Engine Interchangeability/Upgrade

We received a good lead-in question to the subject of engine upgrade - I'm doing a restoration of my '70 VW Bug. I'm wondering if you could explain to me how to upgrade the engine -- say from 1200cc to 2000cc. Will this give me better performance? How efficient will it be? Will a different carburetor be necessary? Will this swap/upgrade still work if I have a 6v system?

You can swap a smaller engine to a larger one - that's the easiest way. But if you have a 1200cc engine, it's a little harder as things like the clutch might need changing when you put a larger engine in. The 1300cc, 1500cc and 1600cc single port engines are almost identical, so swapping to a larger engine is easy if you have a 1300cc or 1500cc. You can buy brand new 1600cc engines... they were made in Mexico up until about 2000, and they are supposed to be quite good engines.

The voltage is irrelevant, so long as the engine has the correct 6v components (coil, choke, generator and such). But changing from 6 volt to 12 volts is not too hard either.

So long as the engine case is in good condition, the 1600cc pistons and cylinders will fit straight into the 1300cc case - no alteration is needed. The outside diameter is the same but the 1600cc walls are thinner, which is why VW never went higher than 1600cc - the walls would be too thin and the case would have needed a slight redesign for larger diameter cylinders. More on this later.

Note: You should also note that the '65 case had the head bolts screwed directly into the soft magnesium alloy case material, so you might need to have case savers inserted into the case, especially if you are increasing its capacity. Case savers are threaded collars which increase the amount of thread grabbing the soft engine case material, so they are much less likely to pull the threads loose.

Engine Case and Cylinder Heads

Making your current VW engine larger is reasonably easy because the cylinders are separate from the engine case. Four separate cylinders sit in 4 separate holes in the sides of the case, and you can buy larger cylinders for the VW engine. Some larger sizes would need the case holes enlarged, but some will fit without altering the case at all.

The 1200cc engine has a 64mm stroke crankshaft and 77mm bore cylinders. You can buy 83mm cylinders (a "big bore" kit) which have thinner walls (so the outside diameter is still the same) which will fit into the same holes in the case and give you about 1385cc. These cylinders are not easy to find though - probably possible in Europe or the UK because a LOT of 1200cc engines were used there, but not easy in other parts of the world.

The case for the 1300cc/1500cc/1600cc engines is different to the 1200cc engine and the enlarging process has more choices. All these engines use a 69mm stroke crankshaft, but different diameter cylinders. The 1300cc engine has 77mm diameter cylinders, and either 83mm 1500cc cylinders or 85.5mm 1600 cylinders will plug straight in - the holes in the case are the same size for all three cylinder sizes (the cylinder walls get thinner as the inside diameter increases).

The 1600cc heads come in two varieties - single-port and dual-port. With single-port heads you can use the 30PICT/2 carburetor (usually NOT the 30PICT/1 - these carburetors does not come with a power jet and will run lean at high speeds with the larger engine capacity, which means that the engine will run hot. But later versions of this carburetor DO have the power jet, so if you can find one of those, they will work with a 1600 engine, though it's a little on the small side.

You can leave the cooling system untouched, although upgrading to the doghouse cooling system would be a good idea, since a larger capacity means more heat, and you have to get rid of it somehow. Upgrading to the doghouse cooler is not a technically difficult thing to do - you just need the right parts.

If you go for the dual-port 1600cc heads, you have to change the inlet manifold to the three-piece dual-port version, the carburetor to a 34PICT/3 (or use the H30/31 with a 30/34 adaptor), and also change the tinware over the cylinders which has the larger dual-port holes for the inlet manifold.

The 1600cc dual-port upgrade will also require upgrade of the oil cooler and fan shroud (see below). Thus the 1600cc single-port upgrade is a less work that the dual-port upgrade.

To get larger sizes than 1600cc, you have to use aftermarket larger cylinders - 87mm for 1641cc, 88mm for 1679cc, 92mm for 1776 and 94mm for 1835cc (all using the stock 69mm crankshaft). You can also use a longer stroke crankshaft - 74mm and 78mm are readily available, so when you use these with the larger cylinders you get even larger capacities.

The 87mm (1641cc) cylinders have thin walls so they might warp and twist after a short time. The original 88mm (1679cc) "slip in" cylinders were even worse - the cylinder walls were almost paper thin. But, there is a modern solution... you can also get 88mm machine-in (thick walled) cylinders. These are stepped, thin at the bottom to fit straight into the unaltered case, but nice thick walls up to the heads, so just the heads need machining to fit over the wider cylinder tops. These are described and "machine-in" 88s. The thin-walled 87 and 88mm cylinders will last for a while, but it's common for them to warp after a while, so the should be viewed with some suspcion. The 88 Machine-in cylinders will last as long as the original 85.5mm (1600) cylinders. For larger capacities, The case needs machining to fit the larger 92 or 94mm cylinders to get either 1776 or 1835cc...both of these sizes are quite popular.

Compression Ratio

If you leave increase the 1300 engine to 1600cc, but use the 1300 heads (machined to fit over the larger diameter cylinder tops), you'll get a compression ratio of about 8.8:1 (larger cylinder volume squeezed into the same head space) which is rather high - you'd need to run about 98RON Octane (about 95AKI in the USA) fuel. But if you also fit a set of 1600cc heads, the compression ratio drops back to a normal 7.5:1 and you can use the normal 91RON octane (87AKI in the USA) fuel.

The 1300cc heads are almost exclusively single-port heads in the US, although the 1300cc (with twin port heads from 71 onwards) continued to be sold in other parts of the world as a popular option to the 1500/1600cc engines. From 1971 they had a 1300cc twin-port engine using a 31PICT/3 carburettor, so it IS possible to get twin-port 1300cc heads which give a higher compression ratio when used with 1600cc pistons and cylinders.

Horsepower

The inevitable question - How much more horsepower will I get? For example, with the single-port 1300cc upgrade to 1600cc, you'll get a useful increase in horsepower from 44 to about 56hp, or maybe 58hp if you use the higher compression 1300cc heads. Same with the 1500 enigne, upgrading ton 1600 cylinders will give you an increase from 63hp to about 56-57hp. You'll get fractionally more hp with the H30/31 carburetor replacing the older 30 series carburetor - it has a larger throat. But any increase in performance is limited by the diameter of the inlet manifold. Those increases in horsepower are very noticable in such a light vehicle, so make sure your brakes are up to the job!

Carburetor and Distributor

Then you have to consider the carburetor and distributor.

If you have a 1200cc engine which had the 28PCI or later 28PICT carburettor, you can get a new H30/31 carburetor to replace the 28 series, or use the 30PICT and 30PICT/2 used on 1300cc and 1500cc engines, or the 31PICT/3 used on Euro 1300 twin port engines. All the 28, 30, and 31 series carburettors fit on the smaller manifold. The 30 or 31 series carburettors will give you a little more horsepower without changing anything else, as they have slightly larger throats, but dont expect miracles.

You can use the H30/31 carburettor on any size from 1200cc to 1600cc and it will work well, so long as you alter the jet sizes to suit the airflow of the different sized engines. It fits the single port manifold, and can also be used on the larger 1600cc dual-port manifold if you use a 30/34mm adaptor (which usually comes in the box with the new H30/31). A word of warning (two actually)...The H30/31 has a low vacuum signal so vacuum distributors can struggle to pull in any/all the vacuum advance, so it's common to use a 009 distributor with this carburettor, which brings on it's own problems. The H303/1 also comes with VERY lean jetting (an emissions thing) which can make it very difficult to tune and to keep in tune. Often a change of jetting to suit the engine size it's used on is needed to make it work well and stay in tune.

The more usual carburettor for the 1600cc twin port engine is the larger 34PICT/3 carburettor and you can still buy these brand new. It fits directly on the larger-flange 1600 twin port manifold. You can also use this on a 1776 engine, but for anything larger you really need larger twin carburettors - kadrons for example.

In all cases use a single-vacuum double-advance (SVDA) distributor for best performance and best economy - the 009 distributor works okay, but it was originally designed for constant speed industrial engines (compressors, generators, etc. which VW made millions of) and is NOT best suited to road work. With the 009 you can often end up with the stumbles on acceleration (called the "009 flat spot" or "009 stumbles"), and the engine will run under-advanced at higher speeds, which runs the engine a little hotter than it needs to. You'll use more fuel with a 009 distributor too. There is more on that on our articles on the 009 distributor.

Oil Cooler

The 1200, 1300cc, 1500 and 1600 single port engines use the old style in-shroud oil cooler, which is JUST adequate for the 1600cc single-port engine. But if you go for the dual-port version, the in-shroud oil cooler is marginal, and you'd also then be better off changing to the doghouse style cooling system -- wider fan, cooling shroud with the doghouse and exit ducting, standoff oil cooler and adaptor plate, front tinware with the rectangular hole for used oil cooler air, and a slotted engine lid or some other form of increased air inlet above the engine for the higher cooling airflow (see below). When fitting the oil cooler to the 1300cc or 1500cc case you must use stepped sealing grommets as the those single-port cases have smaller oil galleries than the standoff oil cooler mounting plate.

Increasing Cooling Air Flow

The doghouse cooling fan produces about 10% more cooling airflow - up from 22cf/sec to 25cf/sec - and needs additional inlet area. The under-window slots are NOT enough once the speed is above about 50mph, and the doghouse fan will start running short of cooling air, so the engine will get hot. The pre 68 solid (no slots) engine lid cannot be swapped for a '68+ slotted style (the shape is different), but if you can find a "2-slot" Cabrio lid from the same era (Cabrios did not have any under-window air slots and used a slotted engine lid instead) that will help a lot. Otherwise you need standoff hinges (which can look ugly but do work), or standoff licence plate mounts with a rectangular hole cut in the lid behind, or slots cut in the sides of the engine bay inside the rear fenders/mud guards. You could also graft slots into the existing lid - perhaps using parts of the Kombi front air grill. These would still be genuine VW and look rather early-Porsche since the slots are vertical rather than horizontal, but of course the car would lose a little of it's "sleeper" look if that's what you wanted.)

Engine fitment

The four mounting bolts for the beetle engine remained the same through it's development, so any engine will bolt up to any transaxle. BUT, the 6 volt engines used a 109 tooth flywheel, where the 12 volt engines use a 130 tooth flywheel which is about 3mm larger in diameter. That means the larger flywheel will touch the bottom two mounting bolt tunnels in the bell housing, so a little grinding of the tunnels nearest to the engine is needed.

Clutch plates changed over the years too. The 1200 used a 180mm flywheel, which WILL survive with a 1600cc engine (the 1600 semi-auto uses the 180mm clutch), but wont survive hard launches and of course it is likely to wear faster. The 200mm clutch came with 1300 and larger engines. The look of the pressure plate changed too - the original style has three large "fingers" and 9 coil springs around the perimeter providing the pressure. The later style pressure plate is a diaphragm style with multiple small metal fingers facing the centre. The new style is a direct replacement for the old style shape. Then in about 1972, the release bearing (throwout bearing) style (and clutch plate) changed. The earlier style release bearing has round mounting ears and simple round shaped clips holding it to the operating arm. The operating arm has round shaped hooks to hold the realease bearing. The clutch pressure plate for this style MUST have a metal ring in the middle of the metal fingers. The later style release bearing has square shaped ears and complex wire clips, and the clutch pressure plate has bare metal fingers. The pressure plates are identical apart from that metal ring, but the pressure plate MUST match the release bearing style - round ears = metal ring in the pressure plate....square ears = bare metal fingers in the pressure plate. If course the operating arm changed to suit the square shaped ears on the release bearing too.

Bottom Line

As you can see there are lots of possibilities and you really need to decide how much you are prepared to spend - then perhaps speak to a local VW enthusiast so you can work out the easiest way to get what you want.

Oh - and don't forget that when you increase the performance of the engine you MUST also make sure your tyres, brakes and suspension are in the best condition, or (better still) upgraded too.