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.
In case you were wondering how I “got” to go with Mrs. the Poet, it’s almost but not quite the exact opposite of “simple” (and I stole that from Douglas Addams description of the beverage dispenser on the “Heart of Gold”).
Mrs. the Poet has a back condition that precludes her from walking to the bus stop 0.42 miles (0.676km) from Casa de El Poeta, and Mrs. the Poet does not have a smart phone which precludes her from hailing a ride share. I have a smart phone and the Lyft app. Guess who “volunteered” to get Mrs. the Poet to the courthouse for her jury duty? Guess who further “volunteered” to get up less than an hour after normal get-to-sleep time to hail said Lyft? Yep, little old nightowl me.
The only thing worse than jury duty is having to go with someone to make sure they get to jury duty but not able to actually do anything useful once you get there. I wasn’t just bored, I was B-O-O-R-E-D all caps and extra vowels and hyphens to extend the pronunciation and emphasize how mind-numbingly tedious it is. Seriously given the choice between taking someone to jury duty, and say having a tooth extracted, go for the tooth. It will hurt less and there will be something of value attained, assuming the costs are roughly equal. Seriously.
Other news I’m still perusing the manuals for installing and programming the Microsquirt ECU, the latest version of the firmware allow for self-learning to get the VE tables set to the desired AF ratio. This will make tuning for 87 octane easier, and give me a better start for tuning the E85 table. The Microsquirt controller has a flex-fuel setting that I can use for doing the E85 tuning, not the actual tuning but using the algorithm they use to adjust fuel and spark to set partial throttle tuning to get close to the spot on setting and good enough to use for off-throttle driving that doesn’t require top power or fuel economy. I mean they post it right in the manual under “flex-fuel” that they just multiply the fuel setting by 1.63*Ethanol% to get the injector time and just add 4 to 6 degrees of advance to account for the slower burn rate of E85 compared to not-enriched gas, which is a good starting point for a performance tune. I’m also working with the knowledge that while the burn rate is fixed, the time available for the burn is less as the RPM increases and more advance is needed as the RPM rises until it reaches the point that there isn’t enough time to burn the fuel before the exhaust valve opens without the rising piston on the compression stroke having to fight combustion pressure, the compromise then being having as much pressure working for you as possible on the power stroke to overcome the pressure working against you on the compression stroke. So, that’s my place to optimize for power and economy, minute adjustments in ignition timing in the 87 octane tune at the eventual cruise RPM, while watching the AFR like a hawk to keep it at the “economy” setting that’s slightly lean of stoichiometric.
And it’s gotten late and I have other “stuff” to do since Mrs. the Poet is dog sitting for a neighbor while her husband is in hospital…
That’s basically all I have to say right now. I have been looking at an engine controller that costs less with the tuning software than the OBDII Dongle to control the factory controller for the LS Family of engines. But I still don’t have an engine to use it on, so …
I just got finished watching a good race, Denny Hamlin won, Kyle Busch won 2 of the three races this weekend but not today, and I have to go do things tomorrow. I need to pay for my phone, I need to shop for a new mattress for the bed in the big bedroom, and I need to get a massage.
Also I need to figure out where the links for the front axle are going to fit on the frame so I can make the links to length in scale for the Mini Sprint-T. It’s basic trig and geometry, the axle is x distance from the front hoop, the lower rail is y inside to inside and y+3 outside to outside and the links have to be l distance apart to clear the tires at full lock. This has been determined previously to be 31″ outside to outside, and the links are 1″ diameter so the links have to be 30″ center to center. The only dimension that is unknown at this point is the altitude of the triangle formed by the front hoop and the lower frame rails, because I still haven’t set how far in front of the axle the forward crossmember is, because I still haven’t decided if I want big or small body shocks. The big body shocks use 3″ OD springs, the small body use 2″ OD springs and there is 0.5″ difference in how far forward the front crossmember sits which means there is maybe 0.125″ difference in where the lower rails are 30″ apart center to center measured from the front hoop.
And it has occurred to me that some of you don’t know where the transverse structural parts go and what they are called on the Sprint-T and because it is the same but in scale, the Mini Sprint-T. From the front, there is the front crossmember that holds the front coilovers over the axle and the radiator gets mounted to the front of it and the mount for the track bar that locates the axle from side to side, then the front hoop that is 1.5″ X 0.120″ for most of the structure and 0.060″ for the rest of it because it’s part of the roll cage that has to be 0.120″ wall thickness except for the part that isn’t roll cage but frame, then the rear hoop that is the same as the front hoop, then the rear crossmember that basically doesn’t do anything except hold the rear of the frame apart and protect the fuel tanks in a rear end crash, and provide additional torsional rigidity by increasing d4. The point of interest in today’s post is the front crossmember because the lower rails meet at the center and the upper rails are right over the coilover mounts and also pick up half of the mount to put the upper mount in double shear. The triangle formed by the lower rails determines how far the rear mount of the links that mount the front axle are from the front hoop because the mount has to be 30″ center to center. The links have to be parallel to work best with no bump steer from moving the ends of the axle when the car rolls in a turn. So the center of the rear mounts on the frame have to be the same distance apart as the mounts on the axle to keep the links parallel.
Anyway finding the location for the rear mount is a simple ratio. The problem is I don’t know the terms for the ratio beyond the first term. That term is 30/46.5 or 0.645161290323. That’s the ratio of the center separation of the links to the center separation of the frame rails at the front hoop, the term I’m missing is the distance from the front crossmember to the front hoop to multiply that by. I know about how far that is but not exactly how far that is. But if I think about it some more I can make it so there won’t be a difference because I’ll use the distance for the larger spring and just enjoy the extra clearance if I decide to use the smaller spring instead, so doing some quick calculations, the rear axle is 5″ behind the rear of the body, the body is 52″ long and the rear axle is 100″ behind the front axle and the front hoop is right in front of the firewall and where the frame rails meet the front hoop is 58.5″ in front of the rear axle or 41.5″ behind the front axle and the front crossmember is 1.5″ in front of the front axle, so the distance from the front hoop to the front crossmember is 43″ so the rear mounts for the links are 43-(0.645161290323*43) or 15.258064516111 from the front of the front hoop. Rounding makes that 15.26″ from the front hoop and links that are 23.25″ center to center after using the distance from the center of the rear axle to the center of the holes for the Heim joints on the 4-link brackets and the size of the vertical member supporting the rear mount which will probably be 1.5″ X 0.060″ to make it stiff enough in bending with the load triangulated at both ends, which I just decided. The diagonals will run from the top of the front hoop and the bottom of the front hoop so there will be no possibility of hitting the frame with the front tire at full steering lock. And as previously stated there is another diagonal that runs from the top of the front hoop to the top center of the front crossmember so there is a parallel frame member to capture the top of the rear mount for the links and make that area fully triangulated.
And this has turned into one of the longest non-wreck report posts I have done. So since I don’t want to overload people doing an archive dive, this seems like a good place to take a break and put this post to bed.
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 saw a video on YouTube about choosing the best LS family engine for your car, and boiled down it was “The best engine is the one you can afford with all the bits still attached”. So I have been prowling the FB Marketplace ads for truck and SUV engines from the right eras and there are a bunch that are more-or-less in my price range, but the big problem is I need a truck to get one home. That means unless I can convince a truck-owning friend or family member to help me pick it up, I’m not getting that engine. Impasse. I can afford to buy it but I can’t afford to get it, which negates my ability to buy it. And if I can’t bring it home it doesn’t matter if I can afford to buy it.
And once again I’m facing frustration because I don’t have the resources needed to complete a project. This has become a familiar situation, but unlike previous times instead of dropping it and moving to something else, I’m persisting and moving as the opportunities present themselves. There will be other engines, I will have access to vehicles that can transport one and I will have the funds when the opportunity presents itself to avail myself of the situation. In simpler terms, eventually things will fall my way. I just have to keep working to make sure that when things fall my way I’m in the right place to catch them. Prepare for the worst, expect the best, and just be ready no matter what happens.
One way to be ready is information, know what you can use so you can use it when you have access to it, which is why I have been snapping up LS family swap and performance books every time Amazon puts them up for loss-leaders at the Kindle store. Information is one of those things you don’t know you need until you need it, and it’s better to have and not need than need and not have. And on that note I’m putting this one to bed.
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.
And keeping me awake at night.
Remember that dyno test video I linked to last week? The one that had 490 Ft-lbs of torque but only 405 HP? I keep going back to the graph that could be seen near the end and wondering why the power graph just went flat above 5000 RPM. A flat power graph usually indicates maximum airflow has been reached and no matter how high you twist the engine T*RPM/5252 just isn’t going to get any better because torque is falling as fast or faster than RPM is rising. You just can’t burn any more fuel because you can’t get any more air in the engine. And what has been keeping me awake has been where is the restriction? The possible sources are the manifold, the heads, and the camshaft profile not allowing the other two to work above a certain RPM. If it’s the cam or the heads then that means just a different choice of parts during the expensive part of the build, but if it’s the manifold I might be able to crutch around the problem with gearing.
Because that torque number is freaking ridiculous. This is a normally aspirated build that had higher torque numbers than some supercharged or turbo builds, meaning the ram effect was taking the engine to >100% Volumetric Efficiency (VE) at torque peak. And looking at the torque graph in the video the peak torque was on the second torque peak, there was another peak at much lower RPM that was almost as high. For a NA engine that would be a torque number more natural for a much larger engine, the engine was taking in way more than its displacement without the use of mechanical assistance. Now all I need to do is figure out how to keep that up well past torque peak or I’m going to be stuck with a power band that is only about 1000 RPM wide, the space between peak torque and peak power. I’m still talking about installing a crazy cam profile, probably stupid high lift, to keep the airflow up well past the torque peak, and adjusting the gearing to put the power higher in the vehicle speed range, which would be fantastic for fuel economy. I mean the gears in the transmission are set in the factory, so the only thing I can change would be the final drive ratio to a higher (lower numerical) ratio. And because I don’t have room for a clutch pedal with a SBC that means if I set the final drive to hit redline in first at 40-60 MPH the cruise RPM would be ~4.6:1 lower than that. Which would mean very low cruise RPM and pretty good fuel economy.
Now I need to get ready for game.
Life has been very uninteresting lately, it’s winter and that uncomfortable kind of cold that can’t be dressed properly for. I’m either still cold, or sweating because I have too much on, or both because the temperature can’t figure out what it wants to do. I still have to pay my property taxes now that I found out that at least one of the offices does not accept debit cards and I managed to track down my checkbook that I hardly ever use except to void a check when someone prefers to pay by direct deposit.
So I have my checks for whenever the weather improves to the point I can do the walk between the three offices on State St. in Garland. In good weather it’s a nice walk from 5th to Garland Ave, less than a mile. And there are bus stops on both ends but it is only a short walk from Downtown Garland station to the first tax office, less than a quarter of a mile.
And at some point I really need to stop at a CVS or other store that carries butane to fuel the torch that heats the bender for the plastic rod I’m using for the frame of the Mini Sprint-T. And while I’m on the subject of cars I found a really good intake manifold for a SBC to use should I wind up running a SBC on the 1:1 Sprint-T. This manifold is an evolution of the TPI GM intake from the late ’80s early ’90s, that produced prodigious low-end torque but ran out of breath above 3000 RPM partially because of the state of the art for EFI at the time. Well this version breathes all the way up top, with “top” depending on displacement but generally higher than a factory cast crank will live with. The tech person I was in chat with says for a 383 the “top” is above 6000. The tech manual advises against using E85 but the only thing I can find that might not be compatible with the fuel is possibly the fuel injectors or the rubber injection lines supplied. Those are all easy to replace with alcohol rated devices or materials. The crank and piston kit I’m looking at has a max continuous of 5200 RPM or a short-burst redline of 5500 RPM.
Finding a kit to build a 383 that runs on 87 octane NA is another problem entirely. Most of them are too high a compression ratio for 87, or built for forced induction and cost too much because they are designed for higher HP than a NA engine can make on either 87 octane or E85. Sure that makes for an engine that is unlikely to fail even during racing, but I could buy a kit not made for boost that would be just as reliable and a bunch less expensive if they would use the same parts they use for 93 octane except for the extremely dished pistons in the hyper eutectic material instead of forged used in the boost-capable kits. Locally the difference between 87 and 93 octane is $0.30-0.50/gallon, or about 20-30%, and E85 is about a penny more than 87. Depending on tune it might be cheaper to run on E85 all the time using the 93 octane kit if I wasn’t concerned with availability for long trips. But for that I have the possibility of running a storage tank in the tire trailer to extend the range enough to get between E85 stations on the Interstate when driving between races, and there are plenty of places to refuel locally.
OK I got some more raw stock for the Mini Sprint-T yesterday. Basically I got 0.040″ thick styrene for making brackets and steering arms and the spindle backing plate where it connects to the axle. The amusing part is the minimum order was 4 sheets of which I will use maybe half a sheet if I’m profligate in my layouts, and when they packed it they included an extra 2 sheets to “protect” the actual material I paid for. So I needed less than ½ of a sheet, bought 4 and got 6, for a total of 12 times as much material as I need. The other funny part is unlike the rest of the raw stock I got this was sent in a padded envelope instead of a cardboard box stuffed with crumpled paper.
This sheet material is going to model structures that will be fabricated box structures on the real car like the engine and transmission mounts, or actual parts that are just that heavy because of the stresses involved and the critical nature of the part like steering arms. A major part of model building is “representation” rather than actually reproducing something in miniature. The exhaust system will be a good example of that for the Mini Sprint-T. The 1:1 version will have what is called a “tri-Y” or 4-2-1 exhaust system that improves torque below the torque peak but doesn’t change peak power much. It doesn’t get every last HP at peak though, so drag racers don’t use them much, but road racers, short-track oval racers, and autocross racers spend more time well below the torque peak and the tri-Y manifold is popular in those applications. Well this is a type of manifold that requires a large amount of fabrication for smooth flow, and ditto on the fabrication level for the scale version, and because of the difference in materials is actually easier to build full-scale than in miniature. Well to get around that I’m going to use the fact that the exhaust is going to be wrapped in insulating material to hide the fact that I’m just going to butt-join the rods representing the tubes of the manifold and not build the streamlined joints. The work would have been hidden by the wrap anyway and this saves a lot of work that will never be seen. The real tricky part will be the wrap, I’m still experimenting with stuff for that. My thoughts are whatever I use will require a paint wash to get the color right so it will have to be something that takes paint well. But that is something that comes much later in the build, so I have time to figure that one out. The current leader for that is hypoallergenic bandage tape, but I still need to do the paint test. And like I wrote, the actual wrapping will be in the future.
But at any rate what I have now will fill in for complicated fabrications that would be a nightmare to produce in scale and not be discernible from cutting it from a single piece of heavy sheet. End of the current chapter. Next will be actually building the frame, which is like 80% of the build for this model. There are a few dimensions I’m not entirely positive about, some of which need to be hashed out during the model build because I can’t import the parts to my CAD program. The other ones are because I have to build to a rulebook that’s a bit vague about certain things like roll cages, and another rulebook that is more than a bit vague about the same things, and doesn’t mention anything about it except that for my car it’s required without any dimensions or tubing sizes. That is a really big help GoodGuys. “All Roadsters must have a roll cage.” That is verbatim everything printed in the rule book about roll cages. So what I’m doing is using the SCCA Solo rule book for roll bars and applying the rules to the rear hoop, and treating the car like it weighs 2500+ pounds, when I’m looking at maybe 1800 if I run iron heads on the SBC engine and something along the lines of a 4l60E transmission and the Ford 9″. Now if I get a quick change I can get the TH350 and take about 45 pounds off the car because I can change the gears to something really tall for the freeway and gas mileage without having to compromise to get the right gearing for racing. Just jack it up to unload the gears, pop the rear cover off, and swap the race spur set for the highway spur set and refill the rear end then go. And the car will be slightly quicker racing because the race gear doesn’t have to be compromised because of 9″ gear availability or having to get good highway mileage. But the other side of that is quick changes are much more expensive than the common 9″, and other junkyard rear axles are even cheaper and “close enough” on the gear ratio. But in the model I will be using the quick change, because I have 4 of them and no 9″ Ford in that scale. I have 2 of the V8 size housings and 2 of the 10″ ring gear size housings, but no 9″ Fords 😐. And you can see how decisions for the 1:1 car affect the 1:25 model.
And it’s getting late and I should be going to bed soon.