Roman

Haha crackup! This is kind of the flaw with measuring Coefficient of Drag, frontal area is part of the equation. If he's kept the same CD but increased frontal area by a fair bit, then he HAS increased drag. For the Kayak to be "cost neutral" he'd need to have ended up with a lower CD to offset the extra area. Not sure why he's bothered calculating CD anyway because solidworks would have given him the total drag number (which is more meaningful) in order to run his calculation with. His numbers are way off anyway, with a sanity check there's no friggen way a late model BMW has a CD over 0.5 It's a nice model of the car though! Wish I knew how to draw stuff that well in Solidworks haha.

No I cannot. Warmest Regards, RomanDave

Thanks man! That would be great.

Joker said in the fuel economy thread that waxing your paint can actually help marginally for whatever reason. It wouldnt make any difference to my bonnet or windscreen, as its completely dead air at this part of the car. But might make a slight difference at the areas at the back where flow detaches or reattaches.

Driving with the economy meter is interesting! Basically you'll be driving along fairly normally at say 70kph, the needle will be on say 7k on the tacho. as you slowly accellerate, the needle will drop and drop, and then when you get to a certain point it just stops and doesnt go down anymore. If you keep accellerating from there, the needle starts going back up. So once you get to that low point, you back off the gas to hold that speed, and the needle will drop down to say 2krpm or 3krpm. Whether you're on a hill, a downwards slope or whatever. Within the space of about 10 seconds you can find the most economical load and rpm combo which is pretty cool. It's amazing how deviating just a few kph either way of that point takes away economy really quickly. I found that my throttle was quite jumpy when trying to fine tune that needle angle, so I have revised my e-throttle curve to be even less sensitive below 70% throttle. I might setup a second throttle map so that if you ever go above 6000rpm, it will start a timer and switch to the "race" throttle map which is linear. Then if you havent gone over 6000rpm again in the space of a minute or something like that, it goes back to the mushy throttle. So congratulations to me, I've just figured out how to make e-throttle as unresponsive and mushy as OEM cars, the thing that everyone hates about it hahaha.

Haha, their "about" page cracks me up: Sucks when the market runs out of "greater fools" and you're the last one haha. Wonder how much they forked out for that.

I cant commit to a time for a west akl pre-meet this time sorry. Anyone else want some tyres or just pooman.

Ahhh one other thing. I made a table in the ECU that temporarily converts my tacho to a fuel economy meter. It's not as simple as just measuring injector pulsewidth, because you could have the same pulsewidth at a higher speed means better economy. So it uses some calcs based on injector pulsewidth, rpm, and vehicle speed in order to wave the needle around, it's a bit unnerving at first haha. But if the needle shows between 2-3k rpm you're doing good, and if its pinned at 8krpm you need to revise your driving strategy haha. Will be interesting to keep an eye on it on longer trips. I dont think it's useful for quantifying changes to the tune etc in the same way as taking averages from the logs though. I also found that I'm a bit of a noob and had my fan switch-on temperature and hysteresis set to a temperature where my fan would just be on all of the time. ha. So fixed this and now the fan runs only very minimally.

Coming back to this overly simplistic model I drew ages ago: As previously mentioned I've got a spare map sensor hooked up for datalogging (well it's not a map sensor anymore, just a pressure sensor) Tonight I thought I'd finally put it to use and see what sort of air pressure I'm getting at various points up the bonnet, up the windscreen, and start of the roof, and on the front bumper area. So, tape the hose to a certain part of the car, go for a run to 110kph on the motorway, log results, move the hose and test again. Results not as expected! Nothing I initially measured, varied by more than the margin of error of the sensor. As in, if it showed 101kpa when stationary it showed 101kpa when going 110kph as well. And yes I did double check that the sensor works haha. The only tests which showed any variation were taping the hose to the glass on the rear of the side mirror. (Showed a pressure drop, as expected) And having the hose in the rear of the wheel well area. (Showed a pressure drop, as not expected! Thought it would be high pressure area here) I saw more of a change in barometric pressure, than actual pressure variations across the front of the car. It may be that a more sensitive sensor is required like a 5kpa manometer or something, but then is it even really worth bothering about trying to change something if the pressure difference is actually so immeasurably low? I suspect that the rear of the car will be the interesting part for pressure drop etc, however probably what would be more relevant and interesting will be doing some wool tuft tests to see where the airflow detaches. Similar to this: I might need a volunteer or two to help out though at some point, to follow the car down the motorway and snap a few pics so I can see what's happening. Anyone out West Auckland interested in participating in some Dave Science? Disclaimer: actual scientific content may vary from advertisement

Haha, these two cars are the yin and yang of fuel economy.

Hmmmm I'm in two minds. My car needs 25hp more to push through the air at 200kph, which doesnt seem much. So what are we left, with, good fuel economy? Nah because the engine in the XT was rubbish. A modern engine into an XT could be interesting, but then I guess if you wanted something slow and economical, it's not like there's a shortage of other options. Then if you wanted something fast and aerodynamic, there are a lot of other options which will be more reliable. Cool gimmick factor though (the importance of this cannot be understated!) but largely pointless to own one unless you like the shape. (and fixing cars a lot) I've still super keen on a Subaru Omega/Leone coupe though, haha.

Oh yeah, good idea. I'd need to pull the dash pad back off to change any wiring though, so I think I'll be happy enough just switching the tune back and forth for now

For your claim to be true you will have found/brewed/invented a liquid with a higher energy density than petrol. This is a chart below lists energy densities of known types of fuel. Your mystery gas would need to sit somewhere much higher up the page than gasoline does but still have very similar combustion properties. (Aluminium doesnt flow through a carb and burn in a triumph engine all that well) Notice how other types of gasoline substitutes have a considerably lower energy density. Dont forget to collect your Nobel Prize on the way home today

A while back I calibrated my tacho and speedo with some custom values so they are more accurate. Lately though I've been trying to get a feel for how economically the car runs at various speeds. So I've had to to take some datalogs, and then do some maths on the logs which is time consuming and it's hard to relate back to what I was doing at the time. So I've come up with a better idea, I'm going to make it so that my tacho only activates when in 6th gear. but then the sweep of the needle will be based on a table that has Effective Injector Pulsewidth and engine RPM as the axes. The values populating the table will represent what sort of economy you're getting. So when you're driving along if the needle is showing 2k you're doing well but if it's pinned at 8k you are doing it wrong haha. When I get a new wideband and controller I'll switch to modelled fuel equation, which natively gives fuel consumption info which makes everything easier. So I could make this same thing work in all gears instead of just 6th. It would be cool if I could switch between tacho or economy gauge, either with a switch or with some logic/criteria. But I think I'm stuck with one or the other. Maybe I could permenantly repurpose the oil pressure gauge needle to fuel economy instead. And then wire in an oil pressure light, I've never liked the idea of having to look at a gauge to see low oil pressure rather than having a bright light blaring in your face to tell you there's a major problem. I've got a blue shift light mounted in top right corner of my dash cluster which works well. I've bought a second one that's red that I'm going to mount on the other side, as a general purpose "Turn this shit off somethings fucked" light that could have a few different criteria making it work. At the last superlap event, Barry manon lost a very fancy engine due to oil pressure issues. Looking back through his footage he said that his oil pressure gauge showed low oil pressure for half a lap but the oil pressure light never came on because the threshold was set too low. (something like 4psi) and no one ever looks at a gauge while you're going 10/10ths. If he had better warning it might have saved him an engine. It could be a good plan to have a warning light operated by a table maybe relating to engine rpm and oil temp, so you can run the light at say 20% below the threshold of what you'd expect oil pressure to be in every situation.

Then bought himself on aliexpress and got back here for free shipping

I'll accellerate slow-ish up to say 95-100kph Then put car in neutral and coast down to say 80-85. then accellerate again, rinse repeat. You only end up with foot on the gas for about 1/4 of the time or less because it actually takes quite a while to scrub off your speed. What I find is that I am generally travelling at the same speed as traffic around me anyway (Most of my trip to work is 80kph zone) but using 20-30% less gas.

40 litres per 100km Hahaha that is quite impressive. So from my house to Christchurch, assuming using 98 instead of Avgas would cost.... $870 each way for gas alone.

I quite enjoy the contrast between the outside of the car (swooshy lines, and quite frankly beautiful appearance) Compared to the strut towers in the engine bay (Which look like a high school metal work project) It obviously does the job etc, but just not quite what I was expecting to see!

I have been maintaing the just under/over 4l per 100km on each trip in the daily. Based on 45l tank, if I can maintain this I should be able to go 1100km before next refill. (?!) Auckland to Christchurch on a tank of gas... Which is nearly 5 weeks of driving to work and back, West Harbour to Penrose. It'll be interesting to see how the OBD2 compares to the fuel top up + check kms method though. I have started using fuelly so time will tell at next fill up... in a few weeks. It's taken hilariously long to go through just under 1/4 of a tank. On my other car, there are a few plastic underbody panels etc that have been off the car that I'm refitting to see if it helps at all. Some look to just be stone gaurds, but I think some of the other bits would contribute in a useful sort of way towards reducing drag a little.

I dont think so, if you look at F1 cars from the 60s they would have massive power V12s and skinny tiny shitty tires and were absolutely nuts to control. They all would have been way more drivable and faster with aero stuff.

Awesome! What's interesting from some things that I've been reading at the moment. Unknown to me in the 30s or whatever people had a VERY good understanding of aero stuff. (It never made sense to me that people knew how to make aircraft, but gave zero consideration to car shape) Although it still seems odd that aero downforce came into play quite late in the piece. In my mind it's always seemed that the 90s were the first sort of times that aero was considered for mass produced cars. Oh how wrong I was!

Does anyone want some free tyres? If so I'll bring them along. I've got: 4x 205/50/15 Toyo Proxes T1R. With maybe 2-4mm tread left, one has a flat spot and the other has some aggressive wear on just the outside edge, other two are pretty good. 2x 225/50/15 R888. Have had burnouts done on them so they are preeeeeettttyyyyy worn out. Good for seeing if 225 semis will fit on your car though, which is what I used them for. Still usable for a little bit longer I guess. 2x 235/50/15 R888 Same as above but a little more tread and no skids done on them. (probably still good for a trackday or two) but these are hyuuuuggggeee so not sure what they would fit.

One for Flying Brick. http://www.equipmentworld.com/dont-lower-your-tailgate-gm-details-aerodynamic-design-of-2014-silverado-and-sierra-2500-debunks-myths/

Does your carb have a return line though?

So it turns out the hilariously boxy looking Subaru XT is actually some genius aerodynamic masterpiece that spent countless hours in the wind tunnel during it's design. Clocks in with a very surprising c.d. of 0.29 Pretty impressive for something that looks like its design was based on a tupperware container https://en.wikipedia.org/wiki/Subaru_XT#Aerodynamics