Over the last week about 200 miles was put on the car, cruising up and down the coast, racking up miles testing out the new turbo and generally checking out overall reliability. As far as the engine goes, well, wow. My favorite thing to do is head up freeway on ramps and really get on it. The last time I did that I could hear and feel the tires start slipping in second gear – nice. It really keeps your attention and it accelerates so fast there’s simply no where to stay on it more than a few seconds – I can live with that 🙂
This weekend I was on-duty and had to go into work. I double-checked the weather forecast and headed in, driving Midlana. Got about half way and splat, “What was that?” Splat, splat, “uh oh.” Yup, it started raining. As it got heavier I weighed pulling under a freeway overpass and waiting it out, but it never really let loose (after all, it IS California so we know the rain’s just teasing). It gave a chance to check out airflow over the windscreen and somewhat surprisingly, there wasn’t any. That is, the rain drops never moved from where they landed, up, down, or sideways. Huh. Anyhow, the rain moved on, leaving a damp freeway and I saw in the mirror that I was throwing up enormous rooster tails of mist, something I’m sure endeared me to everyone following immediately behind. Took the next exit to work, which happens to be near a Home Depot, and bought a small tarp just in case. It now lives under the doctor’s bag of tools in the front of the car.
As far as the continued reliability testing goes, well it worked: the stupid alternator bolt broke again, this time the one I cut really short and used as a simple guide pin. Okay, the gloves come off – the upper alternator mounting will be redone, with a steel substructure picking up several bolts on the block to fully triangulate the mount – I’ve had enough of this nonsense.
In other news, my brothers LS-power Super Stalker will likely be done in time for the SCCA Runoffs in Laguna Seca. Our plan is to drive both our cars up (just as spectators) which is 350 miles each way. A flaky/unreliable alternator bracket isn’t acceptable…
Boost was further increased to 15 psi and it’s now scary-fast! No timed runs have been done since there are so few places to time it; there are no local dragstrips (anymore) and deserted streets are rare. It’ll be interesting to see what 0-60 is since it can probably be run entirely in second. Traction in second is now iffy; it stays hooked up but slips a little here and there. The car is almost telepathic; on the freeway you find yourself thinking “I want to be over there” and it just happens. That ability however comes with knowing that Midlana is small and hard to see, so I have to do the seeing for them. Timed runs will happen eventually but don’t count on it being instrumented.
First, a couple pictures of the defective engine mount; it was pretty disgusting with the rusty-looking oil stains everywhere.
Regarding the mystery modification, can you spot it in the engine bay? The car was tuned at Church Automotive to tune the new GTX3576R turbocharger! The gain was about 10% due almost entirely to running higher boost than when the previous turbo was tuned. The graph overlays the new turbo results over the original GT3071R. What’s striking is how the larger turbo spins up at virtually the same engine rpm as the old one, and in driving the car, I can’t feel any additional lag. The new turbo has three things going for it in that respect: a new compressor blade design, twin scroll, and ball bearing. With the larger turbine wheel, exhaust backpressure is lower which allows more oxygen into the cylinders. Also, the larger turbo allows the engine to pull hard all the way to redline with no sense of power dropping off. I’ve had a number of cars that at mid-rpm, where right when you start thinking, “man, this thing’s really going to take off”, it sort of dies off at the high end – not so with this turbo.
One side effect of a twin scroll setup is that boost pressure is often different than the advertised wastegate spring rate, and with the larger turbo the difference was even more pronounced; with 13 lbs springs, boost never rose above 11.5 psi. Tial (the spring manufacturer) notes that boost will only match the spring rate if the intake and exhaust back pressure are the same – clearly mine is not.
Afterwards, the tuner said that 11-12 psi should be good for trackday events, though I’ll add some race gas to ensure no issues on-course. He also noted that “if this was my car, I’d be running 15-17 psi on the street.” The reason this can be done is because the car’s so light that it’s simply not possible to stay on the gas long enough to build up engine heat – the car will be going at “ludicrous speed” by then.
The only bummer on the trip is that I recorded the tuning session with my old camcorder – completely forgetting that my new PC doesn’t have a Fire Wire port (remember those)? There’s simply no way to get the video out of the camcorder – the pc recognizes it as a USB drive but can’t see the video files (only still photos). To make up for this, here’s the video that probably had the greatest effect on me for deciding to go with a larger turbo, the Ferrari F40 LM – be sure to turn it up good and loud. I’ve read that Porsche and Ferrari use large turbos to lift the high end of the power band instead of the low or mid-band and I’ve not seen another video that demonstrates this better – enjoy!