Lotus 40 Engine

Researched by Richard L. Keyes and Denny Aldridge:

After studying possible configurations and consultation with my engineer, Denny Aldridge, Ford Racing Performance Parts, at Aldridge Motorsports & Engineering, Tel (503) 284-8484, Fax (503) 284-8522, aldridgeracing@comcast.net, we think the Lotus 40 Ford engine was accomplished using the following procedures.

Incidentally, Denny is presently (2017) building us a Replica Ford GT-40 Gurney-Weslake 5.0L LeMans Spec. engine. We are using the Mathwall 5.0L, ex David Weir/Alain deCadanet ME 135 engine as the ‘Master’ but with all new GW parts from Peter Knight, Tel +44 (0)1327-871177, Fax +44 (0)1327-704193 of Daventry, Northants, U.K. We have substituted the original block with new, high-nickel Boss 5.0L because in my conversation with Don McCain, Shelby American Engineer, (from ‘Dragon Snakes Cobra’ fame) any engine with ‘EX’ casting # (4-bolt mains) would break bottom webs at 7200 revs as redline.

Lotus started with a 1965 Ford ’90deg V’ family 289 cu. in. block, 4.00 in. bore X 2.875 in stroke.  (pi = 3.14159)(2.0 in. sq’d) = (3.14159)(4) = 12.566 sq in X 2.875 in = 36.12725 cu in X 8 cyl =289.02 cu in.

This would have been a ‘High Performance’ block with casting #
C5OE-6015-E, (17,000 produced), these were stouter blocks with thicker cylinder walls, high-nodular (think nickel) iron (Denny can’t confirm nickel content, but from his experience, despite popular press of the day which didn’t think so). The crankshaft used were from 312 cu in “Y-block” extended skirt style and forged steel. Forged steel connecting rods with 3/8 inch bolts, pressed freeze plugs, dual point distributor, stronger main bearing caps (2-bolt but fully as thick as webs). 6-bolt bell housing ( these can be identified in car by checking bell housing bolt heads being 5/8 in with 7/16 in NC bolts).

The 289 ‘High Performance’ heads has screw-in studs, slotted pushrod guide holes and cast-in valve spring seating bosses. Of course, porting and matching to intake manifold performed.

The first check for core alignment should be visual. Looking straight
down into cam lifter bored holes, check to see if holes are centered on the raised casted bosses. Core shift will show itself as having unequal thicknesses, fore and aft of boss. After sonic testing cylinder wall thickness and selecting only block capable of being bored 0.060 inch they would overbore. Popular literature of the day wrote a 0.040 inch is maximum for performance, so checking for core shift is essential.

Denny, after many decades of building racing engines, thinks Lotus used 1956-57 Thunderbird 312 forged steel crank (stock stroke of 3.44″). Rod bearing shaft dia of 2.188-2.189″ with main bearings shaft dia of 2.623-2.624″. The stock crank 3.44″ divided by 2 (because stroke equals distance of both up and down movement) = 1.72″ crank-pin offset.

They then de-stroked the crank offset by 0.1496875″ by grinding down the journal (1.72″ crank offset – 0.1496875″ = 1.5703125″ new crank offset X 2 = 3.140625″ stroke.) Note however, this requires first welding up or plasma depositing steel on crank centerline side.

Following math explains why –  Main bearing journal = 2.6235″ divided by 2 for radius = 1.312″, Rod bearing journal =2.1885″ divided by 2 = 1.0943″. Take the 1.0943″ radius of Rod bearing and move it toward crank centerline by 0.1496875″ which leaves 0.9446125″ X 2 = 1.889225″ as maximum diameter of Rod bearing journal. This is insufficient, thus requiring metal deposition on crank centerline side. This also requires ‘Line Boring’ of block to fit 312 crank Main bearings of 2.6235″ vs 2.2486″ dia of 289 block. Of course custom rods are required.

One is left with the following math to determine engine size. 0.060″ pi rad squared = (3.140625)(2.03 inch squared) = (3.140625)(4.1209) = 12.942 sq in/cylinder, stroke of 3.140625 X 12.942 sq in = 40.647 cu in/cylinder X 8 cyl = 325.173 cu in engine divided by 0.061024 = 5328.6 cc.

As for the Techlamit injector manifold, think Lotus probably had them cast and machined. They would also have used sheet metal valley cover.

REV 1.0 – 21 Sept 2017

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