Alfa Romeo DOHC High-performance Manual

Chapter 1

Engine

BASIC DESCRIPTION

The origins of the Alfa double overhead camshaft (DOHC) or twin-cam, four-cylinder engine can be traced back to the nineteen-fifties. In its most common form, the engine has an aluminum alloy sump, block and head; a forged steel crankshaft rotating in five main bearings; and forged steel connecting rods. The four wet cylinder liners are virtually of the drop-in type, and the cylinder head, one of the better parts of the engine, has two camshafts acting directly on the valves (i.e. without pushrods) through bucket tappets (followers).

Up to about 1970, when the Spica mechanical fuel injection system appeared in some versions, fuel supply was entrusted entirely to carburetors. A few years later, Bosch EFI (electronic fuel injection) also made its debut in Alfa engines, but the use of double sidedraft carbs continued until 1989, with the Alfa 75 being their last DOHC application. Normally-aspirated 105 series

Cutaway view of the Spica-injected 116 series engine version.

2-liter engines put out up to 131 DIN horsepower on carbs (as advertised) and the Motronic EFI 8 valve TS up to 148hp (again, as advertised) in the version without a catalytic converter.

There were three DOHC turbocharged engines: one in the 2-liter GTV Turbodelta, producing 150hp with Dellortos; one in the

2-liter Giulietta Turbodelta, producing 175hp with Dellortos; and one in the mass-produced 1800cc 75 Turbo, producing 155hp with Bosch L-Jetronic EFI, and 165hp with the later Quadrifoglio version in 1990.

The 155Q4 and early 164 cars had a 2-liter turbo engine but this came from the Lancia Delta Integrale.

In 1968, the very special (and rare – only 10 cars were made) GTA-SA appeared as the only modern supercharged Alfa. This had a 1600 engine, and produced 220hp from twin, oil-pressure driven centrifugal blowers and 45 DCOE carbs.

A 105 series engine being lowered into a Spider engine bay.

Front cutaway of the Alfa164 TS engine.

Three-quarter cutaway view of the 164 TS engine.

Smaller 1.8 TS engine for the Alfa 155.

The bad news ...

Now, let’s proceed with the ‘bad’ news about the shortcomings of the engine, and, unfortunately, there are a lot (no disrespect meant to the designers).

First, the combustion chamber is rather large, out of necessity, of course, which is not very conducive to keeping generated heat inside the chamber itself. The size of the valves and the central spark plug (well, almost central) dictate a large dome with a consequently large angle between the valves (80o). This is, of course, an improvement over the 90o of years past. This large valve angle, and the decision to locate the intake and exhaust systems where they are, makes for a less than perfect arrangement of the intake and exhaust tracts within the head.

The shape left empty when the piston reaches the top of its stroke (Top Dead Centre/TDC) is exactly like that of a large contact lens, which is unfortunate, as the top of the piston should really be as flat as possible (like that in the Twin Spark, for example).

Moving on to the cylinder block; the liners aren’t very reliable under extreme conditions, like racing, for example. A better solution would be to have a set of four in one piece, like that used in the GTAm and 16 valve Autodelta race engines.

A limiting factor to potential power is the long stroke of the larger engines. You can only make a rotating assembly turn so fast before pieces (like pistons and connecting rods) start flying off. Power produced is proportional to engine speed (expressed as revolutions per minute/rpm) provided engine breathing and mechanical limitations are not exceeded. For the 2000 and 1750 engines, we must be happy with a maximum of 6500-6700rpm for a well-built motor with standard parts. The works GTAm cars were turning up to 7800rpm, and the 16 valve 2-liter at 8200rpm. However, these engines don’t have much in common with their cheaper relatives fitted to standard cars.

The good news ...

That’s enough negativity for now, so let’s point out the highlights of the motor. An engine design in use for over 40 years is a remarkable feat any way you look at it, especially so for a performance-oriented product. If this alone doesn’t qualify as an automotive engineering success story, I don’t know what does!

Starting off at the head once again, we find an excellent system of valve actuation, using tappets (or followers) with shims to adjust individual valve clearance. This system has the lowest possible reciprocating weight, so gives the potential to use radical cam designs with steep acceleration ramps. Granted, with Alfa’s valve actuation design adjusting clearances is somewhat difficult and time-consuming, but once done properly, they stay correct for a long time.

Second on the advantages list is the fact that it’s possible to set the intake and exhaust camshafts separately (relative to the crankshaft) to obtain different characteristics than those the factory intended. Moving a bit lower, we find an almost centrally located spark plug igniting the combustible mixture without excessive spark advance. Lower down inside the block, we have a very strong crankshaft, and equally well-built, but not excessively heavy, connecting rods. Fortunately, the rod bolts are also of high quality, a very important point.

The Alfa engine is fitted with a large, finned oil pan (sump) which helps to keep oil temperatures within bounds.

The shape of the intake valves is very good (though not the best) and their size, given the space limitations in the chamber, is near optimum. Exhaust valves, especially in the 2-liter engine, are much larger than necessary, not only for standard applications, but for high performance use as well! However, they are sodium filled for better heat transfer and longer life. The double chain driving the valve gear has proved to be a strong component, and accurate in its mission, if a bit noisy.

How Alfa improved the design

It’s interesting to look at how the factory improved the design of the engine over its life. The 2000 Twin Spark and its smaller (and relatively unknown) derivatives, the 1.7 and 1.8TS power units, feature a twin ignition cylinder head with a reduced valve angle, from 80_46o. Valve head sizes for the 2-liter unit are 44mm intake and 38mm exhaust. By comparison, the 105 series

2-liter exhaust valves are 40mm in diameter, much too big for the job. Certain GTAm versions had 46 and 38mm valves. On the other hand, the old and revered GTAs had 45 and 41mm intake and exhaust – an obvious error, exhaust-wise, especially when coupled to 34mm inside diameter headers (exhaust manifold). Note that the GTAm homologation documents list valve sizes as 45 and 41mm, intake and exhaust respectively. It seems that someone in the old Autodelta establishment had the feeling that the 46/38mm valve combination was better than the official 45/41mm! We can see now that the modern TS with its revised head design, correct valve sizes, two plugs per cylinder for better ignition, and practically flat-top pistons, has a greater potential for tuning than the older 105 series motor.

Because the Twin Spark burns fuel more efficiently in a more compact chamber, it can produce more power (as evidenced by its advertised 148hp at 5800rpm). The necessity of using two plugs per cylinder was brought about by the requirement for a reduction in valve angle. The valves are closer together now, and there simply is no room to fit a central plug. Putting a single plug to one side would make for uneven burning characteristics and possibly necessitate a higher advance curve because of the longer flame travel path. However, by duplicating the spark plug on the other side of the chamber we shorten flame travel, decrease advance requirements, achieve better ignition altogether, and can use domed pistons for a still higher compression ratio in racing, without all the disadvantages of an ‘orange peel’ combustion chamber as is the case in 105 engines. Add to all this the capacity to fit very large valves and there you have it: the true potential of the new GTA type head. Using two distributors, one in the normal place and one driven off the exhaust cam, takes care of spark requirements. To increase low speed torque, this engine even has a variable intake cam timing system, electronically controlled, of course.

This is what Twin Spark is all about!

One may wonder how the new engine manages to keep proper advance characteristics using two separate distributors? In this age of Bosch Motronic engine management systems, the two distributors are merely distributing high voltage, everything else is being taken care of electronically by the ECU microprocessor. In F3 guise, this engine uses a single distributor driven by the intake camshaft. The next step was for the distributors to disappear altogether, as evidenced by the 155 TS engine which utilized the so-called ‘static ignition’ (wasted spark) principle.

Although Alfa used a 16 valve head in a number of racing engines, it was not put into production, even though competitors (such as Fiat, VW, BMW, Mercedes, Toyota, Saab and Peugeot) were doing so. The factory’s response to competition needs was the variable intake timing system which offered higher torque low down without decreasing power at the top end of the rev range. Low and mid-range torque has always been the Alfa’s strong point, and it was not about to relinquish this established feature. So, the 8 valve TS engine stayed with us for a long time, as the rest of the automotive industry moved to 16 valve motors. It was only when the 75 finally disappeared in early 1993, that 16 valve engines popped up in the company’s model lineup. Soon, only the 2-liter V6 Turbo would have 2 valves per cylinder. This change, however, was coupled with a sweeping switch to front wheel drive, to the dismay of many dedicated rear wheel drive enthusiasts.

Incidentally, all 16 valve motors are of Fiat origin, except the 24 valve 3.0 V6, which is the last real Alfa Romeo engine design, before the Fiat takeover.

Back to the TS: I believe that using 8 spark plugs has no disadvantage at all! The fact that the 75 Twin Spark has ‘only’ 148hp DIN at 5800rpm tells me that it’s a wolf in sheep’s clothing. The potential is there and that’s important. Race examples of this engine built in the UK by Rossi Engineering have exceeded 220hp on carbs, a very impressive figure for any 2-liter engine!

Alfa 75 Twin Spark engine.

Alfa 75 TS engine, this time in auto-show silver.

Possibly, the thought of having in-house model conflicts did not appeal to Alfa brass. It wouldn’t look right having the top sports model the GTV, with six cylinders and 158hp and the four door model with four cylinders and more power! They must have thought of this because along with the 75TS they announced that the 2.5-liter engine has been brought up to 3-liters. To be truthful though, part of the reason for deciding on the TS scheme was the hope of capitalizing on the old GTA fame and glory, a point made clear in the company’s internal marketing documentation of the time.

Nice as all this may be, I believe that in the quest for power there is nothing a true Alfista would like more than a Montreal engine in a GTV! Dreams sometimes come true, but not often and only for a special purpose. The dream here is of course the Group 5 Alfettas campaigned in the seventies. 22 GTV-V8s were (supposedly) made with their Montreal engines resized to 2800cc at the request of Alfa’s German importer of the time.

On the other hand, most true enthusiasts like to keep their cars in the original specification with increased power from the original engine. Whether you’re modifying the original engine or a bigger one to fit in the old engine bay, I hope to provide you with real help through these pages as well as a pleasant reading time.

Perfect-looking Alfetta engine bay.

Another cutaway view of the Alfetta engine.

What you can do

You will be able to do a great deal of the work described in this book yourself. Depending on your experience and confidence, there are some jobs where you’ll have to make the decision between doing it yourself or having a machine shop do them. Of course, a small number of the tasks can only be done by a machine shop, though you must ensure that such work is done exactly to your specifications.

Basic areas to improve

Unless otherwise stated, this book uses the 105 engine as the basis for descriptions. When sizes and measurements are quoted without reference to a particular engine size they will apply to the 2-liter (used as the default, as this engine seems to be the most popular among Alfisti searching for more power). Except for the cylinder head, all measurements given also apply to the TS engine enjoying as of late an increasing popularity. However where required, data covering other engine sizes is included.

Let’s see which areas can be modified with increased performance and reliability in mind. We can work on the engine’s breathing system which offers the highest gains in power without using any special parts. Unfortunately, it’s the area that will cost us the most in time and effort too, but the results will be worth it. By the term ‘breathing system’, I mean everything over the block and not just the cylinder head. It starts at the air filter intake and ends at the tailpipe - chrome or not. Improving the engine’s breathing will take up most of our time and will be followed by cylinder block work, assembly procedures, oil system modifications and then by one of my favorite subjects: camshafts.

The Project Engine

Carrying out the modifications described in this book will enable you to build a 2-liter engine with around 160-165hp at the flywheel, produced at a modest 6800-6900rpm. The car will be entirely suitable for town driving with no jerks, kinks or coughing. I would even go so far as to call it economical by fast car standards! Performing the same type of modifications to the smaller capacity engines should result in about 120hp for the 1300, 140hp for the 1600 and 150hp for the 1750/1800 engine.

You might like to know that 2-liter engines can be installed in any model of the 105/115 series car with minimal problems, though if the donor car is a 116 series model you’ll have to do some swapping of oil pans, oil pumps and flywheels. You’ll also need to swap the water pump to get the necessary tachometer drive. More serious is the clutch shaft hole required in the crankshaft, when a 116 engine is transplanted into a 105 chassis.

The same holds true for a TS engine transplant into an older chassis needing additionally a special exhaust manifold – available from EB Spares and Autocomponenti.

Cylinder head – 105 Series

Cylinder head & intake manifold – optimizing airflow

What the cylinder head ports do is allow the flow of the required air/fuel mixture into the cylinders and the exhaust gases to flow out. Intake flow results from the vacuum created in the cylinder by the descending piston and exhaust flow from the rising piston and partly by gas pressure: we must strive to remove all possible obstacles in the way of good airflow.

By using instruments known as flow benches, airflow into and out of an engine can be measured and the value of modifications to the intake and exhaust ports assessed. Large flow benches can also be used to evaluate air filters, exhaust headers, silencers and everything else where good gasflow is important to performance.

Coming up with guidance on how and where to modify heads is a painstaking procedure, involving many hours of trial and error work with constant flow bench measurements. It is more than usual to destroy a couple of heads before being able to visualize how a good port, conducive to high flow, should look. This painstaking work on intake and exhaust ports can then be coupled to measurements taken with different valve shapes at various lifts until optimum results are achieved. This way, an improvement over what the factory has given you can be obtained; but do not - even for a moment - assume that the manufacturer doesn’t know how to improve the heads he makes. It boils down to economic considerations, and an understandable reluctance to over-design a product and, therefore, build in more manufacturing time and cost. Alfa heads as they come from the factory, flow very respectably – better than a lot of other makers’.

I have experimented to see how much more a modified Alfa DOHC head can flow and used the 105 series 2-liter head for my work because: a) it will yield more power than its smaller capacity counterparts and b) I had something almost perfect with which to compare it - a GTAm head (1985cc, twin-plug). Using the GTAm as a target standard, and applying all I have learned from the masters of the trade (like Vizard, Wilson, Yunick, Bell, Facchinelli), various professionally modified race engines and my own experience, I have carried out a series of experimental modifications to standard Alfa dohc heads.

Ported 2-liter 105 series head, prepared to accept 46mm intake and 38mm exhaust valves.

Ultimate Alfa Twin Spark head, the rare GTAm. Note integral intake manifold, ready to accept the throttle-slide or a short carburetor manifold.

I have flow tested various modified head versions, with several valve combinations. These experiments have resulted in two stages of head modification: the first stage offers a sizeable flow increase over the standard head (about 14%) but retains the standard valves; stage two goes further and increases flow by 25% above standard by using 46mm valves and appropriate valve seat inserts. I must say that these modifications provide very satisfactory power gains: a standard valve (stage one) engine with 12mm, 303º cams, 11.8:1 compression ratio, 2x45 DCOE, Asso 7003 pistons, 4 into 1 open exhaust and running on AVGAS showed 192hp at 7100rpm on the engine dyno. This engine was subsequently installed in a road-going Bertone Coupé and the car was fast! The only further modifications needed were a different advance curve (necessitated by lower octane pump fuels) and a specially fabricated 4-2-1 exhaust system. Final note: it idled perfectly at just 900rpm! What (in retrospect) should have been done was to measure power on a chassis dyno, to identify the impact of real-world necessities like fuel type and a complete exhaust system.

Top view of GTAm head. Two observations for the purists: these are not the original spring retainers, and someone has done a real hack job of cam rotation clearance cutouts.

Power from the big-valve head (stage two) had not been measured on a dyno at the time the original version of this book first came out, but more than ten years down the road, we know! We