Something completely different - a very long term tube chassis project
09-06-19, 08:33 AM
#51
Rotary Enthusiast
Cool stuff! I wonder if this company, https://mx3d.com/, could just print you up a frame 
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VA RX7 (10-29-20)
09-06-19, 05:23 PM
#52
spoon!
Thread Starter
I think I'll stick to the manufacturing method I can afford. Believe it or not, in a lot of ways tube chassis is simply the easiest and cheapest way to build a car of this caliber.
09-14-19, 11:51 AM
#53
spoon!
Thread Starter
Because people have asked here and there - there's a screenshot with a camera placed at the human dummy's eye location and about a human FOV. So yeah, the windshield diagonals are visible but not too bad IMO.
09-18-19, 01:09 PM
#55
spoon!
Thread Starter
Slowly hacking away at suspension geometry up front; scrub radius is basically zero without going to anything truly weird like centerlock stuff, roll centers are about where I want, just going to add some more steel to the chassis to accept the pickups and stuff and check camber curves. So much easier to do this all in digital where changing stuff is some clicks and typing, vs doing it later when changing stuff is cutting and welding.
Also I'm about at the point where I need to seriously think about induction. On the "driver's eye" shot you can see 3 runners that I just sorta arbitrarily stuck in there - they don't play all that nicely with structure if I add an airbox. Probably going to have to curve them up and over like the 13J-MM. I was already planning on casting a new water pump housing that puts the alternator low and on the right side like the old competition water pump; would give a good location for an airbox on top of the engine.
09-19-19, 12:58 PM
#57
spoon!
Thread Starter
You're not wrong, but I can only really do it right through iterating on a dyno. What I'm thinking though is that where the end of the straightish runners end up, there's not really as much room - even if I cut out some relatively important chassis tubes, it would basically put the airbox in the wheel well. If I wrap the runners over enough though, the airbox can end up on top of the engine (... like basically every pro GT-class RX-7 or RX-8... hmm...) and there's a lot of design freedom.
12-24-19, 12:01 PM
#58
spoon!
Thread Starter
Some more work on this - found a commercially available FB body, cut a lot of unecessary parts off of it, reduced the polycount and scaled it. Good to see that it pretty closely agrees with my not-very-good attempt at bodywork where the stock contours are. Also raises questions about if I should just CNC rout a whole plug to pull molds from or use one of my spare shells for the stock bodywork - in the grand scheme of things I'm not sure how much it matters either way.
04-04-20, 08:57 AM
#59
spoon!
Thread Starter
Where was I... oh well.
Basically, "hey if I do some changes I can use the same chassis for GT-2 and GT-3 - and I can afford to do GT-3 much more easily" combined with "bleah, I really don't feel like doing another unibody race car."
So have a picture dump a bit.
Back on Wide 5 because boy the costs are attractive. Narrower bodywork because 60" track width and 10" wide tires means I only need about 2" of flare per side - haven't modelled it yet, may just pull molds from EProd stuff.
Round one of tweaks.
Round two. Just a few details here and there. Also got the suspension geometry firmed up and moved tubes around to meet the loads. Part of that is found a narrower commonly available steering rack.
Cut through the plane of the front axle centerline for suspension geometry. Scrub isn't ideal but that's a consequence of Wide 5 - on the other hand, Wide 5 gets me cheap light wheels. If it's too much of a bear I can always modify the design of the 4x100 Howe style hubs later but to start I'd rather have as few custom machined parts as possible.
Dig that driver setback. Going for as much rearward bias as possible.
Starting to order parts... 3.5 gallon dry sump tank, small enough to fit behind the rear bulkhead and in front of the rear axle.
In the next week or two I'm taking a bunch of stuff to work and welding up my chassis table then doing a steel order for chassis tube - I'm happy enough with the chassis design to start cutting and welding.
Oh yeah, also have a bunch of shock parts coming - picked up a used circle track Penske for a shock dyno mule, and have about a dozen different piston types in the mail. I have first draft of spring rates and shock valving figured out, so I'm basically going to figure out how to get there and, for a first cut on shocks, DIY valve a bunch of ebayed used parts. I'm also looking at making a quarter car model (IE, wheel, tire, suspension on a fixture to hold the geometry in the right place, weighted so that the corner weight is right) and running it on one of the servohydraulic tables at work. Basically like a 4-post test but just one corner, lets me try a bunch of stuff in isolation.
Basically, "hey if I do some changes I can use the same chassis for GT-2 and GT-3 - and I can afford to do GT-3 much more easily" combined with "bleah, I really don't feel like doing another unibody race car."
So have a picture dump a bit.
Back on Wide 5 because boy the costs are attractive. Narrower bodywork because 60" track width and 10" wide tires means I only need about 2" of flare per side - haven't modelled it yet, may just pull molds from EProd stuff.
Round one of tweaks.
Round two. Just a few details here and there. Also got the suspension geometry firmed up and moved tubes around to meet the loads. Part of that is found a narrower commonly available steering rack.
Cut through the plane of the front axle centerline for suspension geometry. Scrub isn't ideal but that's a consequence of Wide 5 - on the other hand, Wide 5 gets me cheap light wheels. If it's too much of a bear I can always modify the design of the 4x100 Howe style hubs later but to start I'd rather have as few custom machined parts as possible.
Dig that driver setback. Going for as much rearward bias as possible.
Starting to order parts... 3.5 gallon dry sump tank, small enough to fit behind the rear bulkhead and in front of the rear axle.
In the next week or two I'm taking a bunch of stuff to work and welding up my chassis table then doing a steel order for chassis tube - I'm happy enough with the chassis design to start cutting and welding.
Oh yeah, also have a bunch of shock parts coming - picked up a used circle track Penske for a shock dyno mule, and have about a dozen different piston types in the mail. I have first draft of spring rates and shock valving figured out, so I'm basically going to figure out how to get there and, for a first cut on shocks, DIY valve a bunch of ebayed used parts. I'm also looking at making a quarter car model (IE, wheel, tire, suspension on a fixture to hold the geometry in the right place, weighted so that the corner weight is right) and running it on one of the servohydraulic tables at work. Basically like a 4-post test but just one corner, lets me try a bunch of stuff in isolation.
07-19-20, 08:47 AM
#60
spoon!
Thread Starter
OK, got some stuff done...
Chassis table basic structure welded up and it's home now! Now just need to get steel.
Latest tube chassis version... and I think I'm good.
Been doing FEA on tube locations to try things... that's displacement graphed but stress is less pretty but more useful.
I'm not going to go back and fix the geometry on the first try (in this thread a couple years back) but the very first version was sitting at 400 pounds. The previous peak was about 19,000 ft/lbs per degree of twist, and that version was 350 pounds. Now, tested the exact same way, it's sitting at 28,000 ft/lbs per degree of twist, and 250 pounds. Probably that will go up with paneling and stuff - I'll twist it on a fixture table when I'm done, for fun. But that's good enough.
Chassis table basic structure welded up and it's home now! Now just need to get steel.
Latest tube chassis version... and I think I'm good.
Been doing FEA on tube locations to try things... that's displacement graphed but stress is less pretty but more useful.
I'm not going to go back and fix the geometry on the first try (in this thread a couple years back) but the very first version was sitting at 400 pounds. The previous peak was about 19,000 ft/lbs per degree of twist, and that version was 350 pounds. Now, tested the exact same way, it's sitting at 28,000 ft/lbs per degree of twist, and 250 pounds. Probably that will go up with paneling and stuff - I'll twist it on a fixture table when I'm done, for fun. But that's good enough.
08-03-20, 07:40 PM
#61
spoon!
Thread Starter
More stuff... parts coming in.
Not a 13B flywheel, but it doesn't know that. To fit a Jerico or Hewland trans, I need to make a custom bellhousing anyway, so why do it based off stock dimensions?
Next to an NA diameter Centerforce steel flywheel, for perspective. Also the new flywheel is all of 4 pounds.
Speedway Ministock QC I found a hell of a deal on; apparently they'll last behind a 13B but not behind the Nissan that's in the class. Works for me!
Not a 13B flywheel, but it doesn't know that. To fit a Jerico or Hewland trans, I need to make a custom bellhousing anyway, so why do it based off stock dimensions?
Next to an NA diameter Centerforce steel flywheel, for perspective. Also the new flywheel is all of 4 pounds.
Speedway Ministock QC I found a hell of a deal on; apparently they'll last behind a 13B but not behind the Nissan that's in the class. Works for me!
08-03-20, 07:55 PM
#62
spoon!
Thread Starter
Tomorrow will be some fun stuff with adapting that flywheel to an RX-8 counterweight. Eventually I have a spool coming in for the quick change - my intent is to find a limited slip that I can modify to fit in that space. Found places that'll broach holes to standard stock car style splines... so like hypothetically, take a Miata OS Giken LSD, weld some stuff to it and re-broach the side gears.
Less technically interesting, but how come every time I post in this I need to resub to my own thread? Ugh.
Less technically interesting, but how come every time I post in this I need to resub to my own thread? Ugh.
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mustanghammer (08-05-20)
08-10-20, 06:52 AM
#64
spoon!
Thread Starter
Thing that's been bothering me for a while... finally sat down and designed it.
I need to get a real RPF1 to figure out if the internal profile is right, but, basically a hub to take standard (big, used in circle track) bearings, and go to 4x100. If the mockup Enkei model I have is right, it gets me the ability to push the brake rotor 2" further outboards, which means the outer pivot points move out by 2" which means less scrub, longer control arms and other goodness.
The big thing though is that this time I actually did some research on what bearings I can easily get, and did some thinking on what machining processes are simpler. First hub I did would have taken CNC machining, last hub I did copied something else which was fine but geometry is much more optimized on this for what I'm doing.
I need to get a real RPF1 to figure out if the internal profile is right, but, basically a hub to take standard (big, used in circle track) bearings, and go to 4x100. If the mockup Enkei model I have is right, it gets me the ability to push the brake rotor 2" further outboards, which means the outer pivot points move out by 2" which means less scrub, longer control arms and other goodness.
The big thing though is that this time I actually did some research on what bearings I can easily get, and did some thinking on what machining processes are simpler. First hub I did would have taken CNC machining, last hub I did copied something else which was fine but geometry is much more optimized on this for what I'm doing.
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gracer7-rx7 (11-14-20)
09-14-20, 03:58 PM
#65
spoon!
Thread Starter
Oh yeah, I had more cool parts come in a while ago.
Itty bitty quick change rear end! Speedway Engineering Mini Stock for those keeping track at home. Ring gear is only a little bit bigger than Miata. Ring and pinion are trashed on this one but they almost never come up on the used market and rebuilding is cheaper than new.
One of the side bells to show how it goes together. Not doing that snout solution but the steel tubes just come out.
Riley and Scott water to oil cooler, as used in a lot of stuff. Not sure if that'll be a race car thing or a dyno thing.
Pimpy Alcon rear pivoting master cylinders and fabricated bracket to adapt them to normal pedal setups. Paid nowhere near list value for them, too pimpy not to jump on.
Things are a little bit slower due to income levels but I realized I never had pics of this stuff.
Itty bitty quick change rear end! Speedway Engineering Mini Stock for those keeping track at home. Ring gear is only a little bit bigger than Miata. Ring and pinion are trashed on this one but they almost never come up on the used market and rebuilding is cheaper than new.
One of the side bells to show how it goes together. Not doing that snout solution but the steel tubes just come out.
Riley and Scott water to oil cooler, as used in a lot of stuff. Not sure if that'll be a race car thing or a dyno thing.
Pimpy Alcon rear pivoting master cylinders and fabricated bracket to adapt them to normal pedal setups. Paid nowhere near list value for them, too pimpy not to jump on.
Things are a little bit slower due to income levels but I realized I never had pics of this stuff.
09-24-20, 08:24 PM
#66
spoon!
Thread Starter
Well, since I'm not buying tube, might as well focus on stuff that's cheaper. So, that's a Jerico-to-13B bellhousing setup for the small diameter flywheel setup I posted before. Going to work on pattern making and sand casting - might take a few tries to get right but what the heck, I've got a bunch of scrap aluminum around.
09-25-20, 07:20 AM
#68
spoon!
Thread Starter
The Mini Stock is designed around 28 spline axles; apparently they'll do a crown spline outer end too. Actually, probably those axles could be used for a Mazda based floater, or at any rate I've seen the Aussies broach the Mazda diff gears to Ford 28 spline.
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mustanghammer (10-29-20)
10-31-20, 11:59 AM
#73
Rotary Enthusiast
Forgive my ignorance, what's the reason to do this?
10-31-20, 12:36 PM
#74
spoon!
Thread Starter
Resonance tuning - a bit cruder but cheaper, more reliable, and easier to package version of the R26B sliding trumpets. With the trumpets down the runner length is about 450mm for a tuned rpm of 7k-ish rpm, with them up the runner is about 375mm for a tuned rpm of 8200ish. So for no performance penalty, either extends the torque peak downwards or carries it upwards compared to a fixed length.
10-31-20, 08:47 PM
#75
Rotary Enthusiast
Interesting, thank you. And it sent me off looking at the R26B system that you referenced. Cool.