25 Hidden Hop Up Tips
Be hot, look stock
by Tom Shaw
12. Pipe Streams
Exhaust gases that hang around for the next combustion cycle show up as drag on the piston which has to force the exhaust up past the valve, and takes up space in the cylinder that could better be used for fresh, power-producing intake charge. Exhaust is critical, especially on Fords, so give yourself every advantage here. Start with pipe size. Bigger is better. 2.5-inch pipe is good, 3-inch, if you can fit it under your car, is better. Either way, use mandrel-bent pipe, formed with a slug inside. The slug is the key. Mandrel bent alone is not enough — every muffler shop in the world wants to sell it to you, but just say “No!” It reduces the pipe cross section. Going up just .25 inches to 2.5 inch pipe diameter and using mandrel-bent/slug inside head pipe and making no other changes has gained 3 lb-ft of torque and 3 hp in dyno testing a stock 400 cid musclecar engine. Bonus tip: make sure all pipes fit inside of the next pipe as exhaust flows rearward. You don’t want exhaust gases “hitting” the edge of a pipe as they flow downstream.
13. High Flow Valves
Every cubic foot of air your engine breathes has to get past a valve, and the easier that valve is to get by, the better your engine can breathe. Pretty logical, that. Swirl polished valves offer a smoother surface for the air to flow over. Another step towards better airflow are commonly known as necked-down valves, which reduce the diameter of the portion of the valve stem which runs through the port. This is considered pretty advanced stuff. Bang-for-the-buck factor isn’t as high as with headers because all the machining (X 16) can be pricey, but the gains are real — and hidden.
14. Stroker Crank
Here’s a quick way to get more cubes and more horsepower. A stroker crank kit increases your displacement by increasing the distance that the piston travels. As the downward stroke is increased, the intake cycle breathes in that much more air and fuel. Competitive racers love long-stroke cranks because your engine looks completely stock — even numbers-matching —and only a P&G meter can detect the advantage.
15. Getting Cross
X-pipes, like this universal 3-incher from Year One Next Generation, make more horsepower. And they’re hidden under your car. Sound good? They do to us. And we have a little saying concerning exhaust, “bigger is better.” We have seen musclecars make more horsepower with pipes that seem like overkill. If you’ve got a tame 302 or 289 and you’re really running slow engine speeds and driving like a geezer to cruise night, then maybe you could get by with 2.5-inch pipes. But if you have any interest in actually going fast, get the biggest pipes your car will swallow. 3 inch is not too big, especially for big blocks seeing any WOT (wide open throttle) time. Adding an X-pipe ahead of your mufflers is a good thing. We can’t explain the science of why, but they do make more hp.
16. Recurve Distributor
We used to call it super tuning, but that term’s fallen out of fashion now. But whatever you call it, setting the advance curve on your distributor is a big boost for hp and the best way to do it is on a distributor dyno like this vintage Sun machine. Factory settings were notoriously conservative. Getting a total advance of around 38-42 degrees of total advance in by around 2500 rpm usually gives the best response, but experiment a bit. Different engines prefer different advance curves.
17. Port Matching
Casting and machining tolerances are why the port openings between the heads and manifold don’t align smoothly. In production form, there are edges that protrude into the airflow. That’s not good. Using a hand grinder to open up the port to match the opening of the gasket eliminates the obstruction. Multiply that improvement by eight cylinders and you’ve got a sizeable increase in airflow. The higher the revs, the greater the improvement.
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