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Dry Sump a 907?  Rating:  Rating
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 Posted: 10-07-2007 01:18 am
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discogodfather
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Hello all,

I am rebuilding a 907 engine from an Elcat and have gleened the forums for all the helpful modifications:

1) Restricted flow to the head
2) Hinged baffel
3) Pan mods

Main question is: Would setting up a 907 to be a dry sump aid in some of the 907 oiling issues?  What would the mods have to be?  Is it as simple as running an extra pump and drawing 15inches or so of vacuum, getting an external tank, modding the oil pan to hold less oil, etc?  Or is this a job for a fluid dynamics engineer with a masters degree (i.e. oiling jetting needed internally, major mods to the oiling system design?)

In my research into the Lotus engine familes I noticed that, starting with the 912 (turbo) Lotus went to a dry sump in 1980?  I am wondering how they did this, what the changes are compared to the 907-911 engines, etc. 

Did Lotus use a belt driven pump?  How much vacuum did they run?

As we all know, Jegs, Summit, Pegasus, etc. all sell belt driven pumps for running vacuum. 

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 Posted: 10-07-2007 11:27 am
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Judson Manning
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A dry-sump alone will not solve the problem.  Lotus did build the 1979(?) Esprit with a factory dry-sump, but dropped it after one year.  Retrofitting a dry-sump system to all but a Chevy 350 is ridiculously complex and especially expensive option.

As we all know, the 907 was really a prototype and there were a number of running changes that culminated in the extremely powerful and reliable 920 variant circa 1995.

The most critical change (IMHO) to the 9xx series oiling system was made circa 1987 when the HCI was introduced.  Along with a number of changes (HTD timing belt, Nikasil liners, etc.) this marked a change from 360^ grooved bearings to 180^ grooved bearings and a cross-drilled forged steel crank.

At it's very core the 907 oiling problem begins with the main-bearing design which allows WAY too much side-leakage under pressure (groove is too wide and shallow).  At temperature, it is impossible to maintain more than 50-60psi with stock bearings.  Anyone understanding why the JH was retrofitted with an oil cooler???

When the mains can't hold pressure, the rods can't be fed enough oil at higher revs = boom!  Utilizing a higher-volume pump and/or a dry-sump only throws more oil at the mains and makes them leak more. 

Retrofitting to the HCI bearings are an obvious choice, but they are more expensive than JH bearings.  Elsewhere in the forum I've posted my solution using Chrysler 318 bearings.  I've used both the HCI bearings and the Chrysler bearings in a few cars including Ron's ITS car with great success.

Given the success I've had with changing over to 180^ bearings, I've since abandoned my dry-sump aspirations except for E-prod racing engines.

 

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 Posted: 10-10-2007 06:01 am
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discogodfather
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Thanks for the info Judson.  I remeber asking Demetry Elgin in his high performance engines class about 10 years ago (in community college) about dry sumping an engine.  We rolled his eyes and told me to get an engineering degree- it's not easy. 

I did manage to find some photos of a 2.2 Lotus racing engine from a Talbot Sunbeam rally car cira 1979.  Looks like they used a belt driven pump in a very logical location- but the photo makes it look so simple. 

Of note on this engine is the wierd intake manifold- looks like a euro manifold chopped in two and rewelded together??  Also the coolant rail (??) running on top of the intake manifold? 


Attachment: Lotus Talbot Sunbeam 2.2 Rally Engine [cira 1979] c.jpg (Downloaded 86 times)

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 Posted: 10-10-2007 10:59 am
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Judson Manning
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The dry-sump grafted to the engines in the picture appears to be an aftermarket design.  The factory Lotus unit was in a similar location, but used the stock oil-pump as one of the scavangers.  I've got a pic around here somewhere... Unfortunately, that location corresponds to where the JH engine mount is located and really isn't an option for us.

To make room for the dry-sump pump Huffaker replaced the stock accessory housing with a custom Weaver pump.  It required re-designing the timing belt, changing over to distributorless ignition, etc.  Ridiculously complex and expensive...but when you have Huffaker resources...you win championships!

The Sunbeam 911 is an interesting variant (forward sump), and was quite right for the times.  Lotus spent another 15 years refining the 910/912 so I find myself searching for inspiration from later designs (ala 912SE and 920).

I really can't argue with my success:  At the Gainesville Solo I back in March, a wet-sump 910 block backed up by an Accusump was more than adequate to maintain good oiling despite the car leaning over 18"!

 

Attachment: GainsvilleSolo1.jpg (Downloaded 151 times)

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