Engine Interchangeability/Upgrade



Upgrading a VW Engine

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?

Swapping to a Larger Engine

You can swap a smaller engine for 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 hew 1600cc engines... they were made in Mexico up until about two years ago, 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).

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.

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.

Making Your Own Engine Larger

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 large 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 crankshaft and 77mm cylinders. You can buy 83mm cylinders 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 1475cc. 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 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 (NOT the 30PICT/1 - this carburetor does not have a power jet and will run lean at high speeds with the larger engine capacity, which means that the engine will run hot.

You can leave the cooling system untouched, although upgrading to the doghouse cooling system would be a good idea.

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 lot 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 87 and 88mm cylinders have VERY thin walls so they might warp and twist after a short time. Just to confuse things, you can also get 88mm machine-in (thick walled) cylinders where you have to enlarge the holes in the engine case. The thin-walled 87 and 88mm cylinders will last for a while, but it's much better to machine the case for the larger 92 or 94mm cylinders, and get either 1776 or 1835cc...both of these sizes are quite popular.

Compression Ratio

If you leave the 1300cc heads on, 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. If you 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 continued to be sold in other parts of the world as an 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.


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. 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.

Carburetor and Distributor

Then you have to consider the carburetor and distributor.

If you have a 1200cc engine, you can get a new H30/31 carburetor to replace the 28PICT (and also the 30PICT and 30PICT/2 used on 1300cc and 1500cc engines). It will fit straight on the manifold and give you a little more horsepower without changing anything else, as it has a slightly larger throat/venturi.

You can use this 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).

The more usual carburettor for the 1600cc engine is the larger 34PICT/3 carburettor and you can still buy these brand new. 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 can sometimes end up with the stutters on acceleration, and the engine will run under-advanced at higher speeds, which runs the engine a little hotter than it needs to.

Oil Cooler

Most 1300cc 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 case you must use stepped sealing grommets as the 1300cc single-port case has 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. The solid (no slots) engine lid cannot be swapped for a '68+ slotted style, but if you can find a "2-slot" cabrio lid from the same era (they did not have any under-window air slots and used a slotted 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 holes cut in the lid behind, or slots cut in the sides of the engine bay inside the rear fenders. 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.)

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 improved too.


Questions and Answers

We have received a few questions on engine interchangeability that evoked some great responses from Rob -

A question - I have a ‘64 Beetle; the only reusable parts out of it are the motor and transaxle. I think the motor is a 1600cc. My dad works with someone who has a ‘74 Super Beetle without the motor. I was wondering if I could switch the motor and the transaxle out of the ’64 and into the ’74 SB. If I did that would I be able to keep the original Super Beetle axles or would I have to keep the axles with the ‘64 motor?

Rob responded - Almost any VW engine will plug into almost any transmission, so the general answer is "yes" -- that engine will fit, but it may not work. Read on.

You can get a lot of information about what sort of engine it is by looking at a few features.

First -- the engine number. The initial letter tells you what the engine was originally -- D - 1200; H - 1500; B - 1600single port (1970 USA only engine); AB, AC - 1300 dual port (not seen much in the USA); AD, AE, AH, AS - various forms of the 1600 dual port.

For more information on engine types, have a look at our article on The VW Beetle -- Changes Through the Years -- this article gives a complete listing of engine and chassis numbers.

The early (pre-‘71) engines have only one pressure relief valve at the rear of the case -- have a look under the rear (pulley end) of the case for a larger aluminium plug with a screw driver slot in it - about an inch in diameter. ALL VW engines have this plug. Now look in the same place at the front (flywheel ) end of the engine. If it's an early engine case, there will be no matching plug there, but the later cases have the extra plug.

Since any of the 1300/1500cc engine cases can very easily converted to 1600cc and you can't see anything from the outside, the only way to check the real capacity is to remove a head and measure the piston tops -- 77mm for 1200cc and 1300cc single-port engines (different crankshafts), 83mm for 1500cc engines, and 85.5 for 1600cc engines.

The transmission is a different matter. If your ‘74 has double-joint rear axles (IRS) with a constant-velocity (CV) joint at either end of the stub axle, then you must use a "one sided" gearbox for a replacement. "One sided" means that only one side of the transmission case has a removable plate around the axle -- the swing axle cases have a removable plate on both sides of the case, and these can only be used with swing axles.

So it's highly likely that your ‘64 case cannot be used in the ‘74 car, and you can't (without a LOT of trouble) convert a later IRS suspension back to a swing axle suspension (your question about using the ‘64 suspension).

If the transmission in the ‘74 is OK, then the engine (whatever it is) will plug into the transmission, but there might be a problem if it really is a ‘64 type engine.

The earlier engines have a different main seal arrangement behind the flywheel, and since you CAN’T use a 6-volt ('64) flywheel) in a 12-volt Bug you may not be able to make it all work unless you can convert the starter back to a 6-volt unit (which will survive quite okay for many years on 12-volt).

The early engines used a metal/paper seal behind the flywheel, and the later (after about '65) engine have a rubber ring around the shaft and a larger oil seal outside of that.

The clutch throwout bearing is different too. The early throwout bearings have rounded ears holding the bearing in place and these use a clutch plate which has a metal ring in the middle of the clutch fingers. The later style (from about ‘71 onwards, have a throwout bearing with flat ears and these have no ring in the middle of the clutch plate -- the fingers are bare.

So although the engine will fit, the clutch may not be compatible without changing some components.

And another thing -- if the engine is a ‘64 model, the clutch is a 180mm version. The 1500/1600cc cars use a 200mm clutch. The smaller clutch CAN be used with a 1600cc engine (it is used on the 1600cc semi-autos) but it won't last as long, and you'd need to be kind to it -- no hard launches.

Lastly - is the engine in the ‘64 a doghouse engine? That is, does it have a box-like structure on the outside front (front is front of car) of the fan shroud, on the left side, or is the front of the fan shroud flat from one side to the other?

The ‘71 and later cars are all designed to have the doghouse engine for better cooling. If your engine is the earlier variety it would still work, but pushing the heavier ‘74 body around it will be working harder than it was designed for and you might get overheating problems.


Another question - I recently bought a rebuilt "long block" via the Internet, and made the mistake of thinking the engine that was in my son's '68 bus was "stock". What we have is engine type "AD", dual port -- apparently 1971. The carburetor is Solex 30/31 PICT.

The engine we received is what SHOULD have been there -- a single port. While it has no engine ID stamped, it has all the earmarks of a 1968-70 Type 3. The vendor says that as well.

Rather than pay shipping to send it back I'm looking to see if we can adapt the carburetor to a single port manifold ... or do we need a different carburetor AND manifold? Also, are the flywheels are interchangable?

Rob responded - The H30/31 carburetor has a small flange so it can directly replace the 28 and 30 series carburetors, which use the small flange manifold. From ‘71 onwards a larger flange manifold was used which suits the 34PICT/3 carburetor (for the 1600cc engines) and the 31PICT carburetor (used on 1300cc engines and very common in Europe).

The H30/31 carburetor can be used with a dual-port or any large flange engine by sitting it on a 30/34 adaptor (available at any VW shop). (Or if I am wrong and it has the larger flange it will sit DIRECTLY on the large flange manifolds).

If it's a '68-'71 Type 3 engine, the flywheels should be the same -- both later Type 3 and '68-'71 Bus flywheels are 12-volt (130 tooth) and have a 200mm clutch.

Some earlier Type 3 engines ('65/'66) were 6-volt (109 teeth) but still had the 200mm clutch, and this one can NOT be used in your '68 Bus unless you convert the starter and pinion bearing to the 6-volt variety (which will survive happily on 12-volt if needed - that's common practice with converting 6-volt Bugs/Buses to 12-volt).

I have a 1600cc dual port engine in my ’68 Bug, with a 30PICT/2 carburetor sitting on a 30/34 adaptor so it works with the dual port manifold.

There is no problem in using this Type 3 case in a Bug -- the only "curious" part is the missing dip stick hole, but yours probably now has a plastic fitting on the back of the case (close to the original position) for one -- that's how they usually do it with the Type 3 case.

* * * * *




Design by Erin