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 Posted: 06-25-2019 04:42 am
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Esprit2

 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 512
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You stated that the Dellortos are 45mm DHLAs, and you quoted a Lotus part number for the manifold. That would be a match. All Lotus 907, 911, 912LC and 912HC engines used 45mm DHLAs. Only the Jensen-Healey 907 used 40mm DHLAs, and I'm not aware of the JH intake manifold is uniquely JH/ 40mm, or just the same Lotus manifold. Off topic, but perhaps the owner of a UK/ Euro/ ROW JH with an original Dellorto intake manifold can look for a similar part number on it.

Three 'Lotus' Dellorto intake manifolds were used through the years, and they're all basically the same... they all have the same bore diameter. They just moved heater hose spigots around and grew additional drilled & tapped holes for later thermal vacuum switches (emissions stuff, easily plugged), and that warranted different part numbers. The induction portions & mounting flanges were all the same.

The gating item as far as bore diameter is concerned would be the bespoke Lotus die cast spacer plate for the soft mount. It's bore is funnel shaped. The bore is larger at the carb flange, and smaller at the manifold flange, with a lip extension going slightly into the bore. The small end is smaller than the manifold bore. That may sound restrictive, but it actually improves flow and carb performance. There are all sorts of funky flow dynamics going on in an intake manifold, including pressure pulses, reversion waves and reverse flow. That funnel/ lip was developed via Fluid Dynamics (KAMM theory) in order to scrape any reverse flow off the wall, cleaning up flow, and preventing them from getting inside the carb and screwing up the metering dynamics. If you have the Lotus spacer plates, keep them. They're the best available, the only ones with that KAMM lip feature, and none of the aftermarket plastic spacer plates, or the thin steel plates with over-molded O-rings work as well.

JH p/n 93552 = J-H Manifold, used with 40mm Dellortos. I don't know if it's the same as...

B907E0123Y = Lotus Manifold, 907 & 912LC.
A912E2184K = Lotus Manifold, 912HC, more emissions fittings.
B912E2184K = Lotus Manifold, 912HC, even more emissions fittings.

B907E0129Z = Lotus Spacer/ Soft Mount, used with all 907, 911, 912 engines.
A907E6027Z = O-ring, Soft Mount, used with all.

Regards,
Tim Engel

Last edited on 06-25-2019 04:44 am by Esprit2