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motorisations
The History of the 900 series Lotus Engines
By Tim Engel <tengel@isd.net>
Fri, 10 Jul 1998
The production 9XX engines are Lotus designs. To expedite development, early versions of the cylinder head was bolted onto a Vauxhall block. No non-Lotus blocks were used beyond the first prototype iteration (904) and certainly not in production.
The thread on whether the 907 is a blueblood or a bastard is one that periodically repeats on this list. The following is a reply from my archives... sorry about re-cycling old stuff.
16 Apr 1997, Erik Berg <Erik.Berg@trw.com> wrote:
OK, does anyone know more about the history of the development of the 62 engine? My recollection is that it was *not* in fact a 900 series engine, but was a 4 valve head adaptation of the existing Vauxhall 2 litre block.
The Mk 62's 904 engine was a development mule for the 907, and was a composite of a Vauxhall 2 litre iron-block assembly, a Lotus-spec'd, longer stroke crank and a Lotus prototype cylinder head. Lotus recognized that the most development intensive part of the engine design was going to be the head. To expedite head development without waiting for the complete engine to be designed and prototyped, they "borrowed" the cylinder block from the very similarly sized/ configured (slant four) Vauxhall Victor 2.0 and mated it to the prototype head.
Later, the Mk 62 received the 906 engine, which was a further development of the Lotus design with a prototype sand-cast aluminum block. The 906 eliminated the Vauxhall crutch that had allowed the development program to get a faster jump start and got the engine closer to it's final, all-Lotus design.
The Mk 62 car was built as much as a development test bed for the new engine as a race car. It was felt that racing the engine would accelerate the learning curve.
The aluminum 907 block is very different from the iron Vauxhall block and not just an alloy adaptation of an existing design. However, it's probably (I'm jumping to a conclusion) more than coincidence that the bore centers are the same. The head was first designed to fit the Vauxhall block. Once that was done, why incur the extra work of re-designing it to fit a different bore spacing? Just design your new block to fit the head that was developed in advance of the rest of the program.
- Iron block 2.0 race engine with T-J fuel injection, July '68 (aka, LV220 = Lotus-Vauxhall, 220 Bhp)
- Iron block 2.0 road car engine (non-production, test only).
- 906 Sand-cast aluminum block 2.0 race engine (aka, LV240)
- Die-cast aluminum block 2.0 road car engine
- Aluminum block 4.0 V8 race engine
- Aluminum block 4.0 V8 road engine
- Die-cast aluminum block 2.2 Turbo road car engine
- Die-cast aluminum block 2.2 N/A Sunbeam-Talbot engine
- Die-cast aluminum block 2.2 N/A Lotus road car engine
The 904 had a 95.25mm (3.75 in) bore x 69.85mm (2.75 in) stroke for a 1995 cc displacement... just under the racing class limit. The similar Vauxhall Victor 2000 used the same 95.25 bore, but a shorter 69.25 stroke for a 1975 cc displacement. As installed, the 904 crank was a Lotus specific part; however, I don't know if it was machined from a Vauxhall blank or made from scratch.
Later, the 907 used the same 95.25 (3.75) bore as the Vauxhall, but with a claimed 69.2 (2.72) stroke/ 1973 cc displacement. Just a weeee bit smaller than the Vauxhall engine. The Elite/Eclat/Esprit manuals give the bore dimension to 4 decimal places, but leave the stroke at 69.2 (2.72).
I wouldn't doubt (but I don't know) that the stroke and displacement numbers (.05mm / 2cc smaller than the Vauxhall) were more of a weak marketing attempt to give the 907 it's own non-Vauxhall identity by simply rounding off the numbers.
The 907 was supposed to be an important step for Lotus in establishing itself as a stand-alone manufacturer. However, when Lotus fast-started it's development program by basing the first prototypes on the Vauxhall block, the press grabbed onto the Lotus-Vauxhall identity with a death grip and Chapman couldn't break it. After a while, hearing the press continually refer to his new engine as a Vauxhall or Lotus-Vauxhall started to SERIOUSLY rub Chapman the wrong way.
(Editor's note: There is a copy of a spec sheet for the Lotus 62 in the Race Cars area)
907 Electronic Ignition
By Bernie Benz
Most of you will agree that the original Lucas point driven inductive ignition system is a high maintenance, poor performance nightmare. The later "Lumenition" system (Lucas #41626 distributor), I understand, was not much better because the optical sensing system was unreliable circuit-wise and the LED I.R. emitter and the photodetector are both ultra sensitive to dirt obstructing the optical path.
I have discovered that Lucas has a magnetic pickup electronic distributor (Lucas #41808) and electronic module package used on 1980ish MGAs that is an exact replacement for the above 907 ignition systems. The electronic packages uses the common GM HEI module to drive most any coil. I am using the distributor to drive a MSD capacitor discharge system and stock coil. This distributor is set up for vacuum retard, as is the stock point unit, but unlike the point unit, this distributor is easily converted to vacuum advance by merely inverting the vacuum module and moving the advance plate drive pin to the other hole. A good source for this electronic ignition systems is British Parts and Service, 335 West "A" St., Hayward, CA 94541. Talk to Dorene Carlson at (510) 783-6487. The system, distributor and electronic module, lists for about $200, but with sweet talk she will sell it for about $150.
One more thing... Does your distributor (any and all of the above) leak oil all over the right side of the engine? Replace the distributor shaft oil seal! A superior American made shaft seal for these Lucas distributors is a CR #721513 which can be ordered through any bearing supply house for about $2.
