Locofinn's Dmod Seven

locofinn · **Posted:** Mon Jan 05, 2009 8:38 pm

Been on page 2 of builders log too long. Got to update.

I have been working on the chassis floor pan. This took supprisingly a long time to do. If fact the chassis with all brackets and parts fitted could easily be well over 50% of the build time for a race track-only build since the final fit for a street legal car would take a lot more finish type work.

For those keeping track the chassis weighs in at exactly 240 lbs as it sits in the picture below. I have a 16 gauge floor pan fully welded around the perimeter and stich welded on the interior braces. It is solid. If I am going to add weight to the car this is where I want it.

locofinn · **Posted:** Mon Jan 05, 2009 8:47 pm

More pics of the floor pan.

Blackbird · **Posted:** Mon Jan 05, 2009 10:10 pm

Making the minimum weight for D mod?
That'll be a good place to put it, right at the bottom.
Nice work!

Moti

locofinn · **Posted:** Sun Feb 01, 2009 9:40 pm

Garage warmed up a bit this weekend. Finished the rear diff mounts for the 3 link set up. Also got the panhard mount done. The existing lower control arm brackets on the 1st gen RX7 axle worked out perfect as is. I installed the new shock brackets as well as upper third link bracket. Lots of measuring and taking the axle in and out about 4 times. At least it does not weigh much. Always measure twice cut once.

locofinn · **Posted:** Sun Feb 01, 2009 9:55 pm

One more shot showing the axle panhard bracket and lower shock bracket. Yes, it is slightly over engineered but I will be pulling major G forces in autocross. I am also using all aircraft bolts & hardware with the right grip length. Read Carroll Smith Engineer to Win and Prepare to Win cover to cover. Your life may depend on it. :wink:

B85 · **Posted:** Sun Feb 01, 2009 10:28 pm

Looks very good!
I like the three link!
Maybe my next car??
Well done!

locofinn · **Posted:** Wed Feb 04, 2009 9:22 am

As I am working on other design aspects like fuel systems and brakes, I contacted Tilton Engineering to confirm the dual master cylinder sizing using the mustang II front calipers and Mazda RX7 rear calipers. Here is is my input data and their response.

Quote:

Vehicle Info

Make: Lotus Seven Clone
Model: Seven

Front Brake Information

Number of pistons within each front caliper: 1
Are pistons on one side or both sides of caliper: one

Diameter of pistons on one side of caliper (list all):

Piston 1: 2.597 in
Piston 2: mm
Piston 3: mm
Piston 4: mm
Front rotor diameter: 10 in

Rear Brake Information

Number of pistons within each rear caliper: 1
Are pistons on one side or both sides of caliper: one

Diameter of pistons on one side of caliper (list all):

Piston 1: 1.375 in
Piston 2: mm
Piston 3: mm
Piston 4: mm
Rear rotor diameter: 8.70 in

General Information

What is the motion ratio of your brake pedal (5.5:1, 6.2:1, etc)? 6.0:1
OR
If using a Tilton pedal assembly, please provide part number: -
Vehicle weight (with driver and fuel): 1340 pounds
Vehicle Weight Distribution (with driver and fuel): 49 / 51
Vehicle wheelbase: 88 in.
Front tire diameter (outer): 20.5 in
Rear tire diameter (outer): 20.5 in
What is the vehicle being used for (street, road racing, circle track, drag, etc)?: Autocross Hoosier Slicks

The response

Quote:

Hello Mark,

That caliper is way oversize for the front at 2.597" diameter. If you must
use it, you will need a bigger master cylinder in the front to reduce the
line pressure enough. You will need more than twice the line pressure in
the rear than the front and that is the reason for the big difference in
master cylinder sizes. Also included are part numbers for the 74 and
75-Series master cylinders.

1-1/8" front, 74-1125U, 75-1125U
13/16" rear, 74-812U, 75-812U

Results are not guaranteed since calculations require estimates for the
vehicle center of gravity height, tire grip, brake pad friction coefficient,
how hard this particular driver prefers to push on the pedal, and other
factors.

Regards,

Mike O'Neil
Technical Director
tel:      805.688.2353 ext. 103
fax:     805.686.1176
cell:     805.455.4475
mikeo@tiltonracing.com

I am glad I checked with Tilton, my math did not work the same using a common XL spreadsheet for brake sizing. :oops:

You can visit their website and submit your info. They responded in 24 hours. http://www.tiltonracing.com/content.php?page=faq&view=9

I will be buying Tilton master cylinders....

Mark

chetcpo · **Posted:** Wed Feb 04, 2009 9:24 pm

Sweet 3 link. I wonder why we don't see more of those? Well done.

locofinn · **Posted:** Sat Feb 07, 2009 10:18 pm

Finished the panhard bar mounts.

locofinn · **Posted:** Sat Feb 07, 2009 10:22 pm

Fuel tank location options. It is a 3 gallon vertical unit. Not real big but in a little book-sized chassis, it is HUGE!

SkinnyG · **Posted:** Sat Feb 07, 2009 11:37 pm

Passenger footwell.

Blackbird · **Posted:** Sun Feb 08, 2009 3:42 am

If you don't have to use this unit I'd say build a fuel tank like the one in the book and run a pick up point to each side.
It's low, it's in the back and you won't have fuel starvation.

Moti

locofinn · **Posted:** Tue Feb 10, 2009 10:20 pm

I finally put all the front control arm part together for the first time to try a mock-up and see if my calculations are right. I discovered my top control arm mounts are a little low giving me too short of a swing arm lenght. They will have to move. Good thing I only welded the top of one side.

The parts I am using are all off the shelf stock car parts available anywhere. Proven design, lightweight, strong enough for a car weighing much more than my locost. I also can get them sent to me overnight if UPS delivers to the track or my hotel. Not real expensive.

The parts are easy to find and fit the Mustang II spindles. I am using monoball studs for the lower spindle mount in leiu of ball joints. I like how the lower shock mount is very close to the lower spindle mount.

pmatolcsy · **Posted:** Tue Mar 03, 2009 12:47 pm

Just wondering, What keeps the forward lower control arm from rotating along its long axis. The heim joints and ball joints all have freedom of rotation. Most coilovers also have a ball type joint. Wont the arm rotate until it binds?

Phil

KB58 · **Posted:** Tue Mar 03, 2009 1:30 pm

Phil, you get points for being sharp spatially.

I'm afraid he's right. When the shock/spring presses down on the lower control arm, being above the centerline of the arm, it'll "fall over" to one side or the other, jamming the spherical bearing.

About the only way to fix it so to get rid of one of the outboard pivot points, like the one hanging down below. That's one way to keep the assembly from rotating.

Another fix is the lower the shock mount so it's below the centerline of the lateral tube, but only if it remains on centerline fore/aft. If you had two tubes with it in the center that would work, too.

LocostUSA.com

Locofinn's Dmod Seven

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