Vauxhall 8 Valve Twin Cam slant four (Part one)
Many years ago I tripped over an engine down the side of a house (literally), at first it didn’t mean a thing to me (apart from a sore foot), it was just another big old Vauxhall engine out of a Viva. The truth is that I had only owned a Viva for a few months and knew next to nothing, having the opportunity to pour over the rarity of this engine (if not uniqueness) was lost on me at the time.
Let roll forward to today and I now find myself with a Lotus twin cam in my Viva GT. I have also done some research on the history of the Lotus 900 series engine. I have reported upon a prototype Lotus engine being fitted to a Viva GT, which was owned by Lotus to test the engine. I also now know several others GT owners with hybrid twin cam engines in their Vivas, (Hybrid is where a lotus head is grafted onto the Vauxhall cast iron block) or have fitted a complete Lotus engine like myself.
So is this the complete story then? Either a Vauxhall 8 valve single cam cast iron Vauxhall engine, a Chevette 16v twin cam head (on the same Cast iron Vauxhall unit), a Lotus head on a Vauxhall engine (hybrid) or the full Lotus engine (be it a prototype or factory unit)? No, that is not the complete story, this article is about that other engine (the one I tripped over years ago). The prototype 8 valve twin cam Vauxhall slant four. Designed by Vauxhall tested and researched by one William Blydenstein during 1970.
Part of the story of the Slant four engine, was a leap from 1600cc & 2000cc to 1800cc & 2300cc around 1970. There were two paths followed by Vauxhall, because more power was required to push ever-heavier cars along. The first of the two paths was an increase in the CC of the engine (which was the route adopted by Vauxhall. The other less well know path is that of the twin cam.
At Vauxhall once the FD was launched the slant four engine found its way into the HB in both 1600 and 2000 GT versions and from 1969 in the Bedford CF Van. However, future model plans would require power, the FE Victor was already in development and was bigger and heavier than the FD. Late in 1968 two lines of development were started, a straight forward increase in capacity or by using a twin overhead camshaft but still using 8 valves, although Lotus were already using their 16v engine it was felt to be too complex an arrangement for the family car market Vauxhall aimed at. The other option to increase in capacity was tried in the following sizes: 1685cc 1759cc, 1889cc, 2105cc, 2279cc and 2390cc, the 8 valve twin cam head was fitted to the 2279cc and 2390cc engines for evaluation with both single and twin carburetor breathing. In April 1970 the choice was made for a straight increase in capacity to 1759 and 2279cc.
This story starts in early 1970 when prototype heads given to Bill Blydenstein were tested and results reported back to Vauxhall. The engine design obviously predates 1970, possibly by a number of years, but that data is not available to me at this time. The reports suggest Vauxhall had themselves played around with this engine.
The engine is shown here on a test frame, note the angle of the cam boxes, which mark its design as very different from the Lotus twin cam or Chevette HS twin cam designs:
This engine still exists and is today in the ownership of friends, who wish to get it put back in a Viva GT (where sit belongs). I can see an interesting line up of GT’s in the near future, where all manner of prototype engines reside under the bonnets. The actual engine will appear on this blog in time.
The story as always for me starts with some paperwork found online, which appear to have been typed, photocopied, faxed, re photocopied and scanned at a terribly small resolution. Never fear I have retyped it produce it here. This is part one of a three-part reproduction, finishing with the actual engine itself.
Preliminary Technical Report
The basic engine parts were delivered to us towards the end of February. As we did not receive all the parts required to build the engine it was decided to order not only the outstanding parts but also various other parts required for the development program. The tappet shins were the last to be delivered to us and the engine was started within a few days of receiving these shins, on the 3rd of July. The events leading up to the first engine runs and conclusions to date will be dealt with below.
Preparation of workshop, engine test stand and test vehicle
It was decided to build a separate workshop for this project. This workshop is completely s elf-contained with its own tools and workbenches and is normally kept locked. All twin OHC parts are stored in this workshop.
We also decided to build a test stand for the engine so as to check all basic functions of the engine well before installation in the test vehicle. The test car is, in fact, an old left hand drive Viva GT bought from Vauxhall Motors. The chassis is being modified for right hand drive and the car will be used for road testing the engine.
Basic Engine Block Assembly
We dismantled the engine block assembly to check the condition of the various parts. It was found that a new crankshaft and main and big-end bearings had been fitted and that…
Cylinder Head and Manifold
… the connecting rods had already been polished. Piston weight, although not accurately checked, was found to be considerably greater than that of the normal 2 litre single overhead camshaft engine. No parts were changed or modified at this stage except for the oil pump, which was uprated to give the higher running pressure of 70 lbs/ sq. in.
On examining the head and manifolds it was found that the inlet ports were enormous and it was decided to sleeve the ports down from approximately 48mm to 42mm diameter on both head and inlet manifolds. It is thought that as our racing single overhead camshaft engine is giving 180 BHP net using 40mm diameter ports with plenty of development stretch we shall get all we want from 42mm diameter inlet ports on the twin overhead camshaft engine.
The smaller inlet port diameter is intended to make the engine much more tractable for road use and immediately allows the use of 42 or 45 DCOE weber carburetors as well as Tecalemit Jackson petrol injection equipment on existing manifolds. We are, meanwhile, manufacturing some specially designed inlet manifolds for the racing engine, which are semi-downdraft at the angle of the inlet port in the head.
We reduced the diameter by using a plastic metal, recommended by our pattern maker, normally used for the repair of damaged aluminum castings. This “plastic aluminum” gives a very strong bond but tends to be brittle and the material itself has only been tested up to 100°C temperature. It remains to be seen if this temporary modification of the ports will stand tip to normal engine operation.
As we had been told that excessive quantities of oil seemed to collect in the cam boxes, we took particular care to check the oil drain passages. It would appear that oil drainage from the inlet can box is no great problem, although it is suspected that valve stem seals will have to be used. The exhaust cam box, on the other hand, did not have any drainage from between the strengthening ribs connecting the material round the tappet sleeves to the side of the casting. It was decided to drill oil drainage holes through to the main drainage gallery so as to avoid excessive puddling of the oil by the cam at high speeds. The positions of the holes are shown clearly in one of the accompanying photographs. It was thought that valve stem oil seals would be virtually essential on the exhaust valves.
The only carburetors obtainable at the present moment arc 42 DCOE Weber sidedraft carburetors. These were fitted to the sleeved-down inlet manifolds using the normal flexible mounting plates and ‘O’ rings.
We have to-date received two standard camshafts with a road profile and two blanks with bearing surfaces machined as well as the original camshafts supplied with the engine. Of the latter, one had a damaged cam after a tappet failure whilst on test at Vauxhall Motors. The damage was superficial only and this set of cams was re-profiled to our GT4 profile. The standard camshafts were re-profiled to our GT1 profile and the blanks have been, re-profiled to our GT6 profile. I enclose lift curves of these profiles with this report.
The camshafts assembled into the engine were those with the GT1 profile. No problems were encountered with installation and assembly and we aimed for a clearance of .006″ to .010″ on the inlet side and .010″ to .014″ on the exhaust side. The valve lift with this camshaft is about .395″ and duration and overlap are approximately 290° and 75°according to tappet clearance used.
A simple test rig has been built so as to enable us to start up the engine and check that everything is operating normally and satisfactorily before installation in the test car. The engine started immediately and ran extremely well and smoothly. It idled at about 500 rpm without any tremor or vibration. We used the standard exhaust manifold and, for the time being on the test bed, a Viva GT exhaust system.
Once the engine warmed up however, it was found that on blipping the throttle, puffs of oil smoke appeared from the exhaust system. We removed the exhaust cam cover and found that oil drainage seemed to be satisfactory. On removing the exhaust manifold however, we found that No.4 exhaust port was covered in oil and that No.3 was also running distinctly rich. It is obvious that a head of oil is building up and in the case of slightly worn valve guides; oil is escaping down the valve stems. We think can cure this problem by fitting valve stem oil seals and we may have to think in terms of longer exhaust guides as well to try and get above the head of oil at the rear of the exhaust cam box.
The cylinder head is to be lifted and valve stem seals fitted throughout before the engine is installed in the test car.
We did a test installation in our Group 2 car and found that the standard exhaust manifold was virtually touching the chassis side rail. It is our intention to modify the engine mounting plates so as to give at least ¼” bias towards the right so as to make sure that we got sufficient running clearance between the exhaust manifolds and chassis members.
Conclusions and Development program
It is intended that we test the engine as it stands in the test car. Carburation settings can then be finally checked and an initial power curve will be recorded on a chassis dynamometer. We hope to be able to report on the results f the initial road test program by the end of August. 45 DCOE Weber carburetors will also be tried and test results recorded.
It is already apparent that an oil drainage problem exists but that careful development and small alterations in the cylinder head cores on the exhaust side should take care of this problem in a production engine. It would appear that the inlet valve is the optimum also for the bore of the engine but that the exhaust valve could, with advantage, be enlarged by .100″. This will, of course, only have an effect at power outputs above 150 BHP net but is nevertheless worth considering as it would be easy to incorporate and would give benefits to any future competition engines.
There would still be sufficient clearance between the valves on overlap using the GT6 camshaft. The piston is of course very heavy and, whereas it might be acceptable on a possible production engine, it would become necessary to use either stronger con-rods and/or preferably lighter weight pistons for racing engines
It will become necessary to use a strengthened cylinder block as soon as we start using 7,000 + rpm on this engine. It is hoped therefore, that we shall be able to build up another twin can engine based on a strong cylinder block and using the spare cylinder head, which is in the process of being machined at the present moment. It is not advisable to use the present engine for any high power output testing as it is likely that we shall have a block failure if 7,000 rpm is held or exceeded for any length of time.
If we can get the necessary parts without too much delay this would mean that we could not only produce near optimum power output for competition but we should sometime be able to do some very useful road testing with the present road engine. The initial road tests will use the present engine with the existing exhaust manifold but we are going to send the whole car down to Randall of Carshalton in Surrey to have a proper free-flow exhaust manifold made up which will be suitable for both road and competition use. At each step of the development program, test results will of course be noted and it is hoped that, barring major failures, we shall be able to give a very comprehensive report on the development of both engines by the end of this year as planned.