Celebrating the fact that the Seven is up and running with an autocross video from Marina. The car still has an intermittent misfire that I am trying to iron out but it is running well so far.
Posts Tagged ‘Setting up a Seven’
Back up and Running
Thursday, November 8th, 2012Brake Bias Issues
Friday, February 3rd, 2012The only major dynamics complaint I had about my Ultralite was the rear lockup issue under hard braking. The car comes with a very nice set of Wilwood brakes (front and rear) with separate master cylinders for the the front and rear so it definitely wasn’t a component quality problem.
The issue I was having is that under hard braking at autocross the rears would immediately lock up and cause a lot of oversteer. This was even worse at the track where braking at the end of straights would lock the rears well before the fronts leading to bad porpoising at the rear. The whole issue was being caused by having equal braking capability front to rear which meant that once the weight transferred forward under braking, the rear wheels had very little weight on them and were prone to locking up while the fronts were still spinning. You could avoid this by braking earlier but this would mean that the front brakes would not be used to their full ability and would lead to longer stopping distances. The real solution would be to move the brake bias forward which I first attempted to do using the balance bar in the pedal box/master cylinder setup. This made no noticeable difference to the brake bias which meant that the bias issue was worse that I suspected.
Step two was to install an inline proportioning valve(below) on the rear circuit which could reduce the rear line pressure by up to 57%. While this did make the autocross situation much better I still had the problem of rear porpoising at the track albeit much better than before.
After consulting with some of the folks on the various forums I came up with two options: 1) replace the brake caliper with a smaller caliper and 2) replace the rear master cylinder with a larger piston. Since the piston was significantly cheaper than getting 2 brake calipers I decided to replace the MC with a 7/8th inch piston (originally 3/4 inch) which has been a great solution so far and has allowed me to run a much more balanced car at the track.
If you are building a car from scratch I would recommend going for a smaller set of calipers in the rear and/or smaller brake rotors both of which will save you some unsprung weight as well. I believe that the later Ultralite owners went to using stock 12-inch Subaru rotors in the rear which sounds like an economical solution as well. If you have a car with the original setup I can say that this solution of larger MC and bias valve has worked well for me.
“Diff”icult times
Thursday, February 2nd, 2012After 18 months of procrastinating about updating the blog about the Ultralite I figure its time to start putting pen to paper (or fingers to keyboard). Regular followers of the blog may remember that my Buttonwillow adventure ended with the Ultralite being flatbedded home as it looked like on of the two bolts holding the diff in place had backed out and gas tank prevented me from doing a roadside fix. I was thus still quite happy on the truck ride home as I thought it would be an easy fix and I should be back on the road soon – little did I know that I was in for some “diff”icult times.
The first thing to do was to empty the fuel tank and then remove it. As you might see from the residue above, the gas cap had been weeping fuel for a while and I figured that this was a good time to replace the gasket around the filler and see if that would fix the problem. I stuck my hand into the empty tank to see what size spanner I would need to remove the nuts on the cap fitting when I was shocked to discover that the cap ring was attached using just sheet metal screws with no nuts or backing plate inside the tank. While I could probably have fixed the issue fairly easily, I figured I had ridden my luck hard enough by tracking such a shoddy fuel setup and decided to go with a proper fuel cell instead. I gave Fuel Safe a call and they were able to create a custom bladder that fit inside my existing tank. Not only was the new custom cell much safer than the original setup but it has a proper racing collector which meant that I could ditch my external surge tank setup and save some weight. If you are looking for a custom fuel cell I highly recommend Drew Barney at Fuel Safe who was the guy I dealt with to create the setup below.
While my tank was at a Fuel Safe, I got busy actually fixing the diff mounts. Removing the gas tank had shown that the bolt had not backed out and instead had snapped from the torque. After removing the bolt and drilling out the snapped section in the unit I found that both rear bolts were metric grade 8.8 which sounds fine but actually equates to SAE grade 5 which is not what you want for something load bearing like this. I swapped both the bolts with metric 10.9 grade (equiv SAE grade 8) hardware and refitted the fuel cell thinking I should be good to go. However as soon as I backed out of the garage I heard the clunk from the drive train which meant that things were still not ok.
Pulling the center console off the shifter area showed the second problem (above). The front mounting point was created by welding a single mount onto a cut down version of the differential member assembly from a Subaru legacy. This mount was attached to some very thin metal and had basically ripped itself loose from the member assembly. After speaking to other Ultralite owner I found that this was a common failure point and needed to be reinforced for track cars in particular. I thus had a thick steel plate welded to the existing assembly to moth create a new mount point and also spread the load more widely on the Subaru part (see below).
Talking to the other owner also brought out that the diff bolts breaking was a common occurance and that many owners had created a brace that attached to the frame and helped spread the engine torque loads beyond the two diff bolts. Rob at Dietschwerks created this brace for me that had been on my car for over a year now and has been through several track days with no issues.
If you are an Ultralite owner I recommend that you check that you diff bolts are metric 10.9 grade and also create a diff brace for your car to avoid the painful debugging process that I went through.
Setting Up a Seven – When things just work
Tuesday, October 19th, 2010I have made a long list of modifications to the Seven since my last blog update which I still need to document on here. In the meantime I wanted to share this video from the GGLC autocross on Saturday (watch in fullscreen).
The Seven may be unreliable, impractical and difficult to live with but the few days like this when everything works are absolutely worth the hassle. Incidentally we found the reason for the surging idle it ended up that I couldn’t drive the car for the rest of the day 
Buttonwillow Weekend
Monday, June 7th, 2010
After going through many of the initial setup issues on the Seven and giving it a quick shakedown at Laguna Seca, I decided that it was time to take it on my first road trip. I drove it down to Buttonwillow Raceway Park to join a group of other Se7en owners for a track weekend. The fact that there were going to be other owners there made me feel more confident that there would be enough mechanical expertise to solve any mechanical issues that may crop up. Having been to Buttonwillow once before, I knew that the heat would be brutal and was glad to pitch in with the other folks to share a couple of garages with the other folks.
The drive down was uneventful and took me a little over 4 hours to complete. The fact that I was using my cool shirt on the drive down meant that I was extremely comfortable on the drive despite the high temperatures (80+ in Santa Clara to 98 in Buttonwillow). I even got to stop at the San Luis reservoir for a couple of great pictures.
There were 6 different Sevens taking part in the event including a Birkin, a Superstalker and 3 Caterhams (including the only R500 in the country) and we even had another Ultralite owner drop by to to say hi. The coolest car there was this maroon Caterham whose owner had put 70,000 miles on the car over 11 years but still had its looking like new. The even more amazing part was that he drove the car up from LA, completed a 2 hour enduro in it and then packed up and drove it to Lake Tahoe the next morning. 
The track action was organized by NCRC and was up to their usual excellent standards. All of us had a blast and got to spend some quality time studying each others cars and talking to fellow Seven fans. As a bonus, Vanhap Photography got some excellent shots of the track action including a couple of staged shots of us together on track.
My favourite part of the weekend was a 4 lap sequence where I was tryng to keep up with the Caterham R500 above. The car has only slightly more power than mine (263 bhp Vs 240 bhp0 than mine but is significantly lighter (1200 lbs Vs 1400 lbs) which makes it much faster in straight line. The video below (watch it in HD) shows the action from my point of view and you can see that every time we get onto a straight he is able to pull away from me. the only reason I was able to keep up at all was because he would have to wait for point-bys from slower cars while I could just stream through the openings he made. Might be a good excuse for me to get that supercharger after all 
The car performed very well on track and only had a couple of minor electrical issues. I had no heat issues and the coolsuit helped keep the driver cool as well. The tires performed very well and the only real problem was the too much rear bias in the brakes. Since the Ultralite has equal size brakes front to rear and equal sized master cylinders for each as well, the rear brakes are much too powerfull and will lock up way before the fronts even with the balance bar set all the way to the front. This means that I have to brake very early to prevent locking the rears and unsettling the car. I will likely be getting wither a smaller master cylinder or a smaller rear caliper before the next track day.
After packing up early on Sunday after I headed out early hoping to make it home before dinner. I was just over the half way mark when the car suddenly started producing a loud clunk from the rear when I either accelerated or decelerated. I pulled into the nearest gas station and looked under the rear to find that one of the two bolts holding the differential in place had backed out and that the diff was actually twisting around the remaining bolt and hitting the chassis to make the clunking sound. Unfortunately replacing it will require removing the gas tank which is not the kind of job to be done by the side of the road. Luckily I was less than a hundred miles from home which meant that AAA towed me back home for free
All in all it was a fun trip and I’m surprised at how happy I am despite having being towed back home I had a great time at the track and made some great new friends. The car was fast, fun and fairly reliable on the course. I may have broken down at the end but its an obvious problem and should be easy enough to fix in time for the next event. In the mean time you guys can check out the rest of the pictures below: