stock pistons, but it is going to be a mistake. Even in 1970, the factory 318 pistons were typically way in the hole, like .060-.080-inch. These engines were not known as powerhouses, even with mild bolt-on parts, and a lot of it had to do with compression ratio. The other factor was the heads: puny ports and valves. So by the sound of it, you are going to keep the low-compression pistons, and go out and get some small-valve heads with puny ports to fix it. Not a good plan. The 318 swirl-port heads, which came on '85-and-newer two-barrel LA engines, have just one thing going for them, and that is the small, heart-shaped, closed chamber. If you have the talent, time, and equipment, they can be made to flow very well, but I'm talking extensive expert porting, a competition valve job, and installing larger valves. It may not be a practical or cost effective approach for you.
Consider all of the head work necessary to get the 318 swirl ports to move air, and a new set of pistons look like a real bargain. Getting a set of aftermarket pistons is going to be a lot less work, and will probably be a lot cheaper than trying to raise the ratio with those 318 heads, and then working like crazy to make them flow. Even with the small chamber, the compression ratio will work out to around 9:1 with your stock pistons. If that's not enough to make you reconsider your plan, you are going to be limited in valve-to-piston clearance with those stock slugs, and that can get ugly pretty quick with a high-lift camshaft.
The "X" heads and the other 2.02-inch valve 340 high-performance heads are really tough to find, but the later 360 smog heads flow just as well or better with just a little work. These are easy to find, and also came on factory four-barrel 318s. Just have them machined for 2.02-inch intake valves. With a minor bowl clean-up, they will be as good or better than the 340 heads. The problem with all the 340/360 heads on a 318 is the chamber measures about 70 cc, which will drop the compression to an unworkable low ratio on a 318. You can forget about decent performance with these heads and the stock pistons, so again, a set of moderately priced aftermarket pistons is the answer.
I'll spell out the most cost effective and simplest combination. Start with the new domed Keith Black 318 pistons, which have a net dome volume of 6.2 cc. Drop these hypereutectic pistons in your block, and you'll have about 10.5:1 compression with a set of 360 or 340 heads, without having to spend the money for milling the heads or decking the block. The short dome is perfect for this combo. Just grab a set of 360 smog heads, have them rebuilt, machined for 2.02 intake valves (including a 75-degree bottom cut), and finish with some mild bowl work. Toss that Torker intake in the garbage (it's junk), and get an RPM AirGap intake and a 750-cfm carb. Use a .904-inch tappet hydraulic cam (Comp, Hughes, Lunati, or Engle) with between 224- and 230-degrees duration at .050-inch on the intake side, and a lobe separation no wider than 110 degrees. Put this combo together with headers, and you will be a 318 legend.