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Unread 01-25-2016, 03:42 PM
Fair!'s Avatar
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 January 22nd, 2016: Well the C4 has logged a successful test track day in 2016, where we tested a lot of big and small updates to this car (and a new BMW we're running in TTD this year). There was one fairly big change with Project #Dangerzone that we have been holding back - because, honestly, I didn't know if it would work. I will explain "the what, why and how" below. We also finished lots of little prep work to this car, installed the rebuilt wiring harness and 1995 ECM + MAF, got the stock rebuilt engine dyno'd (twice), added some tow hooks, fixed the front air dam, finished the brake cooling and rear Plexiglass hatch, lost some weight, and more.



After my last thread update I was posting the above pictures on social media with captions like "almost finished" or "finally track ready". This was somewhat of a disinformation campaign, which might help me if I ever run for president, hehe. Gotta keep you guys guessing a little, but the big reveal is shown below. Let's get caught up...

PLEXIGLAS HATCH PAINTED AND FINISHED

In my last update I showed the slightly unfinished work on the lightweight polycarbonate rear hatch replacement. Shortly after I wrote that, our guys got it painted and installed and it looks good.



The rear frame was made from thin wall 1/2" steel tubing, which is tricky to bend. This structure forms a frame that wraps around the back glass in 3 axis. Olof welded some tabs in place for the small diameter Quik-Latches that secure the bottom of the hinged rear glass, as well as tabs for the hinge mounts at the top.



The mating pins for the Quik-Latch kits were installed in some simple brackets that Olof built and attached inside the rear of the hatch opening. Not only did the heavy 46 pound glass go away the big, electric solenoid operated, clunky steel latch mechanism also went away. The optional spring kits were added to the QuikLatches and that made them work a lot better. The rear frame was painted while hanging on a rack, and I snapped the pic in front of the LS1 Miata - which is about to get a big project thread update. We neglected to snap a picture of the final weight of the Plexi hatch and frame, but it looks like we lost 30-ish pounds - the new hatch is super light and much easier to lift.



I had the guys paint the back of the plexi around a ~3" border, to give it an OEM look. Trust me, its worth the time and makes a helluva difference. Brad and Olof taped up and covered the area not to be painted then peeled the protective covering from the inside of the Plexiglass (both sides come covered in a protective film). The clear plastic was scuffed with ScotchBrite then cleaned and let dry. Then it was painted with two light coats of semi-flat black.

The painted hatch was then allowed to dry, after which time the frame was bolted to it on the inside and the QuikLatches installed. The frame was bolted to the factory hinge using the same stainless washers and flush head bolts we use on all Lexan window installs. The latches lined up and the spring poppers were added to the Quik-Latch assemblies.



You have to see it in person but the finished hatch looks really good. Going the extra yard to paint the border (on the inside) makes it look so clean and factory, covers up the steel tubular frame inside, and finishes off this mod well. The Quik Latches work great and we can access the rear hatch easily now (before you had to crawl through the back of the car and pull a cable - total PITA).

1995 ECM, MAF & HARNESS INSTALLED

Updating the ECM and harness on this 1992 Corvette was the least fun part of this project to date. What a giant hassle, but the old 1992 computer can no longer haunt us, the engine runs now, and we learned a lot about the differences between the 1992-1997 LT1 engines & cars.

Just finding a used 1995 Corvette Engine Control Module proved to be difficult, as all of the sources we saw that had them in stock back in October had dried up. Lots of calls, emails, and finally the guys at True Street told me about a possible source. We paid too much ($315) and its a used ECM (not "reflowed" or rebuilt), but they do program the VIN # into the ECM for us and ... well... they had them in stock. Since it came pre-programmed at least it worked on their bench harness, which is a plus. The VATS would be turned off so the engine could run with our key, too.



You can see how different the 1992 (left) and 1995 (right) ECMs look. This is why we needed to have the harness rebuilt - to fit this entirely different pin-out for the later model ECM.



Here you can see the Delphi replacement MAF (Mass Air Flow) sensor, which is part of the later 1994-96 Corvettes' EFI systems. The online resellers show the same stock replacement part from 1994-2001 Corvettes with prices from "cheap" to "not as cheap". These sensors have a "hot wire" that sits in the intake airflow path, voltage is applied to this, some wizardry is used, and the amount of airflow is measured more directly. The 1992-93 Corvettes used a "speed density" method of airflow measurement, where intake manifold pressure was used to infer the airflow. The MAF cars still use the old intake manifold pressure sensor, but use that data for fine tuning, not engine airflow measurement.



New intake hose ends were needed on either side of the MAF sensor to connect it to the air box and throttle body. The sharp eyed among you might realize that these are not OEM replacement rubber bellows, so they aren't technically TTC legal without taking 1 point for an aftermarket "cold air". There's a reason why this doesn't matter that will soon become apparent.



Going from the jumbled harness right out of the box at left to the completed and running engine harness install on the right took a few days, mostly chasing down "old car things". First it was the O2 sensors, which are different on the 95 vs the 92 (went to a heated, 4-wire O2 @ $29 each x 2). Then there was the IAC valve changes. The rebuilt harness was setup for the 95 Corvette computer and they updated the ends for all of the 1995 era sensors, too. Cheap, easy fix that will likely work better than the old 2-wire O2 sensors.



Next was the computer itself, which had such a different shape that the (complicated) fiberglass bracket made to hold it was different. So Steve called up a salvage yard in Waco we know that keeps a lot of C4 Corvettes and he got this new bracket for $40, which arrived the next day. Could we have built one? Sure, but the shape and how it mounts was complicated enough that making one would have taken an hour or more, and every hour we're spending on this shop car is an hour we're missing out on customer work. $40 for the factory piece was the right move here. Remember: even though you can make something from scratch, doesn't mean that you always should.



Yet another "learning more about 25 year old LT1 engines" thing here - the Idle Air Control valve (IAC) is an electronically controlled device that meters air around the (closed) throttle blade, so the car can idle with your foot off the throttle pedal. GM changed the mounting shape and the 4-wire connector for the IAC from the 1992-93 LT1 cars to the later 1994-97 LT1 cars. The way the IAC mounts to the throttle body is via a small "manifold" (above right) that bolts underneath. As far as I can tell the throttle body didn't change much, so we just needed this 1994-97 IAC/coolant manifold, which bolted to our 1992 throttle body.



After a full day searching we realized this part wasn't available new, and even Nook & Tranny was out of stock (they carry a lot of LS1 and LT1 stuff - helpful website for engine swappers). It was late in the day when we realized how scarce this manifold would be, and our Waco Corvette salvage yard was closed by then.

So we started looking for LT1 throttle bodies locally... my Facebook call-out was a miss but someone there suggested a junkyard here in town that had one for $50. So the next morning, the highlight of my birthday was trolling around in the bad part of town and grabbing up this 1996 Camaro throttle body. Ryan cleaned up then transferred over the IAC/coolant manifold and the new 1995 Corvette IAC ($53) to the 1992 throttle body and it was ready to fire. Curiously the shape of the throttle blade cable pivot cam was very different from the Camaro to the Corvette parts.

TOW HOOK + FINAL BRAKE DUCT ROUTING

We've not had good tow hooks on this car, which is pretty short sighted for a track-only car. This is one of the first mods usually done to a race car, and we were lucky we never had to be flat towed in at the track, because there's not good places to latch a tow strap onto in this car. The front of this car is all plastic and there's nowhere good to bolt or mount a tow hook, so we had to get creative.



We figured out on a previous C4 race car how well a roll cage mounted top tow hook works, for both winching a car into a trailer as well as for towing behind a wrecker. The top hook eye Ryan added to the cage also works as a great grab handle to winch yourself into the tight cabin of a C4. It will be easier to get into this car once I have sprung for a Quick Release and a real steering wheel, but for now this works great. Have already used this new hook to winch the car into and out of our trailer multiple times.



Ryan also installed this roll cage mount "bus stop" mirror, a low cost convex mirror that lets you see into blind spots. We already have a 14" wide parabolic rear view mirror mounted in the cabin, but the right side factory door mirror broke decades ago, and the FIA cage tube on that side blocks my sight line to it anyway. This new spot mirror fills in the right side visibility gap from the side window to the high mounted rear view mirror perfectly. Bolted on in minutes and the old, dead door mirror housing was removed (less drag).



The guys also got the final routing of the 3" brake duct cooling hoses nailed down. There's a number of zip ties that attach the hoses to moving suspension components, like the upper control arms. And some that hold them to fixed items inside the engine bay.



These hoses even clear the 335mm tires on 18x12" wheels up front at full lock, so they really got them tucked in there nicely. Oh yea... did I forget to mention the little wheel and tire upgrade??

BIG TIRE TEST

What and why have we changed from the 245 R7 tire to a 335 front and 345 rear Hoosier A6?? Well let me try to explain. And remember, this was only a test - it might have been a complete disaster and I would have un-done the work and slapped the TTC legal 245s right back on.



Last year we only built this Corvette to run for one season as a "tweener car", after the TT3 Mustang was sold and before our next big crazy shop BMW V8 build was ready. Well we never started that big BMW build, which was delayed for multiple reasons. So this old 1992 Corvette was quickly shoved into the "fast shop car" role, with some planning that began last October.



It also didn't make sense (to me) to have both of our shop cars in NASA TT Letter classes - the red BMW E46 330 in TTD and this white C4 Corvette in TTC. That's a little nuts. So back when we were looking at a TTD build for a BMW E46 coupe, we had already decided to move the Corvette out of TTC, or at least test some "big tire theories", with a wheel and tire upgrade to the C4 early in 2016.



I suck at keeping surprises, and not sharing pictures of these wheels when they arrived and were initially tested was killing me. Just the 335 Hoosier tires were mocked up on the front (above) a few months back, but I couldn't share that either. These were some new A7s I had sitting around, winnings from the TT3 Mustang. We have half a dozen sets of scrubs, too.

continued below

Last edited by Fair!; 01-25-2016 at 05:49 PM.
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