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Learning how to build Lotus Seven replicas...together!
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PostPosted: Wed Jan 25, 2012 12:11 pm 
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homebrew wrote:
It seems most race sanctioning bodies want the main hoop to start on the lower frame rail then up to the required height and across the cockpit to the opposite side lower frame rail then tie in your upper frame pieces to that hoop. If I were to build another car that is how I'd start. If you look around on this site there are some good examples of this type of construction.
Can you point me to any online discussions or clarifications on this? When I've looked for detailed explanations either way specifically regarding the tube frame chassis design of sevenesque cars by the major sanctioning bodies (SCCA & NASA) that most others take their lead from, I have found little to none. Straight out of the SCCA GCR:

SCCA GCR wrote:
E. ROLL CAGE ATTACHING POINTS
1. Improved Touring, Showroom Stock, Spec Miata, AND Touring
classes–The roll cage must attach to the vehicle structure
(floor pan/ rocker boxes/ sills) within the passenger compartment
in a minimum of 6 points and a maximum of 8 points as specified in these rules.

2. All other classes–There is no limit on cage attachment points.
The roll cage shall be integrated into the frame or chassis.


An interesting point of note is that even in SCCA Spec Miata there are numerous cars legally running their main hoop to the parcel shelf behind the driver, rather than all the way to the floor, and virtually all SCCA Solo legal (no homologation required) Miatae rollbars do the same...I am also 87.4% certain that I have seen recent SCCA Production class Lotus 7's running the main cage hoop to the top of the structure behind the driver.

That being said, finding a way to run the main hoop all the way to the floor is always going to be the safe-bet as that leaves absolutely no room for argument either way.

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Last edited by Driven5 on Wed Jan 25, 2012 1:10 pm, edited 1 time in total.

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PostPosted: Wed Jan 25, 2012 12:37 pm 
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Your frame is not complete yet under the roll bar mount. When it's done it will have 3 or 4 tubes under it. Four tubes would add up to 3 times the cross section of the roll bar tube. Their roll bars bolt to the floor, which is just thin sheet metal. Since cars have become much heavier in recent years, much more powerful and their sheet metal has become thinner it is no longer as safe a practice as it was years ago. We have pictures on our site of a Mustang which simply punched the roll bar thru the floor during a track day.

There is also a set of rather wild videos of a big major incident in a Locost race in the UK where a car goes airborne and flips several times into a barrier and then over it.

Good luck talking to them. Their cars aren't as safe as they think and that makes for a bad situation with over confidence. The high power and high weight typically available these days makes for long sliding distances and heavy impacts. They are also engineered to "feel solid", which is different to being strong...

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PostPosted: Thu Jan 26, 2012 11:04 am 
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SCCA and NASA both allow the main hoop to mount on the parcel tray and not go to the floorpan. I build all of our Spec Miata and T-3 Honda S2000 cages this way and they have never had issues in tech when acquiring a new logbook. You will more than likely have issues with the front roll-hoop or as some call it, the "broomstick" test. Some marques groups use this as their rollbar test in convertible cars where the windshield surround is non-structural. Years ago when confronted with this issue, I used the argument that the broomstick test should be from the main hoop to the front of the valve cover since that is the spot that will contact the ground should the car get inverted. It worked for NASA, EMRA, PCA, NCCC and SAAC here in the northeast.

Just my .02


S-2000 drivers side
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Miata passengers side
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Miata drivers side
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PostPosted: Fri Jan 27, 2012 3:13 am 
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When I started the discussion about rollbars my intentions were to point out to Tongboy what he might face when he gets to tech if he enters an event with ICSCC here in the Northwest. Not create any controversy over the main roll hoop location. I'm just trying to help a local guy avoid the pitfalls I've encountered.

Tech issues can be interpreted differently by each tech inspector you encounter and you're left dealing with how they interpret those rules. My experience here was one tech guy questioned my roll bar and then kept pecking away and suggested I buy a new roll bar from Caterham when in my foolish self pride told him I built the car myself in my garage. Instantly I could tell by the look on his face that I had just made a very big mistake. He then wanted to use his influence to try and get the Executive Board to create a rule to ban homebuilt cars from participating in Conference sanctioned HPDE/driver training days. It was pointed out to him that virtually every car on the track could be considered homebuilt. Then as this got passed on to other officials in the organization I kept hearing time and again how the main hoop needed to or should be attached to the lowest part of the chassis, or on these cars the lower frame rail. That's where I came up with my earlier statement about main hoop location. Again it comes down to how that tech guy interprets the rules.

This happened to me last March and hasn't been and doesn't look like it's going to get resolved anytime soon. I was told if I can get an SCCA stamp to participate in Solo 1 (or as they now call them track trials) then I'm good to go. As I stated earlier this group likes to deflect responsibility/liability to other racing organizations.

Dan thanks for some clarification and by the way nice fab work on those roll cages.

Jim


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PostPosted: Fri Jan 27, 2012 4:58 am 
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Jim - got your email - I'll give you a call to chat

Spent the day in the shop trying to get some forward progress

weights of the diffs
s2000 without stub axles weighs just shy of 60 lbs
Image

open-diff miata diff weighs 62lbs and change
Image

putting a limited slip in the miata would add a few lbs - the stronger s2k diff is the clear winner for the weight.

the complication comes down to the axles - the miata inner and outers aren't compatible at all with the s2000 parts. I'm going to talk to dutchmen in town about sticking the miata outer CVs on shortened s2000 axles because I really like using the miata outer spindles/hubs.

I then went onto sticking the engine in the bay to see what changes were needed.

before any modification this is as far back as the package would go
Image

the fitment was tight at the bellhousing - the s2k trans has a HUGE bellhousing in comparison to other common options

the bottom frame tie-ins didn't fit at all so I had to knock them out - you can see them hitting hte oil pan even when it was high
Image

I ground the bottom of the trans fins down to help bottom clearance and ended up knocking part of the top bar out to get the bellhousing farther back
Image

that put the shifter back right where I wanted it and left the engine about as far back as it can comfortably go in the bay.

bellhousing bottom fitment
Image

that leaves the oil pan sitting about an inch below the frame which is lower than I would have liked but the engine is just so damn tall...
Image

In comparing the height of the engine and fitment with the hood/nosecone it leads me back to again considering going drysump... I was hoping to put it off for the time being to parlay the costs to down the road but I don't want ~2 inches of engine sticking out of the hood getting in the way of my vision.

I need to get some more accurate measurements with the bellhousing fins all cleaned up and the engine sitting exactly where I want it rather than closer to get a good understanding if I can put it off for now.

I put the hoist away and propped the setup in the chassis on some 2x4s and left it there to admire how damn tall it is
Image

I think I'm going to pick up a set of these http://www.speedwaymotors.com/Rod-End-B ... ,1583.html (very locost in comparison to the other similar options) to use for the rear lower outboard mounts to the spindles (similar to how mattrogers did his minus the energy suspension parts costs) and just get the correct size DOM tubing locally - I think they'll also make good engine/trans mounts as well and a single set should do both the rear lowers and 3 engine & trans mounts.

the rear miata spindle upper bushing housing ID is spot on 1.5" in diameter and 1.85" wide - according to http://www.suspension.com/4-bar.htm I can pickup a pair of #9.9483 and trim them down a bit in width and run 1/2" bolts with ease.

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PostPosted: Fri Jan 27, 2012 9:12 am 
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Yes, the F20C is TALL! Unfortunately the way that the pan is a structural/stressed part of the motor/bellhousing I don't believe it can be cut-down without a fair bit of compromising its strength. If its something that you may consider, I can pull apart one of the spare motors I have here at the shop and see how much you can gain.

Let me know and I'll take some pix and measurements.

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PostPosted: Fri Jan 27, 2012 9:31 am 
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In a book frame, that lower crossmember under the trans is supposed to be cut out after welding the chassis. This would allow for some lowering of the engine. Many of us hang the engine no more than 1" below the frame. Not something I would recommend if you don't have to. but it is an option you amy consider. Now if you are running 2" frame to ground clearance, I wouldn't even think about it. I am running 4-1/2" ground clearance to the frame with 3-1/2" to the lower bellhousing and oil pan with no problems (yet).

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PostPosted: Fri Jan 27, 2012 10:48 am 
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Tongboy wrote:
...In comparing the height of the engine and fitment with the hood/nosecone it leads me back to again considering going drysump... ...

Keep in mind that doing so won't improve things unless you also modify the transmission bellhousing, which on most drivetrains hangs down as low as the pan...

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PostPosted: Fri Jan 27, 2012 8:48 pm 
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w650gb500 wrote:
Yes, the F20C is TALL! Unfortunately the way that the pan is a structural/stressed part of the motor/bellhousing I don't believe it can be cut-down without a fair bit of compromising its strength. If its something that you may consider, I can pull apart one of the spare motors I have here at the shop and see how much you can gain.

Let me know and I'll take some pix and measurements.


I'd love some measurements - the only source on the subject that i've been able to find that was meaningful has been http://www.speedracersportscars.com.au/PRBS2K.htm - obviously a dry sump is appealing for other reasons, love the oil control with high lateral load but the downside is the cost and complexity - I tend to like to do a project in manageable scope and then make improvements to it after the fact so I actually see things getting done.

That guy cut both the oil pan and the bellhousing without interfering with anything and the lowest point at the end of his work is the bellhousing and rear of the oil pan by a far amount compared to the front sump.

rx7locost wrote:
In a book frame, that lower crossmember under the trans is supposed to be cut out after welding the chassis. This would allow for some lowering of the engine. Many of us hang the engine no more than 1" below the frame. Not something I would recommend if you don't have to. but it is an option you amy consider. Now if you are running 2" frame to ground clearance, I wouldn't even think about it. I am running 4-1/2" ground clearance to the frame with 3-1/2" to the lower bellhousing and oil pan with no problems (yet).


yeah, with 2.5" ground clearance or so (depending on what ends up being fastest but that's the design model for now) and some known ugly autox areas locally I don't want to have the motor/trans be much more than maybe 1/2" lower than the frame. I know the book calls for removing that post welding, we'll see, it would get the trans a pinch lower but the very front of the trans is the lowest part of it and that cross bar doesn't interfere with the lower part of it.

I got my nose cone from Jack today so i'll pop that on the chassis and see what it looks like - I tend to decide a lot easier when I can visualize it instead of just measure it out.

thanks again all for the insight!

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PostPosted: Sat Jan 28, 2012 6:14 am 
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When you build the frame you decide how low it is. I actually dropped the engine almost 2" below the frame and will be making a lower sub frame with a skid plate (im using a F20c as well).


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PostPosted: Tue Jan 31, 2012 5:11 am 
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Ordered piles of parts from speedway and the chassis fab shop and a few other places. should all be here the end of the week.

in the mean time i've been making very slow progress on the rear-end - I'm using the vodou miata rear plans as at least a basis - the s2k diff is bigger requiring some changes there etc around but it's nice to have some actual plans to look at in the shop.

how my evening started:
Image

how it ended:
Image

Image

I'm not finished with hte placement of the diff yet, I think i'm going to take the rear bar back another inch to make it easier to install/remove the diff when it's all finished

been trading a few emails with the ARE guys regarding their dry sump setups for the f20c. their pans and even their pumps are priced pretty well, it's the rest of their complete system that isn't that appealing with the used nascar parts saturating ebay... I'm working on getting a dimensional layout of their pan with the pump on it to see if it will fit or if i'd need their flat bottom pan and then make my own mount setup farther up the engine side.

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PostPosted: Mon Feb 06, 2012 1:11 am 
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Been working on the chassis pretty regularly. had a few days of shop drama that kept me away but I was finally able to get back in today.

Received a bunch of fun parts from speedway and A&A chassis fab as well as a far used nacar parts - the screw-in ball-joints are the nice low resistance style and on the used market they are very inexpensive

the outer ball joint parts
Image

what the rear end looks like now a days
Image

side shot of the rear
Image

start on the engine mount area
Image

I'm putting the lowest point of the oil pan about 3/4" below the chassis for now. I'll probably migrate to a dry sump in the future and bring the engine down further but for now i'll be satisfied with it being not too low.

I'm going to try and button up the diff, engine & trans mounts shortly and then start working on the wishbones... or potentially farm that part out because i'm not very excited about working with the round DOM tube.

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PostPosted: Sat Feb 11, 2012 12:52 am 
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Tongboy, Don't I know you from the Bimmerforums? LS1 E36 M3 swap?

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PostPosted: Sun Feb 12, 2012 8:24 pm 
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bremms wrote:
Tongboy, Don't I know you from the Bimmerforums? LS1 E36 M3 swap?


that's me! that car is what got me hooked on autox & track driving. what's your username over there?

I've been slaving away - have the engine, trans & diff living in their permanent place and have the driveshaft measurements done to get that cut down.

engine mounts
Image

diff mounts
Image

close-up
Image

lots more welding cleanup to still do, I've just been welding the few area that I need to support things - i'm going to have a race car builder TIG the whole frame when it gets to that point.

fuel tank mounts roughed in place
Image

I'm still really torn on the suspension options. I was originally looking at fabricating the lower front arms but now i'm looking at using circle track stuff - similar to [url]http://southwestspeed.com/?sec=view_menu&cat=Suspension&sub=A-Arms,%20Lower&ssub=!!!Racing%20Tubular%20Arms&sssub=!5/8\%22%20Rod%20End%20Mount,%20Screw-In[/url] with the associated strut-bars. Using the upper and lower stock car stuff leads again to using the mustang 2 front spindles instead of the miata. I measured the miata stuff and compared it to all of the available screw-in ball joints and it's all way too small - addressing the extreme angle of the tie rod as well as the upper and lower ball joint angles on the miata (20' - something that I didn't find documented here) using the mustang parts looks a bit more straight forward and easier to get spares for as well. On the plus side the rear seems fairly straight forward. I know a lot of people get lost on this part of the project and I really just want to get past it while still leaving myself adjust-ability - I don't expect that I'll get it 100% right the first time so i'd rather have some adjustment options and get past the design portion of it. :BH:

I'm having the same gentleman that is TIGing the chassis fabricate my exhaust header as well - having seen his previous work I think that it's going to be nothing shy of art. The collectors will be here early next week- doing a 2 step Tri-Y setup - 1-7/8" oval output from the head to match the ports to a pair of collectors that merge up to 2" and the third Y that merges up to 2 3/8" with a 7' megaphone out to 2.5". I'm hoping this will provide a nice increase in mid-range torque compared to the stock powerband of the motor.

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PostPosted: Sun Feb 12, 2012 9:30 pm 
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Tongboy wrote:
The collectors will be here early next week- doing a 2 step Tri-Y setup - 1-7/8" oval output from the head to match the ports to a pair of collectors that merge up to 2" and the third Y that merges up to 2 3/8" with a 7' megaphone out to 2.5". I'm hoping this will provide a nice increase in mid-range torque compared to the stock powerband of the motor.


It doesn't. BTDT

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