This section will cover various aspects of taking the car from the completed state and developing the handling and various systems on the car. I feel that building the car is only half the journey...making it run and drive to it's full potential is the other half.
12/27/07 - Wrapping up the year and looking towards 2008.
Well, 2007 has come and is nearly gone. It was a great year, filled with fun and frustration getting the car finished up and out on the track. There was one more event that I did near the end of the year that was fun. I went to the North Carolina Motor Speedway (The Rock) and participated in a time trial during the course of that track weekend. I ended up qualifying 2nd overall, right behind an Ultima GTR. As it would turn out, despite him getting off to a slow start, he did end up beating me out for the overall victory by about 2 seconds. But 2nd overall out of approximately 30 cars was not bad. Here is the time trial session video.
So, what is ahead for 2008? No major plans at this point. Just a few minor changes and improvements. The rear axle will be coming out of the car and the axle housing will be finally straightened up the rest of the way. That should help a good deal. I plan to check the car over really well and disassemble some of it to make sure things are holding up well.
I plan on getting a sequential LED shift light for the car. Having to peek at the tach is a distraction that keeps my vision down too much. Having the shift light just below my line of sight should help keep the vision up all the time. I also plan on trying the car on full slicks in '08. Up to this point, I have run the car on DOT R compound radials and bias ply tires. More grip should be had from a set of true slicks.
This will be the last entry for this section. I plan to start a new section for 2008.
9/23/07 - More changes and a BIG discovery.
In between the trip to CMP and a recent trip to VIR, I really looked the car over well trying to figure out if anything was out of square with the car. Despite increasing the front spring rate, the car was still very loose at CMP and still had the tendancy to be looser on right hand turns. I had measured just about everything that I could and the rear seemed to be square in the chassis. I finally got a set of toe plates because I wanted to verify my existing method of checking toe (using two long pieces of square tubing running back to the rear of the car). I checked the front and verified that it did indeed have zero toe. Just for the heck of it I checked the rear expecting it to be zero as well (live axle). Much to my surprise, I found it to be toed out by 1/2" and mostly on the driver's side. BINGO! That explained pretty much everything that had been happening since I put that new Toyota rear axle in the car. I had checked the axles themselves in a lathe and they were true. I did not expect the housing to be bent. Live and learn.
So now I am faced with this problem, and only a couple of days to get ready for VIR. A friend suggested that I run a weld bead on the front of the axle tube to get it to move in a way that would take the toe out while it was in the car still. I ended up running three beads on the driver's side and one on the passenger side in the end. I did not get all the toe out condition fixed, as there is still about 1/8" toe out still left. It is still way better than what I had to begin with. Along with this "fix" I increased the front spring rates again, making them now 500 lbs/in. Looks like a winter project will be straightening the existing housing or maybe making up a new one with nice DOM axle tubes.
So I head to VIR with Tarheel BMWCCA on the full course. The car drove much better than it had since installing the new rear end. It was still a little loose in right hand turns, but much better. I was able to increase my pace overall and the car was more stable in the high speed "bravery" sections of the track. My confidence in it came up a good bit and I was able to put down some pretty decent lap times. I took a little bit of video on Friday during the Instructor day:
The car ran really well for all three days that weekend, which puts it now at three weekends in a row with now mechanical problems being driven flat out. The next area of focus (besides the axle housing) will be the brakes. They work well, but I am convinced they could be better. The rears still lock up way before the fronts do. I am out of adjustment on my balance bar, so I will probably go with a different rear pad, with a less aggressive compound. The calipers that I have are new from Wilwood, and there are not a lot of choices out for them yet. The ones I picked were fairly aggressive because I figured that the smaller pad area might hurt me with the new setup. Guess it did not hurt that bad...
The car continues to improve with each outing, and my confidence continues to grow in it. The good news is that there is still room to improve it and that only means that it should continue to get faster.
8/9/07 - Lots of catching up...New rear end, GRM UTCC, first trip to CMP.
New Rear End
The new rear axle is finally under the car. This process ended up being really long and drawn out due to supplier problems. I swear that sometimes folks just don't want to stay in business. Anyway. Here is the setup. The axle is out of a '73 Toyota Celica and features the 10-bolt 6.7" center section. These are popular with the Legends and Dwarf car folks and parts are plentiful and relatively cheap. It has a TRD Limited Slip unit that is a 2-way clutch type unit and the new ring and pinion ratio is 3.42. Through a dwarf car supplier I was able to get some nice bolt on caliper brackets that work with Wilwood Calipers. The rotors are now 10.25" in diameter. I did not weigh them, but the new axle is a bit lighter than the old one just picking them up.
GRM Ultimate Track Car Challenge
The UTCC has come and gone. All I can say is that it was really fun to be a part of it and WOW, what an incredible field of cars that were assembled for the event. GRM wanted this to be an sample of the cars that show up for a typical track weekend. I am not sure where they do show up at, but they are not what show up around here on a typical weekend. Tommy Archer ran a 1:28 second lap around VIR North Course...I have never seen ANY car run that fast there...amazing. There were also 10 or so cars that ran under 1:40. That is something that you don't see very often either.
So how did I do? My best official lap was a mid-1:43, which was a personal best for that track. That put me 20th overall (out of 36) and 10th in class (out of 19). The car ended up running varsity independent study which was a tall order. Originally, they had classed me in JV, but do to some grumblings about my car being tube frame, they moved me up at the last minute. 1-liter normally aspirated power did not really have a snoball's chance at anything. As it was, I would have only finished 3rd in the JV class...
I had a great time at the event, and was honored just to be a part of it. However I was a little let down because there was no time to test the car out before hand (do to the vendor problems) and it was a bit of a handful for the event. Despite being faster overall, the car was extremely loose overall, especially on right hand turns. Also, the new rear brakes were mighty strong and prone to lock up. I ran the balance bar all the way to the front and managed it the best I could. My friend Alan was crew chief for the day, and between us, we adjusted on the car all day long. The changes we made helped the car each session, but unfortunately the track kept getting hotter and hotter which meant the times stayed about the same for the most part. Most everyone else slowed down as the day went on. The overall result would have not been much better, but a couple more seconds would have been nice and doable.
Leading up to the event, it was brought to my attention that my car was featured in a quick lead up story in Classic Motorsports hyping up the event a little...cool. I did take some video from the event and have basically an entire session here: GRM UTCC Vid Here are a few pics from the event as well.
First Trip to CMP
This past weekend I made my first trip to Carolina Motorsports Park in Kershaw, SC. Several changes were made to the car based off of the data we collected at the GRM event as well as from driving feel. The front spring rates were raised 100# from 300 to 400. Some negative camber was taken out of the front as well making the setting now at -1.0 degrees. The rear master cylinder was increased in size to take away some line pressure and to bring the car back to more neutral braking.
Overall, the car was much better and handling was a lot closer to neutral, but still a little on the loose side. The brakes are a lot more balanced as well. I think that going slightly more aggressive on the front compound will put them just about perfect and give me a wide range for adjustability.
Despite this being my first time to this track, and much to my surprise, I managed to put the car on "pole" for the Time Trial event on Saturday by having the fastest preliminary lap out of roughly 30 TT participants. Feeling a little pressure by leading thing off, I went out and managed to find a little more time (in the heat of the day) and shed a couple more seconds off my best time. The best lap for me ended up being a 1:49.6 but ultimately was only good enough for 2nd overall and a trophy. A well driven and prepped V8 Z-car beat me by about .7 seconds...just when I had a glimmer of hope for my first TT FTD. I was happy though to have done that well on my first trip to CMP. Here are a few laps of video from the TT. As you can see, the track is sort of friendly for Sevens... CMP TT
The car is getting better, but it is a long way from being done. More tuning on the chassis will be needed to get it a little more dialed in. One of the next things I am going to work on is getting more forward bite in the car. I really get a lot of wheel spin coming off of the corners and that is costing my precious time.
7/9/07 - Went to Summit Point and getting ready for the GRM UTCC
Back in June, I was able to make it out to the track again. This time it was at Summit Point Raceway in WV with NASA. The weekend went really well and the car performed flawlessly. It drove well and I loaded it on the trailer in the same condition as I unloaded it in. This was the fourth track weekend for the car and the first without any mechanical issues whatsoever. I was happy for sure. Of course, there was still the annoying gearing issue, but that is going to fix itself soon enough.
Here is some in-car footage from the weekend: Summit Point Video
Parts for the new rear end are still coming in and the car is about to come apart so that can be installed. I also ordered a new set of wheels and tires for the car that should provide more mechanical grip for the turns. I decided to go with Avon ACB-10s this time around. We will see how well those do... I have a lot of work to do over the next couple of weeks. The work on the car needs to be completed in time to shake the new parts down at a local autocross the weekend before the GRM event.
Details about the new rear end will be in the next installment.
5/9/07 - More track time after lots of work...
Since the car broke the last weekend that I had it out, there was a good bit of work to be done between events. The entire rear axle assembly had to come out (in pieces). Room is tight back there and I basically had to disassemble the whole axle before it would come out...repeat to put it back in. While it was out I knocked out two projects. The first was the repair of the broken axle bracket. The driver's side had come completely off and the passenger side was starting to crack and was going to fail eventually. I re-welded both brackets being extra careful to get good penetration into the axle housing and making nice big fillets with lots of surface area. I also added a circle bracket around the front and tied that back into the original bracket. Even if the weld cracks again the axle should stay located.
Next I made a quick and dirty panhard bar to try in place of the Mumford linkage. As mentioned earlier the car had a noticeable amount of understeer overall and the rear was rolling more than I wanted it to. I figured that I just placed the roll center too low and the back was just in charge a bit more than it needed to be. The panhard bar raised the roll center by a little more than 4".
Also, while the rear was out, I took the opportunity to redo the fuel feed line from the fuel pump to the fuel filter in the engine bay. It was not until after I had already mostly plumed the original setup that I found out about the Bundy style fittings. These are what Ford uses for OEM stuff and they work with special nylon fuel line. My original setup had quite a few adaptors in place to get from one type of line/fitting to the other and I was not happy with several points for failure. The new setup is a straight shot from the pump to the filter...simple.
Also, this past week I was able to score a Toyota 10-bolt rear from a '73 Celica. This will be the basis for a new rear end setup. For this I can get lots of gear ratios (including the 3.30 that I need) a nice limited slip, and as radical of an axle and brake setup as budget allows. Thanks dwarf car guys! I searched and searched for the odd gear sets that I needed for the RX-7 axle, but just kept coming up empty. There will be a nicely setup disk brake posi Mazda axle for sale in the future.
After all the work...the payoff.
This past weekend I was back at the track. This time at the South Course of VIR with the VSCCA and the Mid-Atlantic Alfa Romeo Club. The car ran just great and the changes that I made to the rear suspension worked out well. The car was much more neutral than before and nearly perfect in the lower speed corners. I think that I may have some high speed aero induced understeer, but it is not nearly as pronounced as before. The panhard bar did make the car feel a little different and I could feel it "jacking" the car around as the car rolled and moved up and down. It was not as smooth as the Mumford linkage, but the raised roll center really helped the balance. Ultimately, I may go with the watts linkage at the same roll center height.
The weekend was almost perfect from a reliability standpoint, but with about five minutes to go in the last session of the weekend the throttle cable broke. It failed up near the gland that hooks to the throttle bodies and one of two things happened. Either I had it adjusted incorrectly and my "lift and shift" actions finally broke it, or it was weakened there when the cable supplier had to remove the gland and braze it back on because of an assembly error. Regardless it is off being repaired and I have a spare unit being made as well.
My in-car video setup screwed up and I did not get any of that, but my good friend Stefan took some external video of the car so that I could see and hear what all the fuss was about from those trackside.
4/10/07 - Two Weekends at the track!
Well, I just got done with running two weekends back to back at the track. The first weekend was with NASA on VIR Full Course and the second was with Tarheel Sports Car Club on VIR North Course. All I can say is WOW, this car is an absolute blast to drive on track. It is about as close to a sports racer or formula car as I may get for a while and is just highly addictive. Out of the box the car drives pretty nice overall. It has no real bad habits to speak of and is pretty darn quick. It has some noticeable understeer (which is probably good at first) that I am going to have to work on. I am a little suspicious that I may have picked too low of a roll center for the rear of the car which is causing it to dominate the handling. I don't want to go up much more on spring rate back there because the car already skips the rear a little anyway. I may end up making a bolt on panhard bar to try a higher roll center with. Plus that would give me a comparison of that vs. the Mumford link.
One other glaring problem is that the car runs out of gear in a hurry. Based on the gear calcs, that should be at about 120 mph give or take a few. It gets there quick and I just have to modulate the throttle to keep it off the rev limiter for better than half the straights. Looks like I am going to have to source a junkyard 3.31 ring and pinion to get the top speed up. (that ratio figures in at about 135) I figured that the aero wall would hit somewhere close to 120, but it is still pulling strong there...who knows if it will make it to 135 or not.
When I was going over the car after the first weekend at the track, I discovered that the rear brakes were doing all the work and the fronts were barely doing anything. This was perplexing because I spent a great deal of time collecting and inputting data into the brakemath spreadsheet rather than just taking a SWAG at it. Originally I had a larger MC on the front circuit and a smaller one on the rear. Because it was all I had time to do, I simply switched the two which gave the front more line pressure and the rear less. This seemed to do the trick as the car was better under braking and I was able to get the fronts to lock up. I made a couple of turns on the balance bar during one session and the car seemed to brake well without lockup after that.
The car has impressed me with its out of the box performance, but not everything has been perfect. During the first weekend I had a "come to Jesus" moment at the top of the uphill esses on the Full Course. Somehow a small piece of gravel managed to hover in just the right spot and when I lifted to brush the brakes for the upcoming turn the throttle stop managed to capture said piece of gravel between it and the floor. This of course kept the throttle stuck partially open which is not good. Quick thinking helped me realize what was going on and I first dipped the clutch in while I was reaching for the kill switch. By the time I shut her down I was out of track and had to pretty much drive off at better than 100 mph. I think I was airborne for just a little bit and the downward slope made for a soft landing in the grass where it coasted to within 50 yards of the corner station for Oak Tree. I was amazed to look down and see the rock in there...the floor is totally flat right there with no place to accumulate anything. Just a total freak of nature. When I got home from that weekend I took a picture of just how it happened so you could see how bizarre it was. The second picture shows the rock under the stop.
Before the second weekend, I took the stop out of the pedal and made it come up through the floor. If a rock finds its way on top of that, I am just not living right...
During the second weekend out I noticed that the bracket for the gear linkage was flexing a little and started to bend slightly. That will need a bit of beefing up.
Also during the second weekend at the start of each session from about mid-day on Saturday on, the clutch started slipping a little for a few laps and then worked fine from there on. That one has me baffled but it will have to be checked out before the next outing. I may have to set the Barnett clutch up all the way stiff.
On Sunday I managed to actually break the thing. On the North Course there is a heavy transition at the crossover which is pretty brutal on the cars. Once, while going through there the car lurched to one side and started making a funny noise. This sent me off the track near the top of turn seven. At first, I thought that maybe someone had blown the braking zone and had hit me from behind, but I quickly realized that something was just broken in the rear suspension. The initial assessment was that the bracket that the 4-link and the shock had broken free of the axle...not good. Rather disgusted I threw it in the trailer and brought it home. Sure enough the welds had pulled out all the way around the "C" on both sides of that bracket. Inspection of the other side revealed cracks starting from the bottom of the "C" and going about half way up. All I can figure here is that the torque from the axle is twisting them out of the brackets. If you notice in the videos the car does skip the back end a lot and I am sure this shocks that joint real good. The thing is a little monster after all and I have been running the snot out of it. Someone also mentioned to me that maybe the metal in those old RX-7 axles is not the greatest either. Regardless the bracket needs a redesign/reinforcement. I am going to have to six-million-dollar this thing for sure. The bracket itself if pretty sturdy and attaches to the axle in "book" fashion. Obviously this arrangement is not up to the task. I will update when the redo is done. This will give me a chance to take care of that gearing as well.
Despite the initial problems, I could not be happier with how the car performs. What it has clearly demonstrated to me is that it has a LOT of potential to be tapped into. The fact that the car drove as well as it did and had no real bad tendencies, makes me feel that many of my assumptions were pretty close. Once the suspension, gearing, and tires (the hard compound Hankooks I have are not very inspiring...) are sorted out, the car is going to be a guided rocket. Many folks have told me to expect some bumps in the road along the way while in the process of making the thing bulletproof and I guess I can deal with that. Every time I drive it I come back in with a big smile on my face...so that is good.
My wife bought me a nice little bullet camera setup for my birthday recently with a nice roll bar mount so that I can capture plenty of good video from various angles.
Of course, I took some video both weekends. The first one is some highlights from the very first day on track. That day left me with a truly awesome feeling when it was done...
The second is a video of my entire time trial session from this past Saturday. The temperature was pretty cold and you can see how long it takes me to get up to speed before the tires started working well.
I have a month to get the rear end fixed and to take care of the other housekeeping things before the next event. I can't wait to get it back out on track again. :)
3/12/07 - First Autocross Weekend
This past weekend was spent driving the car at speed for the very first time. The format was just about perfect for the first time out. Saturday was a test and tune for club members only which meant many runs on a small course just to adjust the cars and experiment with settings. I was not sure what to expect as this was the first time the car has been driven hard (it had only been driven around the block once before then). I had made my best estimates as to what the initial setup would be and how the car was adjusted. For reference here is the initial setup:
Springs: 300 front/200 rear
Caster: 4.5 degrees
Camber: -1.5 degrees
Tires: 185/60-13 front / 205/60-13 rear
The first few runs during the test and tune were challenging. The car is an absolute monster to drive (in a good way). The acceleration is blistering and the car just hooks up and goes. The course surface was very bumpy which upset the car somewhat, but considering the power level, the car took it pretty well. I noticed that the car had a tendency to understeer, especially from the middle of the turn on. I think that several factors contribute to that. 1) nearly a 60% rear weight bias 2) an aggressive limited slip and 3) based on the tire wear, the front could use some additional negative camber. The first runs were sketchy and left me on sensory overload...lots of new information to process. After lunch we went out again, this time with better results. I started to get used to the car and feeling things out a bit. Once I adjusted to the cars power/handling traits, things started moving pretty quickly. By the end of the day, I was feeling pretty awesome. The car ran flawlessly and had no nasty habits right out of the box. Enough information was gathered to make some minor changes to the alignment before the next outing. I had the camera onboard to be able to review video later and see just how the car (and I) was acting. Here is a clip of a few of the afternoon runs. Test and Tune Video
Sunday was the autocross event. It was at the same location but with a different and longer course. There were only 4 runs to get the best time so making the most of each one was important. Having more time to think about how the car was driving overnight helped me to adjust more to the car and how it drives. Two of the runs were pretty solid. One had me going off course do to getting out of shape in the slalom and avoiding cone carnage. Another run was going well until I broke into a short drifting session... In the end I was able to be fast enough to get FTD for the event. Here is video from a couple of runs. Autocross Runs
In the end I could not be happier with the weekend's results. The car ran flawlessly the entire weekend and proved to be quite the monster on the autocross course. It exceeded my expectations (which were high already) on many levels. I can only imagine just how fast the car will be with some slicks and sorted handling. It left me with a huge feeling of satisfaction considering the years of work and effort that went into the car. It also started to affirm that the designs that I have put into the car are working as intended.
The car heads for the track in a few weeks...