David Hempy's Miata +442 Locost 7

[Blackbird]

And I thought I'm complicating my build... I would've never thought about doing the whole thing while hanging myself upside down from the ceiling!


BTW, I just recalled the explanation I got about the floor welding the way I told you, I allows for progressive break-away in order to absorb the energy in a front end crash.

Moti

[dhempy]

Started ciphering on pedals. I sat in the seat and adjusted it so my hand fell comfortably on the shifter. I then marked my heel line. Everything about the pedals is oriented around that line. When it's all said and done, I'll probably weld in a heel rest of some sort.

[dhempy]

I'm going with swinging pedals. I think they'll feel more "normal" than floor-mounts, even though some of the experts say floor mounts are better for racing.

Primarily, I'm doing this to retain the stock Miata exhaust header. There's no way do do that (I think) with the master cylinders down there. I may be a bit goofy, as no one complains too much about making their own headers, but I like the idea of stock equipment generally, and specifically on engine systems. Plus, it's one less thing to build!

So, I rigged up a simulated pedal with a folding measuring stick and used the chop saw to sever my left foot. I was going to use the torch, as it would cauterize the arteries at the same time, but I couldn't find my welding goggles so I made do with the saw. Safety first!

[dhempy]

This is my rapid prototyping tool. Makes it *real* easy to try a bunch of different scenarios, and you don't need a dummy sitting in the seat.

I have a theory, that I haven't seen addressed in any of the books I've read. I'm wondering what you all think of this, or if you can point me to an authoritative source regarding pedal ergo.

Anyway, the theory is that the foot pivot (aka "heel"), the brake pedal pad, and the pedal pivot should all be in a line. Well, not always, but let's say at the midpoint of the pedal action. I think this minimizes the sliding between your shoe and the pedal.

For example, the pedal pivot in the photo below (at the 12" mark), was too far forward in the car. As the pedal was pressed, it "lifted away" from the foot, ending up on the toes, not the ball of the foot. Similar if the pedal pivot was too far back.

So perhaps a good starting point is to figure out at what angle your foot is comfortable in the car, then project a line up the soul and put the pedal's pivot point on that line. With a given pedal length, it seems you'd have a pretty small target to find.

What do you think? Are there other factors I'm overlooking?

[dhempy]

I didn't have any pool hose, so I used a coiled air hose to simulate where the exhaust will go. This approach clearly eliminates floor-mounted pedals.

[dhempy]

My oil sump hangs about 1.1" below the frame. I'm thinking I'll give it 3.5" of clearance on the streets, hence about 4.5" of frame clearance. Is that enough?

Depending on geometry and if I ever get some suspension smarts, it will be an inch lower for autocross, or if I ever do any track days.

I'm going to mount a 1" tube in front of it to "take one for the team." Sort of a tiny skid plate. As long as I'm adding a tube there, I'm thinking of making it a diagonal across the open part of the engine bay floor to improve rigidity. Having the skid plate at an angle seems better in the case of bottoming out, as the strike will be less violent and support the car longer as I grind over the speed bump or whatever, instead of just one big bang.

I'll need to confirm that it won't interfere with pulling the engine, of course.

Thoughts?

-dave

[zetec7]

As to floor-mounted pedals - I was originally going to use top-hinged pedals, but found that commercial pedals, to have a reasonable ratio, hung down so far that the pedal pad area was at the instep of my shoe. This was with a low-ratio Wilwood pedal setup, at that, so floor-mount became mandatory. I'm still messing with placement of everything (so that my M/C's don't end up in my motor mount or exhaust), but there wasn't any option. I don't know what foot size you have, but I wear size 12's , and have looong legs.

Just a thought - you might want to try a top-hung setup (maybe out of a donor or something) to see where the pedal pad will end up, before you decide on top-hung pedals.

[davew]

Dave

I have about the same ground clearance to the bottom of my skid plate and have not hit any thing on the road. And Michigan has enough pot holes to completely test the design.

The "X" brace will surely help take some of the twisting loads in that engine bay area. "where you need it".

One more option for your brakes. Take a look at placing the master cylinder to the rear of the pedal if you do not have the room forward of the front fire wall. I would mock up your hood clearance first so you can get the best leverage ratio. An extra inch in the pedal will make a big difference in the set up.

You're making good progress, I wish it was 72* here so I could go bare foot. I'm @ 28* for a high, Dave W

[chetcpo]

Dave, you could always hang them from above like I did. I recommend getting a scuttle and nosecone first thought. I used a straightedge between the two to make sure I had adequate clearance before mounting the pedal boxes. My frame is book so you should have much more room to play with. I also made an adapter plate to utilize the stock master cylinders. Hopefully the pedal effort will still be reasonable. If not I can always retrofit Wilwood masters.

As for an X brace, that's a great idea. My engine hangs down nearly 1.75" and I still have plenty of clearance over it. I could have moved it rearward another couple inches and still been able to get the motor in and out.

[dhempy]

As to floor-mounted pedals - I was originally going to use top-hinged pedals, but found that commercial pedals, to have a reasonable ratio, hung down so far that the pedal pad area was at the instep of my shoe. This was with a low-ratio Wilwood pedal setup, at that, so floor-mount became mandatory. I'm still messing with placement of everything (so that my M/C's don't end up in my motor mount or exhaust), but there wasn't any option. I don't know what foot size you have, but I wear size 12's , and have looong legs.

Yeah, that's what I'm working on (more pix to follow). I've got a reverse-cylinder hung Wilwood pedal (MC's toward rear of the car), and it looks promising.

It seems hung pedals with forward-facing MC's may offer the best vertical clearance, as the pedal pivot is the highest point of the bracket. This lets you get the pedal pad higher. The trade-off (there's ALWAYS a tradeoff... ) is that the bracket and MC's start to crowd the steering column. More on this when I post pedal pix...

BTW, my foot is size 11.

I have about the same ground clearance to the bottom of my skid plate and have not hit any thing on the road. And Michigan has enough pot holes to completely test the design.

The "X" brace will surely help take some of the twisting loads in that engine bay area. "where you need it".

Excellent! Thanks for the info, Dave!

Dave, you could always hang them from above like I did. I recommend getting a scuttle and nosecone first thought. I used a straightedge between the two to make sure I had adequate clearance before mounting the pedal boxes. My frame is book so you should have much more room to play with. I also made an adapter plate to utilize the stock master cylinders. Hopefully the pedal effort will still be reasonable. If not I can always retrofit Wilwood masters.

Yeah, that's where I'm headed. I ordered a Super Scuttle and a TTL nose cone from Jack (free plug! http://www.kineticvehicles.com ) and have them taped in place. I'm too chicken to cut them to fit yet, so both sit optimistically high. A dangerous way to err when fitting brakes under them!

As for an X brace, that's a great idea. My engine hangs down nearly 1.75" and I still have plenty of clearance over it. I could have moved it rearward another couple inches and still been able to get the motor in and out.

Good to hear it. I think I'll wait on that step until the very end...

I went back and read the pedal part of your build log again, Chet. I like your design, and may end up very similar to yours.

One thing that's not clear to me from your photos is how the pedal bracket is supported. The Wilwood installation instructions make it clear that bracket needs to be supported by the horizontal part of the bracket. The vertical part of the bracket (where the MC's mount) is not adequate to support the bracket.


Thanks, everyone for the feedback.

[chetcpo]

Yes Dave I agree the top needs support as well. If you look at the photo I attached to my next post very closely you can see the 1", 1/8" steel support that runs across the top of the pedal mount. This would probably be sufficient but further bracing will be done before the paint goes on. I'm notorious for posting pics of things before they are done.

[dhempy]

Sooner or later, I'll need to address this broken thermostat neck. I haven't pulled the cover off yet, but I'm hoping this is a bolt-on part. The pulley is bent, also. I'm not sure if I'll be able to swap just the pulley, or have to put a whole new water pump on. I probably won't fool with this until I get close to starting the engine...no time soon!

-dave

[chetcpo]

OMG Dave you are giving me flashbacks.

FWIW, I found the thermostat housing for around $15 on Ebay IIRC. It is held on by two bolts, I attached a pic for you. I ended up getting a water pump for around $60 and a pulley for around $14 IIRC. I first bought a pulley off Ebay and they sent the wrong one and wouldn't exchange it.I remember reading that you had a broken diff carrier too. I could make you a good deal on one. I bought one for mine before breaking down and buying a complete RX-7 LSD.

[dhempy]

I bought a Wilwood dual-MC brake pedal on eBay, with the same size MC's that Keith Tanner used. (3/4" and 7/8", IIRC) It was a nice enough price, I'm not too worried if this didn't work out, and I *desperately* needed some hardware in hand to visualize what was going on and spec out exactly what I will end up with, even if it isn't this particular pedal.

You can see half of the Super Scuttle on the passenger side, and a wireframe model (literally!) of the same on the driver side.

I think this can work, although it intrudes a bit into the scuttle, which I'm okay with. The reservoirs might fit there...if not, the remote mount reservoirs could be mounted a few inches away. There's a fair amount of leeway, moving fore or aft, or tilting the entire assembly. Moving it any further aft would require remote reservoirs moved forward of the scuttle, or commit to pulling the scuttle to check the fluid...probably worth avoiding.

(edit: It looks like Tilton MC's may be a little shorter than Wilwood's...might be enough to keep my scuttle intact.)

I'm currently working with the brakemath.xls spreadsheet, but I don't really have enough specs to get too detailed with it. I don't know the vehicle weight, CG height, weight bias, etc., so it's kinda like playing darts blindfolded. But, I'm not too worried about it, given that I'm following the path laid out by all you great guys before me, and that it will be easy and not terribly expensive to change later on if needed.

I'm trying to work the Miata clutch pedal and MC in, but it's not going too well. I think I'll just buy a two-pedal, three-MC set and be done with it.

[dhempy]

OMG Dave you are giving me flashbacks.

FWIW, I found the thermostat housing for around $15 on Ebay IIRC. It is held on by two bolts, I attached a pic for you. I ended up getting a water pump for around $60 and a pulley for around $14 IIRC. I first bought a pulley off Ebay and they sent the wrong one and wouldn't exchange it.I remember reading that you had a broken diff carrier too. I could make you a good deal on one. I bought one for mine before breaking down and buying a complete RX-7 LSD.

AWESOME!!! Thanks, Chet, I was really worried about that. I kept waking screaming in a cold sweat that it was part of the crankcase casting or something and that the entire engine was trash!

Is the pulley a universal thing, or does it need to be a Miata part? Water pumps don't normally come with the pulley, do they?

A few months ago, I probably would have bought your diff. I got mine TIG welded by a pro for about $100, and it looks plenty good. If I break it again (and live to tell about it!) I'll look you up!