Tag Archives: technical stuff about building cars

A Meandering Post

This post has a lot of subjects to cover so it may seem like the literary equivalent of a one-man ping-pong match.

First things first, I had some kind of gunk in my eyebrows when I took my shower this morning. I don’t know what it was, but it was itchy and took several tries to get it out of the eyebrows. I’m blaming allergies because pollen was deadly high this morning and it wasn’t there when I washed my face before bed this morning. And that’s not a typo, I usually hit the hay between 0300 and 0500.

Sprint-T: The pullrod suspension will lower the C of G very slightly while it also improves shock cooling. It lowers the C of G by letting me lie the shocks down at the bottom of the car instead of standing them up on top of the axle, and it improves shock cooling by collecting a larger mass of air and forcing it around the shocks than they would get just up in the airstream. It seems paradoxical, but you can actually get more cooling by putting something inside a duct than by leaving it in free air. And I was looking at the available springs, I do believe there will be a problem in getting a soft enough spring if I let the motion ratio for the rocker get too large.

My employment situation has gotten worse again. The company I have been getting gigs through has been having problems getting customers to pay for completed projects after delivery, and the standard agreement with us working drones has been payment on delivery to the customer. This has left the company covering for the customers between delivery and payment, but the customers had been paying on time so everybody was good. But lately us drones have delivered on time while customers have been paying late or not at all. Because we drones are technically contractors, or even guns for hire for some of us, we don’t have much recourse when the customer doesn’t pay except to sue the company in the middle that also did not get paid. We can’t sue the customer directly, and the guy we can sue doesn’t have much money to sue for. How this directly affects me is I ordered an expensive comic book (a $20 trade edition) that I was expecting to pay for with my share of a completed project that as of the first of the month hasn’t been paid for, and had to ask Mrs. the Poet for the money so I could keep my account at the comic book store current so I could keep getting my pulls. I only get one pull but there are one-shots and trades I want to get and I have to keep my account out of the red to order them. And yes I do like this particular comic Unbeatable Squirrel Girl enough to actually buy it every month. But with income getting dicey again I’m going to have to change my pre-order to pre-pay when ordering to ensure I get my books.

And I need to pu this to bed and take care of e-mails.

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Not feeling good today

I did several days in a row with 2-3 miles walked with allergies and now my back is complaining, not loudly, but making its presence known. This is my notice to take a break and not overdo things. Also after several days of good behavior the “m” key on the keyboard is acting cranky again, and Google keeps sending me notices that my OS is no longer supported.

Now this can be dealt with in many ways. I can buy a new computer (ha, ha), I can get the keyboard fixed and install Linux, I can install Linux on my Dad’s old computer after I drag it out of the box it has been stuck in since 2012. And one of my friends might have an old laptop they can give me. First I need to call and find out how much getting the keyboard fixed will cost, then work from there.

On the Sprint-T I have been contemplating a frame revision that would add maybe 40 pounds but provide a major increase in torsional stiffness. It isn’t as pretty now, but it will be much more tunable for handling. Basically what I did was make sure all the possible load paths were continuous and triangulated in all 3 dimensions and clear the body. It was that last requirement that has been the monkey wrench in the works, as the body is 34″ wide underneath and 45″ wide at the top and there has to be a structural member to meet the mounts underneath or the body would have not crashworthiness. That’s not the problem by itself, the problem is the diagonal from the top of the rear roll hoop to the bottom of the front roll hoop. Now I thought I had this solved a while back, but when I traced the load paths I found it went all wonky at the front roll hoop. The loads went from in line to bending around the front hoop because of having to have a member under the body and the diagonal snake around the bowed-out sides because there is no straight line from the top of the rear hoop to the bottom of the rear hoop. Interestingly enough, there is straight line access from the top of the rear hoop to the middle of the front hoop, and back to the bottom of the rear hoop, but that places bending loads on the front hoop unless there is a corresponding member from the front suspension support to the front hoop. And that is what increases the weight so much, about 8 additional members about 50″ long each weigh 30 pounds total plus the gussets at each intersection add about 8-9 ounces each end. If I could reduce the size of the structural members any more without worry about damage from people leaning or climbing on the car I could make it lighter, but I have to use the frame as a ladder to get in through the top of the cage.

While I have been writing about fixing the mistakes in my frame I had a show about engineering mistakes and fixing them on the Science Channel on the Tee Vee. Some of those mistakes cost hundreds of millions of dollars to fix, some couldn’t be fixed for any amount of money. I’m just glad I’m finding my mistakes before I spend money building unusable junk.

Happy Beltain!

Today is the arguably the second-biggest holiday in the Wiccan liturgical calendar, after Samhain (pronounced Sow-when (more or less, depending on your particular accent of English)). There’s a rude rhyme that goes with the holiday about how the usual weather on the British Isles is warm enough that sexual activity in the out-of-doors is unlikely to cause death by exposure after this date. If that’s what you’re into, enjoy. Here in TX we have been enjoying that particular activity for over a month now.

I’m not going to explain the holiday here, Witchvox used to have a nice explanation of our liturgical calendar and what the holidays meant to our ancestors, but that was then and this is now. It’s still a celebration of the Earth and its fertility and ability to give life, but we don’t have sex in the fields to show the plants how it’s done. My eyes and nose are ample evidence to plants already knowing how to have sex, and that they are unable to keep their sexual activity to their own species. They don’t need any training on this. I’m just going to say if that’s your thing then party on dudes.

I’m still thinking about the Sprint-T, and how to wrap the cage and frame around the body without any need to cut the body for clearance except the firewall and the bottom where the engine and drivetrain make that a requirement. I have also been looking real hard at the Winter’s catalog for lightweight alternatives with the required 5″ driveshaft offset to match the engine and reduce u-joint angularity. So far the best I have found is the 8″ with the aluminum billet locker as the best compromise between street manners and light weight and also able to handle the HP of the mighty Pentastar. The 7″ is lighter but might be marginal with a Pentastar for street driving and autocrossing. The setup for one or the other would work, but trying to do both requires changing too much going from one to the other. The harder ring gear that would work on the street is just too brittle for the shock loads of the autocross standing start. Think drag racing with 1st and 2nd gear left and right turns and you’ll have a good idea of the stresses of autocross, but the materials that work for that are too soft for street driving and will wear out quickly. The larger 8″ ring gear has enough inherent strength that the harder material will work for both applications.

Well I need to put this one to bed while it’s still Beltain.

Still thinking about the Sprint-T and Happy Earth Day

I was walking and thinking about the Sprint-T. The main thing I was thinking about was torque control of the rear axle and how to do it without spending any more money than I already have. The current plan and existing hardware for locating the rear axle and also mounting the springs and shocks uses a part called a “swing arm” that I have shown a picture of in the past.
These are MY swing arms
Well, I can slightly modify one piece to run a steel link with rod ends that runs from a bracket on the rear axle to a bracket on the nose of the swing arm. This would triangulate the swing arm and make it a rigid link that would prevent the axle from rotating under power and because it’s offset to the right also plant the wheel that lifts when power is applied. Basically what it amounts to is welding a pair of plates to the nose of the arm with a hole to run the mounting bolt through, then running the previously-mentioned link from a bracket under the axle to the nose of the swing arm. Now I couldn’t do this for the 3000 pound car this part is intended for, but for ~1500 pounds and 300 or so horsepower it should be adequate. And if it isn’t the part that would bend or break is not very expensive and is easy to replace, that being the rod end on the front. So I guess I would need to keep a pair of those rod ends and a pair of generic vice grip pliers to remove the broken bits from the swing arm for a roadside repair. But I should be good because the Speedway catalog torque arms for this size vehicle use the 5/8” rod end while this part uses the 3/4” rod end which is up to 30% stronger. And another benefit of controlling the rear axle rotation like this is the ability to almost instantly change the pinion angle from street to race and back again. It’s like a turnbuckle to control the pinion angle.

And with a torque arm this short I would need to run brake floaters to prevent wheel hop under heavy braking. The floater decouples the brake torque reaction from the rear axle and sends it directly to the frame via another radius link, making the rear frame area visually cluttered but dynamically simple. Because the Sprint-T has such limited wheel travel short links from the brake floater to the rear hoop of the roll bar will work in spite of there only being 5″ from the center of the axle to the roll hoop. Then instead of using spring rates and shock absorber settings to control the brake reaction at the possible detriment to handling and grip while turning I can leave those settings for hustling through the corners. And these links will be under very little load, because the torque reaction under braking would be forward from the axle, while the traction reaction from the axle would be backwards. So lightweight aluminum links would work fine between the floater and the frame.

And while I realize my little project isn’t as earth-friendly as riding a bicycle, it’s still an order of magnitude better than anything on this list . So, have a happy Earth Day anyway.

No NASCAR race, and trying to rain here

No race to watch on the flat screen, and the weather is threatening so I can’t go for a walk. That means I have to post something here or go crazy. Going crazy is no fun, and I think you have figured out by now what choice I made.

On really good thing about the Pentastar for the Sprint-T is its extremely short length. There’s 43″ between the firewall and the centerline of the front axle on the Sprint-T and allowing for movement the steering linkage is 7″ behind that so 36″ from the firewall to the effective limit on the space. There’s a 3.5″ thick radiator to leave room for and a 9″ long steering box with a steering shaft that has to snake around the radiator, that goes between the radiator and the axle. Measuring the space from the part where the Pitman arm bolts to the rearmost part of the box as installed on the car and adding the working length of the Pitman arm (7″) I get another 12.5″ between the steering linkage and the radiator leaving just 23.5″ unless I put the radiator over the steering box like they do on the Speedway T-Bucket kit. Putting the radiator in the space between the front of the box and the steering linkage solves a lot of steering issues at the cost of raising the CofG slightly, but the radiator is only 19″ tall and there is literally 27″ to put it in. Mounting the steering linkage below the axle leaves even more room for the radiator in front of the steering box because the radiator can go over the linkage and still leave room for the axle to travel up and down. At this point in the design the radiator is a box that is 26″ wide by 19″ tall and 3.5″ thick that can be moved back and forth and up and down until room has been found for everything else. Anyway, the engine is a 20″ box in front of the firewall that leaves 16″ for everything else. And here you are reading in real time my thought processes as I build the front end of the car.

Recentering my thoughts, there is 16″ between the steering linkage and the front of the engine, the problem is the steering box and the radiator are trying to be in the same bit behind the axle. I could put the radiator on the right and the steering box on the left and have room for both. The steering box is 4.5″ from the mounting face to the right side of the box, 5.2″ total width, and I have 34″ of width to play with behind the axle, 17″ on either side of center. That means I could stuff a 28″ radiator in the car and still not hang out past the frame rails/4-bar if I put the radiator next to the steering box. If I choose to slide the radiator between the steering box and the steering linkage then I have more room for radiator width, but only just, and the radiator outlet would have to be passenger side to prevent interference. The widest radiator I can get a passenger side outlet at the places I’m looking is 31″ which is the inside to inside width of the bottom frame rails when I build to a width of 34″, serendipitous isn’t it?

And it’s time to check e-mail and get ready for bed.

OK I scaled that picture

And that is one tall engine, 29.25″ ±. And about 27″ wide. That means while it will fit nicely between the frame rails that are 27″ inside to inside it won’t fit under a hood that matches the contour of the firewall at 22″ tall. Heck, it’s more than 2″ taller than the entire 27″ tall body, and that’s not even counting the crossmember that needs to go somewhere near the bellhousing to triangulate that plane of the frame. Even without the rather tall intake manifold the engine is 23″ ± tall to the cam boxes on top of the heads, which are also 23″ wide.

This is doable, but I’m going to have to put the driver up a bit to see over/around the engine, and the hood is going to look funny sitting higher than the rest of the body. Possible workaround would be to mount the body higher over the bottom of the frame instead of just on top of the bottom rail, while keeping the driver in the same location inside the body with the seat bottom 3″ above the bottom of the body. This will raise the driver 7″+ in relation to the frame. This is not a good thing from a handling perspective as the driver is one of the heaviest items in the car and needs to be kept as low as possible. But a car you can’t see out of forward is not safe to drive even on a drag strip, so I guess the only choice is raising the body to raise the driver’s eyeline above the engine and put the floor at 11.5″ below the seat. Now how to raise the body 7″+ above the top of the bottom frame rail without adding too much weight to the frame? Since the body is not structural in this car, maybe some thin aluminum structure between the frame and the body, or dropping everything the 7″ and making a bellypan to cover the bits. No that part wouldn’t fly as I wouldn’t have the frame to protect everything should I run over spike strips and get 4 flat tires or as it is put in the original design spec nothing below the bead of the rims except tire at normal ride height. But raising the body does improve the space for people as the driveshaft tunnel would be dropped below seat height, making the possibility of a passenger bench seat next to the driver’s race seat for taking someone to the races or on a ride-along at the race.

I guess I could get someone to print up a manifold that drapes over the camboxes on either side and get a smaller vertical profile that way, and maybe even free up a little horsepower without having to raise the body if I get the top lower than the bottom of the windshield at 24.5″ from the bottom of the body, but that still requires a funny-looking hood that sticks up above the top of the firewall. Not to mention the throttle bodies hanging off the sides of the engine, that would stick out the sides of the hood.

And I really should link to the source of those pictures I have been scaling from in this forum thread . Thanks to myduster360 for starting this thread with the build.

Interesting changes as new technology is applied to old engines

I have been reading articles, and watching YouTube videos, about people putting throttle-body fuel injection on what are now called “Traditional V-8s”. The goal is better fuel economy while maintaining or improving performance. And what they are finding out is that the parts they used to use to get fuel economy with a carburetor don’t work with fuel injection. And also it has been so long since I worked on cars with carburetors that I forgot how to spell it.

Anyway, theory of operation of a carburetor is they suck. Literally, they work by drawing air through a venturi, which creates a lower than atmospheric pressure that pulls fuel from a small chamber inside the carburetor through a metering orifice called a jet, that is then atomized by the airflow and sent to the intake manifold and into the engine. Because of physics explained by Bernoulli’s Law, the faster the air is moving the lower the pressure inside and the stronger it sucks fuel into the manifold, and because our monkey brains won’t stop trying to put 5 pounds of stuff into a one-pound rated container, compromises had to be made in engine design. Since only one cylinder at a time can draw on the carburetor engineers made intake manifolds designed to only use ½ of the carburetor at a time.

dual plane intake manifold

Now we could literally get the same performance with half a carb used all the time, but like I said, monkey brains. Anyway, because of compromises to split the engine in half so that succeeding cylinders draw from opposite halves of the carb, mixture distribution gets moved down in priority by actually having fuel mixed with air. This means that when you use a throttle body fuel injection on the existing dual plane fuel economy manifold, you get an engine that runs like crap because of incompatible fuel delivery methods. You get some cylinders that get too much fuel and some that don’t get enough and maybe one or two that are right but only if you’re lucky.

Now the thing about single plane manifolds is they get all the fuel and air through just one hole in the top, or several holes that are connected inside, so after that they try to get the same mixture of fuel and air distributed to all the cylinders in the same volume of air distributed to each cylinder, so that each cylinder makes the same power and the engine makes as much power as possible for the amount of air it is consuming.

single plane intake manifold

side by side in the wild

The thing is single plane manifolds were generally considered race-only equipment, not suited for street applications and most definitely not for fuel economy on the street, but EFI is changing all the rules. Since fuel delivery is no longer dependent on airflow through a venturi it becomes more important to make sure cylinders all get the same amount of air mixed with the same amount of fuel, to all make the same amount of power so they use less fuel, and don’t just dump it out the tailpipe unburned. And in spite of initially being designed as race-only, with EFI they become the preferred application for street fuel economy. With EFI the Edelbrock Victor Jr. becomes the preferred street performance manifold over their RPM Air Gap dual plane, simply because it’s physically impossible to get equal mixture distribution with EFI from a dual plane manifold. With a carb you could never get decent street performance out of the Victor Jr. manifold because the intake velocity would not pull enough fuel from the carb or atomize it properly. Note in the links the RPM range for the manifolds when used as intended with carburetors, and then realize with EFI that doesn’t apply. That is what modern technology does when used properly. It makes ancient engines run like modern economy engines, almost. And even Edelbrock’s EFI kit comes with a modified Victor Jr. manifold. Notice I have no relationship with Edelbrock other than having installed one of their manifolds on an engine about 35 years ago when I was racing and working on race cars.

Well, that was fun

The auto racing season is underway. The 40th Advanced Auto Parts Clash (originally the Busch Clash) ran at Daytona this afternoon (congrats Brad Keselowski on the win) and as I type this the semifinal rounds of the NHRA Winternationals are live on the tube flat screen. I have never been a drag racer, but they are fun to watch. As an engineering problem the physics are fascinating. The ultimate goal in drag racing is to reach the finish line immediately after the light turns green on the start line either 1320 or 1000 feet away, driven by the wheels in most classes. The chemical and physical bonds between the tires and the track, the thermodynamics inside the engine as fuel is turned into power, and the mechanical transmission of that power to those bonds at the tires, that to me is fun.

SCCA Solo racing is drag racing with left and right turns, so there is some overlap in application to my kind of auto racing in terms of execution but almost nothing in engineering. Drag racing has no lateral acceleration as long as everything runs right as shown when Brittany Force wrecked in the first round of Top Fuel. The word is there will be a report from the hospital at 0800 Pacific on her condition. I sincerely hope she will be OK. For a sport so embedded with fossil fuel use and abuse, there are a surprising number of bicycles in use in the pits and elsewhere in drag racing, so some of Them are really Us.

Brain shutdown thoughts have been on the fact I haven’t included the mounts for the rear springs and swing arms in my plans for the Sprint-T frame. They have a specific place they have to be because the swing arms have a fixed length and connect to something that has to be in a certain place, and they have to be braced in at least two directions so the rear axle doesn’t move around and steer the car from the back independently of what is input at the front. Which is the reason why I didn’t design in roll steer for the rear suspension, because roll steer becomes rear bump steer when you’re just driving down a bumpy road. The slight performance advantage possible racing is more than offset by the possibility of losing control racing or driving on the street. So, the swing arms are level at normal ride height, preventing roll steer or rear bump steer.

And the cat is trying to sit on the laptop so I guess I’m finished.

I need something that will let me turn my mind off

OK I had another situation where I saw something on the internet that caused my mind to run around saying “This is perfect! This will fix all my problems!” and happily run rampant as I try to sleep. What started this was Cleetus finding a Renli 4X4 with nothing except the front and rear diffs left of the drivetrain. A little research tells me those differentials have 1:1 gears and are purpose made to turn a transverse FWD engine and transmission mounted longitudinally into an all-wheel drive drivetrain. And guess what I have with the Town and Country donor vehicle?

I could regale you for pages upon pages of discarded concepts and wild-assed ideas that I came up with while trying to get to sleep last night, and I still haven’t decided yet what I want to do. If I go with the AWD that destroys the sunk costs of the parts I already bought and/or built for the RWD version I have been working to build all these years. Basically the only thing I could use would be the fiberglass body, the windshield posts, and the steering wheel. All the suspension parts would be essentially trash as they couldn’t be sold for as much as half what they cost, especially the custom front axle and the steering parts. That loss would come to about $500 plus my time and labor preparing those parts for installation. In the grand scheme of things that’s not a lot of money, but it represents a ton of hustling for a buck here and a buck there to accumulate that money, like the job that makes $6/month, times a lot of months and a ton of other hustles like it that made $1 and $2 there, scraped together and hoarded to get me as far as I got so far.

Conversely I solve a bunch of problems with weight distribution and tire sizes by getting the mass more forward and centrally located. The Plan is mount the engine and transmission in the passenger side of the body and squeeze me in as best I fit on the driver’s side and all the main masses are right there in the middle of the car, engine, transmission, and fat-assed driver all in one place. Toss all-wheel drive into that equation and I get a race car that works, pretty much in any weather conditions. As a street car I get twitchy but controllable and decent gas mileage because everything’s covered in bodywork or a bellypan out of the wind. There are still some major compromises to finagle, like getting squeezed to the left by the engine and transmission or widening the body by 10″ so I can sit on the left side of the body with nothing intruding from the drivetrain. I am really divided about this, because on the one side I get comfort and space to spread out, and on the other side I get better gas mileage from reduced aero drag and slightly better handling, and a cozy cockpit that keeps me in place because there’s no room for me to move around 🙂

OK just from a performance standard cramming that engine and transmission into the passenger side of the body and cramming me into whatever space is left over will get both the best handling and the best gas mileage and is a lot less work to produce, so I’ll be seeing if there is enough room left for me after the engine is installed in the unmodified body as soon as I finally get said engine and transmission pulled from the donor vehicle, so basically … never. Even if I get the engine into the body I’m going to have to do a lot of work on the body to be able to service the engine for things like oil changes and tune ups. Because of the computer control tune ups are going to be few and far between and consist of removing the injectors and getting them cleaned or replaced and replacing the spark plugs every 60K miles or so. The most frequent service I’ll be doing is changing the oil and filter every 12 months or 12K miles whichever comes first. But I’ll still need to be able to do it without removing the engine first, so either the body comes off or I have to cut holes in the body where I can get to the oil filter and spark plugs on what is now the front of the engine that will be the right side of the engine as it will be mounted in the car.

And just now on my YTM app it pulled up one of my favorite “go get ’em” pieces, the Emerson Lake and Palmer version of Aaron Copeland’s “Fanfare for the Common Man”. That bass line, man it just makes me want figuratively to kick butt and take names. If you haven’t heard it, recently or ever, give it a listen on YouTube. The complete string to enter is “fanfare for common man emerson lake and palmer” don’t even need to use caps or punctuation. This is Montage Music, when I do the video of building the TGS2, this is the music I’m going to play while the pictures flash by.

And it’s about time to put this to bed so I can go there too.

Spitballing other gas tank options for the TGS2

I have been thinking about other places to put the gas tanks than inside the body with me.

One place they will have an aerodynamic effect is between the wheels to fair them in aerodynamically and keep the undercar and top of the car separate aerodynamically. This design would basically be a wall instead of a fence keeping the high-pressure flow constrained to the top and not letting it spill over into the low pressure flow under the car, and also clean up the wake from the tires. This will increase downforce and reduce drag at freeway speeds which will help the gas mileage. Now the bad parts, the tanks will be pretty vulnerable stuck out on the far edge of the car even if I put a protective cage around them. Also putting the fuel out there does bad things to the polar moment of inertia, which is a measurement of how much energy needs to be expended to change direction of the car. The further away the tanks are from the center of gravity the higher the polar moment and the harder it will be to make sudden changes in direction. I could make this work for me in setting up the car for highway use where a high polar moment is good for stability, and run pretty much empty tanks for racing and a low polar moment for a car that changes direction almost telepathically.

A quick punching of numbers on the calculator app gave me over 700 pounds of E85 for near coast-to-coast unrefueled range (2900 miles), so I don’t need to use the entire volume available for fuel, some could be empty space for strictly aero purposes, or the tanks partitioned for ballast use to make the polar moment higher when I want it to be high. But with the tanks out on the edge I’m still stuck with the vulnerable in a wreck scenario. Now the other setup with the tanks inside the body with me but outside the frame gives me a low polar moment with tanks full and even lower with race levels (almost empty) than the outrigger tanks because even the empty outriggers have some weight and so does the support structure even without crash bars.

Something else that occurred to me was that I could use a 1 gallon fuel cell as a surge tank when in street mode and the total fuel capacity in race mode. On the street or even in race mode there wouldn’t be any time that I would drain a 1 gallon tank. In an autocross the longest courses I would run are less than 2 minutes long, while on the street even frequent stop-and-go traffic would not use fuel faster than a low-pressure pump could refill the surge tank, or gravity if the level in the main tanks was higher than the surge tank. There are several models in the current JAZ catalog from a quart to 3 gallons capacity set up for use as a surge tank so I don’t have to design this bit from scratch, just buy and attach the plumbing and drive it, NBD. And looking at the catalog I could easily stuff 2 10 Gallon cells per side into the outriggers without much effort. The only thing that might make it tough is the 9″ width getting towards the front of the enclosure where the tire it’s chasing is only 7″ wide. But a 9″ wide tank can fill the wake just as good as a 7″ one, if not better.

OK then, the fuel system is 4, 10 Gallon fuel cells with foam, 2 per side inside the wheel fairings on the outside of the car with the low pressure fuel pumps mounted between the tanks on each side, connected to a 3 gallon Pro Mod cell with foam as a reserve/surge tank feeding the high pressure injection pump. This gives me a system with enough range to get to El Paso from Dallas with reserve for adverse winds and also use crash-resistant containers to prevent leaks in case of a wreck. Also, dividing the fuel load between several containers limits the amount of fuel spilled in a wreck. Still subject to revision in case of a different donor vehicle, because changing the location of the engine changes everything else, and changing the donor vehicle can change the end of the vehicle the engine is placed in.