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| Joined: | 05-01-2005 |
| Location: | Minneapolis, Minnesota USA |
| Posts: | 575 |
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There are several variations on the 'DHLA 45' theme, designated by a alpha letter suffix. I'd prefer a 45E, but there's also plenty of Lotus OEM carb set-up info for the 45 (no suffix) as well. Use those Lotus OEM set-ups as a starting point for tuning your carbs. DHLA 45, 45C & 45E all have two circuits, Idle & Main... like 'normal' carbs.
The 45D & 45M re-wrote the rules and have three circuits... Idle, Main & Power Jet. That allows the Main circuit to be jetted leaner for emissions, and relies on the Power Jet to take care of full throttle power. The 45D was used on the Lotus 912HC engine. The 45M was fully sealed so it could be used in 'flow-thru' turbo applications.
You specifically mentioned the 45M. That would be my last choice for a 2.0 or 2.2, naturally aspirated J-H or Lotus 9XX. Neither J-H nor Lotus ever used the 45M on a production 907 or 912, so there is no OEM set-up to mimic as your starting point. You would be starting from scratch, on your own. I have no recommended starting point for you.
Target a Dellorto DHLA 45E as your first choice, 45C as your second choice, and 45 (no letter suffix) as an acceptable last choice.
Are you choosing a '45' as a performance upgrade? J-H chose the smaller DHLA 40 & 40E. Smaller throats & chokes will produce better low end torque and driveability. Many J-H owners go with smaller-than-stock chokes combined with the milder 107 cams in an effort to further improve low end torque and driveability.
But you're choosing the larger DHLA 45 carbs. Is that an intentional choice to hotrod the engine a bit, and improve top end power & performance at the expense of low end easy driveability? That's what the larger '45' carbs will deliver.
So, what's your goal? Easier cruising, or improved top end performance. It's an either/or choice, and "both" isn't a realistic answer. If you want both, then your first step should be to stroke the engine to 2.2 Litres (like the Lotus 912), or to 2.5 or 2.6 Litres as provided by Lotusbits' billet crankshaft kits (Good, but very pricey)
Regards,
Tim Engel