I forgot the picture of the stuff I got for the Sprint-T, and I forgot to tell you what I weighed after fasting at the Lab Rat Keeper. And other things as well.
First things first, this is a picture of the stuff I got combined with stuff I already had so you can see how it goes together.
These Heim Joints have 3/8” holes and 5/8” shanks to fit the brackets and the links available. The brackets obviously have the holes and can’t be drilled larger without weakening them to the point that a minor wreck would tear the holes, requiring major repairs to the axle. So what I have planned is making the weak link where the links meet the frame. The plan is to use cheap, fragile aluminum body Heim joints that break at impact loads but still strong and rigid enough to not flex in regular use. And the next weak link is the links themselves, internally threaded aluminum tubes, that bend under impact loads but like the frame mount Heim joints don’t flex during normal operation. The intent is to absorb impacts by bending or breaking cheap parts that are easy to replace without damaging expensive parts that are difficult to replace, or have a long lead time to replace like the 4 week lead time for the front axle.
Now, my weight at Wednesday’s visit to the Lab Rat Keeper showed just how much I have for breakfast, particularly how much coffee. I weighed 211 pounds (95.7 kg) the previous visit, but only 208 (94.3 kg) this visit. My normal breakfast before a visit is a package of PopTarts and a “my cup” (750 ml) of coffee, and I usually have a light meal right before bed at about 0300. I have measured the capacity of this “cup” several times and the only way it reaches the manufacturer’s 1 quart rating is to leave the lid off and fill it to the brim, but measuring to the inside top of the lid gets 750 ml. But anyway no 0300 meal and no breakfast has me at 208 pounds.
Also there were races today, but if you were interested in that you would either have watched them yourself, or accessed a sports site to find out who won. I will say that the semi-local IndyCar race Will Power broke while leading. 🙁
I have been thinking about the Sprint-T again. Specifically thinking about that super muffler that will require I drill hundreds if not thousands of holes for exhaust pulses to pass through so the gas flow is not impeded by shock waves, like the walls of a supersonic wind tunnel. And doing some research on those tells me that if this muffler is long enough I don’t need to use any absorption material between the core and the shell, just a bit of empty space to let the sound pulses bounce around and dissipate. Now exactly how much empty space is “enough” may require some experimentation.
The thought of running experiments for not enough, just right, and too much empty space has me slightly excited. After all, this is the Holy Grail for street performance, and more than a few race tracks. A muffler that is both quiet and doesn’t choke the engine down at higher RPM is seriously sought after, especially if it lasts at least as long as the straight pipe it would be replacing. Now the down side of this would be the problems in mass producing the core. Obviously doing it the way I’m going to, drilling holes in a tube by hand, just ain’t going to fly. Other ways could be a CNC machine that drilled holes in a tube, welding perforated sheet as a tube, forming perf sheet into a flanged half tube and then welding or using screws to make the half tubes into whole tubes, or some other method I haven’t thought about yet. And a quick Google search showed there are companies making perforated tubing to order in whatever diameter or wall thickness I can imagine. But anyway the experiment for me requires making the core then attaching the outer housing some way that centers the core and makes sure it stays centered, and making the same core fit different sized housings to see which one makes the engine quiet without packing material. That one I already have figured out, make toruses with the inner diameter the same as the OD of the core, and the OD the same as the ID of the housing. Most of the rings would be tack or skip welded to the core to keep them in place as the core is inserted into the housing but the ends would get fully welded to prevent noisy leaks…
And after building one would get installed as a control on one side of the engine, while the rest are installed on the other side for comparison, with both getting measured so if the sound level changes I can be sure it isn’t because of changing conditions, and if conditions change use the control muffler to normalize the test results. Now if I had unlimited test resources I would test things like if the space between the centering rings changed the results, how much changing the diameter of the housing compared to the core changed the sound, and if there was an optimum length for the housing beyond which the noise level didn’t go down, that kind of interesting stuff that can only be determined by cut and try or by using a supercomputer to model the gas flow. And three guesses what I don’t have access to here at Casa de El Poeta, first two don’t count because there are only two choices. With what I have now my experiments are limited to outer housing diameter and length, after I get an engine to test them on…
And it looks like I have typed enough tonight, this should hold your imaginations for a while, while I think some more.
That used to have “and the Feed” back in the day when I was still covering bike wrecks every day, but since I stopped doing that my mental health has improved considerably. That’s a little on the scary side that this state is “improved” over where I was just a few years ago.
Anyway, the race was in Las Vegas and was 400 miles long, and Joey Logano won. The new package has slowed the cars way down on the track but they still have the same pit road speed limit they did at last year’s Las Vegas Spring race which means the pit crews are still facing Certain Death if they get in the way of cars moving at or near highway speed, but the cars are now going slow enough on the track that there is very little possibility of one leaving the track and going into the stands and killing a bunch of people. The last time they had a car going too fast for the retainment system they got really lucky and there were only minor injuries to the spectators hit by debris. The new rules can be summarized by “Big spoilers, tiny spacers” as the Big Tracks (basically anything over a mile long) have tapered spacers between the throttle body and intake manifold that reduce engine power to about 550HP or a bit less, partially because that was the cheapest way to do it and partially because the cars were Too Fast everywhere except short tracks and road courses. So now they have most tracks limited to 550, Daytona and ‘Dega are going to be about 400HP if I’m remembering that right, and short tracks and road courses are going to get full effective use of the intake system to make the 750 HP those engines are capable of. To make sure everybody stays inside the track fence and out of the crowds they bumped the rear spoiler from less than 3″ to
almost 8″ tall and added a bunch of front downforce to keep the cars aero balanced with about the same downforce on each end. Teams are still trying to figure out the suspension settings that work with the new package because this was a major change from last year even though they kept trying to say it was only a “minimal change.”
One thing that is changing on the Mini Sprint-T and Sprint-T is how the rollover structure integrates with the frame structure. Simple terms the upper frame rail is getting moved back out to the furthest edges of the frame again by squaring off the corners of the roll hoops but also leaving the hoops inside exactly like the SCCA wants it. The hoops will be bent from a single length of tubing as specified in the rules, but there will be short stubs of frame-size tubing welded to the outside of the bends to pick up the upper frame rail. The diagonals will still be rollover structure wall thickness and also have the bends to catch the top of the rear hoop, a bent gusset to catch the vertical leg of the hoop, and a frame thickness stub to catch the intersection of the tangent stubs from the vertical and horizontal legs of the hoops and tie everything together in a lightweight super triangulated space frame, and also what I hope is a rule-complaint roll cage. I’ll have to wait until tech inspection to find out, though.
I have a visit to the Lab Rat Keeper the day before Valentine’s day for a quick blood draw and BP check, and maybe a hamberder or something at one of the several fast food joints in the area. The covfefe house is closed, but despite having a large chunk of the building burned away the Mexican chicken place almost across the street from the office is still serving food. I’ve never been there, it might be a good time to try it out.
On the Sprint-T and Mini Sprint-T front, there has been a minor change in the design around the main cage. Basically the upper frame rail is now running in segments inside the hoops instead of over the corner after I did another stress analysis that showed too much bending stress on the hoop with the rails running outside the bends and the diagonal braces welded to the top and sides through bends and/or bent gussets. What I had before was the rails welded to plate brackets on both sides of the hoops in line with the horizontal and vertical legs of the hoop. What I have now is the rail welded to the top of the hoops right at the end of the bend and also where the diagonal welds to the hoop, kinda sorta. Actually the diagonals have the same size bends as the hoops so the bends line up, and using the same bend to make the connection to the vertical leg as a gusset to carry those loads directly into both legs of the hoop without imposing bending loads that have to be carried through the bend in the hoop. That’s because the bend is the weakest part of the hoop, but by using gussets and routing loads away from the bend it can be made to not fail in a wreck.
On the down side dividing the upper rail into segments and welding it to the top hoop next to the bend slightly reduces the d4 effect for torsional rigidity, because this change moves the top rails about 9″ closer together side-to-side. Instead of being 48″ apart they will be 39″ apart across the top of the cage. That’s a 56% reduction in stiffness in that plane, but that plane only contributes 25% of the overall torsional resistance of the frame. Basically this keeps both of the side planes that resist forces up and down of the total twist vector at the same stiffness, and has no effect on the bottom plane at all so even though that one plane is reduced 56% the total stiffness is only reduced by about 13% total in torsion. Noticeable but not critical. Second downside is the reduction in the access hole in the top of the cage by 4.5″ when it was already barely wide enough to get in and out without twisting sideways. So guess what I get to do getting in and out of the car?
In things that have nothing to do with me or the Sprint-T personally, the squirrel apparently made its escape prior to the arrival of the people we paid almost $400 to remove it. Also Mrs. the Poet has fallen and bruised her backside, enough that she makes involuntary noises about every other step, sometimes very loud noises accompanied by rude words. I’m not so bothered by the rude words as I am the volume used and the frequency. If her butt hurts she needs to lie down and let me take care of her instead of running around complaining I’m not doing anything for her.
I found a You Tube video that makes me seriously reconsider using the FIRST TPI efi manifold. One of the things I had been led to believe was this manifold had an extended RPM range and kept on making power at high RPM. Well, I guess compared to the original TPI from the ’80s and ’90s that would be true, but this test showed a power peak well below the calculation crossover at 5252 RPM (HP= Torque in Ft-lbs*RPM/5252, the point where Torque = HP is 5252 RPM) and the BluePrint crate 383 makes more power and continues to breathe through a Chinese dual plane manifold and 750 CFM carburetor. Now granted the FIRST manifold made 44 more Ft-Lbs of torque, the type of head used for the FIRST manifold test was not listed, and the cam was not mentioned, but the BluePrint engine made the same torque (440 Ft-Lbs) with both a flat-tappet and a roller cam and that Chinese dual plane manifold and Holley 750 CFM carburetor. Something else not mentioned was the headers used in the FIRST test, where the BluePrint tests with 13/4” long-tube headers. Now for an engine packing 383 cubes that is a low-end torque header. Note edited 2019/26/1 to correct header tube diameter from 15/8” to the current size after getting better information.
Well, I plan on making a trip to Lowe’s today to get a couple of 5/16” bolts for the roll cage bender, a 5/8” bolt for the exhaust turnout bender, and a can of butane to make the bender work. So I should probably get to bed now.
I have been sitting in the new seat to further evaluate it for further adjustments. Right now the biggest concern is the rib support impinging on the latissimus dorsi when I try to turn the steering wheel. The upper corner of the rib support is all I need to adjust, because everything else is Big, Too Big. The seat is 14.5″ wide at the back of the seat pan and I can get a hand between the seat and my hips, thickness, not width. And I can get a finger between the rib support and myself about ½ up the support, but right at the top corner it like negative clearance when I simulate turning a steering wheel, like right under my armpit.
Secondary concern is the fact the seat is aluminum, and like all aluminum structures is subject to fractures from work-hardening. What that boils down to is “adjusting” the seat could cause a catastrophic structural failure in a wreck that could cause jagged pieces of aluminum to be exposed right under my heart. This can be prevented by annealing the metal. This requires heating the seat to a point well below melting but still pretty warm, the standard test being to take a wooden matchstick and rub it across the surface and see if it leaves a streak of carbon on the surface which Google says is 800 – 1000° F and can be done with a propane or butane torch but only just barely because of the heat required to raise aluminum to that temperature. Aluminum moves heat like mad away from the heated area, called high thermal conductivity, and also I think it has a high specific heat the amount of energy required to raise the temperature of the material. But anyway, if I am careful I can soften the aluminum enough to make the adjustments without damaging the seat.
And I have to get up early for an RPG session that starts at noon and requires catching a bus at 1030 to catch the other bus that leaves the station at 1100 and gets to the stop closest to the game about 1135 or so, and then it is a 0.65 mile (1 km) walk from the bus stop to the house where we play, which gives me about maybe 3 hours of sleep if I quit now and play solitaire until my brain shuts down from lack of use.
Well, something for the 1:1 scale Sprint-T arrived, inspired by free shipping and Mrs. the Poet giving me the engine hoist for Christmas, and it’s something essential for driving the car second only to the steering wheel. Let me show you what it is.
As you can see, without the mounting bracket it doesn’t set straight inside the body. The black stripe is where my personal centerline is supposed to be inside the car, and the seat is a bit off to the side and a few degrees off plumb. Also I was in a hurry to check the fit both inside the car and on my backside, so I didn’t take the seatcover out of the separate box inside the delivery box. That delivery box was almost as big as I am. This was also before I tweaked the rib supports to not bite me in the latissimus dorsi quite so much. The seat was actually a bit wide through the butt, but painfully tight in the chest area the first time I tried to sit in it even without the cover. The only way I could breathe was to keep my arms up and my lats stretched out. Getting back out to adjust the rib supports was really tricky and brought much amusement for Mrs. the Poet.
These pictures were taken prior to “adjusting” the left side rib support which you can see in the top picture is a bit closer than the right. I might need to “adjust” both sides a bit more before I start building the seat mount, because I literally can’t put my arms down from the “9 and 3 o’clock on the steering wheel” pose even without the cover. By using my body weight and holding the seat down with one foot I was able to use the other to move the left side rib support out until it was even left to right with the right side. Now I need to figure out how to move them both out by about an inch so I can sit in the car without holding on to the steering wheel, which comes out by the way. If Mrs. the Poet didn’t recycle the old phone books I think I might be able to do it without scratching the shiny aluminum seat.
And it’s kinda late at night/early in the morning (0500) so this seems like a good spot to wrap this up and go to bed.
I have been watching Facebook and catching really cheap SBC engines and corresponding transmissions. Cheap as in $350 for a running engine and $500 for a rebuilt transmission. Or a mostly-built complete powertrain for <$1000. I might even be able to compete equally at Goodguys with it against the pro builds, if I get the suspension sorted properly. Even with an iron block and iron heads, and what they call an “RV” cam which is what most rebuilds get because they’re cheaper than a stock replacement cam when the cam is worn out, the power to weight ratio will still be sufficient to fry the tires if I put too much pressure on the right pedal. At this point I know I will need to dial the suspension a bit on the “tight” side (understeering), because I can get sideways (“loose”) with pressure on the “loud” pedal. This is called “power oversteer”.
Also the extra weight will help with the ratio between the spring/unsprung weight I brought up in an earlier post talking about the weight of the front axle assembly compared to the total weight of the mid-engine version of the car. Basically I need to get the weight distribution as close as possible to 50/50 because of how heavy both axles and associated elements are. There is only so much I can do for the rear axle, basically go as light as I can with brakes and brackets, but there are limits because I need to get a rear axle from a full-size car or pickup truck, and the parts have to fit and work with that. Even a relatively puny V8 build will destroy all the lightweight rear axles I can get in local junkyards, just look at what happens to Gen3 Camaros with the factory 7″ ring gear axle that started its production life under the 2.3L 4 cylinder Vega from the ’70s. Even with the OE 305 engine good grip and a heavy foot would cause broken differentials, ring gears, and pinions, what have you it probably broke on the V8 Gen3 Camaro. And for those thinking that won’t be a problem with the Sprint-T as light as it is, the load is independent of the weight of the car to a large extent, being mostly determined by power applied and grip. And grip is more dependent on tire choice than applied weight, and is highly dependent on where on the grip curve the particular tire is for the applied load. Which brings us back to tires being the most important choice in the design process…
So, there might be a budget to build the Sprint-T with an SBC and automatic transmission after all.
Nothing of interest has been going on the last few days except paying the phone bill and buying a lottery ticket. I have decided to start getting the materials for the frame because except for a few brackets the design doesn’t change with any of the engines I’m looking at. The reason I’m doing this is Mrs. the Poet has declared my Christma$ present this year is an engine hoist which won’t be much use aside from building a hot rod or frying a turkey. And I’m not kidding about deep frying a turkey . Well, at least I’ll have something I can use it for after I build the Sprint-T.