How To Build An Engine For High End Horsepower Or Low End Torque #MuscleCarTech

One thing I've noticed during my period of learning about engines is that you have an either or scenario when it comes to how they make power. While there are engines that make both a lot of horsepower and torque, power modifications often improve one aspect of an engine's performance. I'll talk about each section of an engine and which types of those parts make more horsepower or torque...

Intake Manifold

It’s safe to assume that tall single plane intakes are better for engines that make the most power near redline while a short dual plane intake is better for motors that need to produce good grunt without revving too high. Another way to put it is that short and wide intake runners are better for high RPM performance while low end torque is better with long and skinny intake runners. There are some high end cars like the Ferrari F12 that have variable intake runners which gives you the best of both worlds, but a vast majority of cars have static intake runners.

There is an anomaly to all this, “‘For street use, a single plane manifold works great on stroker motors,’ says (Smitty) Smith, adding that the larger cylinder volume helps dilute the fuel-to-air ratio into a more optimized combination at lower rpm.” -enginelabs.com

Summary: fat and short intake runners for horsepower, long and skinny intake runners for torque

Here's a good example of a tall single plane intake on a V8 engine...

Cylinder Heads

Cylinder heads can make or break an engine, just porting them really good can yield almost 100 horsepower like Engine Masters recently did with a modified 410 cubic inch Chyrsler V8. However, it’s important to note that this extra power was being made at very high engine speeds. Cylinder head design effects where your engine makes the most power a lot like your intake manifold. The cylinder heads everyone raves about will make the most difference in power near redline, not just above idle. A smaller combustion chamber yields a higher compression ratio but can create valve clearance issues if you aren’t careful.

Summary: big intake runners and a closed combustion chamber for horsepower, smaller intake runners for torque

Camshaft

You would think that a camshaft with big valve lift and duration would be the best choice in every aspect, but that’s not really the case. It is true that camshafts with a lot of valve lift and duration make great power when the engine spins fast but camshafts with a smaller lift and duration make better power at lower engine speeds.

Lobe separation angle on a camshaft dictates when the intake and exhaust valves open in relation to each other. For example, a camshaft with a 100 degree lobe separation angle means that the time when both the intake and exhaust valves are both closed is very short, or it could mean there is a short period of time when both of them are open at the same time; there’s a word for this phenomenon, it’s called overlap. When people talk about “cammed” Mustangs with a lopey idle, it has a camshaft with a lot of overlap. Camshafts with a large lobe separation angle make better horsepower up top while low separation angle camshafts make better torque at low RPM’s.

Summary: camshafts with small lift and duration and low separation angle for torque, camshaft with big lobe separation angle, lift and duration for horsepower

Bore And Stroke

An engine’s bore is the diameter of the cylinder and the stroke is how far up and down the piston moves in the cylinder. Engines with a bore that’s smaller than it’s stroke make a lot of low end torque but can’t rev as high because of frictional losses and the smaller bore limits the size of the intake and exhaust valves you can use in your cylinder head. On the other hand, engines with a bigger bore can rev higher because of less friction and allowance for bigger intake and exhaust valves in the cylinder head.

Side note, installing thinner piston rings can reduce friction and increase horsepower at the top end.

Summary: big bore for horsepower, big stroke for torque.

Exhaust System

One thing some people do to help exhaust scavenging in cars that don’t have inline engine is creating an intersection in between the two exhaust pipes exiting the engine; the two types of these intersections are called X-pipes and H-pipes. The names of these intersections is pretty self explanatory and both systems have their benefits; H-pipes increase low end torque while X-pipes increase top end horsepower while giving your car a more high pitched “European” sound.

Another thing to consider with your exhaust system are the headers that connect to the cylinder head of the engine. Long tube headers can help increase exhaust velocity and scavenging by increasing the distance when all of the exhaust runners converge into a single collector; this helps to increase high end horsepower. On the other hand, shorty headers give you more low end torque because of increased back pressure. If your exhaust system is too big in diameter, exhaust velocity can drop which can hurt power. The size of your exhaust pipes should be determined by how much horsepower you’re making. A 300 horsepower small block won’t need as big of an exhaust system as a 600 horsepower big block.

Equal length headers improve top end performance but don’t have the burble to them that Subaru WRX’s are known for having because they have unequal length headers. Unequal length headers can help a turbocharger spool faster (wow, that’s the only time I’ve mentioned turbochargers in this article).

Summary: X-pipe and big long tube equal length headers for top end horsepower, H-pipe and smaller shorty unequal length headers for low end torque

These are long tube headers, not shortys.

Conclusion

This kind of engine theory doesn’t just apply to iron block American V8’s, it applies to all engines, whether they’re made in Germany or Japan.

There are many ways to build and engine and there are parts that are more of a middle ground performance wise so you could get the best of both worlds. At a certain point, no matter how much you modify your engine, it will make the same peak torque but at a different RPM in the power curve.

This content was originally posted by a Car Throttle user on our Community platform and was not commissioned or created by the CT editorial team.