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Yesterday afternoon a little tuning took place. Finally got some time to get out of the city and actually see some real boost.
First the low load was cleaned up so that at light throttles and in vacuum, A/F ratios are rarely richer then 13.5. This made a huge difference in the way the car drives, not to mention fuel consumption. I'd go as far to say that it drives nearly as easily as stock. You can cruise all day at 2000 RPM without issues with the A/F ratios in the high 14s, and the car can be launched at 1700 RPM without any major drama.
Slowly we worked up to 10 PSI and past, bringing the fuel down to reasonable levels. At 10+ PSI, the car is a beast. Even with A/F ratios of 10:1, the thing just hauls hard. At 14 PSI the turbo really comes alive and the car looses traction in 1st, 2nd and 3rd. It's my guess that at less then 15 PSI, the car is easily a mid to low 12 second car and that's with A/F ratios probably costing 80HP. Once things are a little saner at 11.5:1 under 10 PSI and probably 11:1 or high-10s at above 10 PSI the car will really start to pull.
No real videos right now of the tuning, but here's a little teaser showing the real response of a ball bearing turbo:
GT4088R Turbo on Bridgeported RX-7 Rev, Spool and Shutdown (YouTube)
Count how many seconds it takes to stop spinning after the car is turned off.
A little more tuning yesterday. The car has lots of fuel for probably as much as the turbo will throw at it. At 13 PSI (current wastegate spring, no controller) injector times are less then 4 mS and A/F ratios are still in the mid 10s. I'm slowly cleaning up the car and aiming for high 11s before 10 PSI, low 11s at 13 PSI and high 10s at higher boost. Timing is currently very conservative under boost with a linear progression from 15 degrees or so around 8 PSI ending up at 10 degrees at 13 PSI and above. Certainly there is more power to be made with timing but I'll cross that bridge on the dyno and not the street. The car is rapidly becoming too fast to safely tune on even the most remote and deserted roads. Rolling on the throttle will result in loss of traction in 1st, 2nd and 3rd gear at nearly any speed.
Boost control is rock solid. It spools to 13 PSI then just sits there regardless of load without a hint of creep.
I must say that the data logging feature of the Nexus gauges has made this process very simple. Of course the Microtech does data logging, but it's far more convenient to grab the Nexus remote and step through a run while tweaking the fuel map at the same time. Currently I have a 512MB SD card in the remote for logging which is about 30 minutes worth of recording. Very handy for the drive to and from work to clean up cold start and cruise.
The DEI heat shield is dying a slow death. Where the inner surfaces touches the turbine housing, all the aluminum coating has flaked off. Every time I was the engine bay I end up with a shiny aluminum coated towel. Will it get worse? Don't know at the moment but it certainly does not look as good as it did in the original pictures.
I'd have to say that because of this, I am not happy with the product and would not recommend that anyone else spend their money on it when there are other well known blankets that can stand up to rotary exhaust heat. I'm going to send a letter to DEI asking them to make it very clear that the product is not rotary compatible.
As for the tuning, the car is coming along quite nicely. I've been data logging nearly every day and working out the kinks in the light load map in the hopes of getting reasonable gas mileage. Currently the car cruises in the high 14s/low 15s most of the time, falling to the high 13s under light acceleration. Because of the general leanness of the map it's taking some time to really dial in the cold start (there's only one chance per day to work on it), and as the engine breaks in fully I've needed to tweak the idle a few times. Nothing out of the ordinary really.
In general the car is terrifying to drive under WOT. It's still running pig rich under boost in the low 10s but it's slowly coming around as I've been leaning out the map. Soon I'll need to book some dyno time because as the A/F ratios improve, power is improving dramatically and the car is too fast to safely tune on the street.
This Friday (tomorrow) I'm going to make a trip to the 1/4 mile to make a few easy runs and just see what the car will do right now. Primarily I'll be looking at MPH at the end of the 1/4 mile as it's the best indicator of potential. I'm not going to beat the car at launch yet with things like the anti-lag until the A/F ratios are a little more sane.
As promised, here are a few 1/4 mile videos from a few weeks ago. No hard launches or really serious runs, just testing and getting used to the car:
Project Tina Quarter Mile Test Runs (Windows Media Version, 22MB)
Project Tina Quarter Mile Test Runs (YouTube Version)
The car ran far slower then I thought it would at around mid 13s but mainly this is a traction issue. Launching results in a flurry of wheel spin due to the instant boost from the GT40. It's going to take some practice to get a good launch and 60 foot time. The power is there as evidenced by the 109-111 MPH trap speed.
On Monday I booked some time at Chandler Technologies to run the car on their Dynocom dyno. I was initially worried that the day was not going to go so well as my passenger side front caliper stuck on the way there (what the hell? Seriously....) but then again, you don't need front brakes to dyno a car!
After the car was strapped in, the baseline run made 320 RWHP at 13 PSI. Much more then was expected (I guessed it would make 266, others guessed 275) keeping in mind that the current "tune" in boost just meant that the A/F ratios were barely registering on the gauge at something other then 10:1 flat.
With each successive run we pulled a bit of fuel and gained between 10 and 20 HP every time. After approximately 6-8 runs (I lost count) the final number was 387 RWHP, 279 FT-LBS @ 13 PSI. A conservative estimate puts that right around 420 HP at the flywheel. Not half bad for an hour on the dyno on low boost. A/F ratios are in the mid 12s until about 5 PSI, falling to the mid 11s to 10 PSI, then low 11s to 13 PSI. Timing is still VERY conservative at 10 degrees. I could put a few degrees of timing into it right now and pick up a few more HP but I'd rather wait and borrow an EGT gauge (or buy a cheap one) before I start bumping timing too much.
The video from the last few runs is available to download in two formats. The first is a high quality Windows Media file and is about 15 MB in size. You can really see and hear things the way it took place (the whine from the turbo is unbelievable). You'll probably want to "Right Click, Save As" to download it instead of opening it directly in your media player. The 2nd link is the same video on YouTube but the quality is not that great (especially the audio).
Project Tina First Dyno Runs (WMV High Quality)
Project Tina First Dyno Runs (YouTube Version)
The next step is to install a boost controller and crank that turbo up to 17 PSI where it belongs. I fully expect 500 HP to the wheels once I get into real boost...
Before St. Thomas Dragway closed for the season I wanted to get a few runs in once the car had been tuned. The fuel map was far less lumpy which made launching a lot easier then the previous track outing, and of course 67 RWHP more wouldn't hurt either.
I was hoping to get into the 12s but traction remained the problem. With an open diff, street tires and a cool track surface the car was spinning the rear tires 3/4 of the way down the track. Regardless, this time the car did run much faster and the practice last time let me nail the launches while avoiding excessive wheel spin. In the video below you can see and hear how the car was spinning the tires through 4 gears. In fact, the last two runs were a more then a bit scary as the car lost traction shifting into 4th at around 170 KM/H. I had to quickly back out of the throttle to get the rear end back in line.
I'm going to be stuck in the 13s until I get a limited slip differential installed.
You are going to want to right click and "save as" when viewing the Windows Media version as the video is too high bandwidth to stream.
Tina At Sparta Oct. 6, 2007 (Windows Media, 17MB)
Tina At Sparta Oct. 6, 2007 (YouTube)
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