Vauxhall 8 Valve Twin Cam slant four (Part three)
Right this is the last part of the technical details of the engine, one more instalment to go where we look at the engine as it stands today.
Part Three :
Third Technical Report
Since our last report we have carried on with our road teat program using 2.3 litre camshaft profiles. There is no further news on the racing engine an most parts for this are still outstanding.
Development and Road Testing
While we waited for the 2.3 profile camshaft to be delivered to us we did some further development using the G.T.1 camshaft. As there was a suspicion of valve burning after our bench tests we reground and lapped the valves and removed .020” from the cylinder head face to slightly increase the compression ratio.
We also increased secondary exhaust pipe diameter to 1 ½” inside diameter machining the exhaust manifold accordingly.
Several days road testing finally gave us the ultimate settings for the 45DCOE Webers as follows:
Main Jet 145
Air corrector jet 200
Pump jet 50
Slow run jet 50 F8
All our road tests wore done by myself and I have added 5% to all acceleration figures recorded by me to give the approximate correction necessary for comparison with all normal test figures which are taken two up. Corrected speedometer readings were used.
Whereas we now got really first class standing start figures the engine simply was not flexible enough even in the 60-80 mph range to compare with my own converted car. This again confirmed my opinion that the G.T.1 profile (virtually identical to the Vauxhall “T.C. standard” cam profile) in too advanced for the cast iron primary exhaust manifold.
The figures obtained were:
Test Results +5% corrected
0 – 60mph 8.2 Seconds
60 – 80mph 11.0 Seconds
Max speed 110 Mph.
Typical road petrol consumption 19.0 Mpg.
2.3 Profiled Camshaft
We received these camshafts in November and fitted then to the engine without any further modificaticn3. On taking the car on the road it became apparent that whereas the top end power was hardly affected (maximum speed was identical), the improvement in torque was very much marked. So much so that once we had found the ideal settings for the 45DCOE Webers the standing start acceleration times showed a further improvement as well. We went straight for the best all round effect on the road and these settings are maximum power settings as follows:-
Main Jet 150
Air corrector 180
Pump jet 45
Slow run jet 50 F8
A full set of performance figures were taken as follows:
Performance taken less air cleaners, mean of opposite runs Weather conditions – wet, windy.
S.S. Acceleration T.C. Corrected (+5%) Viva GT Motore Road Test
0 – 60 mph 8.0 secs 10.7 secs
0 – 70 mph 10.4 secs 14.6 secs
Top gear figures T.C. Corrected (+5%) Viva GT Motor Road Test
20 – 40 mph 6.5 secs 7.6 secs
30 – 50 mph 6.5 secs 7.5 secs
40 – 60 mph 6.4 secs 7.5 secs
50 – 70 mph 6.2 secs 8.6 secs
60 – 80 mph 7.8 secs 9.9 secs
70 – 90 mph 8.8 secs 13.1 secs
Typical MPG 20.1 mpg 21.4 mpg
Max Speed 110 mph 99.7 mph
Cylinder Head Bolts
Just after the above test figures were taken we had two consecutive gasket failures on No. 1 cylinder. It was found that the cylinder head bolts were punching their way into and through the washers (used botween bolt head and aluminium head material) which reduced the gasket load considerably.
The reason for this unusual failure was that the head bolts had been machined so that the hexagon of the head was virtually down to the diameter of the bolt, thus giving little or no support for the head bolt washer.
Tho cylinder head had to be re-machined and we increased the area around the bolt holes so that a larger 1/4″ thick washer of 1″ dia. could bo used with normal hexagon headed bolts. This will allow us to tighten the head bolts to 75 lb.ft. instead of the 65 – 70 lb.ft torque which was all that could be applied.
We shall use a special socket spanner for those head bolts. A production version should use Vauxhall 2000 type bolts of extra length to accommodate an extra large washer to spread the load.
When we received this engine from Vauxhall we were told of the problems of sealing the top end. We found the answer to this problem by drilling suitable drainage holes (see First Technical Report).
We have now further improved drainage by drilling also the small reservoirs formed by the tappet carrier strengthening webs.
Even so, although no excessive tightening of the camshaft cover studs has been necessary we find that the covers tend to fracture longditudinally between the stud lines. the cover castings must be strengthened and the obvious remedy is to increase the transverse internal web thickness to 5/16″.
Valve Stem Sealing
It is essential to seal the valve stems effectively as there is a great deal of oil circulating through the camshaft housings. So far we have found the best seals to be those from the Volvo engine as the 2000 Vauxhall seals tend to be too tight on the valve guide. A modified 2000 seal would be necessary for any production twin cam engine.
Oil gallery Seal
The problem of sealing the oil transfer from block to head is made difficult by the open slot in the cylinder bead. It will be necessary to drill vertically and cross drill horizontally to transfer the oil to the gallery. It will then become possible to use the latest gasket sealing techniques on this engine.
The original terms of reference regarding the development of the experimental Twin Cam Engine were broadly speaking to see what power this engine could be made to develop. Our immediate priority was to build an engine out of the various used parts supplied to us.
It was obvious to us that to achieve any power outputs approaching 100 bhp per litre it would be necessary to build an engine from new modified parts. Orders for the various parts required were placed with the Engineering Department in March/April of this year. We also ordered the outstanding parts required to build the engine from the various used parts supplied to us. In order to test an engine as quickly as possible before attempting a bench test we purchased an old L.H.D Viva GT from Engineering Department and started to convert this to R.H.D before installing the engine (see Preliminary Technical Report).
It was while we were still waiting for the necessary parts to correlate the original engine that we were asked to investigate a road version of the engine as soon as possible. This we have done.
The first test bed results and road tests gave an immediate indication of the camshaft limitations of this engine, With its heavy pistons the rev. limit of this engine would be 6,000 – 6,500 rpm. Due to the lack of space when installed in the Viva chassis there was no room for the proper multi-branch exhaust manifold.Both Engineering and our own bench testing showed maximum power to be at 6,500 rpm. The normal rev. limit of such an engine should boe7,000 rpm which in view of the piston weight versus connecting rod and cylinder block strength is unrealistic. Also, the rather fragile torque curve at engine speeds below 4,000 rpm (due largely to the cast iron exhaust manifolding) finally condemned the use of the advanced Twin Cam or our own G.T.1 camshaft profiles for road use (see Second Technical Report).
Engineering Department supplied some camshafts with the new high lift 2.3 litre profile and after many weeks of testing we have been successful in that we have shown an improvement throughout the revolution range, particularly below 4,000 rpm. we can now briefly recapitulate the lessons learnt during the development programme.
1. Whereas the inlet valve is of optimum size the inlet port size of inlet manifold and cylinder head should be 1 5/8th diameter The present standard inlet port diameter of 1 7/8″ is too large.
2. The exhaust valve diameter could, with advantage, be enlarged to 1.5/8″ diameter.
3. Oil drainage holes round tappet sleeves should be drilled (or cored) as outlined in reports to date.
4. Valve stems should be fitted with efficient stem seals.
5. Internal webs of the camshaft housing covers to be widened to 5/l6″ to prevent longitudinal cracking.
6. Oil supply holes in cylinder head to be drilled so as to enable normal gasket oil sealing techniques to be used.
7. Oil pump relief valve pressure to be unrated to on average of 70 ib/in.
8. Exhaust manifold casting to be spigoted to receive exhaust secondary pipes of 1″ inside diameter.
9. 2.3 camshaft profiles to be used.
10. A distributor cut out should be fitted to limit engine revs to 6,500 rpm
11. A strengthened engine block must be used.
Briefly, this engine shows a great deal of promise and apart from detail problems has been singularly trouble free both on the test bed and on the road. The power output on 45 DCOE ‘Weber carburettors fitted with an efficient air cleaner will be 120 – 125 BHP net. at 6,000 rpm (about 130 – 135 BHP gross) from 1975cc swept volume. The torque curve using 2.3 litre camshaft profiles is impressive and it follows therefore that final carburettor tuning will give a good all round petrol consumption.
To date, we have spent a total of £1,869 from our allocation of £2,000. It is hoped that we may continue our development during 1971 on the new engine as outlined below.
Possible Future Development
Having proved the promise of the basic design of this engine we would like to go on with the development of the 2.3 litre version of this engine fitted with:
a) 1 DCD Weber carburettor
b) 2 DCOE Webor carburettors
c) Petrol injection.
As the remaining outstanding parts on order with Engineering Department are now well on the way we could build a now engine of 2.3 litre capacity and prove the various power outputs for road use which would be approximately as follows:
a) 130 BHP net (140 gross)
b) 140 BHP net (150 gross)
c) 145 – 150 BHP net (155 – 160 gross)
the only additional parts required for this development programme would be the need to manufacture some prototype connecting rods about 1/4″ shorter than the present 2000 rods and a DCD type inlet manifold.
If we were to develop a 2.3 litre racing engine we would expect a power output of at least 200 BHP net.