The myth is that stroker motors are not reliable daily drivers. Not True. I’ll give you some things to think about, then you can decide for yourself.
A VW air-cooled motor is 180-degree crank. A bicycle is 180-degree crank. With that said, your motor is just like a bicycle. If the pedals are close together and you don’t have much weight on the pedals what happens? You’re fine once you get up to speed on flat ground, but not so much on a hill.
A 1776, 1835, and 1914 are all motors with stock stroke and bigger pistons, which is like working out so that you can put more weight on the pedals. Back to the hill: Now you can put more weight on the pedals so when you get to that hill you can push harder. You will get further up the hill before you shift but you will be expending a lot of energy to do so.
If you were to move the pedals out on the bike, wouldn’t it take less weight to turn the crank? Yes indeed. You now have torque. Now you don’t need all that weight on the pedals to get up the hill. This means less gas and the motor doesn’t have to work as hard.
Reliability: A reliable motor is only good as its weakest part(s). Everything has to work together. Back to the bike: You wouldn’t move the pedals out and leave a worn out chain on the bike. With more torque, the chain will break.
Stroke Size: You can get up to a 82 stroke in a case with out notching the cam.
Rod Angle: The larger the stroke with a stock length rod, the greater the angle. The steeper the angle, the more stresses on the crank. I have found that 78mm stroke is as large as I want to go with a stock length rod. Here is a trick: Use a 78mm stroke with a B piston. B pistons are made for an 82 stroke and have the wrist pin moved up on the piston. This will give you deck height (piston not coming out of the cylinder) with out shims or very little shim. This way the motor stays stock width, RIGHT ON!
When adding a stroker crank you will have to clearance the case for it. I highly suggest you do not do this yourself. Pay a good machine shop that has cutters for this. A hand job is just that: You will be jerking off if you do! It’s also a good idea to have the center main shuffle pinned to keep the center webbing in the case from walking.
Cam: For a daily driver, we want good bottom end, great mid range, and don’t really care about top end (over 5k RPMs). My suggestion is an Engle 110 or something close.
Heads: You’ll need bigger valve heads. Books have been written here so I am only going to touch this subject. Here is the biggest thing: Over 75% of your horsepower comes out of the heads. Don’t cheat here.
Valve size: On a daily driver, I suggest 40mm X 35.5mm. A 42 X 37.5 is better for a Friday/Saturday car. The big problem for a daily driver is the seats are so close together that there is not much meat under the seats and they tend to sink after a while. Use single heavy duty springs for a daily driver (we don’t need all the spring pressure of duals on a motor that doesn’t see over 5500 RPMs). Also, look at the new heads. Can you see through the fins? A lot of aftermarket heads have more beef to them but lack in cooling fins. Take your stock head and look at all the fins around the cambers and the ports. Your new big valve heads should look the same, especially around the exhaust ports.
Port size: Keep it mild. Bigger ports make bigger power; however, at lower RPMs we lose velocity . All a carburetor knows is vacuum. We don’t want to loose the vacuum signal with too big a port. Again, this if for a daily driver.
Compression Ratio: For me, 7.7 to 8.0 to one seems to be the best for our regular gas. Keep in mind that compression is heat, heat is energy, energy is horsepower. Too low of a compression ratio and we don’t have any power, too high and we have to much heat and motor runs hot.
Read more about Compressions Ratios HERE
Push rods: I use 3/8” aluminum push rods as I want the expansion rate to be close to stock. These engines can grow .020” per side. If you use chromoly, the expansion is less and we have loose valve lash at normal operating temps. If you’re using dual springs, you don’t have much of a choice, you have to run the chromoly push rods.
Carbs: I like the dual IDF style carbs. If your compression ratio is 7.7 to 8.3 then use the 40s. (Again, a daily driver).
Exhaust: Run a good 4 into one header with a good muffler. A stinger gives top end and will actually hurt the bottom end.
So that’s the basics to building a good reliable stroker motor. If you do it right, you can get more reliability out of one than a stock motor because it doesn’t have to work as hard. Back to the bike: If the pedals are moved out and you went to the gym, you can pull that hill in 4th without tiring yourself. If you’re out of shape and your pedals are close together, you’ll struggle to pull that hill. There is a lot more that goes into a good motor, but that is for another article.