Sump - That Sinking Feeling

With less than 40mm of ground clearance, on the low side of the sump, means that even with the biggest diameter tire and wheel set up the there is only going to be <75mm ground clearance. Chopping the sum will give a 13” wheel clearance of 80mm. Add on some big wheels and 115mm can be achieved between sump and road. This however will leave the bell housing at 95mm (3 & 3/4”) Slightly lower than the 4” target. But taking into to account the bell housing is a whole lot stronger than the sump, this should all be viable. So it's time to find someone to mod the sump. Chop some off depth and add a bit extra length so that the oil capacity remains the same. This is going to be quite a blow to the project time scale and budget, but is now unavoidable. Deep deep sadness!

The sump chop has just taken the sum(p) of all fears into the depths of despair. The SAAB oil baffle, deep in the depths of the sump, is not going to take well to the sump chop. Not only that but the pick up is really going to object to the low oil levels. Then add the fact that chopping is going to lose 2 pints of VERY precious bodily fluids and we are now in serious doo dars!

So the whole sump is going to have to be redesigned for a whole new concept of oil delivery. Now I know the term seems to echo the mess the project is now in, but none the less we are going to need a "Windage Tray" system. In one way or another with the low level oil sump pan, something has got to stop the the engines life blood crawling up the side of the engine block and leaving the oil pick up and therefore pump starved of oil. This is going to happen on long corners and possibly on hard braking / acceleration. Baffles! Yeah I know for a while so was I. But Baffles with hinges is even worse. So add mouse trap swinging doors and a pressurised charge cylinder. Confused? Good! Now we will begin.

If we turn left the oil goes right and climbs the right wall of the engine block. Bad! If we turn Right the oil goes left and climbs the left wall of the engine block. Bad!

Hey, guess what if we brake or accelerate, yeah yeah you get it.

So if we design a sump with doors that close on the right when we turn left and open on the right and vice versa and when we brake the doors close at the front and open at the back...... Oh you get the picture. If not here it is.

Windage Tray

So the rat run sump uses G-force to close and open doors within the sump. This traps oil around the pick up so there is always oil to pump, well almost always. With low oil levels in the sump a long long right hand corner could still stave the pump. This is where the charge accumulator rushes in to save the day, hopefully.

Accumulator example: At start up the accumulator is pressurised with oil. A a piston within cylinder is force back against 7 PSI of air pressure. Now when the oil pressure drops below 7 PSI the 2 pints of stored oil in the accumulator is feed back into the oiling system. This can give up to 60 seconds of oil feed when the pick up is starved, because the corner went on longer than the cat flaps could cope with. Now we can drive around the roads (cat flaps) or go racing (accumulator).

Die cast boxes, arc welder and alloy plate at the ready oh and a template of the original sump bolt pattern. This part of the project is going to have to run in parallel with the rest of the build so check back here to see the progress.

23 May 2011 the work on the sump begins

With the rest of the car approaching completion its time to return to the problem of the SAAB B204 sump. A new design has been drawn up on the cad/cam and the materials have been chosen that will enable total fabrication of a new sump.

To save the excessive strain on the oil pump the new sump design has been created so that an accumulator is not required. The SAAB oil pump is already being asked to pump oil into a bigger oil cooler. Not only that, the cooler is above oil pump height. So asking the pump to prime an accumulator at start up and after low pressure times would be asking a lot. Better to design and oil pan that keeps the oil under control.

Next problem is the possibility of a very low ride height. Options here include the obvious dry sump and extra pump. This is complex, expensive and full of reliability issues. Option 2 would be to chop and reform an existing sump. Good cheap fix but can it really control the oil under long 3G corners? Maybe not, but for normal road use this is a great fix. Unfortunately the SAAB sump would have to be seriously reworked to allow a low ride height or the ride height would have to be limited to protect the sump.

Final option build a new sump designed to control the oil. Build the sump from mild steel so it can withstand nudges and scrapes. A pliable sump can save an engine an ally sump usually splits before it bends and in the worst case may weep without notice until the big bang moment. All alloys have a bend radius limit and although some can have a tight bend mass manufactured sumps are not made of this grade. Just take a look at one and see the soft bends, kink one of these are a split is almost certain.

Easy of build, welding and keeping costs down against weight had to be balanced. Alloy with tight bend radius capability becomes tough to weld and is expensive. Not only that but temperature coefficient of this grade may cause problems especially for an oil tight seal.

So the new design in mild steel would be the solution.     

Click here to step inside the belly of the beast

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The Original SAAB Sump

After much sawing and welding the new sump begins to take shape. Maintaining the same volume by not sloping the rear section of the sump and increasing the rear and front depth the initial sump shape has been created. Copying and creating the mounting flange was, to say the least, a massive task. Oh for a plasma cutter. But with true grit, fresh hacksaw blades, a milling machine and a grinder the flange has been created. The B204 sump has the oil pick up pipe as part of the casting. So this also had to be recreated in the new sump. My modifying the sump flange slightly at the pick up end the new pipe work was not to hard to incorporate into the design. Protecting this vulnerable pipe was going to take a little more work but that will come later in the design.    

Sump Side view comparison.

Sump Flange View comparison.

Being able to use a lowered pick up section in the new sump will elevate some of the windage tray gates. This makes the design easier and improves the reliability of the sump.

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New Sump Compared to Old