When it comes to building an engine, most mechanics break a motor down into two basic parts: the bottom end and the top end. The two are most certainly related, and depending on your upgrade path, you should address both as your power expectations increase.

It’s also worth mentioning that not all top end kits are intended exclusively for a performance upgrade. If you’re looking for an easy way to rebuild an engine without going through the hassle of machining your old cylinder heads or sourcing an original replacement cam and matching valvetrain, then a top end kit like the ones we’ll describe below have plenty of upside too.

But first, since we’re focusing on the engine top end in this article, let’s establish the distinction.

What’s the Difference Between an Engine Top End & Bottom End?

While there may be some subtle nuances based on who you ask, here’s the general distinction for a typical V8 engine in a nutshell:

  • Engine Bottom End – The rotating assembly (pistons, rods, crankshaft), along with the oil pan/pump, main caps, and related bearings, gaskets, and seals.
  • Engine Top End – Camshaft(s), cylinder heads (with valvetrain, plus pushrods and lifters, if necessary), intake manifold, timing set (gear/chain), and any related bearings, gaskets, and seals.
man installing trick flow cylinder head
Cylinder heads are often the focal point of the engine top end, but don’t overlook the role of the camshaft, intake, and other ancillary parts. (Image/Richard Holdener)

What is an Engine Top-End Kit?

A lot of initial engine upgrades focus on the top end. With the right complementing parts, it’s possible to build significant power gains over the stock trim—with the obvious caveat that you’ll be putting additional strain on the bottom end. (So you’ll obviously want to make sure that your rotating assembly can handle the expected power output, unless you want to hear a very expensive boom.)

And while plenty of gearheads will gleefully assemble their own mix of top end upgrade parts à la carte—and there’s nothing wrong with that—many performance manufacturers offer complete engine top end upgrade kits that give you all those components under a single part number.

man lubing a camshaft during installation
Starting with the camshaft, it’s vitally important that all the parts in an engine top end play nice together. For that reason, a complete top end engine rebuild kit with precisely-matched components can eliminate a ton of headaches. (Image/Jeff Smith)

A complete top end kit like this has two big benefits. For starters, it gives you an easy, single SKU to remember.

But more importantly, you know that each part in the kit has been perfectly matched by the manufacturer to work together in the engine—and that’s really, really important. For example, running an aggressive cam with the incorrect valve spring package can quickly cause premature wear. Heck, even something as simple as a mismatched gasket could result in leaks, which leads to a frustrating engine teardown and rebuild.

Eliminating that component-matching homework is a big deal, so top end engine kits have become very popular lately with DIYers and pro mechanics alike.

What’s In an Engine Top End Kit?

There’s no clear-cut definition of exactly what components comprise a top end engine kit. For instance, a lot of manufacturers don’t include an intake manifold, in case you’ve already got one—or perhaps you want to pick one with unique characteristics for the type of driving environment you anticipate. Choosing your own manifold just gives you a little flexibility.

You probably wont get valve covers either. There are a few good reasons for that exclusion too, primarily if you’ve got special underhood clearance issues to work around.

trick flow top end engine kit
This is a top end engine kit for the small block Ford V8 from Trick Flow. Note that this specific kit doesn’t include the intake manifold—there’s no official recipe for what constitutes a top end kit, so make sure to check the contents of the one you’re looking at. (Image/Trick Flow)

At its core, a good top end engine kit will include the cylinder head(s) and a matching camshaft(s). And it’s important to note that you’ll also get the valvetrain too, to ensure compatibility between the cam and the head.

Generally speaking though, here’s what you’ll commonly get in an off-the-shelf top end engine kit:

  • Cylinder Head(s), Assembled with Valvetrain
  • Camshaft(s)
  • Timing Set
  • Cylinder Head Gasket(s)
  • Pushrods & Lifters (if applicable)
  • Assembly Hardware

Some of the more robust kits offer additional parts, like these:

  • Intake Manifold
  • Intake Manifold Gasket
  • Header Gaskets
  • Water Neck Gasket
  • Timing Cover Gasket
  • Valve Cover Gaskets
trick flow top end engine kit for mod motor ford
Plenty of manufacturers offer top end engine kits for overhead cam engines too, including the trusty Ford Mod Motor family. (Image/Trick Flow)

Which Top End Kit is the Best Option?

Yup, you get our favorite answer here: “It depends.”

And it depends on a few things, namely your performance goals for the engine. Are you building an all-out race motor? A hot street engine? A standard rebuild? Once you have a clear path in mind, then you can start whittling down your options.

And that’s the really good news. When you start shopping for the best top end package for your specific needs, you’ll find plenty of manufacturers stepping to the plate with a vast mix of available kits—including options from well-known brands like…

Don’t Forget the Bottom End!

We’ve pretty much spent this entire article talking about the cylinder heads, valvetrain, cam, and other top end parts, but—and we alluded to this above—if you start making more power than the rotating assembly can handle, bad things will happen. Quickly.

Admittedly some stock bottom ends have proven relatively tough (cough*LS*cough), but once you start pushing the performance envelope, things like clearances and stress tolerances get stretched to their literal breaking point. In those situations, rod knock is a best case scenario…with separation anxiety being the worst.

So don’t overlook vital upgrades to your rotating assembly and, just as importantly, your oiling system.

bottom view of crankshaft and main caps on a Cadillac dragster engine
Building a fuel motor for a vintage dragster? Yeah, you’ll want to beef-up the bottom end… (Image/Hugh Reynolds, Reynolds Machine)

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All told, a quality top end engine kit is a great option for folks looking to significantly enhance the performance of their car or truck, without having to do a lot of part-matching calculations. And better still, in a lot of situations, a competent DIY’er can install a top end kit without removing the engine from the vehicle—which makes it a fun weekend project for the driveway mechanic.

If that sounds like your kind of jam, click here to check out all the top end engine kits at Summit Racing.