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If you're talking about valuable real estate in a locost, I can't think of anything more valuable than the space taken up by the transmission / driveshaft tunnel. So, I'm looking for ways to cut down on this "lost" space. Hell, I'd shrink wrap the trans and drive shaft it I could!

If you use 3/4" tubes on the side of tunnel, this alone takes out 1.5" from butt space and foot space. If you figure 1" on either side for clearance, you've got 6.5" gone for a 3" dia prop shaft (which is exactly what the Haynes plans calls for).

Likewise, the bell housing clearance is right where you'd like to have more space for the pedals.

So I'm wondering....

The Aussie Mods ("kitcaranalysis.doc") talks about removing those little tubes on the sides, and basically making a square tube out 18 ga steel for the trans tunnel. I'm thinking of having the ""TT1" and "TT7" tubes (Haynes design, bttom and top of trans tunnel) separated by only the minimum amount needed for drive shaft clearance -- about 1/2" on either side, then having sheet metal welded between the 4 tubes, making a tunnel. I'd have to drop something serious (rear end, pull engine/trans) to service the shaft if I did that, unless we could mount the underside with bolts instead of a welded panel?

And, I'm wondering if a smaller diameter drive shaft might work too. I realize there is a bit of science here, but if I'm doing a custom shaft anyway, why not mention it?

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Geek49203 aka
Tim Wohlford
Louisville, KY
Hayes front, S10 +2 rear, Lalo body.

Every decision has tradeoffs. You may be keeping a narrower chassis while widening the butt and foot space. But by utilizing the space as such so you're also reducing the potential strength imparted to your chassis by the tunnel, reducing how far back the drivetrain can sit, and moving the centerline of both occupants closer together which further restricts shoulder room when carrying a passenger.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

Another consideration is what do you intend to do with it?

Some race sanctioning bodies specify a 1" structure around the shaft to prevent it from meeting the aforementioned butt and other dainty body parts, so if you intend to race with any one particular group (or multiples) check what their rules state and then design your left over space from there.

I built my tunnel with 1" tubing with the supports strategically placed to meet the SCCA rules, thereby killing two birds with one stone. I got a really rigid tunnel and if I ever race, I'll be covered!

It's not the building that's hard... it's all the design work!

Cheers!

KS

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Check out Firearm Finishes & Coating for options to ceramic coat your Locost parts. Hundreds of stock or custom colors including Chrome and Clear Coating options now available! High Temp options for hot bits!! Plastics too!!

Never become a pessimist. A pessimist is correct oftener than an optimist, but an optimist has more fun, and neither can stop the march of events.-Robert A. Heinlein

I wish I had got further on my plans for the transaxle locost. Getting rid of the bell housing made a huge difference in room for the occupants. Foot and pedal space are at a real premium. It also added a lot of strength and stiffness to the frame to have a firewall with straight top and bottom tubes and a single simple diagonal. It seemed you could double the frame stiffness right there.

I don't know why the drive shafts are so big in diameter, especially in our use. They are very short and carry less torque then the half shafts.

I think the tunnel can be an upside down U shape, if you have a welded steel floor, and still be strong. You could also skip the square tubes and rely on the steel skin if you do a good job of forming that U shape and attaching it.

You can build protection into the sheet tunnel with a couple of welded in straps.

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
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I used 1"x1/2" tubing to build my tunnel, which bought me an extra 1/4" on each side. Every little bit helps.

Oh sure.... NOW you tell me this!!

HJ is correct, but at a minimum you always need to have some sort of idea about where you want to go before you start the journey.. maybe you deviate along the way, but you have to at least start with an idea.

I needed a flat place for the touch-pad, so mine was a function dictates form and placement. Additionally, I wanted to put as much space as possible between the spinning thingy and the flammable liquid transport lines. Don't forget about those!! Plus don't forget about a place to rest your arms on those long drives... if your planning a street car.

My drive shaft is from my Subaru diff donor and it is 2". My outer tunnel dim is 6" with 1" tube. That allowed an inch of either side in case a mount lets loose, it won't trash the place!

Even with that, I managed to fit two seats that book spec at 19" across... now the passengers seat is ratchet strap squeezed in place, but it's still very comfortable... even for me. Think it came in at 17 1/4"!

Just envision what you want in the end and make plans to get there. It'll happen!

Cheers!

KS

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Check out Firearm Finishes & Coating for options to ceramic coat your Locost parts. Hundreds of stock or custom colors including Chrome and Clear Coating options now available! High Temp options for hot bits!! Plastics too!!

Never become a pessimist. A pessimist is correct oftener than an optimist, but an optimist has more fun, and neither can stop the march of events.-Robert A. Heinlein

I've thought many times that were I to do it over again, I'd go with a removable sheet metal cover wrapped over welded in 4130 straps. My tunnel is conventional, though re-sized a bit. I think it could have been a lot smaller, making seats fit better. Plus, I like the look of the curved tunnel tops. Since I don't race, or even push the car that hard, I'm not too worried about restraining a broken drive shaft. Especially when the shaft and joints were designed for a lot longer and heavier vehicle.

John

It's funny how locked into this particular design we get that even with all the variations of builds, the basic design remains the same.

I was just reading John's post and thinking to myself... Why didn't I taper the tunnel and make it a trapezoid shape? DUH!! No reason to make it rectangular!!

Man... you guys keep changing my plans... I'm never going to get the car done!!

KS

_________________
Check out Firearm Finishes & Coating for options to ceramic coat your Locost parts. Hundreds of stock or custom colors including Chrome and Clear Coating options now available! High Temp options for hot bits!! Plastics too!!

Never become a pessimist. A pessimist is correct oftener than an optimist, but an optimist has more fun, and neither can stop the march of events.-Robert A. Heinlein

Put such a hoop structure on the OUTSIDE (on the human side, not the driveshaft side) of the tunnel. That way the rest of the tunnel is still giving you 1-2" more space?

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Geek49203 aka
Tim Wohlford
Louisville, KY
Hayes front, S10 +2 rear, Lalo body.

You just left the looking cool points at the door! How does that gain you space? 1" on the inside or 1" on the outside... it's still 1.x" thick and it's still taking away from the soft parts (humans) space. Now, if it's a race car... but then you wouldn't be worrying about a pass seat!!

It's like Driven5 said earlier. Everything is a compromise! I made a race ready car, knowing I'd be limited to my choices of seats and mandated safety needs. Many people have used Miata seats... but don't look behind them! Completely gutted and rebuilt. Everyone who has sat in the car, from wife to girlfriend, from young to old, comments on how comfortable they feel despite being quite tight (15.5" on the passenger side) and the hard as a rock appearance. Now ask me that after 1000 miles in a day and it might be different, but things can be done about that.

It seems small on paper, but I was actually surprised how much room there was between the rails after I got the frame basics in place. My twin 19.5" seats are tight, but easily doable.

Get your donor seats and frame together (even if it's in wood) and see what your really looking at before running into analysis paralysis for the tunnel. Between that and talking to a local trans shop to see just how small a shaft you can go with, you might find it a lot easier than you imagine!

Me... I'm off to redo my tunnel. Going to change it to a trapezoid and gain a few inches at the top!

Cheers!!

KS

_________________
Check out Firearm Finishes & Coating for options to ceramic coat your Locost parts. Hundreds of stock or custom colors including Chrome and Clear Coating options now available! High Temp options for hot bits!! Plastics too!!

Never become a pessimist. A pessimist is correct oftener than an optimist, but an optimist has more fun, and neither can stop the march of events.-Robert A. Heinlein

I built a 2-1/2" OD driveshaft, connecting a GM T5 and a miata diff in a miata. The gm shafts often have a step in the OD from 2-1/2 to 3". Also, because it is so much shorter than stock, the OD can be less without whipping at high rpm.

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And if you're not using a 4.x rear end, it won't turn as many revs either. And one can always use thicker walled tube too.

I marveled at my 89 Golf's passenger side half shaft. IT was about 24" long, and the shaft was constructed of tube stock. It handled the stress (gotta figure half of the car's 102 hp) taking shocks that a drive shaft would never take. Have I pondered a 1.5" (or smaller) drive shaft made out of that material, given that my drive shaft won't be much longer that some car's half shafts? Dang straight!

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Geek49203 aka
Tim Wohlford
Louisville, KY
Hayes front, S10 +2 rear, Lalo body.

I never gave the size of the driveshaft much thought. But with some searching, I found this calcaultor: http://www.wallaceracing.com/driveshaftspeed.htm I had to manually enter the modulus of elasticity and the density for steel. It would appear that perhaps 1" dia tube would work without much safety margin. I don't have any idea what a common safety margin should be used. I would think that 1.5 dia tube should certainly work. .062 thick 1.5 dia tube would handle 1.5x the torque and 50% higher speed and be lighter. Play with the calculator.

But my major problem was not one of tube dia, but the yokes and flanges. My diff end yoke/flange extended into the seating compartment, thus requiring some tunnel width beyond the tube dia. Differnent designs may not have this problem. You are left on your own for that evaluation.

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Chuck.

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