Dry Sump and New Transmission

It has been a few weeks since I’ve written an update so here we go:

Most of the changes I have been making lately are minor tweaks to make things fit better or adding detail to an assembly that was only roughly modeled as a placeholder.  However, last week I made a decision which will have a much larger effect on the overall car.  I had been hoping to get away without needing a dry sump oil system mainly due to their high cost.  I knew that it would be something I might need to add in the future based on my goals for cornering performance (2+ G’s) but I wanted to see how the engine held up with just a baffled oil pan and an Accusump.

A dry sump system eliminates any worry about oil starvation due to high cornering (or braking) loads.  Another huge benefit is the very shallow oil pan, which allows the engine to be mounted lower in the chassis while maintaining adequate ground clearance.  That wouldn’t help me much using the Boxster transmission as it was already about as low as it could go.  The axle outputs are about 2.5” – 3” below the transmission input shaft.  Moving the transmission down any further would result in higher axle angles than I would like and possible interference with frame tubes.

There was, however, another transmission option that I briefly considered: the G96 6-speed from a Porsche 911 (996) inverted so the axles spin the right way.  I originally decided against it because the axle outputs were too high (being inverted) when using the standard depth K24 oil pan.  But once you drop the engine a few inches with a dry sump, this transmission becomes a pretty good option.  They are fairly plentiful on the used market and cost roughly the same as the Boxster transmission.

So, as of now, the plan is to run a Honda K24A2 with a dry sump mated to an inverted Porsche G96 Transmission.  This allowed me to drop the engine about 3 inches which will, of course, help keep the center of gravity low but also lower the bodywork height in the rear which will help a lot with the styling I will be trying to achieve.

tt1_layout_5

tt1_layout_6

Something I’ve had to work on is not becoming too attached to a specific design simply because I have spent a lot of time on it.  If something is going to make the car better (lighter, more reliable, less expensive, etc.) then now is the time to do it, during the design phase.  Changes become much more expensive and time consuming to make once actual parts have been produced.  I have already (digitally) “scrapped” 7 versions of the frame but most recently I had trouble giving up on a shift linkage that I had put many hours of work into.  It was designed for the Boxster Transmission and will no longer be needed with the switch to the 911 Transmission.  I though it looked fairly elegant and it is hard to throw it away but fortunately, the new system I am imagining should be a bit simpler and lighter (but maybe not as cool looking).  Well, here it is anyway:

shifter_1

shifter_2

Thanks for reading.

  • Mickey Oswald
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