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conebasher

Project E-Mod MGB-GT

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So, even though we actually broke the car today, I think our first autocross was a success. I drove first and the car really, really bounced around on the rough surface we use and understeered everywhere. I didn't know what was going on until I watched Briget drive, and it looked to me like the car was bouncing off the bump stops. I stiffened the rear suspension a couple of steps and went out for my second run. It was a lot better and started to go through slaloms much easier. For my 3rd run I stiffened the rear another step and also stiffened the front by one step. It was even more controlled but the rear still really bounced in a couple of places. The high speed compression was already at full soft so I adjusted it to full hard but left the low speed compression and rebound at full soft and sent Briget out on her run. Going over the first massive bump on the course, the bracket holding the short arm of the Woblink broke, allowing the rear suspension to move around-our day was done. I got the car back to the shop and took a good look at it. There was enough flex right at the end of the bracket that after Friday's track day and todays autocross, the piece failed from constant flexing. I boxed it so flex has been eliminated and we won't have that problem again. Here's a pic of the broken link:Posted ImageThe data from my 3rd run shows that the car was pulling .6 G at 50 mph (the only time I got on the gas in 2nd gear) and was hitting over 1 G in either direction so it has potential but I certainly was not getting the most out of it. I'm confident that it will be a lot better on a smooth surface without pivot cones. Just check out the video and you will get an idea how violent it was inside the car.

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It's unfortunate you can't tune the car much with our surface, but you can definitely test the suspension for durability. The bouncing in that video looked pretty violent.

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I have to say I have never seen a car move like that anywhere ever! bouncing and sliding that is, definitely looked like a handful, I have no idea how you didn't go off course Mark. Briget looked like a bobble head doll in there. lol it was pretty scary seeing the whole body moving what looked like to be a whole foot from side to side after the link broke.

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I was still trying to understand what the rear suspension was doing (other than breaking) so today I put zip ties on the shock shaft to see how much compression they were getting, and I aimed a camera at them. The car was really unstable under braking but was better over the big bumps. When I got back, the zip ties were shoved up against the bump stops. I changed the high and low speed compression settings from full soft to full stiff and sent Briget out. When Briget was on course I could see the axle moving back and forth and for a moment thought that the newly fixed bracket broke again, but that was not it. The zip ties were not up against the bump stops this time so that was positive. Once in the pits I tried to determine how the axle was moving back and forth and couldn't find anything at first but once I had Briget shake the car back and forth really hard, I found a fracture in a different bracket. Obviously the forces on the Woblink are greater than a typical lateral link like a Panhard or Watts because these brackets were pretty robust and were still snapping solid steel plate. I know from trying different roll center heights at the lapping session and autocross that the car likes it set above 8" high, so I am going to remove the troublesome Woblink and install an adjustable Panhard around that height. Here is a very interesting video of the rear suspension during a run, once you stop being mesmerized by the shocks moving around, notice how much the diff is moving back and forth due to the broken Woblink.

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Wow, so much movement. I haven't seen a rear end shake like that since J-Lo! ;)On a more serious note, I'm glad you were able to use this weekend as a test before heading south and then finding problems there. Hopefully you can get all the pieces together and have another test run before Lincoln. To Claudio's point, our track is as good as any at exposing any weak points in any suspension.

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St. Andrew's Airport: The Nurburgring of parking lots

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Wow' date=' so much movement. I haven't seen a rear end shake like that since J-Lo! ;)On a more serious note, I'm glad you were able to use this weekend as a test before heading south and then finding problems there. Hopefully you can get all the pieces together and have another test run before Lincoln. To Claudio's point, our track is as good as any at exposing any weak points in any suspension.[/quote']St.Andrews is good for revealing weaknesses like welds and brackets and that's all good but adjusting the car to handle the big bumps and the pivot cones is going to hurt us in Lincoln. As an example, we need a quick ratio steering to get through the slaloms but I have had to build a sharper than necessary turning radius into the car just for the pivots. I would like to reduce the turning circle to make steering effort easier but I can't. Also, EMod cars typically run 1.5-2.5" ground clearance and run the splitters even less than that in Lincoln but I have to run at 4" ground clearance to clear the bumps. It is what it is and it's all we have but if the club were to pay a little more attention to the autocross program, we would have seen some improvements to our facility.

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I cut all the Woblink stuff out and ordered bolt-on Panhard bar mounts. When they arrived I was blown away by their robustness, clearly I had underestimated the forces involved. Posted ImageI welded and braced 2" square tubing on the drivers side for the frame mountPosted ImageThe new mounts use 3/4" rod ends instead of 5/8" rod ends, just look at the differencePosted ImageAnd all bolted in place. the kink in the Panhard bar is because I got it from a local dirt oval racer (Ricky Weiss) and in his application, the bar was bent slightly.Posted Image

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I would think so, it's all really robust. It is exactly what I've been telling people about the car: It wasn't designed or built using computers or an engineering degree and with 1000 things being built from scratch, there is 1000 things that could go wrong. I had no idea that the brackets I had been using were too weak, they looked hella strong to me. Next week is Springnationals, I just hope that the other 998 parts hold together for that.

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Well you found the weekest "link" (I know bad pun). Hopefully the next weakest link does not halt your race weekend. Good luck!

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Don't think that vehicles designed on computers don't break things like that too. ;) That's why shaker tables and test tracks exist! What the computer folks miss is the integration and trade-offs you can do when the only design committee is you. It's also easier to make one in steel, and easier to design one in CAD and then make 100 using those plans. Here's hoping that one fix keeps you going for a while!

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We loaded up the Pink Panther and traveled from to Lincoln, Nebraska for the Pro Solo and Solo Tour event known as Spring Nationals. Because of a strong headwind and lack of towing power, we were down to 45 mph with the heat cranked and windows opened to keep our Suburban tow vehicle alive until we got to Lincoln. We tested the car last Sunday and everything was fine except after 3 minutes of continuous hard running through a simulated autocross course, the clutch stopped fully releasing. I assumed that I would just have to bleed the clutch and add a heat shield to the hoses and all would be well. When we unloaded in Lincoln, the problem persisted and made practice launches for the ProSolo very difficult because as soon as I took my foot off the brake, the car would roll through the start lights. In order to adjust the hydraulic release bearing, the transmission would have to come out.The shifter, drive shaft, seat, tunnel and crossmember all had to come out in order to remove the transmission and finally I could get to the release bearing and adjust it out a little. I got it all back together in time for ProSolo practice launches but couldn't do much because we could stage the car correctly but as soon as we took our foot off the brake, the car would roll forward, causing a red light. It occured to me that maybe I could adjust the pedal travel to correct this and amazingly, it worked-except it means that removing the transmission was a waste of time. I went back to do some practice launches and after a couple of 4000 rpm clutch dumps, I snapped a rear suspension mount. Those 14" rear slicks really hook up! Briget and I fanned out in the paddock area asking everyone if they had a welder, none were on site. Many calls to local welding shops also turned up nobody that could come to the site and weld my car. I was forced to drive to Tractor Supply and buy a welder, grinder, helmet and steel for reinforcing the bracket.They told me the welder came with a sample spool of wire, what I discovered when I got back to the site was that it was flux core, and I have never welded with flux core. I got the car done but it was too late for running the test course or doing any more test launches, the next opportunity was the ProSolo the next day. Briget was scheduled to run first and was worried about breaking the car, I told her to go for it and not worry about the car. Briget came back from her runs reporting that the car felt fine but was a little understeery. I attempted to correct this by stiffening the rear sway bar but during my runs I was spinning the inside rear tire a lot. Also, Briget got warnings for exceeding the sound regulations but curiously, I received no warnings. In an attempt to cure the wheelspin, I installed the front sway bar and softened the rear sway bar again. Briget went out for ProSolo session 2 and came back reporting that the car felt better but she couldn't get it to rotate properly.For my second session I tried stiffening the front spring rate and going full soft on the rear sway bar and the car felt better to me as far as wheelspin goes but it could have also been that I was driving better. the Avons were not overheating despite the back to back runs but we were also only pulling 1.3 peak lateral G, which is significantly less than what we should have. We started to notice a strange wear pattern on the outside shoulder of the front tires and pumped up the pressures for the next days runs. I also changed the angle of the exhaust tips from pointing out to pointing in in an attempt to pass the sound regulations.For session 3 of ProSolo, Briget wanted the same settings she had from session 2 so I softened the front spring rate and stiffened the rear bar again. She set her most competitive times yet and the front tires looked a little more normal. I went out for my 3rd session but was late to grid and penalized two runs so I managed only one run on each course. The car still had wheelspin but wasn't hopping around as much in the back so some of the adjustments were working. Briget and I didn't do very well relative to our competition in the ProSolo but the car didn't miss a beat even with 22 hard launches and aggressive runs, which is a victory. However, the car was still hitting 103 dB on the sound meter and something drastic would have to be done. We went to Speedway Motors and purchased two long bullet mufflers and a side pipe kit. Then I got to use my new welder again and added the mufflers to the current ones I had on the car. This significantly reduced the noise level of the car. Now I could hear the gears in the transmission whining and the rubber chunks flying off the rear tires and hitting the wheel wells. Briget was the first to run in Solo competition and had some trouble steering the car due to an arm injury sustained in a motorcycle crash. Her times were close to or quicker than her competition but cones jumped out in front of her on her best runs. Also, ambient temperature was now higher than during the Pro and when she came back from her runs, we needed to spray them with ice water. I went out for my runs later in the day when it was even hotter and tire temps were higher than I was comfortable with. I drove very badly and missed critical braking points, losing a lot of time in acceleration zones. I was second last in class by the end of the day, happy that the car was running but disappointed in the results. For day 2 of Solo competition, Briget started out in wet conditions and had her hands full keeping the car pointed in the right direction. This got better for 2nd and 3rd runs but she couldn't dig herself out of the hole she was in from day 1. I had an hour or two until I ran and during that time, several people came over to discuss the car. They all said that out on course, the car appears to go into a positive camber situation up front, causing rollover and tire smoke. I was so caught up with spring rates, panhard bars, high and low speed compression and tire pressures that I forgot about alignment. I was running very little toe-out and only -.5 degrees camber and wondered how quickly I could change these things because I was already parked in grid. I decided to go for it and loosened off the upper control arm bolts and added some spacers to increase camber, which also increased toe-out. The car responded well to the changes and understeer was significantly reduced, but my driving was still shabby. For my next two runs I removed the spoiler and diffuser and tried to be smoother out on course. The car was actually a little oversteery in places, which was a good sign that the alignment helped. Plus, the car was hitting 1.38 lateral G. I still finished 2nd last in class and way off the leader but the car held together, felt great and is easy to drive. After a lot of discussion with people more knowledgeable than me, it was determined that I need a wider tire and wider track width up front on the car. I already have a set of wheels that will widen the track width by 3 inches and a set of Avons are on the way, bumping tire size from 10.7" to 12.3". In the meantime, I will continue to play with alignment, Panhard bar, tire pressures and shock settings. I am uploading all kinds of pictures and video to my blog right now so check that in the next day or two for even more detail on the event in Lincoln. http://ultimatemgbbuild.blogspot.ca/

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Wow!!! Pit crew and racing. Hectic week I would say. Kudos to both of you for getting the car where it is today.

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Kudos to both of you for getting the car where it is today.

I can't take any of the credit ...this was a 1 man army (Mark!)

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I can't take any of the credit ...this was a 1 man army (Mark!)

Your job is just to look pretty and drive fast, you do a superb job of both :)

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While in Lincoln, some other Mod class drivers gave me advice on my car: increase negative camber and soften the rear suspension. I adjusted the camber to around -1.8 degrees and while I was in there, I decreased caster to reduce steering effort and gave it a little toe out. As soon as I went out on track I felt the difference, understeer was completely gone but I was still spinning the inside rear tire.Between runs I quickly changed the rear spring rate and aimed a camera at the rear suspension to see what it was doing.

The car felt great, I had so much fun driving it that I forgot all about getting on the backside of cones and looking ahead. It's not perfect but it's a lot closer now. Here's a video of my final run with data overlay:

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car felt great" data-cite="conebasher;205803]Between runs I quickly changed the rear spring rate and aimed a camera at the rear suspension to see what it was doing. [url]

car felt great">

same link twice. no suspension view...

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It's the next one in the series

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I have always known that the rear suspension (actually, the front one, too) had a falling rate. In other words, as the suspension went through it's motion, it's stiffness decreases, which is not ideal. I have tried to change the rocker arm shape to improve this but it didn't do much. Today I realized that all I had to do was change the angle of the shock in relation to the push rod, an easy fix. Here's the before:Posted ImageAnd the after:Posted ImageWhen I installed the rear sway bar, I had to move the center suspension link down one notch. Today I plugged the numbers into the suspension calculator and it told me that this moved my anti-squat from 50% to 88%. An internet search revealed that in an autocross car, 50% is far better than 88% so I had to find a solution. what I did was add an extension to the sway bar mount, lowering it below the center link. This also allowed me to reposition the sway bar back which cured some geometry problems when the bar was adjusted in it's stiffest position. In this pic you can see the extension on the right and the center link in the background.Posted ImageI also attached this slick aluminum hinge that I found at Speedway Motors so no more stick to hold up the hatch!Posted Image

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As much as I liked the ram air system I built, it weighed more than necessary and prevented easy adjustments of the front suspension. I pulled all that out and just attached an air cleaner to the mass air flow sensor. I also added a sheet of aluminum behind the tire to protect the air cleaner from debris (after pic was taken).Posted Image

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I pulled the Avon bias ply tires off the car to save them for Nationals and installed a 3 year old set of Hoosier radial tires to run local events. The car needs wider tires in front and I have four 13" wide Hoosiers so that's what is on there. I had to make some adjustments to fit the wider front wheels but I think I'm ready to go for this weekend. Radials aren't as good as bias tires for autocross, and these ones are old so I won't be setting the course on fire but it should still be fun provided the course isn't too tight.

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The car is huge fun to drive but it does have some quirks. Like the super low seating position and long hood which magnifies the "sea of cones" effect. Also, the car has manual steering and I have to balance steering effort, steering angle and number of turns lock-to-lock. It has a rather large turning circle because I need to keep the steering effort and the number of turns lock-to-lock low but those conflict directly with steering angle. Because of this, the pivot turns are the most painful element to negotiate so I pray we have a straight entrance and exit to the pivots, which makes for less time spent at full lock.

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I haven't made any significant changes to the car so I haven't updated this thread but people have been asking so here is an update. I did the math on how many runs the Avons would have by the time we got to Nationals and they would be pretty used up by then so I slapped on a set of old Hoosiers. The Hoosiers are radials and the Avons are bias so there is a big difference, and since I plan to run wider front tires for Nationals, I used the same size on the front as I did on the rear (going from 10.7" wide fronts to 13" wide). I know I should be running the exact same tires I am going to run in order to set the car up but I don't have the budget to run two sets of new tires per year. I also lowered the front of the top link of the rear suspension to move my anti-squat from 22% to 44% anti-squat. This was done to improve my launch at the start of the run because I felt I was losing a lot of time with wheelspin. At the last event I was scraping the sidepipes on the pavement in some high G turns so I reduced the body roll by raising the roll center at the rear of the car by one inch. I did this by raising both sides of the Panhard bar one inch. I expected this, in conjunction with the wider front tires, to make the car oversteer. And oversteer it did, anybody watching my first run watched me wrestle with the car to keep it straight. I lowered the axle side of the Panhard 1/4" and tried again, it was better. I continued to lower the axle side of the bar 1/4" for each run and by the end the car felt pretty stable.Here is a video of the rear suspension during one of my runs, notice that at the 19 second mark, my bellypan hits a bump and gets bent. It looks like there is a lot of lateral movement of the axle but as far as I can tell nothing is flexing or is broken so maybe it's an optical illusion.

The good news is that the car drives like a high powered S2000, the bad news is that I have never been any good at driving S2000's. I suspect this is because I do so many laps in the karts and they reward smooth driving and very little rear slip angle. My car seems to reward really aggressive driving and a lot of rear slip angle. Here is an in-car of my 4th run

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