SCCA Camaro

Upon pulling out of the carport I realized the Camaro was not going to be as docile as I hoped when I spec’ed out that mild 112/118 duration cam!  It was very torquey and surged when attempting to accelerate and torque braked hard as soon as you let off the gas.  This was noticeable even in third and fourth gear.  This made it almost impossible to log useful data in traffic as the only way to drive it without the car violently bucking around was “flat out”.  My first test drive also involved topping off the gas tank and I found out that I had a leak somewhere high up on my tank (it was not leaking when not full but leaked when full).  This wouldn’t be that big of a deal except I still didn’t have a reliable reading from my 68 Camaro’s 40-year-old gas gauge sending unit so I was guessing about how much fuel it had at any moment—making it difficult to fill it up three quarters of the way.

I put the following on the www.pro-touring.com forum board hoping for some help:

When taking off in first, i find it very difficult to not spin the tires. If you are going balls out on a track it might be OK until you have to come off the gas–but in street traffic when taking off at a stop light and then trying to feather back off the gas so as not to rear end the vehicle in front of you, the car surges forward, then if you let off the gas it jerks or bucks very hard due to the torque braking. I have the Commander 950 software running and am looking at my throttle position sensor when i am doing this, and i have a relatively light foot (TPS is 1 closed and 172 for WOT, i am applying values of ~10 when this is happenning). I have found for the street the only way to drive it is to let traffic leave me to create a gap, then take off aggressively in first, then go to second almost immediately, then go to third and essentially allow the car to idle along in traffic (idle is 850 RPM). In third, the ammount of torque on tap is diminished enough relative to the load that i can come on and off the gas (again, i’m talking 3-5% of WOT) with controllable surges rather than violent bucking. Traffic around me still think i’m an idiot because the car bucks with even the slightest progressive addition of gas (i looked at my datalogs and i’m talking TPS values of around 5–roughly 2-3% of WOT).

There were a lot of thoughtful responses, and three things I could implement pretty quickly: double checking throttle linkage and spring tension, moving the idle up higher in the RPM band, and setting the shocks softer.  I disconnected the spring from the throttle linage but didn’t see any other way to make it more progressive in the short term.  I also set the DSE-sourced Koni adjustable shocks at one click out from full soft in the front (they had been set on one click from full hard) and to ½ turn from full soft in the rear.  Then I raised the idle RPM to 950 in the Holley Commander 950 software and adjusted the throttle return set screw to get the idle correct so the idle air control solenoid was in control of the idle.  I figured I would deal with the gas tank leak later since it only leaked with a full tank of gas.  Upon taking it for a test ride, it was still very rough but seemed somewhat improved mainly by the throttle spring and idle speed changes.  Unfortunately upon adjusting the front suspension I was now bottoming out on bumps at speed.  Although I had the 2001 Trans Am as a back-up, I decided to race the Camaro on Sunday and see from there what to do next.  Unfortunately I was travelling on the mainland for work and United Airlines stranded me there on July 12^th, the night before the race I had been waiting 3 months for!  The only good news was that there was another SCCA Solo II race two weeks later, so I wouldn’t have to wait too long to test out my modifications.

 Upon starting my 68 Camaro successfully after the Cam swap and installation of the Holley Stealth Ram and all of the attendant plumbing, wiring, and sensors, as well as the installation of the TPI serpentine belt set-up, I was ready for a little tuning.  With the engine running I kept a very close eye on the Holley wide band air fuel ratio gauge on my dash to make sure I wasn’t running too lean.  The Holley Commander 950 base map I had chosen (WBmp3008) seemed to be close enough—a little lean but still safe at around 15:1.  One thing I had to figure out was the idle speed.  I had set it in the software at 800 once the car warmed up (it starts cold around 1100 RPM).  This was down about 50 RPM from the WBmp3008 base map since I had considerably less overlap than the cam used for the basemap and figured it would be easier to get a nice idle.  But the Camaro was actually idling about 1100.  It turned out I needed to adjust the idle air screw on the side of the throttle body as well as set the actual timing on the car to match that which the Holley.  A few turns of the set screw closed the throttle blades enough to get the idle down where I wanted it.  I had to purchase a timing light with a dial back feature in order to match the timing on the distributor with the 23 degrees the Commander 950 was giving the Camaro at idle, but it was straightforward with the correct tool.

I also noticed a water leak from around the water pump, which meant the block had to be mostly drained of coolant and the TPI serpentine accessory drive had to come mostly off the Camaro so I could pull the long style reverse rotation water pump and try again with a different set of gaskets.  The ones that came with the water pump were sort of a cork-like material and I used the Chevy specification for the bolt torque as well as a thin layer of RTV sealant so I was a little surprised by the leak but I used a FelPro composite-type gasket set re-prep’ed the block and didn’t have any more problems.

 
The Camaro was running lean in the lower RPMs due to the higher volumetric efficiency of the shorter-duration cam I was using relative to the one used for the base map so I added ten percent to the pulse widths in the first three columns of the fuel based map and tapered them off to the rest of the map where the map stopped being lean.  This meant at the higher RPMs the Air/Fuel ratio was a bit rich which I wasn’t too worried about so I left that part of the program alone.  When the dual Spal fans kicked on the idle would start to surge back and forth 50 to 100 RPMs around the set point so I played with that quite a bit.  The Commander 950 Software has two features to keep the idle steady, one involving fuel trimming and one for adjusting timing to keep the idle steady.  I enabled both and still found the idle to hunt a little.  Good enough for a test drive though.

I had just a few things left to do on the 68 Camaro before I could fire it up.  I had to wire the fuel pump, and hang the radiator support and passenger side fenders, and install an air filter and intake to the BBK/Edelbrock 58 mm throttle body.  I also needed to sort out some of the wiring and reroute a few wires that were originally routed to the passenger side via the core support but would now reside on the driver’s side because of the relocation of the alternator when I installed the TPI serpentine set-up.  I would also take this opportunity to put the Spal fan relays on the driver’s side to keep the wires to the alternator short.  Wiring the Walbro 255 external fuel pump (PN GSL-392) went pretty quickly:  I grounded it right at the rear frame rail it was mounted on; the Holley Commander 950 is pre-wired to run a fuel pump.  I merely ran the wire under the door sill and drilled a small hole in the floor under the rear seat.  I used a rubber grommet around the wire passing through the floor of course and crimped a connector on it there.  Rerouting the wires of the front wiring harness was just a matter of cutting my cable ties, unwinding some of the wires, laying them back out headed in their new direction, and putting cable ties back on. 

Hanging the core support was equally uneventful, as was putting the passenger side inner and outer fenders back together.  I measured the diagonals across the engine bay and had to push the front end around a bit to make sure it was perfectly square.  I had saved the shim pack for the fenders so it was easy to get everything lined back up properly again.  I put the hood back on by myself, which is a little less fun than with a helper by the way.  I purchased a cone-type air filter with plumbing for the throttle body on eBay and I had to do two slight modifications to make it work.  The first was that I needed to get a larger diameter, six inch worm clamp, because I was running the 58mm throttle body.  I found an inexpensive stainless steel clamp at Home Depot.  The second was the tubing didn’t line up well with my core support and radiator.  I cut about two and half inches off one of the aluminum tubes to fix this problem.

At this point I was ready to test the fuel plumbing.  I reconnected the battery and put the ignition in the accessory position so the fuel pump would develop some pressure.  Several cycles of the fuel pump revealed minor leaks at a few of the couplings, all of which were stopped by simply tightening up the connections.  It was time to load an appropriate program into the Holley Commander 950 ECU and attempt to start the Camaro!  I decided to use the Wbmp3008 base map, which was described as: 355 small block Chevy, 30 lb./hr. injectors, Stealth Ram intake, 58mm throttle body, 20 degree Holley heads,

Lunati 30142 cam (235/245 @ .050, .507/.534, 112 LC), 9.5:1 compression, 43 PSI fuel pressure, 418 HP @ 5500 RPM, 422 ft./lbs. @ 4700 RPM.  While the duration on my Comp Cam (PN 12-465-8) was a little shorter at 210/218 @ .050, I had higher lift at .560/.555”, so figured it would be pretty decent base map to start with, although volumetric efficiency for my car would probably be a little higher at lower RPM and a little lower at higher RPM.  I figured my AFR heads would perform similarly to the Holley heads.

The 355 sbc roared to life on the second cranking attempt and then it was time to start tuning!  I had exactly one week before my next SCCA Solo II autocross event.