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Month: April 2017

Graph

Graph

It is surprising what can be seen in a single simple graph, and what questions it can lead to. Look at the attached picture, a simple graph from a simple tool. It shows an acceleration in 2nd and 3rd gear on my drive to work today. The blue line near the bottom is the air temperature after the intercooler. The white line is the temperature before the intercooler and right after the turbo. The red line is pressure after the intercooler, right before the throttle body, and the green is the pressure right at the turbo outlet. Finally the yellow line is the cars acceleration in g’s.

From the start, the contrast from the white to the blue line shows the extreme effect of an intercooler. Life without an intercooler would be a different, more disappointing life. At 264 degrees F the air is cooled to 70F before heading to the engine. Thermodynamics is a wonderful thing.

The red and green lines shows the difference between what the turbocharger is producing, and what is making it to the engine. That is an almost 4psi difference across the intercooler, and some of that change in pressure is the result of the significant cooling imparted on the air by the intercooler. You can see the downward slope of the red line as the temperature differential increases.

The end of each gear has a few interesting properties. You can see the effect of the closing of the throttle by the nearly 6 psi spike right before the throttle plate as it is closed. The slope of both the red and green lines right after that point are almost perfectly aligned. This is with a system of piping and intercooling measuring in the feet, yet the latency is nearly zero. On the downslope you can see the oscillations caused by air bouncing off the throttle plate and reflecting back to the intercooler, and perhaps even back to the compressor cover. If you took that little section of the graph and did an FFT you could measure the frequency of that oscillations and correlate it to the size and temperature of the tubing.

My shifting clearing sucks, as you can see the car actually slows down between shifts. Acceleration in 2nd is higher than in 3rd, and that ratio will be close to the actual gear ratio difference, plus the effects of drag. The shape of the yellow curves are a proxy for the shape of the torque curve of the engine, and you can see the slight fallloff at higher rpm.

The noise is something else to be investigated. Are those pressure variations real? If I overlayed the duty cycle of the wastegate, would they have an obvious interaction?
Lots of questions you can ask yourself, and lots of things to learn to explain something as simple as just a few lines.

Wires

Wires

Since I need a ton of air temp sensors in my GTR build, I’m taking a crack at making my own using a very fast response bead NTC element. Tony Palo already makes a really kick ass one that uses a TDK glass bead NTC element that has a ‘still air’ thermal response time of ~3s. That constant is an indication of the time to cool 63.2% of the way from a chosen heating point to ambient air temperature in still air. In fast moving air the response time would be much much faster, and in a liquid even more so.

I built these two test units using a similar NTC sensor from Cantherm that has a similar response time but slightly lower thermal mass. Since I have two ports in my Pre IC pipe I can directly compare both of these to not only a GM AIT, but also a low mass thermocouple. I also have a couple of other glass diode elements to try out.

For reference, the thermal response time of the typical ‘fast response’ GM AIT sensor is on the order of 15s. Both of these types of NTC sensors are of the fastest available in that form factor. An exposed tip thermocouple can have a response time as low as 1s in still air, and .01s in liquids, but the accuracy can be as low as +/- 5C.

I used a 3M epoxy potting compound to put the sensor inside a small 1/8NPT to hose adapter along with some Tefzel wire. I made these probes stick out a little bit more than normal because of the location of the adapter I need to use them in. I’ll post up data in a few days as to how they compare.

If you are looking to buy something to put in your build, just get the ones from T1. If you want to experiment with getting that extra 1%, follow along. 😉

EFR

EFR

This EFR8374 is not a bad turbo for an STI. Given the size compared to the 7670, the spool is pretty good. In 3rd gear, over 25psi at 4150rpm, 16psi at 3500rpm. First graph has Pre Intercooler(RED) and Post Intercooler(WHITE) pressure, as well as Exhaust Backpressure(Yellow) and RPM (Green).

Second graph is a scatter over a drive, and you can see a 4th gear pull does even better with 25psi at 3780rpm. That is fantastic for a 79lb/min turbo.

The biggest gain in spool during calibration came from lots of intake cam advance and exhaust cam retard.

Bugeye

Bugeye

Time for some safety upgrades on the bugeye. New roll cage, seats, harnesses, fire system, nets, HANS. Next up is new sleeved engine and *edit* a GTX3582R Twinscroll turbo. Turbo Flat 6 is good. 15 years old and 15k miles.. hmm..

Tree

Tree

Cornell Rd now open thanks to Eric Rosenberry and Eric Bryant and a few other helpful motorists!