VW Beetle Engine Upgrade Guide

If you are chasing a few extra BHP for your classic VW Beetle, this article is for you. Let us walk you through the various engine tuning options available for the aircooled Type 1 motor, with a brief rundown of what is involved, why it works, and how complicated or expensive it may be! 

If you own a 30hp VW vehicle, we have written a specific 30hp tuning guide here. 

A few words of advice before you stick a rocket up the rear of your old VW. If you want your modifications to last, then your engine should be in good shape to start with - that means minimal end float (check the bottom pulley for movement in and out) and no knocking, rattling, or smoking under load, and a recent service completed too. 

Want to know what engine you have to start with? Here's all you need to know about aircooled VW engine numbers. 

Likewise, if you have plans for high performance please ensure you have brakes, steering, suspension, and suitable structural integrity to cope with the additional power! 

You'd also be wise to renew the clutch or even upgrade it to handle the additional load generated. Read how a clutch works here. 

As we've mentioned many times before on our blog, the more fuel and air you put in, the bigger the bang, and the more power you can generate. Starting at the top of your trusty Type 1 engine, a larger single carburettor, or better still a pair of balanced twin carburettors will keep your combustion chambers fed with plenty of fuel. 

For 1600cc-1641cc engines, we've found the EMPI 34 EPC / Weber 34 ICT carburettor kits to be the ideal match, offering a good blend of performance and economy, although they do not have choke mechanisms fitted for cold start, so the engine will require warming up on colder days before you drive off. 

For larger engine builds (and we'll come to how you do that in a minute) the EMPI 40 HPMX,  EMPI 44 HPMX or the Weber IDF equivalent will work wonders, just remember the bigger the carburettors the more fuel you'll need to pay for, although you needn't suffer from poor fuel economy. A mildly tuned motor with components that work well together can return better MPG than a stock set-up and deliver approx. twice the power! 

Speaking of fuel delivery, your stock mechanical fuel pump should cope up to around 100bhp. Beyond that, you will need an electric fuel pump and a fuel pressure regulator to help keep a smooth and reliable stream of petrol to your carburettors. 

With more fuel mixture arriving at the cylinder heads, there are a few opportunities for performance improvements. For those on a budget, or who enjoy hands-on work, porting and polishing the cylinder heads can return good benefits as long as you have access to a die grinder and go steady (It's much harder to add material back on, but you can always take a little more away at a later date!)

The principle behind porting and polishing is to encourage a greater volume of fuel mixture to pass through to the valves and then back out again as exhaust gasses. This is done by enlarging the 'ports' and 'polishing' the inner surfaces so everything can move nicely and efficiently through. Along with enlarging ports, bigger valves can be installed to handle this increase in flow. 

For peace of mind and convenience,  we also sell performance cylinder heads. Please note some of these are cut for larger barrels (85.5mm is stock 1600cc) 

Whilst a performance camshaft is a very useful upgrade on an aircooled engine, you'll be needing to split the crankcase to install a new one and feel the benefits. You can read all about how performance camshafts work in our blog here. 

A great alternative is to fit a set of ratio rockers which are far more accessible, being located inside the cylinder head. Ratio rockers work by increasing the valve lift (how far the valve is open) by a specified ratio. 1:1.25, for example, will give an additional 25% lift over standard, although the duration of the valve opening will remain the same as the camshaft. 

Valve geometry will be altered when going down this route, so factor in a pushrod measuring tool and a set of cut-to-length pushrods to ensure everything still works as it should. 

As the old saying goes "There's no replacement for displacement" and increasing the cubic capacity of your aircooled VW engine is a well-proven method for upping the power, and there are two things that can be done to change this. 

The first method is to increase the bore of the cylinders and the pistons to match. The standard 1300-1600cc crankcase will accept up to 87mm pistons, and by reducing the cylinder wall thickness, larger 1641cc barrels and pistons can be bolted into place without any additional machining work. 

Should you wish to go larger (90.5mm and beyond) you will need to employ some engineering assistance or purchase a ready-modified crankcase and cylinder heads. 

The second route, which can also be combined with a larger bore, is to increase the stroke length. Stroke is controlled by the crankshaft, mounted inside the crankcase, and refers to how far the pistons, on their con-rods, will travel up and down within the cylinders. 

A longer stroke will benefit the engine by providing more low-down torque, however, this will be at the detriment of torque at the top end of the rev range. 

It is also worth noting, that a longer throw crankshaft will require clearance work inside the crankcase if you extend the stroke beyond 74mm. 

For reference, 1200cc engines use a stroke of 64mm and 77mm pistons, 1300 engines use 69mm stroke and 77mm pistons, 1500cc use 69mm and 83mm and 1600cc engines use 69mm and 85.5mm pistons (these standard specs are shown in italic). See the chart below for the possible stroke/bore permutations. 

We've touched on crankshafts above, and while on the subject of increasing performance, it makes sense to mention the big heavy component that bolts to the end of it - the flywheel! A lightened flywheel will reduce the rotating mass of the crank, help to improve acceleration, and can be used with both standard and stroker crankshafts. 

It is worth noting that going too far (like the race car example below) it will make the vehicle run lumpy and almost undrivable on the road. But an off the shelf flywheel should be fine. 

In the same way that putting extra fuel and air in will increase performance, so getting waste gasses out the way more quickly will help with power figures too. The good news is that not only will a performance Beetle exhaust add a few extra BHP, but they look great and sound pretty awesome as well. 

Check out our range of VW Beetle sports exhausts here and should you wish to brush up on your theory, our article about how exhaust systems work can be found here too. 

Forced induction is used to describe both supercharging and turbocharging. In short, they are both systems for getting as much air (and subsequently fuel) into the engine as possible. 

Turbocharging works by using spent exhaust gasses to spin a turbine wheel, which draws additional air from the atmosphere, puts it under pressure, and forces it into the engine. The more air, the more fuel your carb or throttle body will mix, and the more power you create. The downside with turbocharging is 'turbo lag' which is the delay between the throttle pedal being pressed and the turbine spooling up to generate boost, and of course, there is the extra load it puts on your engine components - you could easily blow your engine up if you were too keen on high boost pressures. 

Supercharging works in a similar fashion, although the turbine is belt driven from an engine, which means as soon as the RPM increases, so does the boost pressure. Systems such as the Judson Supercharger have been available for classic VWs for years. They would typically develop less power than a turbo but can be more useable and reliable. 

To round out this article we'll make passing reference to fuel injection and forced induction ie. Supercharging and Turbocharging. We'd imagine if you are considering any, or all of these options you'd be pretty well clued up on what it all means, but for those less technical here's a quick run down. 

Fuel injection was actually fitted as standard on the later Mexican built VW Beetles. The throttle body (an electronically controlled carburettor linked to an air flow meter) sits in the same place as a single carburettor, on top of the inlet manifold, in a set up known as Single Point Injection. 

More modern vehicles, and later classics such as the Golf GTI, use a system called Multi Point Injection, which has one fuel injector per cylinder, and these are either fitted direct to the cylinder head spraying into the combustion chamber, or into the inlet manifold where the fuel and air can mix, just before the inlet valve. 

Whilst it sounds simple enough, there are some electronics involved, including an ECU (electronic control unit) which would need to be programmed for your specific application. Unless you are searching for big power and maximum efficiency and have a healthy bank balance to support it, or you REALLY like a challenge, it's probably one to pass over!

And that in a nutshell, is how to upgrade your VW Beetle engine. As always, if you have any questions ping our tech team an email help@heritagepartscentre.com and they'll be able to advise the best available products or course of action to achieve your aircooled engine goals. 

Andy