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15psi...Miata performance

IC Tests

I am putting together a test of the many Intercooler options that are popular in turbocharged Miatas.

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Process:

The goal is to test the efficiencies of different Intercoolers on a Greddy turbo Miata. I’ll be measuring the differences in boost and temperature before and after the intercoolers.

Ideally I want to make the tests @ 90~100 deg ambient temperature. This is where I have experienced my Starion setup struggling to cool the charge.

The testing starts with the basic Greddy turbo kit 2” mandrel bent piping, Link MK1, JR catback. The car has both PS & AC. In order to minimize variables in the wastegate, I have shimmed the WG rather than using a manual boost controller. For the initial tests I’ll be testing a 14 row Starion IC (1.75 inlet/outlets), RX7- J spec IC (2” inlet/outlets), and a Saab 900 IC (2.5” inlet/outlet)

Controls

I have attached a barb to a 2” pipe just after the turbo and will use an extra boost gage to measure the pre-IC pressure. My current boost gage will measure the pressure at the manifold. I tested the gages against each other. The black one (pre IC) was optimistic by~ 1psi.

I am using a Fluke dual sensor temperature meter. I checked both sensors against each other in a controlled environment of heated water. They were with 2 degrees of each other @ 150deg and within 3 deg of a thermometer.

I have placed the sensors near both pressure-testing locations. The boost gages and meter are near the tach so I could record all measurements at the same time. I used a Sony DCR-TRV 350 digital video camera to record the tests. I then playback the results on a HiRes Proj TV and view the results frame by frame.

 Tests

The test runs are in the same exact location. The road is uphill, limited traffic and doesn’t have side access during the runs. The ambient temperatures have been very cool, but I decided to run the tests and see the results for the time being, plus learn what I need to do to improve the testing for future warmer retests. The ambient temps were 72~82deg. I ran through the gears, starting in 1^st gear and shut down towards the end of 3^rd gear, so I could reduce speed before I reached side access streets.

Results

I recorded the data into Excel spreadsheets for analysis.

In a perfect world, I could eliminate all outside variables, but that is not the case. So I’ll review the results (my interpretation) and discuss the variables. I’ve included some of the videos, the Excel spreadsheet of each test and a comparison of the IC specs. My intentions are to rerun the test when the temperature is in the 90deg zone.

 Overall observations:

I displayed either the pre IC temp or the temp difference. This didn’t always allow you to compare temps since the IC & turbo would produce different temps depending on if I had just made a full throttle run or not. Thus the turbo side (pre IC) could increase in 1^st gear by a few degrees or 70 degrees. Variables!

The manifold temps stayed pretty cool through 1^st gear, as the throttle closed the temps skyrocketed and then they were often 50-70 deg higher on the pre-IC side during 2^nd gear. They continue to increase as the EGTs increase and heat the turbo. The IC s typically cooled the temps ~ 100deg as the turbo outlet passed the 200 deg point.  The higher I revved the engine (7000prm) the more heat the turbo produced. I tried to heat the IC before a run but unless I ran a full throttle

 The boost pressure differential was typically 2psi and increased to 3psi at high revs (& heat).  This was pretty consistent from one IC to another. But the boost did change during the test process. I noticed that the Saab (last test) was showing a higher psi at lower rpms. This seemed strange, so I checked the Starion (1^st test) again after I put everything back together. Sure enough the Starion was also boosting earlier as the Saab was. I would conclude that the many hard runs might of cleaned out carbon from the exhaust and it was breathing better. The car typically runs very short trips and spends most of it’s time in the rich warm-up stage. Possibly the cat was flowing better?

 Starion: The Starion is the 89 version with the 14 larger rows and with the stock 1.75 inlet/outlets. I’ll be interested in rerunning the tests with 2” inlet/outlets. It was a shame that the largest IC had the smallest pipes, but it represents what many use. My first test was with the shrouding, but I didn’t see any difference. As with the cooling system, it might only make a difference with much higher ambient temps. I recorded the turbo temps but for some reason not the manifold temps. I’ll be retesting since the Starion is back in the car.    

 RX-7:  The RX7 IC also had a 2-3 psi differential. And was cooling the charge by ~160 deg at higher boost. The performance was closer to the Starion that I expected. It will be interesting to see the comparison at 90~100 deg  temps. 

 Saab: The Saab performed much like the RX7. The benefit for the Saab is that I use 2.5” pipes from the IC to the manifold. The RX& uses 2” and the Starion’s outlets are 1.75, that increase to 2” and then 2.5 for the elbow. Kinda backwards huh?  

Having the Saab back in the car gave me the opportunity to modify the design so the pipes are sitting a little higher (more ground clearance)

Final thoughts: I am very interested in doing the tests again with higher ambient temps. In the past, the only time that the intake elbow was ever hot after a hard run was 100deg days. I did find it interesting to view the relations of boost produced, at partial throttle. The turbo was building boost and the manifold was still in medium vacuum.

A lot of heat was built up during gear changes, but that makes sense. An automatic would be beneficial in this matter.

The Starion could really benefit from 2” inlet, and 2.5” outlet all the way to the throttle. I’m already working on this and will modify the 5 Starions that I have.

I am also going to experiment with using a taller gear instead of running through the gears. I'll probably need a longer stretch of road.

It would also be nice to view the 'temp diff' and the manifold temp at the same time. The newer Flukes can be connected to a computer. Or maybe use the TEC2 data, but that is on the computer. Hmmmm.

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I will include:

Tests will include

Here is a preview of the ICs.

Here is the Starion vs the smaller NPR. They are very close in core size. (they are made by the same company)

Here is a comparison of the 2 RX-7 ICs that are  available