Why was I so enthusiastic? Well for those that have done this type of stuff before you will understand that some ideas come and go and one or two just stick and scream “Do it…a gut feel that come hell or high water, this will work”…. It Did.
I still don’t know exactly why but a manifold having an offset primary running into a secondary blasting straight down into meat of the channel……it well just felt sufficiently different to either ‘bomb’ heavily or lead me on an adventure rarely encountered. There was no maths in this other than calculating the volume increase required in the runners to get to 95bhp (a 1272 version of the engine is on the cards), up from the stock 1200’s 60. I cut the two 1200 manifold in ‘half’ lengthwise and offset each so as to arrive at an assembly of the two wider halves that would entertain about 50% more flow. That done I added the 36DCD adaptor, Bolted & Glued it all together. More of this later.
Having come from an engineering environment in which a large part of the learning curve came from the GM engine plant at Aloes in PE, I could never understand the anachronisms that existed in engine manufacture at the time. We could build an engine requiring tolerancing in the piston to bore area of less than a thousands of an inch but in other performance enhancing areas, things were as rough as bears backside…but just as controllable as the piston fit requirement. The issue of blueprinting an engine was a reality, the variation in engine performance between engines was real and much of the improvements seen on modern engines are in exactly those areas today
So in the build of this engine I use that thinking to spec a package that could have been built exactly like this one in the old days. What am I talking about? Firstly, tolerancing in areas critical to stable ignition/cam timing. Crankshaft end float tight, camshaft end float tight, Distributor drive gear clearance minimised. These all end up resulting in absolutely mimimum spark scatter. Linked to similar controlled clearances like piston to head clearance on each cylinder, it simply results in an engine that responds to tuning and if packaged correctly gives consistent results.
The next move was to tighten up on cam timing. I threw away the ratchet plate tensioner used on the more modern versions of the engine and replaced it with the original hydraulic unit. One mod. The unit converted to a manual adjustment to prevent hydraulic flop. In addition the slack side of the chain has no runner. So the wear block built into the cover was moved to provide tension on the slack side. That camshaft was going nowhere.
NOW….the choice of camshaft. What does one do when you have a fifty year old piece of Iron and the only cam grinders you know are purely commercially inspired with no real interest other than the commercial proposition?. You find someone that is driven by wanting to do a steller job. I found that person in Nelis in Cape town. What a breath of fresh air. One telephone call and a few E mails and we have nailed the possibles down to a few and, amazingly again, the profiles are out of a little black book from the sixties.
One thing quite surprising about this OHV Opel engine is the ability to live with ‘bigger’ cam profiles than one would expect for such a small capacity. I had stumbled on the use of Cosworth based profiles in the late 60’s and never moved back. The race profile ended at an A6 and the road profiles other A’s, I seem to remember an A3 for the road 1000 back in the day. Nelis’s suggestion is surprising, “what about an original Meissner” This was a local profile used very successfully on quick 1498 and 1640 versions of the Cortina GT engine back in the day and at a duration around 268° was a little wilder than I had planned. In the 1088cc OHV it may be a handful. Valve lift was OK at 9.6mm. ….That gut feel was still running wild and somehow I had the thought that if I got the dynamic CR right we would be OK on both low speed and mid-range response. We selected an appropriate Lobe split and held our breath.
Valve springs. With the target safe rpm set at 8500, readily available aftermarket springs are just scarce and if available, out of the budget. So the set up was to use the 1200 conical outer from the stock Opel and the Terrys based inners from the race engine. Each spring was individually tested and put together in matching pairs to arrive at he required seat and valve open loads.
The Engine block and cylinder head prep. Old parts need TLC and the first task was to de-scale the block/head water channels and get back to virgin material. When looking for max detonation resistance the need to channel heat away from the working face is critical. This done, the block had been bored to the new piston clearance spec. The piston/ring package was original and not being happy with previous hone jobs from this engineering operation decided on a flex-hone alternative which I know is done brilliantly by Maurice Rosenberg. This was the best decision possible, as once I did get to starting the engine, the rings sealed in minutes….no blow-by and stellar cranking pressure.
Choice of exhaust manifold? This was a bit of a head scratcher but in the end sense prevailed and I went with a known performer rather than a fancy tubular arrangement. The cast stock dual outlet unit off the 1200 FWD engine is known to give good flow performance and a small mod to fit the centre port to the modified cylinder head was needed.
Oils. Old engines need Zinc and modern oils are zinc free so camshaft lobe wear is guaranteed if one does not have a working alternative. Fortunately a local oil manufacturer makes a synthetic mix which so far has done the job. Just to be sure, I used an additional shot of the Zinc additive during start up and the hardening phase of the newly ground camshaft.
Dynamic compression ratio. Despite working at an altitude of 1500M I have calculated DYn CR using sea-level values This because I want to optimise a production engine at sea level not at altitude. I had, on the proto engine run a dynamic CR of 8.9:1 and found this to be satisfactory at altitude but figured it would be borderline at sea level. The new cam gave an IV closing point of 6° later with a static CR of 10.5, slightly down on the 10.8 of the proto giving a dynamic of 8.6. This was the right move as a recent trip to the coast needed only a reduced vacuum advance curve to prevent light part throttle knock at around 3000rpm, full throttle was clean from idle.
In a nutshell with 95 RON being best octane available at both coast and sea level am sticking with the current set up knowing that the package would be happy with a Static CR of over 11:1 if optimised to 5000ft… Now that is quite something when one considers that we are working with a design out of 1961…56 years ago.
Back to the manifold. On start-up I utilised the modified stock carburettor (enlarged choke tube) and modified stock inlet manifold off the proto. The new 1088 was one of those engines that was ‘right’ straight off the bat. I don’t think I did more than 80km before giving it the full beans and found a sizeable improvement against the clock compared to the proto. Everything was better and when one considers the 28mm choke tube running on a dinky 1088cc engine and 268°cam, low speed response and the lack of low speed ‘up throttle bump’ were staggering. The engine would pull strongly from 1000 to around 6800rpm in third (good test gear) and naturally easily to 7500 in the lower gears. So good, I challenge any of the engines of this era to perform this way with similar mods….I could not wait to get that DCD going.