Tag Archives: arcane technical issues

Nothing much new

I’ve been doing some figuring on the intake manifold and cam combination, but TBH this one is not well covered in the public literature and simulations. Except for the Holdener videos this is pretty much terra incognita for published data. And not to be tooting my own horn, one of the things I was really good at was drawing correct conclusions from insufficient data. And right now I’m dealing with way too little data, essentially only 5 data points between the Holdener videos and two other TPI videos, and those two went with the commonly accepted practice of short duration cams with the long runner intakes. Like 240° advertised duration or less short. My theory hypothesis is 270°@0.050″ lift at a minimum and 290°@0.050 preferred, those are considered radical durations that would have terrible idle and low RPM manners if not for the stupid long runners, but even so would not work without the large cross-sectional area of those long runners giving good airflow for the upper RPM ranges.

On other things I’m putting out an ad for someone to make my car work as DLC for GT5 so I can drive it on the gokart tracks I built with the track editor in the game. Translating that to English I’m asking for someone to code the Sprint-T as Down Loadable Content for Gran Turismo 5, so I could make it usable in the game. I could use the free classifieds in Grassroots Motorsports to request submissions. The thing is I have zero idea of what information would be needed for the game version of the Sprint-T. I know the tuning choices give 3 selections each from 3 categories of tire, and some cars have the option for tuning the power output from the engine, to that means a variable with a range for power and also variables for grip and hydroplane resistance in the tires. Now how sophisticated the tire modelling is??? it could be as simple as a simple ratio for grip that is dependent on tire choice or a multi-variable algorithm that takes temperature and depth of standing water along with a bunch of other things into consideration. And there’s nothing I can find on the internet about it. I can find some of what has to be simulated in this formula “Pacejka Magic Formula” Physics Doctorial thesis on the web and simplified formulas for designers and in video format Brian Beckman: The Physics in Games- Real Time Simulation Explained. The biggest thing is the physical limitations of the CPU and GPU as the formulas get to various limits that end up dividing by very small numbers and the answers get larger than the registers in the CPU or GPU. Which has nothing to do with how GT5 stores its car models, just a taste of what’s involved in building that model. And after all that I still don’t know how to get from the piles of parts distributed around the house to driving pixels on my TV screen, which is why I’m thinking about paying someone to do it for me.

And I just face-planted in the keyboard because I’m glazing over at the programming details that don’t apply to this situation, so this is a good place to put this to bed and me shortly after.

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.

Update on the mystery of the manifold

Right after I posted before going to bed last night I finally got an e-mail from the guy who built the engine in that YouTube video I posted. He went with more duration until he put a cam in so big he couldn’t get the ECU to calibrate and still couldn’t get any power above 5000 RPM. The engine in the video had a cam with a duration of 224°@ 0.050 lift (a standard way of determining useful duration) as that was pretty much the limit for an engine that would have a streetable idle he could get the ECU to work with. Maybe this issue would not be a problem these days with the more sophisticated ECUs that we have available now.

Or I could just get the EFI version of the BluePrint 383 and not worry about it. But the issue seems to be fighting the acoustic tuning of the manifold, not the available airflow. 🤷‍♂️ Also, why can’t my spellchecker handle plurals of words it knows how to spell? 🤷‍♂️

Y’all have a good day now.