The GM “Little Block” and the Magic 1273

Work on the GM’s small four of the 60’s an 70’s continues…but this time on a larger capacity version of the engine. Whilst based on the work done on the magic 1088 I have not simply built a larger capacity version of that engine but looked to optimising a 1300 performance road package.

The outcome?…Startling…and had the general been more serious back in the day. The history of small cars might have been written differently…so read on.

1. Little Block

GM’s Little Block

Again colleagues have asked why the avid interest in the little Opel OHV engine, and why particularly try to resurrect something that is effectively dead and buried anyway. The answer to that is straightforward and I liken it to those who have a curiosity for any of the more well-known classic machines. There are significant numbers and groups, the legions of Alfa twin cam, Kent Ford, ‘A’ series BMC, ‘A’ Series Datsun and legendary Gordini folk are as supporting of their particular steeds as I am of the Opel. My interest stems from a background of tuning these engines back in the day and now, exploring territory we were not able to at the time, look to see how we can get this little machine to at least match and more likely better some of those established engine types.

Bill Blydenstein is without doubt my mentor in all of this. For those of you who have read the story on Park Drive which describes the practical starting point in my tuning of engines, he was the motivator well before that. Blydenstein stood out as one of the few tuning gurus in the early years committed to GM product outside of the USA…* but my respect for the man goes to the fact that whilst most established tuning operations in our world in the late 60’s gingerly dabbled in Vauxhall and Opel product, he was singularly the only one in which his whole business involved a GM Europe product… He attached himself to the brand at a time when VM (Vauxhall Motors) were considered as outcasts in the tuning fraternity. I have covered much of this in earlier posts on Dealer Team activity in the late ‘60’s thru ’70’s era but in a nutshell, Blydenstein’s involvement was eventually to result in absolute dominance on racetracks in the UK, lifting  Vauxhall to the very top of the racing game.

*Australian Holden and South American GM Tuners the only exception to this.

2. Bill Blydenstein
3. VX 4-90

BILL BLYDENSTEIN VAUXHALL TUNING CHAMPION AND HIS VX 4/90 RACED IN THE EARLY 60’s

OLD NAIL …THE BLYDENSTEIN VAUXHALL THAT REWROTE BRITISH SALOON CAR RACING WITH GERRY MARSHALL AT THE WHEEL

OLD NAIL …THE BLYDENSTEIN VAUXHALL THAT REWROTE BRITISH
SALOON CAR RACING WITH GERRY MARSHALL AT THE WHEEL

There was however, one casualty in the process and that was the little OHV engine, built in two versions by Opel and Vauxhall respectively. In the VM case the arrival of the Viva GT in 1968 gave Vauxhall dealers the means to arm-wrestle the Corporate into motorsport, resulting in the establishment of DTV… Dealer Team Vauxhall…with Blydenstein as the boss. The weapon of choice on racetracks became the 2 litre car and at Vauxhall’s direct request, all work on the 1.3 litre OHV racing version was to be stopped, something that Blydenstein had wanted to progress.

Opel were not involved at all and in fact took a lot longer to do anything meaningful in saloon car competition. The Opel rally cars of the mid-seventies established something of a presence but again bypassed Opel’s version of the OHV in favour of the 1.9 and 2litre Cam-In-Head engines (CIH). In fact, my 1160cc ‘A’ body Kadett from the late 60’s and early 70’s was most probably the only really competitive Group 5 version of the car and this done in a complete vacuum with respect to information from Opel.

 

AT 1160cc THIS ‘A’ BODY KADETT COULD HOLD ITS OWN IN THE 1300 CLASS AND…WHERE PILOTED BY A PROFESSIONAL RACE DRIVER… SHOWED A CLEAN PAIR OF HEELS TO THE 1293 MINIS
6. Kadett Renault Racing

AT 1160cc THIS ‘A’ BODY KADETT COULD HOLD ITS OWN IN THE 1300 CLASS AND…WHERE PILOTED BY A PROFESSIONAL RACE DRIVER… SHOWED A CLEAN PAIR OF HEELS TO THE 1293 MINIS

Bottom line?…In both the UK and Germany as well as in worldwide distributors like SA, tuning of the OHV was done in aftermarket operations as a minor ‘add on’ to their core business, if at all.

So …work on this 1.3 litre package is a tribute to Bill and I think from what has been achieved we will have done his name proud..

For the purpose of this piece I stick with the Opel version of the engine for three reasons. Firstly my experience in tuning the Opel OHV goes back to those racing days in the 70’s, secondly the car I have now is a 1963 Kadett and lastly the need for specialist components is dramatically reduced due to the design of the stock Opel components. By comparison, the VM version of the engine would give a similar result but would require a good few more specialist parts.

**The Vauxhall OHV can be tuned in the same manner as the Opel and whilst certain of the mechanical bits are not as durable (due mainly to cheaper production materials being used) street horsepower and durability are similar. The Opel, however, is rock solid in race applications with a formidable steel crank and top quality valve gear able to take high rpm pounding.

WHILST THESE TWO ENGINES LOOK ALMOST IDENTICAL, GM MANAGED TO ARRANGE THAT PART SWOPPING IS ALMOST ZERO. ONLY THE ROCKERS AND PUSHRODS ARE INTERCHANGEABLE.
WHILST THESE TWO ENGINES LOOK ALMOST IDENTICAL, GM MANAGED TO ARRANGE THAT PART SWOPPING IS ALMOST ZERO. ONLY THE ROCKERS AND PUSHRODS ARE INTERCHANGEABLE.

WHILST THESE TWO ENGINES LOOK ALMOST IDENTICAL, GM MANAGED TO ARRANGE
THAT PART SWOPPING IS ALMOST ZERO. ONLY THE ROCKERS AND PUSHRODS ARE INTERCHANGEABLE.

THE TARGET

There is however a bigger target to this whole thing and that is to set an objective to match or better engine performance compared to an established ‘hot’ production engine of the era. I had many to select from but because of the chosen engine capacity for this project at 1273cc, decided to use the  best performer of the 60’s, the 1255cc Renault Gordini engine, as that objective.  My colleagues immediately told me I was crazy… “don’t think you will get that lump of iron in road trim to match a stock Gordini”

Interestingly we have… and then some. To modify an engine to achieve heady power for a road car with no heed to low speed response can be done on most engines. To get this OHV Little Block to match the power of a stock Gordini would not be difficult…BUT…could we do it as a road spec engine and have an equal spread of usable mid-range power and low speed grunt?

We needed to establish some rules first to ensure that whatever was done, was both production feasible and used 1960’s tech.   We have stuck to those rules. All components used are production friendly and the camshaft profiles selected are 60’s items used on Kent Fords back in the day.

Not only have we matched the Gordini but quite a bit more. This engine produces max power of 110 Bhp @ 6800Rpm vs Gordini 103 @6750… and… 125 NM torque from 4800 to 5800 vs the Gordini 117 nm @5000.

Power and torque Dyno figures are from that most reliable of gents, Maurice Rosenberg  of Autorosen who was involved in the project from the beginning and remains a little shellshocked at the result.

 

Dyno Guru Maurice Rosenberg …This pic taken whilst setting up the 1273 Race Engine…

Dyno Guru Maurice Rosenberg …This pic taken whilst setting up the
1273 Race Engine…

But here is the remarkable result from the Road Spec Engine.

The 1273 Little Block has an amazingly wide powerband with 86% of the 125Nm max torque (108Nm) available from 2500Rmin to 7000Rmin. As a bonus, engine response is stunning, so much so that in the lower gears the standard pull/rod accelerator linkage is too sensitive, with road induced pedal movement (bumps) and the instant ‘snap’ from the engine requiring very careful control of the accelerator. I will have to move to a cable actuated system with a Quadrant to manage the beast.

The following two video clips give a very good idea of both the flexibility pf this engine and the full throttle performance. Bear in mind too that these runs are at 1500M altitude. At sea level the engine has 15% more power and torque. Some figures to blow your mind:

Altitude Sea Level
0 to 60 Mph 7.6 secs 6.8
0 to 100 Mph 26.6 secs 23.8
S1/4  Est times 16.4  (81 Mph) 15.7 (86 Mph)

The part throttle acceleration shown in the response video gets the car to 60 Mph in just on 15 seconds…at altitude…that’s faster than stock OHV Kadetts can do at sea level flat out.

So that is what has been achieved…a result that exceeded our expectations and more surprisingly, considering that very little development and variables testing has been done outside of the first stab at this…there is more to come.

HOW WAS THIS DONE

I refer to the OHV as the GM ‘Little Block’ simply because it has so many unmistakeable features which identify it as the small block Chevy’s little brother. Lightweight rigid castings, pushrods and rocker assemblies along with wedge type combustion chambers in tuned form that end up identical in appearance. The engine was designed by a team who knew exactly what they were doing…and this is measured as only an engineer can…by counting and evaluating the number of critical upgrades the engine had in the period after introduction. By that measure, this one was rock solid and had an excellent warranty record, with no major design changes.

 

OHV OPEL VALVE TRAIN AND COMBUSTION CHAMBERS         SMALL BLOCK CHEVY CLONES

Apart from engine capacity related alterations (Bores and Piston size), components from a 1962 993cc OHV, will fit and function on a 1993 1196cc OHV. As engine size changed, oil pump capacity increased as was crankshaft web cross section. But here is the bottom line…In all the years having been involved… 1967 through to the work being done today…incredibly, I have never experienced a catastrophic engine failure. Now, naturally having said that, something could go bang tomorrow but the point is these things are strong… and for that to happen straight off the drawing board, the design engineers need to take a bow.

It is therefore unfortunate that this magnificent piece of engineering has largely been overlooked and I shudder to think what may have happened if a David Vizard had been let loose on this machine with the support of the General.

For those interested, I suggest reading my previous piece “The magic 1088” posted in 2017, That is worth a read, gives the background and allows us to go straight into the 1273.

ENGINE CAPACITY AND THE OHV

The Opel OHV has been built in three engine sizes 993cc, 1078cc and 1196cc…the capacity increases the result of Bore size moving from 72mm, to 75mm and finally 79mm…crankshaft stroke is unchanged at 61mm for all three. At introduction in 1962/63 the power output of the engine was top of the class with 48 nett bhp from the S version of the engine…way more than competitors. The car was nimble and immediately popular.
The Vauxhall version was built with the same stroke but slightly larger bores nominally at 74mm, 78mm and 81mm for the three variants 1057cc, 1159cc and 1256cc and at introduction in the UK went to the top of the class in overall performance.

‘A BODY’ KADETT   993cc AND 665Kg

12. Viva HA Collage

‘HA’ VIVA    1057cc and 680Kg

GM however had probably miscalculated on the exact market the Kadett/Viva should occupy and the original Kadetts/Vivas soon made way for new models only three years into their release dates in ’63. The larger new cars (B body Kadett and HB Viva) arrived in 1966, both with moderately enlarged versions of the respective OHV engines. The Kadett now at 1078cc and the Viva moving from the 1057 to 1159cc…..This where GM lost the plot…and in both cases the engine size increases did not fully compensate for the increased girth, mass, carrying capacity and the fact that competitors were doing things differently. Both companies told us that the new cars were either as nimble as their predecessors or faster…they were not.

13. B Kadett Collage (1)

‘B BODY’ KADETT 1078cc (GERMANY)     1057cc AND  1159cc (SA LOCAL VIVA ENGINE)  AND 765KG
TWIN CARB  SR VERSION (GERMANY) 1078cc.

14. . HB Viva Collage

‘HB’ VIVA 1159cc and 771Kg and the BRABHAM VIVA TWIN CARB VERSION

Both Vauxhall and Opel introduced mild performance versions of their “B” body cars. Opel with the SR spec twin Solex carbs at 1078cc and Vauxhall with the Twin Stromberg Brabham Viva at 1159cc. Both were ‘peppy’ machines but due to their size/engine capacity combination, could never have been counted as serious performance cars.

The third generation cars were even bigger …The HC Viva we knew here in SA as the Chev Firenza and The C Body Kadett which was not built in SA but became GM’s First attempt at a “world Car”.

CHEVROLET FIRENZA (SA) and VAUXHALL VIVA (UK) 1256cc both 880Kg

CHEVROLET FIRENZA (SA) and VAUXHALL VIVA (UK)  1256cc both 880Kg

 

C BODY KADETT 1196cc and 812Kg

C BODY KADETT 1196cc and 812Kg 

From the progression shown, these little engines had to work hard for a living…and as a result…I have done the most sensible thing and bolted the biggest version of the engine into the smallest of the Opels, something that other manufacturers were doing by responding to the growing small engine performance car market in the 60’s.

‘A’ BODY KADETT at 1273cc

‘A’ BODY KADETT at 1273cc

SETTING UP THE 1273

There are always partners in crime and the fun part of this exercise was the planning phase and the Anduccios Coffee shop in Strydom Park… Maurice and I sunk many cappuccinos deciding on the next step in producing the ultimate normally aspirated OHV Road car engine.

In building the 1273, I have used the 1088 as the starting point because numerous decisions on that engine were new and untried but proved to be very successful. We will cover all the important areas as we go along, however, the most critical centre around Camshaft choice and Compression ratio…but first the basic spec.

IT was clear from the work on the 1088 that the 1273 would be able to handle more ‘cam’ and as a result more compression. In addition, the 1088 utilised a standard, cast dual port exhaust manifold, so a switch to tubular ‘headers’ was to help along with alterations to inlet manifold and ‘head port diameters.

For the rest the same cylinder head and valve sizes were used with combustion chambers enlarged to accommodate the increased capacity.

1088 1273
ENGINE BLOCK 993cc Original 1196cc from Kadett D
BORE 75.29 mm 81.5mm
STROKE 61mm 61mm
CAPACITY 1088cc 1273cc
PISTON Mahle Original 4AGE Toyota
CONNECTING ROD OPEL NISSAN A14  + 11mm
VALVE SIZES 34.5/30 34.5/30

The choice of piston and con rod assemblies for the 1273 has nothing to do with the reliability of the Opel components but rather the fact that these engines respond to longer Con Rods (+11mm) allowing shorter piston pin to crown height…the A14 Nissan Con Rod is bullet proof and the 4AGE Piston has light construction and is immensely strong. All features ideal for building powerful engines. One could obviously use specialist aftermarket parts at huge expense… but these are unnecessary.

LONGER CON ROD AND SHORT SKIRT PISTON ..THE 81.5mm ROD/PISTON ASSEMBLY ON THE LEFT IS FRACTIONALLY LIGHTER THAN THE STOCK 72mm 993CC ASSEMBLY

LONGER CON ROD AND SHORT SKIRT PISTON ..THE 81.5mm
ROD/PISTON ASSEMBLY ON THE LEFT IS FRACTIONALLY
LIGHTER THAN THE STOCK 72mm 993CC ASSEMBLY

 

Where to start?…Traditionally in our early days, we thought selecting the hang-on bits to be a good place to start… ie what carburettor/inlet and exhaust manifolds to use, then perhaps moving on to cylinder head mods  and sometimes lastly the camshaft. Compression ratio, despite the fact that we thought we knew quite a bit, was generally a thumb-suck based on some level of historical ‘mumbo jumbo’.

Here are a few Tuning chestnuts we believed in:

  • Long duration cams result in poor bottom end response
  • Big ports result in poor low speed torque
  • Large exhaust manifold pipe diameters kill engine response
  • Compression ratios higher than 10:1 will likely result in detonation
  • Short stroke engines suffer poor low rpm power and need to ‘buzzed’.

Whilst these could be regarded as accepted norms from the old days, this 1273 shoots down every single one of those handsomely.

 

First… a little background.

Very often have we seen engine mods done on classic cars where the result is not only below par, but in some cases combine all the nasties noted. These vary from less than best power, lack of mid-range, meagre response, early detonation (knock) and many others…. one of the worst being poor sensitivity to tuning on the Dyno. Don’t worry…I’ve been there and it is part of the never ending learning curve.

As I see it there are two basic avenues to this learning, the first is getting to know a particular engine type, the characteristic do’s and don’ts as it were…that comes with time. The second is about getting to know those very basic issues that tend to work on any engine…we will cover both in this piece on the OHV 1273.

A note. I am constantly surprised at the number of contacts requesting more tech stuff on old engine work. This comes from a wide spectrum of readers and particular interest is shown by young folk dead keen to know more about old school tuning. So as part of this piece on the 1273 I go into some detail on general tuning issues which I consider to be important. This is not meant to teach experienced engine tuners to suck eggs, far from it.. but rather to put out there what I find works well and the hope that it resonates.

CHOOSING THE RIGHT COMBINATION OF PARTS FOR A CLASSIC ENGINE JOB

Never underestimate this part of the work because the benefits here provide the basis for a bad, good or unbelievable engine and I am going to start by combining two issues many folk have little idea are in fact directly linked. Compression ratio and Camshaft Choice. We tend to think of an engine mainly in its mechanical sense… and that’s ok…but…an IC engine is, first and foremost, just a pump… No different in basic function to a bicycle pump in the way it that it ‘sucks’ in air (oxygen) and blows it out again. Yes, the IC Engine has the extra bit of kit that adds fuel and a spark to the process….but we need to focus on the first bit…FILLING THE CYLINDER. That is where the magic is.

Us oldies suffered from a syndrome back in the day where we accepted (and maybe even enthused over) the fact that a ‘hot’ cam would knock the bottom end out of engine response and come on like gangbusters when ‘on the cam’…never thinking of course that it is possible to have good response throughout the rpm range. Filling the cylinder at low and medium engine speeds is to a large extent about maintaining inlet charge velocity and that gets killed when we do not think hard about the correct matching of the bits we chuck into the mix. The current growth in the business of turbocharging everything in sight these days has also tended to mask the art of Normally Aspirated tuning on old engines.

For me, the learning was about connecting the dots on as many seemingly unrelated issues as possible so as to better understand engine characteristics…. as an example, I am going to repeat a story on the Firenza Can Am to make the point.

FIRENZA CAN AM…    LEARNING ABOUT CYLINDER PRESSURES

Let’s start with that evergreen …compression ratio…. and very briefly shoot down most of what we have learnt as the do’s and don’ts.

Having started my career in the Service division at GMSA in the late 60’s when we had small block Chevy  V8 engines in most of our bigger cars, I soon learnt that on 93 Octane fuel (highest octane available) some of the Chevy small-blocks were sensitive to knock. On engines used in the performance cars like the Monaro and Chevy SS (Holdens) the 327 and 350 versions ran 9:1 compression ratios and, even where timing was accurately set, would often be close to knock.

So…a few years later, having graduated to the Experimental Engineering  division and the midst of the Can Am project… the specially built Z28 based 302 DZ V8’s were on the way from the Tonawanda engine plant … this Chevy small block runs an 11:1 compression ratio.

FIRENZA CAN AM DZ 302 SUPER HIGH COMPRESSION ENGINE

FIRENZA CAN AM DZ 302 SUPER HIGH COMPRESSION ENGINE

I was concerned…and despite assurances from Chevrolet Engineering that there would not be a major problem … I was not convinced.

As it turned out, there was no problem… and with the engine installed in the Firenza, all that was needed was a two-degree ignition retard from the Chevy spec to give something of a safety margin on lower octane fuel than available in the USA.  Yes, a street car fitted with a production engine, running at the coast on 93 octane fuel and a 11:1 compression ratio…unheard of in those days.

This was the first lesson on how valve timing effects cylinder pressure…the solid lifter ‘30/30’ long duration camshaft reduced cylinder pressure at low to medium engine speeds, making it able to run happily without any trace of knock. The particular feature of this camshaft is the late closing of the inlet valve. The engine was however characterised by soggy low engine speed response and would, as the saying goes, come on like a hurricane at 4000rpm.

We have now touched on that little known but critical phenomenon… Dynamic Compression Ratio (DCR). I mentioned this in the 1088 article but now go into greater detail.

What is Dynamic Compression Ratio.?… I like to keep things understandable… so we need to look at the fact that the only way an engine can build compression, is after the inlet valve closes…and that happens on 4 stroke engines after the crank passes bottom dead centre… with the piston on its journey upwards to build that compression.

On standard classic road cars this can be around 20-30 degrees After Bottom Dead Centre

On a quick classic road car…around 50-65 deg ABDC. (that ‘hotter’ cam)

On a classic race car …around 70-80 deg ABDC (that ‘wild’cam)

BUT…if the valve is closing with the piston further and further up the bore …there is less effective ‘stroke’ left to build compression.  THE REAL COMPRESSION SEEN IN THE CYLINDER at low and medium engine speeds effectively DROPS as we allow the inlet valve to close later and later….THAT IS IF… WE MAKE NO CHANGE TO THE STATIC COMPRESSION RATIO..

PISTON POSITION AT THE POINT OF INLET
VALVE CLOSING…THIS EXAMPLE 72 DEG ABDC

Just how smart were the Chevy engine men back in the day. They optimised an engine carrying the right hardware spec for racing… and that 30/30 camshaft (erroneously sometimes termed the Duntov cam) was specifically designed to do its job in the power dept… but also to allow this screamer of an engine to run on pump fuel with a safety margin on USA high octane. In hindsight, that safety margin killed the bottom end response but also removed one major possible warranty headache for Chevrolet and we’ll cover that shortly.

COMPRESSION RATIO GIVEAWAY

For those interested in this sort of info you may have read recently about variable compression ratio engines.(NISSAN are doing a lot of work) Whilst I do not want to get into this in detail, there is both a theoretical and practical advantage to being able to vary static engine compression ratios, much for the same reason the industry has taken to variable valve timing (VVT, VTEC etc).This is extraordinarily difficult to do in practise and the reason why there are no production engines with this feature…yet. In theory what the two achieve together is maximise cylinder pressures across a wider rpm range.  Where there is a theoretical opportunity to alter the Static compression ratio but not able to do this practically, we have compression ratio giveaway…and that unfortunately is what happens to all NA IC engines.
A Last word on this and to help the understanding, take a peek at modern turbocharged engine Torque curves. Most are completely flat across a wide operating range. Turbocharger applications on modern road cars are as much a power issue as they are a Cylinder Pressure Control Mechanism where sophisticated electronics keep the engine functioning in its most efficient operating window, achieving constant cylinder pressure. A variable compression ratio NA engine would essentially attempt do the same thing…

TYPICAL MODERN TURBO ENGINE TORQUE CURVE

TYPICAL MODERN TURBO ENGINE TORQUE CURVE

Hold that thought, because we are going to use that to adjust the static compression ratio on our 1273 to achieve the required Dynamic Compression ratio and maximise engine performance. (Detail in Part Two of this story)

We confirm from all this, that compression ratio and valve timing are linked and that together both affect cylinder pressures to a much greater degree that one would think…. This immediately gets us to ask the questions… if DCR drops, and there is theoretically less air in the cylinder, where  does the high end power come from?…and…how do we optimise this in a Normally Aspirated engine build….We must remember that the reason we are doing any of this is to achieve huge power… and to have solid low and mid-range response so as to make the machine pleasant to drive.

I essentially looked to flatten the torque curve on both the 1088 and the 1273 and the following curves show that this has been achieved to a better degree than expected.

Power is shown in BHP and Torque in Nm to compact the graphs and make them easily readable on the same scale.

THE 1273 TORQUE CURVE IS REMARKABLE… BEING ESSENTIALLY “FLAT” FROM AROUND 2000RPM TO 7000 RPM. THE PEAK TORQUE FIGURE OF 125Nm IS VERY CLOSE TO THAT 100Nm/Litre ACHIEVED ON MODERN 4 VALVE ENGINES.

THE 1273 TORQUE CURVE IS REMARKABLE… BEING ESSENTIALLY “FLAT” FROM
AROUND 2000RPM TO 7000 RPM. THE PEAK TORQUE FIGURE OF 125Nm IS VERY
CLOSE TO THAT 100Nm/Litre ACHIEVED ON MODERN 4 VALVE ENGINES.

The target Bhp figures for the two projects were 70Bhp/Litre for the 1088…and achieved 75Bhp/Litre. From this, I set the 1273 target to 81 Bhp/litre (that Gordini at 103 Bhp)… and achieved 86 Bhp/Litre. The increase in specific Bhp over the 1088 was expected due to the alterations in camshaft, compression ratio and manifold changes…however…the significant gains in torque, way in excess of the engine capacity increase throughout the range, are a result of getting the match of components just right… some of that brought about by circumstance rather than calculated endeavour. At this stage I am in that rather nice position that engineers very seldom find themselves, where unravelling the reasons why we have beaten the objective becomes a fun exercise.

But let us look at some of those figures. Firstly, any NA engine with torque figures approaching or greater than 100Nm/Litre can be regarded as top drawer in modern engines. Variable valve timing and four valve tech are used to maximise cylinder pressures throughout the RPM range and many ‘cooking’ engines of today beat the performance of engines like the Gordini back in the day. A good direct torque comparison of the 1273 against a current Honda Jazz 1.3 (1314cc) incorporating four-valve tech and VTec looks like this:

1.3 Jazz Nm 1273 OHV Nm
1500Rmin 82 72
2000 96 108
3000 111 110
4000 118 112
5000 123 125
6000 119 123
6500 100 119
7000 112

Having been successful in flattening and stretching the Torque curve on the 1088, the thinking behind the 1273 was to improve on that. We needed to achieve better specific torque at low and medium speeds (Nm/Litre) as well as improve (bhp/litre) at high rpm. These are the target parameters:

  1. Camshaft Duration increased from 262 Deg (1088) to 276Deg (1273)
  2. Inlet valve closing point moved from 62 Deg ABDC to 70Deg ABDC
  3. Compression ratio moved from 10.8:1 to 11.6:1 (optimised DCR on 95 RON fuel)
  4. Tunnel Ram high velocity inlet manifold with modified internal section + longer inlet tract with tapered spacer block. Carburettor Weber 36 DCD progressive.
  5. Tubular Headers 4-2-1 manifold 38 mm Primaries and 45 mm secondaries

The increase in camshaft duration would result in improved high rpm power but we needed to improve low speed response. To do that, the increased compression ratio compensated for possible low speed cylinder pressures loss… and staying with the two barrel downdraught Weber 36DCD /Tunnel ram inlet manifold, figured that low and midrange torque (Nm/Litre) would at least be maintained.

Many folk questioned the continued use of the rather old fashioned 36DCD Weber…but there is a specific reason for using this carb in preference to more modern twin choke downdraught units. The ability to change choke tube sizes to suite engine characteristics was one, but more significantly, another feature we will cover in Part Two of this story supported the decision to stay with the Downdraught Carb. Moving to a sidedraught carburettor often used in these applications was not considered for a number of reasons. These included part throttle economy and low speed engine response.

FABRICATED TUNNEL RAM INLET MANIFOLD… SPACER BLOCK INCREASES RUNNER LENGTH AND IMPROVES CYL DISTRIBUTION.

FABRICATED TUNNEL RAM INLET MANIFOLD… SPACER BLOCK
INCREASES RUNNER LENGTH AND IMPROVES CYL DISTRIBUTION.

 

ROCKER COVER SIDE VIEW OF INLET MANIFOLD AND TAPERED SPACER

ROCKER COVER SIDE VIEW OF INLET MANIFOLD AND TAPERED SPACER

VIEW OF UNFINISHED INTERNALS

VIEW OF UNFINISHED INTERNALS

CARBURETTOR, HEAD AND EXHAUST ASSEMBLY

CARBURETTOR, HEAD AND EXHAUST ASSEMBLY

DOWELLED MANIFOLD POSITIONING ENSURES PORT MATCHING

DOWELLED MANIFOLD POSITIONING ENSURES PORT MATCHING

4-2-1 EXHAUST MANIFOLD 38x45mm PIPE DIAMETERS

4-2-1 EXHAUST MANIFOLD  38x45mm PIPE DIAMETERS

CAREFUL CHAMBER VOLUME CHECK – ALL CHAMBER 26.15cc

CAREFUL CHAMBER VOLUME CHECK – ALL CHAMBER 26.15cc

FINAL CHAMBERS WITH SPECIAL COPPER HEAD GASKET

FINAL CHAMBERS WITH SPECIAL COPPER HEAD GASKET

993cc CYLINDER HEAD CASTING REQUIRES CAREFUL ASSEMBLY

993cc CYLINDER HEAD CASTING REQUIRES CAREFUL ASSEMBLY TO THE CYLINDER BLOCK

993cc CYLINDER HEAD FLOWS BETTER INLET AIR THAN 1078 or 1196 Cyl HEADS. THIS SHOWS LARGE 33mm INLET PORTS AND SEPERATED CENTRE EXHAUST PORTS.

993cc CYLINDER HEAD FLOWS BETTER INLET AIR THAN 1078 or 1196 Cyl HEADS. THIS SHOWS LARGE 33mm INLET PORTS AND SEPERATED CENTRE EXHAUST PORTS.

SAMPLE COVER CUT OPEN TO MEASURE CLEARANCE BETWEEN GUIDE AND CHAIN THIS IS SPACED ON THE FITTED COVER TO ENSURE SNUG CHAIN POSITIONING.

SAMPLE COVER CUT OPEN TO MEASURE CLEARANCE BETWEEN GUIDE AND CHAIN
THIS IS SPACED ON THE FITTED COVER TO ENSURE SNUG CHAIN POSITIONING.

INLET VALVE CLOSING POINT ON THE 276 Deg CAM. CAMSHAFT SET TO 2 Deg ADVANCED

INLET VALVE CLOSING POINT ON THE 276 Deg CAM. CAMSHAFT SET TO 2 Deg ADVANCED

COOLANT TUBE MODIFIED TO INCREASE FLOW TO THE COMBUSTION CHAMBER WALLS AND VALVE SEATS.

COOLANT TUBE MODIFIED TO INCREASE FLOW TO THE
COMBUSTION CHAMBER WALLS AND VALVE SEATS.

MODIFIED PISTON CROWNS ON TOYOTA 4AGE 81.5mm PISTONS

MODIFIED PISTON CROWNS ON TOYOTA 4AGE 81.5mm PISTONS

In Part Two of the Blydendstein Project entitled simply… “26.15”…I show how optimisation of the DCR on the 1273  was done and look at those areas needed to maximise cylinder pressures over as wide an rpm span as possible.

We will also cover the Following:

  • How to avoid Combustion Knock (Detonation)
  • Keeping things cool
  • Keys to Tunability on the Dyno.
  • Cool air to the Engine
  • Killing the Inlet tract standing wave pulses.

HOPE YOU ENJOYED THIS AND MORE TO COME NEXT WEEK.

READ PART 2 HERE