Throttle-limited testing methods (Constant Throttle)
 

I am going to combine Vekke's “Constant Throttle” technique with Julian's “Throttle Stop" technique. Both use throttle limiters for on-road testing of the aerodynamic drag effects of modifications.

Earlier this year, Julian recommended making a simple “throttle stop" to insert under the gas pedal. His goal was built to reliably set the throttle plate opening for a consistent power output. Stepping on the gas would offer a consistent baseline speed under controlled conditions, for example perhaps 18% throttle for 65 MPH. After an aerodynamic modification, any increase in speed at 18% throttle would indicate a decrease in aerodynamic drag.

Vekke wrote about something very similar in 2015 in two or three separate posts. He called it “Constant Throttle," or “CT" for short. In one post he suggested placing “a stopper under the gas pedal" that could hold the vehicle at a specified speed, but he switched to placing the throttle limiter on the spring throttle on the intake manifold. Once he had a speed he liked from the limiter, he inferred changes in aerodynamic drag from recorded changes in engine RPM (not speed).

Both approaches have advantages for the testing I want to do. Julian's is elegantly simple and quick at the expense of a little precision and safety. Vekke’s is somewhat more precise and safe at the expense of slightly more complexity. Bolting the throttle limiter firmly in place on the intake eliminates subtle movements of the stopper under the gas pedal that might change throttle position unexpectedly. An intake mount also eliminates any chance the stopper could get under the brake or clutch pedal in an emergency. (See my last post in Julian's throttle stop thread for more on this).

There are also benefits to monitoring both speed and RPM. A good GPS can be reasonably accurate and can automatically track speed averages. Monitoring RPM digitally from the engine sensor means having a second independent data source to compare. If everything goes correctly, percent changes in speed and RPM should be similar.

Here are some pictures of my throttle limiter, made for free from salvaged materials. Part of it is permanently mounted, replacing one of the throttle cable bracket bolts (picture 1). This allows the rest of the device (picture 2) to be quickly and securely mounted or removed in 30-45 seconds (picture 3). The result is 16.1% throttle (picture 4), which seems to correspond to about 60 mph in 5th gear.

https://ecomodder.com/forum/attachme...1&d=1595170633

https://ecomodder.com/forum/attachme...1&d=1595171171

https://ecomodder.com/forum/attachme...1&d=1595170743

https://ecomodder.com/forum/attachme...1&d=1595170763

It is a little ugly, and it could be simplified further, but it works perfectly and it eliminates my safety and precision concerns about under-pedal throttle limiters.

PS: “Constant Throttle" seems like a better name than "Throttle Stop" because it highlights the purpose of the technique: hold the throttle plate opening constant. But I will probably use both and throttle limiter and Great Flying Spaghetti Monster occasionally.

:thumbup: Nice solution!

Nowdays I test with limited IQ setting on the program itself. So I have a test ecu programs like 15 mg of injection per stroke on the a4b6 1.9 tdi is about 4 liters of fuel consumption per 100km/h and on 3 cylinder engines it is 3 liters. Program activates when you floor the gas pedal so it works normally on all other positions so its more easier to get to your start speed when you start testing.

This is even more accurate as the map changes if rpms change a lot on a hilly route etc. This way you get even better results when testing different boost, start of injection, torsion value settings. You can also do sweep accerelerations in same way like I have also done. You have different settings for different rpm and each IQ settings levels.

With the constant IQ setting you measure again the time for certain distance and from the time difference you can calculate avg speed--> from that you can calculate the changes in efficiency or drag reduction.

As always when testing drive the car first fully warm before you start measuring. On my diesels 50-100km depending on weather.

At the moment I can say my programs for 1.9tdi, 1.4tdi and 1.2tdi are pretty efficient as I have tested all those settings individually which is most efficient settings for each value. I can sell my programs online if somebody is interested send me email.

Electronically limited fuel injection instead of a mechanical throttle limiter is a new level of precision. It seems you programmed it yourself, yes?

Yes I do the programs myself for vag tdis. I have a feeling that I have done more testing on my ecu maps for efficiency than other companies that make programs. To have this constant IQ level is the best way I know at the moment to do on road testing as it rules out even more errors than the stopper systems. With constant IQ you can test also on hily courses/roads. where I live the problem was that the longest straigth level road sections are only 1-2 km long...

Not all cars are being able to be programmed so that stopper method works also much better than just using your rigth foot to adjust the throttle. Specially if you have flat test ground to do testing it works really well.

Here is my audi A4 b6 1.9 tdi measurement data for different boost maps. There is AFR2 map which is latest and currently in use.
AFR1 map which was "full boost" map
and one run for comparison with stock map of the car what just the ecu map does for efficiency in steady form of driving. With diesels I have limited the IQ to some number. In this car that 15mg gives nice results. With this car the numbers you see again on the memo are speeds in certain measurement points of the route. HIghest and lowest values.

Test route is exatly same as I had in the ID3 testing. I think in this I have measured the distance from google maps.

In the end I am measuring time it takes for the route. and from that I can calculate the AVG speeds and from those the difference in needed HP can be calculated. Again I have trusted these results to be reliable even the difference between these two maps is low 2,2%. Again you can make your own calculations based on the raw data available. If you don`t release the raw data then any measurements or results are not valid. This is true also to measurements done by the oems as you can always get results you want by filtering the results.

https://scontent-dus1-1.xx.fbcdn.net...52&oe=609B6035

Just to remind, manual throttle controls remain usual on military vehicles even though electronic engine management became mainstream.