Tag Archives: technical stuff about building cars

Another update without real information

First of all the good news, Mrs. the Poet has lumbago and can be treated by a combination of steroid injections and physical therapy. That means she might stop yelling every few steps as her back locks up and her feet go to sleep at the same time as her back goes wonky. Her TBF is about 6 feet now when it was 10-12 feet just a few weeks ago. She also has an issue where here spinal column is smaller than it should be where the actual nerves pass through which also contributes to her pain and feet going to sleep.

The “meh” news I was awake all night last night thinking about alternative rear suspension/engine mounting for the A/MOD car and I’m writing sleep-deprived again. Also was thinking about alternative front suspensions for the same car because why only change one thing? This was because I changed the engine from the cruiserbike V-Twin to a Predator 670 V-Twin and the exhaust and the drive are on the same side meaning the engine has to go on the left of the car to keep the engine from blowing exhaust right in the driver’s face. The cruiserbike engine has exhaust on the front of the front cylinder and the back of the rear cylinder meaning it can be run out the right side of the car and the drive is on the left. All this means is the jackshaft for the 670 has to be longer than for the cruiserbike because it has to go all the way across the engine while the bike engine just has to go far enough to reach the drive chain from the transmission.

I also thought about a mount on the rear suspension like the old Malibu Virage cars and some Chinese kart style dunebuggies and some RC cars, but I discarded the idea as having too high an unsprung weight with the engine bouncing around with the rear axle. It sure did simplify the drive to the rear axle though and lightened the car up a bit.

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I have been having bad brain days for a while

This is normal right after my death day, and it doesn’t matter if there’s a big shindig, or I’m all by myself like this year. The difference is when there’s a big shindig it doesn’t last very long, and when I only have the cats to be with I get down for much longer. This year the cats didn’t show up either but they did come back in the morning, but I still got way down. This was a bad year for this particular problem. The only social group I interact with any more is the RPG Group. And nobody responded to my Twitter invite or my FB save the date. I never saw the FB thing go live so that might have been a mistake on my part setting that up.

But anyway, the end result was a lack of desire to write anything more complex than a grocery list, or work on the Mini Sprint-T, or the Sprint-T. I knew I was starting to come out of it when I started thinking about building a car for SCCA Solo racing A-MOD using a V-twin engine from a cruiser motorcycle and a setup that was basically a scaled-up shifter Kart with the suspension and brakes needed to be a legal A-MOD car. I planned on using Midget or Micro-sprint spindles (pretty much the same thing) with pavement brackets for big brakes on both sides (dirt spindles have a smaller brake on the left side only), hung on an axle made from wrapping carbon fiber around a foam core and steel inserts for the kingpins to ride in. The idea was to use a beam axle to keep the tires pointed in the right direction for camber and then make that sucker as light as possible for the lowest unsprung weight. I was going to use a rear axle from the mini- or micro-sprint to connect to the chain drive from the motorcycle engine with a jackshaft for initial gear reduction and moving the final drive to the center like on the Grind Hard Plumbing Princess Jeep only with much less articulation because pavement racer instead of dirt crawler/buggy like the Princess Jeep. But what they did prove was that using a small sprocket on the axle prevented chain bind or jumping when the axle was twisted through a range much further than an A-MOD Solo racer would ever see outside of a wreck. So Imma steal that idea for my car.

Also the reason I’m stealing the jackshaft idea is I’m mounting the engine way off center to balance the driver weight and to keep the polar moment as low as possible by keeping as much mass in the center of the car as possible. Driver to one side, engine to the other with both as close together as physically possible given the need to balance left-to-right and the need for the final drive chain to ride in the center of the axle. I’m leveraging my skinny butt to get as close to the centerline as the chainguard will allow, because I’m only 13″ wide at the hips. This reduces my moment arm from 11.25″ in the Sprint-T to 7″ leaving clearance for the chain and chainguard because I don’t have to leave room for another person, just the engine. I have really wide shoulders and a really skinny butt, like my Dad, and that’s the main reason why the driver moment is so large in the Sprint-T because I have to leave room for a passenger by the rules for Goodguys.

I also knew I was getting better when I started looking through the Hoosier tire catalog looking for the right tire to use when racing the Sprint-T in SCCA Solo events. Basically I was looking for short, wide and sticky that would fit a 15″ X 8″ or X 10″ wheel because there are light, strong, and cheap wheels in those sizes available in several different offsets that fit one or the other of the bolt circles on my hubs. I also used more than just the road racing tires and went into the pavement oval listings to see if there were any tires that came close, and I found a couple in the section for Modified class, and pavement sprint and Supermodified classes which despite being vastly different in layout use pretty much the same tires. Those tires were larger in diameter than my ideal of <23", but were considerably wider than most of the road race offerings with tread widths of 11-13" compared to the 8-9.5" of the road race catalog. The suitable tires for the pavement oval racers were 24-25.5" in diameter compared to the road race tires in the 22.5-23.5" diameter but much narrower as the diameter decreased. Also the oval racing tires are bias-ply while the road race tires came in a mix of bias and radial depending on the size, which tosses another variable into the mix. Radial tires have higher peak grip given the same size and compound, but bias tires are much more controlable at the limit and come in wider tread widths with stickier compounds, so ultimate grip becomes a wash. Also, the reason why there are so many size and compound choices in the oval tire section of the catalog is oval cars run different size and compound tires at each corner in the sprint and Supermodified classes to balance the handling or to use different diameter tires to force the car to turn left when running a locked rear or a solid rear axle (same thing, just built differently) so the right tire drives the car to the left.

It has been a bit difficult to type this in as Clint has decided to lay on my lap on his back demanding tummy rubs which means I have to type with one hand while holding the cat with the other to keep him from sliding off my lap and grabbing me with his claws to keep from sliding. That usually results in long deep scratches. And now he lost interest and has left the room.

Which makes for a good time to end this and hit "Post"

OK Finished the Archive Crawl of QC

I finished the archive crawl of Questionable Content last night early early this morning and saw patterns in his creative processes, but I really didn’t help my problem. I did see an ongoing art evolution that gradually became more of a character evolution, but aside from taking my mind off the subject enough that I am able to post this about my observations I didn’t find anything that would break my creative block, at least as far as writing is concerned. Now for the Sprint-T and the Mini Sprint-T I have found a few things to move that design along, but only in details. So far the major parts of the build are pretty much set in stone, but there are a ton of details that have to be resolved before the design can move forward as the tiny details cascade backwards into major changes in other parts of the build.

One of those tiny details is the steering arm location and orientation on the spindle. There are two locations and two orientations that result in 4 different locations for the drag link connecting the pitman arm on the steering box to the steering arm on the spindle. This cascades into different locations for the steering box because the drag link needs to be pretty level, or close to it if other things get in the way, which basically means there are 3 different places I need to put the steering box depending on how I mount the steering arm on the spindles. That’s because there are 2 combinations of mounting position and orientation that put the drag link in pretty much the same place.

Actually there’s no real technical reason for making the drag link level. The drag link and the panhard rod or lateral link (same device, different names) need to be parallel to prevent bump steer, and ideally the lateral link should be roughly level with the ground to prevent excessive side-to-side motion which would change the way the car turned depending on ride height. In the end it just makes things slightly easier to finagle to have the lateral link level at design ride height, and as stated earlier having the drag link parallel to the lateral link prevents bump steer and other steering maladies.

Another tiny detail is mounting the alternator, and I think I have that one nailed down. The only belt-driven device on the engine will be the alternator as the power steering will be electric, so no power steering pump, no AC so no AC compressor, and the water pump will be electric to reduce total drag on the engine and also improve cooling efficiency by driving the pump at the speed for best cooling regardless of the engine speed. That only leaves the alternator that needs to be driven by the engine directly. As I pointed out a while back there are 3 bosses on the passenger side of the block that are designed to have a bracket for an engine driven device bolted to them, the bracket for the AC compressor specifically, but there is no reason why that device can’t be the alternator instead. What I was thinking is a plate that bolted to the side of the block and another plate that gets welded to that plate that the alternator bolted to with one bolt hole being the arced slot that the bolt that adjusts the tension of the belt slides through. That front plate can be just bent from the side plate to avoid a welded joint, but that’s more of a “what can I do with the materials and tools I have?” than the other kind of design question. Obviously both bolts that go to the alternator would have to be on the same plane or pretty close (talking washer thickness differences more or less) which means I need to do a little bit of measuring when I go to the parts store to pick out an alternator, but for the Mini Sprint-T I just pull one from the parts box and bend a bracket from sheet plastic to glue to the block and alternator to hold it. I just have to line up the crank pulley and the alternator pulley until the glue dries, then run a simulated belt around the pulleys.

And there is a valid reason the alternator goes to the passenger side of the engine that goes back to mounting the steering box on the driver’s side of the frame and leaving room for the box and the steering shaft. If you thought Tetris was fun wait until you have to package the front end of a hot rod. At least when I have to shave material off the model to make things fit a hundredth of an inch on the model is a quarter of an inch on the full size car, or what’s basically molding flash on the model is major structure on the real car. And the engine and transmission is going to be offset to the right to counterbalance my weight to the left, another design decision made a long time ago. I have to find good weights for the engine and transmission.

I have a weight from a GM technical publication of 255 pounds full of fluids for the transmission, and a weight from a GM parts catalog of 614 pounds for the fully-dressed version of the motor I will probably get from the junkyard but nothing accurate for the junk I will be pulling off. Anyway I can assume about ~50 pounds for AC and power steering and assorted junk brackets so 565 for the engine and 255 for the transmission and 30 for the full of fluids torque converter adds up to 850 (!) pounds for everything on the right side of the car, balanced by my 210 way further from the center on the left. Doing the math my moment is 210 pounds times my arm of 11.25″ or 2362.5 Pound inches of moment and dividing that moment by the 850 pound engine gives a 2.78″ moment to balance or 2.8″ to take the driveshaft into account. That works out to 0.112″ on the Mini Sprint-T which is enough to be noticed on the model. The inside to inside on the Sprint-T cowl is 26″ and the bellhousing on the back of the engine or front of the transmission is 19″ outside to outside and moving the engine 2.8″ to the right gives me 0.7″ clearance on the right side of the engine if I use a mini starter instead of the honking huge OEM starter that actually sticks out from the side of the engine, getting back to the subject of Tetrissing the engine compartment. And I know I did this calculation for an SBC a while back, but I didn’t feel like going through the archive to find it because I just finished diving the QC archive in the way early hours of this morning and diving a comic archive is much quicker than looking for specific words in a blog archive.

And it’s getting late because I have been watching YouTube videos between paragraphs and I have almost 1200 words according to the editing program that comes with WordPress. So this seems like a good place to wrap this and post.

I have other things to think about than the Sprint-T

I sometimes try to not think about the Sprint-T, and think about other things I want to make, like bicycles and furniture (I have a plan for a bed stand/storage thing to put a mattress on that has been rattling around my head for years ever since the last repair to the futon frame), but for some reason I always seem to keep coming back to race cars for SCCA Solo Racing A/MOD class. The rules are simple, minimum wheelbase of 72″, minimum tread of 42″ and minimum weight of 900 pounds with driver. A few safety rules to protect the driver in case of a rollover, and that about covers it. Oh and a maximum of 20 ft2 total wing surface and unlimited underbody downforce developers, bodywork covering tires optional, that kind of thing.

My design philosophy has been lots of tire and suspension built to keep it square to the road, lots of brakes and an engine that can motivate without adding too much weight. Usually I come up with motorcycle or go kart powered things that have all the weight in the center of the wheelbase and as close to the centerline of the car as possible, but the latest fantasy was an LS7 coupled to a shorty Powerglide mounted to the right of the chassis and the driver seat to the left just enough to balance left-to-right, and a chain coupled transfer case to get the power to the center of the chassis to line up to the input of the rear, and front, axles. That’s right AWD traction to get 505 HP to hook up on a sub 1000 pound car. Of course I’ll never have the funds or facility to build this mini-monster, but it’s fun to think about. Given that there is scant difference in weight between the various naturally-aspirated LS engines but huge differences in low-end torque it makes sense to go for the 7 liter big dog, and the shorty Powerglide is the lightest transmission capable of handling a standing start that will bolt to the LS family bellhousing pattern (which it shares with the venerable SBC first sold in 1955), and the possibility of 4 smoking tires when the loud pedal is used too enthusiastically were just too much for my fevered imagination to bypass, so I didn’t. Estimated weight is 900 pounds without driver making it weigh about 1100 with my lard ass in the driver’s seat, or about 2 pounds per HP on 93 octane pump gas. The number of cars with this power-to-weight that are intended to make right and left turns on the regular in competition can be enumerated on the fingers of one foot. I think there are a few sprint cars in the same ballpark, but they are literal grenades, and there were some F1 turbo cars back in the 3-liter formula days that might be in the same power range, but again those were literal bombs on wheels with 1499.9 cc turbocharged engines putting out about 900 HP in qualifying trim and good for maybe 3 laps at full chat and very little time at rated output before exposing the inner works to the world. And if you think I’m exaggerating look up some YouTube videos of late ’70s to mid ’80s F1 qualifying sessions especially the Renault powered cars. In comparison the LS7 is an anvil used as a paperweight

So anywho, you have insight on my fantasies of power and glory, enjoy!

Just in case you were feeling generous…

There’s something I need for the Sprint-T build, that might not still be there when I have access to that much money again. This was the oil pan I was thinking of making to get clearance for the bottom part of the front hoop under the engine. This looks like a 50 -60 hour fabrication job for me, vs $330 cost to buy and install. I would need to buy or make the oil pump pickup either way, so that’s a wash.

But seriously I need that oil pan for this build or I need to go dry sump, which is even more expensive because it requires external tanks and extra pumps, or a special crankshaft and front cover if the factory dry sump system is installed, which while better than the wet sump for hard cornering is inferior to the aftermarket, and almost impossible to find in junkyards (they only came on Corvettes and Corvette engines are bought before the vehicles even get to the junkyards).

Now I’m going to go watch the Michigan NASCAR Cup race. Y’all have a good one and remember that Hephaestus wants you to build something that improves somebody’s life. Even if it’s only one person, make that person’s life better.

NOTE I had to edit this after I hit post because I didn’t catch the typo of my deity’s name, now I need to beat on some iron or something in pennance.

What does it mean when you have dreams about fabricating car parts?

I mean besides the obvious that you want that particular car part something fierce. The junction where the discharge ducts from the turbochargers merge together and connect to the throttle body on the truck intake manifold is one of the most important fabrication projects of the Sprint-T, and if I don’t get it right it will both impair the performance and look really ugly and both are deadly sins for building a hot rod. And last night I had a particularly detailed dream of how to build it, down to where to cut the feed tubes and where to make the first tack welds to get the best looking transition from two pipes to a single inlet.

There are usually 3 iterations in building a hot rod, “making it work” is the schematic stage where the parts are assembled into a functional order. After that is the “making it work right” refines the rough edges off the first stage and reduces any inefficiencies in the design, followed by the “making it look good” stage. A seasoned fabricator or experienced designer can usually combine the last two stages into a single build. A freaking genius fabricator or designer can sometimes get through all three stages in his/her head and produce a perfect part/assembly right off the bat, but that’s usually the result of a lot of thinking and mulling over of possibilities that usually not possible before the first stage unless the project has no deadlines to meet.

Well this build is one of those kinds of builds, it can’t even start until there is an actual budget to buy parts with. And right now there basically is no budget, there’s “I have money now, I will buy what I can afford from my build list” parts being bought. Since I never know when I will have money I can’t take advantage of sales unless having money coincides with a sale, like it did for the suspension parts I bought the beginning of this month.

That’s why I have been resorting to Dream Aided Design for this particular assembly. First because of the relative sizes of the parts, the two 2.5″ (63.5 mm) outlets from the turbochargers that have to merge and feed clean-flowing (non-turbulent) air to the single 84 mm (3.3″) throttle body on the intake manifold, and second because this assembly will be front and center on the engine out there in front of Gawd and everybody to see. I’m even thinking of putting the blowoff valve on the underside of this assembly to hide it somewhat, unless the valve I happen to get is especially blingy and worth showing off a bit in which case it goes on top. Which means the final version of the connection between the turbos and the intake may only get built after the blowoff valve is bought. Or it might get rebuilt later if a nicer-looking valve is bought or otherwise obtained after the car is “finished”.

Portions of this build get changed because I see a new part or a part that is old but I never saw before, like the swing arm that is normally used in dirt race track cars to both locate the rear axle fore and aft and mount the coilover spring/shock assemblies that I’m using to do what it’s designed to do in the dirt racers because it means I don’t have to make two separate brackets to attach the springs and the radius rod to the rear axle. Well it changed again when I saw THIS! over at the Speedway Motors web site. Intended for use in building radius rods and track bars, I’m going to weld this particular one into the chassis and use it as a place to bolt things on to the frame, this one in particular is going to be for mounting the front end of the previously mentioned swing arm. I weld the bung to the point in space where it’s supposed to go and then triangulate additional frame members to make sure it stays at that point in space. And I just realized the previous sentence made it look like I was welding a part to the fabric of the universe and then cutting it loose after I welded some parts from it to the frame, instead of what I was thinking and welding it to the frame and then moving the rest of the universe to get the bung where I needed it to go. I will use other sizes to get other bits onto the frame, in particular the 4 ends of the 4-bar that restrain the front axle in 2 dimensions/freedoms of movement.

Last thing, while using the bathroom the phrase “Pain is weakness leaving the body” drifted past my consciousness, which by the way is a total bag of bullshit. Pain is the body telling you that “something is broken, please stop what you’re doing before irreversible damage sets in”, or in my case “You have damaged ligaments and tendons, make an appointment with an orthopedist ASAP” and “You should apologize to the driver of the car truck about his insurance rates going up”. That part was true for 3 of the five times I was hit, one didn’t do a whole lot of damage to either of us and the other just triggered a panic attack for me and caused his driver’s side mirror to fall off and break, with some confusion as to the order of events because I might have broken it before it fell off when he started crowding me into oncoming traffic while I was setting up for a left turn into the bank parking lot.

The economics of hot rods

I did a little price comparison between building from scrounged and junkyard parts, and buying. They say time is money, well the converse is true also.

The junkyard 5.3l truck engine costs about $1k, and the 4L80E transmission about another $1k after rebuilding with high performance friction materials just to be on the safe side, and has to be completed with a $300 controller and a $280 wiring harness and maybe an alternator if there wasn’t one still attached at the junkyard and maybe that alternator will need a bracket to be fabricated to get it away from the intake piping. The turbochargers are $200 total and will require fabricating the piping from the exhaust to the turbos and from the turbos to the intake. Both the engine and the transmission are heavier than their counterparts in the Connect and Cruise package and tip the scales at a combined 755 pounds and the total not including materials and fabrication for the turbo installation and at least one dyno session to get the race tune right comes to about $3k±, plus hundreds of hours fabricating and tuning and fiddling with the bits to get everything singing off the same page in the hymnal. Power potential is about 450-500 HP on race gas or E85, about 300 on 87 octane regular.

GM Performance Parts sells a Connect and Cruise package for the LS3 and a 4L65E transmission that includes everything except the wires to the battery and that battery, for about $12850 ±. It makes 430 HP on 93 octane pump gas and weighs about 600 pounds complete and all it requires is fabricating the mounts and exhaust and plumbing the cooling and fuel and wiring the battery. It even comes with a warranty.

Now the question becomes which is the greatest source of joy in this build: having it done and driving it, or building and fiddling with the bits to make it run right? And is there $10K worth of joy in building and fiddling with the bits?

Still thinking about the Sprint-T

Thinking about the possibilities with the turbochargers linked in the last post has kept me awake at night (maybe a little more than if I hadn’t been thinking about it). OK, seriously, this has been the kind of conundrum my mind refuses to let go of.

Let’s start with the knowns and unknowns in this scenario:
1. The turbos are too small for the engine at max RPM and are flow limited so theoretically the boost curve will peak at some point before redline and decline from there.
2. The wastegates are probably too small to prevent overboost at speeds below torque peak because there is likely more exhaust flow than they can dump (the turbo is designed for a 1.8l engine and each bank is 2.65l). The corollary of this is at some point boost creep will become a problem if the engine can’t handle all the boost the turbos make and has to use the waste gate to dump some of the boost.
3. At this point how much boost the turbos will make is unknown, the only thing I do know is it won’t be as high at power peak as it will at a lower engine speed. Also unknown is how drastic the dropoff in boost will be from peak to redline. The listing claims each turbo will flow 250+ HP so I’m going to get pessimistic and say maybe 400-450HP flywheel HP which would be about 7 or 8 pounds of boost on a 5.3l engine at peak.
4. There is a possibility the engine/turbo combination can be run without connecting the wastegates to manifold pressure and without excessive boost in the low RPM range. This is the Best Case Scenario, that literally the only other thing needed is charge coolers, or running a fuel or water or water/methanol spray into the turbo inlet to cool the charge under boost, or some magics that otherwise don’t require adding more hardware to the engine. And also with this combination the possibility that the engine hits peak power at peak turbo airflow and just sustains almost 450 HP all the way to redline. That would be Seriously Best Case Scenario, peak power in a usable RPM range and no dropoff until time to shift to a higher gear because the engine safely won’t go any faster. I will still need to have some method of bypassing the turbos for running 87 octane between races unless somehow the engine will not self-destruct under boost with unleaded regular, but the probability of that is less than my surviving getting hit with a truck doing 60 MPH. It might happen once, it might even happen twice, but to bet it will happen on a regular basis is playing Russian Roulette with only one empty chamber instead of only one bullet.

Now some of this can be seen in this Engine Masters episode as their single turbo has more airflow than the two turbos I’m contemplating but still it’s a stock 5.3l LS architecture engine identical to what I’m trying to find with boost, just more airflow above torque peak than the two tiny turbos I’m thinking about, but notice how much they get out of the boost they get. Also notice they have an intercooler that will cool far more airflow than what the two tiny turbos will generate and get charge temperature down to a safe level for 93 octane and moderate boost. Also their single turbo probably doesn’t make near the boost the small twin turbos make at lower than NA peak torque RPM, so the Tiny Twins will probably make more torque below peak.

Anyway there are many things I could do, and what I really want to do is leave as much junk off as I can and not put the engine survival in jeopardy.

Can’t stop thinking about the Mini and Sprint-T

First thing I was thinking about was making an oil pan for both that clears the bottom part of the front hoop, as that has to go right where the rear sump for the oil pan goes on both the SBC in the Mini Sprint-T and the LS engine in the Sprint-T. That’s not so hard for the SBC model in the model version of the Sprint-T, just cut the bottom off the oil pan and stick another one on that clears the frame parts. But for the LS engine in the real thing it’s a little more difficult. A completely new pan would need to be fabricated from scratch which is pushing my skills to the limit. I can do some stuff, I know how to do more stuff than I have the eye-hand skills to do.

In other news on the Sprint-T and its smaller cousin, major changes to the forward part of the frame for increased crash resistance and torsional rigidity. The crash resistance would come from bending the bottom frame rail to make it a single piece from the rear hoop to the front suspension mounts and making the full size version from 0.120″ wall instead of the previous version 0.060″ wall. Since the diagonal leading from the top of the front hoop to the front suspension crossmember would still be 0.060″ wall it would buckle first causing the engine to go under the passenger compartment in a frontal collision, with the lower rail failing at the bend to allow this. The other thing was a bolt-in set of diagonals that would triangulate the upper part of the front frame in race mode but be left off in street mode for better forward vision and to allow the upper diagonal from the front hoop to fail in a known way and direct the engine under the car in a frontal collision. The small amount of additional flex in street mode would be offset by the greater safety in frontal collisions, because while the bottom part is completely braced by the welded-on belly pan (with an access hatch for changing the oil) and the sides are triangulated by the upper and lower diagonal braces from the front hoop to the front suspension crossmember the top part is completely unbraced and would allow some deflection in torsion without the bolt-in brace. What I’m envisioning is a double triangle brace that would bolt in at both ends of the top member coming off the front hoop at both the front hoop and the front suspension crossmember and also the center of both the hoop and the front suspension crossmember. It would form overlapping triangles that run from the top of the front hoop to the center of the suspension crossmember, and a second triangle from the ends of the suspension crossmember to the center of the front hoop, and a piece that runs from one side of where the two triangles intersect to the other, making even the braces triangulated. I’m thinking this set of braces would be made from lighter wall tubing and also in a smaller diameter since it wouldn’t be highly stressed and also is mounted fairly high in the frame so someplace added weight is bad for center of gravity issues.

Also on the triangulation issues are the engine and steering box mounts. The steering box mounts need to be braced side-to-side so it doesn’t deflect under cornering loads and cause inconsistent steering reaction depending on speed (faster causes greater side loads on the steering requiring more input as speeds increase not related to slip angles from the tires, which reduces the feedback to the driver as to how much traction remains at the front tires), and the engine mounts need to be braced so they don’t become a point load on the lower rail of the frame and introduce a new buckle point in a frontal collision while at the same time it needs to provide a consistent buckle point for the upper diagonal to direct the engine under the car in that frontal collision. There are a lot of things to think about when you build a car from scratch, like where I brace the engine mounts.

Another thing I have been thinking about was the pushrod and rocker arm linkages for the front suspension. I have been thinking about this because it 1) allows for easy wheel rate and ride height adjustments going from street to race mode, and b) makes changing corner weights super easy. When changing the wheel rate the effective rate changes as the square of the ratio between the leg of the rocker arm attached to the axle and the arm attached to the spring and shock absorber so making the arm attached to the axle longer makes the rate go down while making the arm attached to the spring longer makes the rate go up, and adjusting both can give me the perfect rate for street and race without having to buy two (or more) sets of springs and shock absorbers, meaning I just need to carry extra pushrods that cost roughly $20 each instead of multiple sets of springs and shocks at anywhere from $100 to >$500 each. The ones I’m looking at now are $250 the pair or roughly $125 each. The other thing I have been looking at is how the rocker connects to the moving bits in the suspension, because the pushrod has to be over the axle, while the coilover has to be to one side or the other of the axle so it has room to travel. I guess this implies I need some method to make sure the rocker arm only rotates through the axis it is supposed to pivot on as a lever system and not on the axis between the pushrod and spring attachments because there is a moment arm between the two created by the need to have one on one side of the rocker arm and the other on the other side of the arm and not just on opposite ends of the rocker arm. Hypothetically with the rocker arm suspension one could adjust corner weights without needing to roll the car off the scales and drive around to get the shocks to settle because you never move the shock when adjusting the weight, only the pushrod.

And this is the wordiest I have been in quite a while, which just goes to show what my true passion is these days.

Happy Star Wars Day

May the Fourth be with you 😄! Yes I know I have used the same corny joke for years, think of it as a tradition. After all traditions are just stupid stuff we do over and over.

I’m still working on the details for the Sprint-T. Right now I have a detail that’s kinda important, but not easy to find out: How far below the input shaft does the oil pan of a 4l80E hang? This determines if I have to redesign the front hoop or the engine oil pan, and how high the engine will sit in the frame. Because I’m pretty sure they don’t make a low profile extra capacity pan for this transmission, and the distance from the input shaft to the bottom of the pan determines how low the engine can go in the frame, which sets a bunch of other things. The most important thing is will the bottom part of the front hoop clear the front of the flex plate that goes between the transmission and the engine. Because this is kinda esoteric I’ll explain that the flex plate attaches to the crankshaft on one side, and to the torque converter on the other and the torque converter sends the power to the transmission and also drives the pump on the transmission that powers the bits that allow the transmission to shift and drive the car.

Now the 1/25 engine I have has a manual transmission cast into it, but as explained earlier I only have room for 2 pedals in the footbox, and a manual requires 3, a clutch pedal in addition to the gas and brake. This means I need to alter the bang box to have the same height as the slush box so the engine fits the frame as in the full-size version. Also the intake manifold on the model engine is the LS7 version and the one on the real car has a 99%+ probability of being the taller truck version because that’s the likely source for the engine, and that manifold has better performance in the RPM range I’m going to be racing in. That means I’m going to be modifying the Corvette engine cover to resemble a “shaved” truck manifold to get the height right. Basically I’m just going to remove the script from the cover and narrow it a bit to get the width of the truck manifold, and fill in under the sides to get the look like a shaved truck manifold. Since I’m using this ECU I’ll have to use the older drive-by-cable gas pedal and throttle body which is NBD for the model but a major consideration for the real car. Also, another reason for the truck manifold is better gas mileage for freeway driving than the car-type manifold. And the real reason for the model is to have a 3D reference for building the full-size car since solving these problems in plastic is way cheaper than solving with multiple mistakes in steel or fiberglass and carbon fiber.

And Mrs. the Poet wants me to get to bed “early” because we may need to do the grocery shopping early today, so it’s time to put the post and the author both to bed.