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Learning how to build Lotus Seven replicas...together!
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PostPosted: December 31, 2017, 10:58 am 
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Well, I had a bunch of parts laying around from the evolution of my locat, so I decided that they could be put to better use with the simple addition of a chassis. At the beginning of this month I drew some plans for a +321 frame and ordered the metal. Then jackstanded the trailer and removed the fenders and torsion arms to serve as the platform for the wood building surface. A Duratec 20 and an NC 6-speed followed me home from the local LKQ. The plan (for now) is to build the car just for Dmod use that could be driven by someone larger than my skinny self. My son doesn't fit in the locat (but he hasn't been deprived, he's put plenty of miles on the grey mustang).
So here's the activity that has occurred so far:


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eng location.jpg
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Ft susp setup.jpg
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Rear susp setup.jpg
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PostPosted: January 11, 2018, 5:05 pm 
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It's a roller (well it would if I put air in the tires and you forgive the infinite-rate turnbuckle shocks). :D


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PostPosted: January 12, 2018, 1:12 pm 
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seven13bt wrote:
A Duratec 20 and an NC 6-speed


What was the donor vehicle for those?


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PostPosted: January 12, 2018, 3:20 pm 
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Location: Boise, Idaho
The engine came from an '06 Focus and the tranny came from an '08 Miata.


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PostPosted: January 13, 2018, 9:14 pm 
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Nice simplification of the front frame. I'd be interested in seeing how you did your A-arm mounts in a little more detail, if you have some photos. I'm always looking for good ideas.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: January 13, 2018, 10:34 pm 
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Lonnie-S wrote:
Nice simplification of the front frame. I'd be interested in seeing how you did your A-arm mounts in a little more detail, if you have some photos. I'm always looking for good ideas.


X2 And what steering rack is that? Cut down or stock length?

Nice work!

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PostPosted: January 14, 2018, 12:54 am 
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Location: Boise, Idaho
Photos of the front suspension mounting points. The prefab br@kts are from Coleman as shock mounts including the 1/2" bolt, bushings and nut. The front upper tab is cut from 1 x 2" 0.120 wall box. The front lower tubular section is a carryover from the Lotus design which housed a tapered rubber bushing. The bushing is now a 1" spherical bearing with a 7/16 bore diameter.
The rack and pinion is Triumph Spitfire/GT6 with the stock width ( 24+") but a quicker ratio, 2.6 turns / 5+ inches travel.


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PostPosted: January 14, 2018, 11:04 am 
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Nice progress though your springs might be a little stiff. ;)

Is the forward rod-end on the upper arm going to have enough travel? I initially had the same orientation and later found out that there wasn't enough travel.

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PostPosted: January 14, 2018, 11:50 am 
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The unloaded side (in cornering) will only take half of the angle misalignment available since I'm planning to use the same roll stiffness (very high) as I've been using on the Emod car and I know how much travel is occurring. I've checked it for droop when unloading the suspension completely and it's right on the limit there. So, for now I'm considering it OK.

In the picture, the centering bushings are not installed, so it doesn't look like there's much misalignment available. When they're installed, the spec 12* is available.
Thanks for sharing your experience, Andrew.

Ron


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PostPosted: January 14, 2018, 3:12 pm 
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Thanks for posting the additional photos, Ron.

I have no reason to doubt your calculations, and I'm sure all will work out fine. However, let's say later on you want to change the angle of your front arms for some reason, and you find you need a couple of degrees more. There are some spacers made by Rod End Supply that will replace your centering spacers and give you a couple of more degrees misalignment on both sides. They make them primarily for their own rod ends, but they do machine them themselves, so could undoubtedly make something up for you. Or you could switch to their rod ends, which is probably cheaper. They do drop your bolt size down a little. So, a 7/8" rod end would use a 1/2" bolt after their spacers are added.

Here's their product page on the Internet ==> http://rodendsupply.com/parts/misalignm ... salignment

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: January 15, 2018, 2:48 pm 
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Hi Ron! Some questions about your front end. Are those Pinto spindles? They look like the stock height ones. What size tires and wheels are you using? I'm trying to calibrate the proportions when I look at the pictures.

How do you feel about the steering offset ( scrub )? I'm guessing in general it's not a problem, I do see this on a lot of cars. It seems like it might be an issue if you drop a wheel off the pavement. I suppose puddles are not normally a problem :rofl:

I'm trying pretty hard to reduce my scrub, bit maybe it just doesn't matter very much. It does look like using drop spindles and rod ends or spherical bearings that you could fit the spindle deeper into a 13" wheel. Looking at my parts now the ball joints K772 just barely foul the rim. I'd rather use Heim style joints but am starting with normal ball joints first because maybe it will work better for a street inspection. Just don't know about that yet.

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PostPosted: January 15, 2018, 4:00 pm 
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The spindle is a Wildwood Standard with a Coleman 719 mono ball lower stud. Pic attached with some dimensions. The wheels being used on this car are 13 x 10 with a 4" backspace and 20 x 10 tire. The scrub radius is 4.25". I've used these wheels previously on the EMod car which does have std M2 spindle with a Coleman mono ball stud. (See pic labeled 4" backspace) These turn the spindle into a drop spindle and there is some adjustability on how much drop there is.
When these were used on the Locat in DMod at 1275 pounds (car weight) the 4.25" scrub radius was no problem. After conversion to EMod the weight was ballasted up to 1675 (car weight) per my engine choice. Then the scrub radius was very noticeable even at racing speed. There are pictures of the car on course showing every muscle in my arms getting a workout. The pics were captioned "old school power steering". A couple years ago, I got 6" backspace front 13 x 10 wheels and made 2" longer A-arms. See pic labeled 6" backspace. It is much easier to drive now with a scrub radius of 2.25".
So, if the car is light enough, 4" scrub is OK. If you've got a heavy chassis/engine package, I'd design the suspension/wheel package to be in the range of 2" scrub or less.


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PostPosted: January 17, 2018, 5:16 pm 
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Are those stock Pinto rotors? Just curious how well they work for you, do you do some road racing or mostly autocross?

The longer upper arms you have now should work a bit better for geometry as you corner etc.

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PostPosted: January 17, 2018, 8:20 pm 
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The rotors on the EMod car are 10" Coleman that bolt to the adapter plate on the inboard side of the Speedway Engineering hubs. It's used only for autocross (due to distance from good tracks now). I used to be in northern cali and did many track days at ThunderHill. The brakes worked fine ( as long as the pad compound is correct ). The pad that's worked the best for me autocrossing is Wilwood Polymatrix B. For track days, Performance Friction 82 iirc.
On the new car, I'm going with the 9.25" M2 rotor/hub assembly, primarily to reduce cost and I don't think that the lighter car needs the extra diameter. We'll see. My mileage may very.


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PostPosted: January 18, 2018, 12:36 pm 
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The extended lower ball joint limits turning radius, unless the lower arm is narrowed.
Even then I'm not sure a 13" wheel is going to fit over that?
More back spacing makes packaging even more difficult.

Let me throw a wrench in the thought process here.

I think it was Honda that made a spindle that relocated the upper ball joint above the tire.
What was their goal in that?
Seems like that would reduce king pin inclination and scrub.
I notice a lot of the Mod Lite spindles have little to no king pin inclination.
King pin inclination is a product mostly of packaging.
King pin inclination effects camber in the wrong direction requiring more castor to offset the camber change
This is something I have pondered extensively I am leaning towards fabricating spindles.
Packaging problems fitting brakes into this picture come into play as well.

With the availability of electric power steering, is scrub that big of an issue?
Or is the weight of EPS a bigger issue?

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