Little Block | Opel Kadett | PDM Clark


Hello Little Block folk. I have been intrigued at the interest you have in this little masterpiece and in the type of questions being asked….So…I have decided to put together a very simple guide for tuning the Opel/Vauxhall OHV. Everything is based on the KISS principle (Keep It Simple Stupid) because I have learnt that Common Sense works a site better on this machine than Rocket Science. Also don’t blindly follow guidelines given by the Ford or BMC (Mini) gurus because this engine breaks many of the rules those guys live by anyway.

The first issue in tuning your little block is to decide what you want as the outcome. The large number of engine sizes from 993 to 1256 as well as the VM vs OM designs can be a little daunting, plus the fact that both the experienced tuners and less experienced folk you come into contact with could give you advice often very different to what is noted here….The result of all that can be confusing…Also the loudest and most persistent voices tend to get heard and that is not necessarily going to set you off in the right direction. In addition there is talk of NOS, Turbos, Fuel injection and modified 8 port heads mixing things up some more. So…take a breath…take a read of this….and decide on what is best for you. Those of you who have had the urge to tune your machine using your own ideas….that’s great.  All of us have the need to experiment and try out our methods and from what I see on FB there are smart cookies out there …but the magic of the Little Block remains….nobody has tried everything yet….so, keep an open mind and know that I am here to help….This is simply how I approach the task  to illustrate that getting spectacular horsepower and engine response requires focused attention before you decide to apply expensive hardware.


Must the cylinder head be modified to attain good horsepower?

The answer is YES….and again YES…The single most important issue in tuning the engine…..critical on 1966 and later B body cars. Without this work there is little point in doing the rest ….we cover the basics in this series of posts. Get the head professionally done if you are unable to yourself. This is the one area where spending a few $ is worth it.

Are big valves essential to getting good horsepower?

The answer is no. Keep the initial valve sizes whatever the spec of your engine unless you are looking to extract the max. Big valves help but only become effective and to be considered once cylinder head work is done properly and in conjunction with camshaft and carburettor upgrades. My real-time tune of the 993cc package we are busy with right now uses stock (tiny) 31X27 valves….and from the initial road work done this week, produces surprising engine response..

What compression ratio is best for a good road spec engine?

The answer is that the static compression ratio depends on what camshaft has been chosen to do the job. Broadly speaking with the use of the high-end factory cams  (SR for Opel and “90” Series Vauxhall) C/ratio would be in the order of 10:1. C/ratios of up to 11.8:1 are required when using camshafts with around 275 – 280° of duration in a road car application. Please remember that when these engines were first designed available fuel octanes were as low as 87/93. The availability of 98 octane changes the game completely.
I recommend you read the Blydenstein Project posts to get a handle on Dynamic Compression Ratio because correct DCR largely determines low and medium engine speed response.

How much material can be removed from the head face to increase compression ratio? Here is a rule of thumb:

Firstly up to 3mm can be removed from the heads.
On Opel the reduction in Comb Volume is around 3cc per mm…. also for 1057 Vauxhall
On VM 1159 and 1256  this moves to around 3.8cc per mm.
So typically a 2mm cut will increase compression ratio by about  1.5: 1 … ie move an 8.5:1 compression ratio to 10:1
However… increasing compression alone is not the answer….read on.

What carburettors are best suited to tuning the little block.?

The Answer is any carb that flows more air. In fact the inlet manifold design has a greater effect on power output than for example whether one uses a Weber sidedraught carb or a set of high-end ‘bike carbs. The downdraught DCD range if Webers is excellent both for power/response and good fuel economy but again heavily dependent on manifold design and inlet port configuration.

What power output improvements can be attained?

A good road spec tuning job will net a 50% improvement in power with the basics in place… However attention to detail will net as much as 70%. My current 1273cc Opel is producing a solid 110 Bhp and fitted to the A body Kadett gives mind-boggling engine response. Check out the video in this post.

Are ‘wild’ 280/300°+ camshafts necessary to get good horsepower.

The answer is no. What you want is a flat torque curve with good bottom end response…these engines provide high rpm power with practically any of the longer duration cams anyway. For road work I recommend around 260 – 270° duration with inlet valve closing points between 62 to 68° ABDC. That type of spec will give huge mid range power and pull strongly to 7500 Rpm.

What are the mechanical limitations?

For road spec applications not much. The Opel is inherently stronger due to the use of an all-steel bottom end and excellent individual component quality. However both engines are good-to-go with standard major components  (Pistons, rods and crank) in 1300 cc form able to handle up to 90 Bhp and 7000 Rpm without any difficulty. This is where the Opel gets to have the advantage and that figure moves to over 100Bhp and 8000Rpm using basically stock components..


The Key to all good things on the Little Block is in the cylinder head…. these are pics of the work done on the 993 project.

It has been really difficult to decide where to start this series on tuning the Little Block simply because of the variation in both engine capacity and engine type (VM & OM). So, after an analysis of the comments and general information circulating in social media I realised that not only is there much good work being done out there but  there are a surprising number of very smart folk who want to do this thing properly. …. HOWEVER…. there is something missing….and to put it bluntly…. not much focus on what really works.

OK…having established that…. what would be the best message to apply some focus?

Coincidentally I had started a project to build a 993cc engine (in fact the original engine in the ’63 blue car) and decided to expand what was to be a tuned basic build into a very specific project. The task became the build the engine using modified original components… … and using the basic thinking followed in my articles “The Magic 1088” and the “Blydenstein Project”.  This broadly Illustrates what works on these engines before resorting to specialised hardware and makes the point that attention to detail in critical areas result in better power gains than hoping that a magic camshaft/valve set/carburettor will transform your engine.

You are seeing this done in real time so this is no “smoke and mirrors project”…the engine is now built,  fitted to the car and being run-in as we speak and we are off to the Dyno this week Saturday….However…be prepared to be surprised  because from just the feel of this machine on the road I think we are going to see some magic numbers for what is essentially a mildly modified 1000cc Little Block ….using stock based components..

Our Project Engine the 993.  Running at 1015cc (0.75 Pistons) using original components including single choke carburettor,  stock inlet manifold casting, valves and valve springs… Target Horsepower 65Bhp from 40Bhp stock. (+60%)

Here is the spec of the engine:

Crank, rods pistons (72.73mm Mahle) all stock –  Engine capacity 1015cc from 993 original
Cylinder head stock 60’s 993 casting…modified
Static Compression ratio: 10.7:1
Dynamic Compression ratio: 8.8:1
Valves stock 31×27 Original parts  (1963) Reprofiled
Valve springs Stock Opel 1.2
Inlet manifold stock 993 …ported
Carburettor Stock  single choke 993 Opel… Modified
Exhaust manifold …Stock Opel Dual casting
Camshaft…  mildly modified 256° duration. IVCP 58° ABDC

The 993‘N’  on which this engine is based, produced 40 Bhp net …The target horsepower is 65… that is a 60% increase in power using original  Opel parts…..Let’s see next week.

Now Back to the Tuning Article…. in which we will use the work on the 993cc as we go through each major heading.


Right…..what are we talking about here in terms of a potential outcome in tuning an engine? Well…one thing I have noticed with information being put up on various pages is that it is mostly visual with very little in the way of hard-core power figures being quoted. I mention this because at the end of the day we are talking about horsepower here and one thing you will notice is that my work is biased towards practical result and test outcomes, I quote real horsepower and show resultant visual performance rather than the emphasis of making the work look spectacular as a first priority.

Here is perhaps my only words of caution and this is not meant as a criticism… but…unlike the information available on Fords and BMC product which is very specific…the information available on the Little Block is more like a shotgun blast of data, with everyone seemingly doing everything that comes to mind…The info available talks of cams (most far too wild), carbs, valve sizes, exhaust systems, cylinder heads etc etc is all there…..but very little of what works best with what…in my opinion it’s all just too random. In addition, the basic characteristic of the Little Blocks is unique in the classic tuning world because these machines respond to practically anything done to them…so, almost  anything applied can show mild improvement and that sometimes makes thing ok….however, the magic in real horsepower and engine response (snap) is in matching mods carefully.

And I am not talking in this series about 10, 20 even 30 % increase in power which occurs when one applies random upgrades…but between 55 and 100% increase in Bhp/litre by doing things in a co-ordinated fashion and at the same time keeping cost down by using original components wherever possible.

I also prefer to talk in Bhp per Litre terms because of the different engine sizes we are all working on… and my first  somewhat controversial comment has to do with the ongoing discussions in tech platforms in general covering the age-old chestnut of horsepower vs torque & which rages on …with many of those involved knowing  little of what they are talking about.  Please read my articles on this subject on the blog …but for the sake of this piece I will be referring to only two aspects of engine performance….HORSEPOWER and ENGINE RESPONSE because those are the two that you feel in the seat of your pants when you press the loud pedal. In my engine development days, I spent a good portion of my time studying how engines generated good throttle response, this an engine characteristic to a large extent that does not get the exposure it should.  Torque numbers, despite being used freely as being magic performance indicators, are a measurement tool only…and provide what is no more than a static bending moment from which we arrive at work done …which is horsepower…. And therefore have no place when discussing practical engine feel.

Before we get into the detail we will start by showing what is attainable both in a top end road spec engine and secondly take it a step further to illustrate what is possible from a basic but well specced race engine. I have published one of these clips before but the following brief videos are shown simply to demonstrate to all Little Block folk the potential available from this machine.

This Clip shows both part and full throttle response at its best and, given two factors, Firstly the video is shot
at 1600M altitude losing 16% of the available power it would have at sea level and Secondly the solid mid –
range response is unusually good for an engine with stunning high Rpm power. The point is that if we apply
some simple rules to tuning this engine, that is the kind of result that is attainable.

              Here are a few pics to give those of you who have not read the articles on the Blydenstein project an idea of
what is contained in the article….worth a read.

Cylinder head is a 993 Casting with enlarged combustion chambers to match 1273cc 81.5mm bore.

DCD CARB on Tunnel Ram Inlet Manifold                    


Key Features:  
Tunnel Ram Inlet Manifold with spacer plate
36DCD Weber
Valve sizes 34.5 and 30mm
Static compression ratio 11.6:1
276° Duration Camshaft, 108° Lobe Split, 9.6mm Valve lift IVCP: 70°
Dynamic Compression ratio 8.63:1
Tubular Exhaust manifold 4-2-1
Usable Power range 1800 to 8000Rpm
Toyota 4AGE Pistons  81.5mm (Modified crowns) Pin buttons
Longer Con Rods (133mm) Nissan 1400

Lets face it, 86Bhp/litre in road tune from a 60 year old engine design is pretty damn good and attainable on any of the Little Blocks if one follows the basic tuning rules on this package.


VIDEO 2        BASIC RACE ENGINE             1273cc  102 bhp/litre             Stock 1.2 S 49 bhp/Litre

The Kadett in video is not a lightweight, has full trim, bumpers and is running road tyres. The red car inthe clip is a 162Kw Megan Turbo and the little ‘A’ could out- accelerate the Renault and despite running drum brakes, ended a second a lap quicker.

In this form 0-100 Kmh in 5.8 seconds 2nd gear at 8600 Rpm.

In this spec the engine bottom end is the same 1273 sub used in the road engine noted above with changes to the cylinder head, carburetion and relatively mild (for a race engine) camshaft duration Bhp 130 @ 7200 to 7400 Rpm.

That’s 102 Bhp/litre and certainly not the ultimate power attainable.

THIS CYL HEAD PRODUCES 130 Bhp…Amazingly from a very tame looking chamber… The secret? We will
cover all this in future posts

           45 DHLA Split Dellortos…Longer Inlet tracts work better than short Stub manifolds using Weber IDF/IDA

Key Features:  Modified 993cc Cylinder Head to race spec 35.5 x 30.5 Valve sizes

  • Static Compression ratio: 11.8:1
  • Dynamic Compression Ratio: 7.9:1*
  • Split Dellorto 45DHLA. On Dual Port Fabricated Inlet Manifold with spacer plate.
  • 298° Duration Camshaft, 106° Lobe Split, 10.5mm Lift.
  • Tubular Exhaust manifold as in 2 above 4-2-1
  • Engine Sub Assy as per 2. Above.

*This DCR is an indicator that there remains untapped potential in this engine. By increasing static compression ratio to around 13:1 DCR will move DCR closer to the 9:1 value more  in line with a race spec engine.

Those clips show the magic of this engine… and along with the 993 Project we are doing in real time, we will demonstrate that all engine sizes can be made to perform brilliantly,

First Rule Of Little Blocks


One can get to ‘how long is a piece of string’ in this one because everyone expects something different when tuning an engine. Some don’t mind the lack of bottom end thrust and happy to buzz the engines, others want good response and fuel consumption. Some, rather unrealistically, want to “turn a 1300 into a 1600” just by tuning the engine and don’t quite understand that in most cases the by-product of tuning is raised rpm.

The important point of all this therefore is that if properly set-up, little blocks do not lose low engine speed response. At the risk of repeating myself I need to stress to you folk that all of my recent work has been conducted in the Pretoria/Johannesburg area where that altitude varies between 5500 and 6500 foot (15-1700M) above sea level. This, as already mentioned, results in a straight 15-17% loss of cylinder pressure and consequently horsepower throughout the rpm range as fitted to the car here at altitude…but…those videos show the wide spread of power available albeit at altitude. Also please note that all power figures quoted here show sea level output…and at sea-level the 1273 is close to unbelievable…I have had to build the stock gearbox very carefully to avoid the torque generated by this package (that static bending moment) ripping the teeth off the gears like munching a corn cob.

This is the menu for this series of blogs which will be published on a weekly basis.

Dyno Results of the 993
Cylinder head

Attention to detail – why
Carburetion & Inlet manifolds

Pistons – Con Rods

Exhaust systems
Ignition systems

The work to be shown can be applied to any engine size and O and V engine types and…most important to illustrate that many stock components can be used. Progress on the 993 Project will carry the detail of what can be done and I am taking the car to the Dyno this Week….so lets see the result in real time.