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Unread 03-25-2016, 09:38 AM
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Fair! Fair! is offline
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Join Date: Jul 2004
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Default Re: Vorshlag Budget TT Build: Project DANGER ZONE

Project Update for March 25, 2016: When we last left off the C4 had been raced once at MSR-Cresson and set FTD for the SCCA Club Trials. There were some issues with the brakes, and the shocks didn't deal with the minor bumps at Cresson, both of which gave me pause... but I ignored that and pushed forward on the "Big Tire" TT2 plan. We did some quick fixes to the brakes, then went to with NASA at MSR-Houston, one week later. After that we had a little time, so we made some changes and ran another event with NASA in March, back at MSR-Cresson again. We played a bit of "musical chairs" this time, but I will explain the what, why and how below.

MORE JANUARY PREP WORK

My last forum build thread post ran long and I left a few things out due to space. While I was writing the last few bits of that post, a few extra changes were being added before the January MSR-H NASA event, which I will go back and show below.



For the first "Big Tire" test at MSR-Cresson we had stacked up a bunch of smaller spacers on the rear wheels. We had spec'd these custom 18x12" wheels to actually fit the front with a 335mm tire, hoping that in the near future we would buy some wider 3-piece rear wheels (18x13"?) for the massive 13.8" wide 345/35/18 Hoosiers. If that happened then all four 18x12's we built the same way could become front wheels, leaving us with two full sets of race wheels again. Its always smart to have a full back up set of matching race wheels, so you can practice on your "old scrubs" and save the sticker set of tires for that "golden session" of the weekend.

To make these "fronts" fit out back for now we just used a couple of small spacers. During this January SCCA Club Trials event they rubbed inboard with the 345s, especially in hard corners, so we kept stacking more spacers out back until the rubbing stopped. The result was we were left with a LOT of tire poke at the rear (which I detest), but we were going to cover all this with custom built flares later, so I wasn't too worried. As long as the car still fit inside the trailer (it did, easily) it wasn't too wide. More track width adds mechanical grip, and since this wasn't an autocross car, the added width wasn't going to "kill the slaloms".



After this event, back at our shop I removed a rear wheel and measured "the stack" of spacers. I took this measurement and found 1-piece hub-centric spacer for use at the next event. This would be safer and less janky than a bunch of mis-matched spacers stacked up. I found .875" thick aluminum spacers from Bear Racing - the pair is shown above on the scale. These 1-piece spacers fit the hub bore and bolt circle of the C4 perfectly. I'll talk about how these were re-purposed later in this thread...



I forgot to show in my last post where Jon was adding new graphics for the move to TT2, as well as a few other new decals for Forgestar and the "Rampage" rear license plate. These are made on our 24" wide vinyl plotter, shown at right. Nothing fancy but it works well enough for simple graphics for our shop cars and a few customer cars we maintain at the shop.



Another thing that I had always meant to do to this car, even when it was in TTC (we had taken points for it), was open up the factory LT1 "air box". As you can see above, the intake manifold is fed by a rubber tube (now with a MAF sensor added) from an air filter "enclosure", or air box as we like to call it. By the way, there is no direct path for air to get into this semi-sealed area ahead of the radiator inlet duct. Air just bleeds around and through gaps in the bodywork to feed this area. We can (and eventually will) add a "ram air" inlet on the front of the car (front license plate pocket lines right up) to feed the air box with a good high pressure source of fresh air. For now I just wanted to open up the factory air inlet hole and remove the air baffle on the front of the air box.



Above at left is the unmodified factory airbox, which holds a pleated paper air filter and has a baffle on front - to cut down on noise and to keep the filter from getting wet. The "quietness" of this car doesn't matter to us now, nor does a little moisture from running in the wet (we don't even have real "wet" race tires, so if rain is falling this car isn't likely running). Getting more air into this choked up airbox was the goal. In stock form all of the air flows in through a single rectangular hole, after it travels through a plastic air baffle - which is shown above at right, already removed.



The real fabricators in our shop were busy on billable customer work so I hacked up the airbox myself, after we were closed one day. First thing I did was drill out the rivet heads to remove the air baffle. Then I scribed out two new rectangular openings on each side of the factory hole. This was done quick and dirty, with just a few measurements and a straight edge. I marked, center punched, then drilled some holes in each corner to make the new openings have rounded corners, to try to match the OEM hole. Then I used a small jig saw to join the drilled holes. End result was two new rectangular openings with rounded corners.



For being 25 years old the air box was in great shape. After the 2 new openings were cut, and the edges deburred and sanded smooth, it was ready to prep for paint. I scuffed the painted metal with some Scotch Brite pads and cleaned everything with wax and grease remover. Once that dried it was hit with 3 light coats of black paint.



This is the final result, above. I may have rushed the drying of the cleaning solvent, as the paint fish-eyed in some sports. Oh well, its hard to even see this air box with the clam shell hood up. More importantly - the baffle was gone and the surface area of the opening in the airbox more than tripled.



We looked at some aftermarket "cold air" kits for the LT1 C4 and the few choices still available were not very appealing. Sure, we should add a more direct path of fresh air from the front bumper to this now opened up enclosure, but for now it was a $3 upgrade (cost of paint) that was well worth the hour it took me to do. There is indeed more intake noise, so maybe there would be a tick more power on hand for the MSR-Houston event? I'd be running nearly 100 whp down on what a real TT2 car at this weight should be, so anything would help.



One last little update. After the January SCCA Club Trials, when the brakes failed in two sessions, we replaced the brake master cylinder with another reman unit (we cannot find new master cylinders for this car). This might be the 3rd or 4th reman'd MC this car has seen, but when it was installed and bled the pedal pressure felt right once again. Let's see how long this one lasts? As with all track cars we build, the cap to the plastic fluid reservoir got wrapped with a shop towel and zip tie, which usually soaks up the small amount of fluid that might puke past the cap under high temps. The original vacuum assist brake booster is still on the car - and its a PLASTIC unit that is a known failure point. More on that in a bit.

NASA AT MSR-HOUSTON (CW) JAN 23-24, 2016

The MSR-Houston track is not nearly as smooth as MSR-C, but that thought never entered my mind before we got here. Why? I've always raced cars here with GOOD monotube adjustable coilovers, so it never felt bumpy in the 7-8 times I'd raced here before. Boy was I in for a surprise in #DangerZone!

We took both the Corvette and BMW to this 2016 NASA season opener event at MSR-Houston. We loaded up Friday morning and slogged through 6.5 hours of driving, most of which was burned inside the city limits of Houston dealing with their nightmarish traffic (normally this is a 4 hour drive from Dallas). I was towing our enclosed trailer with the Corvette inside and Amy drove the TTD classed BMW 330 down.



When we arrived it was pitch dark and the paddock was packed. We got lucky and found a wedge shaped spot close to grid where we unhooked the trailer and parked the BMW. Amy had Tech inspect the BMW for Annual TT Tech and a new Logbook.



It was too dark and too late to extract the Corvette and make the close of tech that night, so we got to the track early Saturday morning to take it through annual tech before the first TT session. Well, in the rush we did not put the safety wire into the Schroth harness clips in the C4. Without it, we could not pass tech. I pulled out of line, went back to paddock and added the safety wire to "lock" the clip-in latches closed. I got back in line to re-tech but the TT field had already gone out on track. I got my tech sticker, drove straight to grid, belted up and went out on track.



They threw the checker as I came around on my warm up lap so I didn't get a time. This meant I'd be starting from the back of the grid, which makes for an extra challenge. I was also trying to drive BOTH of our TT cars both days, so I had my hands full.



This was the debut NASA event for our BMW E46, which we had planned on running in TTD for 2016. We're doing a "build progression", with parts being added along a set build plan, hopefully showing incremental improvements along the way and testing products we make or want to offer. So at this event the BMW was PAINFULLY under prepped (150 pounds over weight + 50 whp down). Unfortunately, the Corvette was also very under-prepped for TT2.

We had a little bit of a break after the first "warm-up" TT session, which is only used to get times for the gridding of cars in the first "official" TT session. So I had no time in the TT2 Corvette and gridded at the back in this next session. I went out on track hoping to get the tires up to temp by lap 2 or 3. That ended up never being an issue - even when "cold" these massive A6 Hoosiers make MONSTER GRIP. Lots of people think that if a tire isn't at its peak temperature that it will have zero grip. That was NOT THE CASE in this car... it made TOO MUCH grip from the very start.

Event Photo Gallery: https://vorshlag.smugmug.com/Racing-...A-MSRH-012316/

The massive mechanical grip plus the bumpiness of this course added up to one of the scariest laps Ive driven in my 29 years of experience with track events. There is a straight section of this course between T14 and T13, right before the hill you almost jump they call "the launch", which was especially bumpy. I had to back off a lot here just to stay on the track. I have never noticed the bumpiness there in any previous car I've driven at this course, or in our BMW this same day, all of which had been on proper shocks. Driving this track in the C4 was a "life altering experience". After a couple of laps and almost skidding off the track going in a straight line I pulled into the grid, white as a ghost.

That. Was. Not. Fun.



I realized, right then and there, that this Big Tire test was a terrible idea without buying real dampers and changing some other components. Adding 100mm of tire, and going from an R7 to an A6 compound, showed the true limits of the 25 year old Delco Bilsteins. I had run this track the year before in this same car on the little 245s to the tune of 1:43.7 without any handling drama... this day on 335/345mm tires I could barely manage a 1:48.9 with a fresh motor and many other upgrades.

continued below

Last edited by Fair!; 03-25-2016 at 09:55 AM.
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