Project C4, 85 Corvette

[Steve85]

BLUF - I got new tires which are great and discovered I was 20psi down on fuel pressure at WOT. The car feels better with the much better tires and has about another 50HP with a better fuel pump! The deets:

I decided to finally get new inner barrels for the front wheels since one was welded. 

The plan was to get get a diff't width and then swap the front / rear inners to go from a 12.5 / 10.0 setup to 11.5 / 11.0. I bought second hand and the barrels ended up being same size as rears so the fronts got bigger but the rear didn't get smaller. (weird because I had pics with a measurement, so not sure what happened) New tires were in order and I found some Yoko Advans on ebay that were brand new, just a couple years old and they mounted and balanced with minimal weight. The previous setup took a fruit roll up length of weights to balance and never felt right.

I was very excited until I got 100 yards from the house and couldn't accelerate. So pissed...

It seemed the problem was with #8 so I did all the usual swapping coils, plugs, wires, injector, fuel pressure was good even when it started to stumble. It was just a funny thing, no matter long it idled in the driveway or I revved it without load, it was good, take it on the road and 100 yards out, it would shit itself. I had to try something so I went with an O2 sensor for that bank, no change. Then I noticed this:


I decided on a 25% underdrive unit for mad HP gains. And to hopefully not kill the AC compressor I plan on installing that was originally designed for about a 4500 rpm redline.



The side hope was that the vibration was causing a false knock. The pull and install took a total of 4 hours, 3:45 of that was finding just the right mix of stuff to pull the balancer (borrowed a kit fro Advance but the LS crank has a stupidly deep snout). Got it done without having to pull the steering rack so that was a bonus. I heated the damper as instructed by the manufacturer and it went on smooth.

Unfortunatley, the car still ran like crap. Back to the basics, fuel spark compression. Which really means, the right amount of good fuel, hot enough spark at the right time and enough compression.

I decided to get into the tank and noticed a murky fluid settled on the bottom. Like, you could see stuff floating 3/4 of the way down a full tank. It was actually pretty cool, like a layered B52 shot. Here is a comparison of the fuel from the bottom of the tank and the top layer:


I hooked some fuel line to the pump outlet and pumped out 4 gallons from the bottom of the tank to gas cans. I timed it, it took 1:55 to pump out 1 gallon, which becomes very important... Reinstalled the pump and test drive was great! I had shitty water filled gas. I think it was actually the HEET I put in the night before that pulled all the shit to the bottom.

During the test drive I still had the FP gauge taped to the windshield. At full throttle, and not falling on its face anymore, it quickly dropped from 60 to 40, whoa! I always thought it was a bit flat up top but figured I needed a tune. It has a slight cam and Z06 intake on a standard LS1 tune.

So I pulled the Walbro 255 out of the drawer (I have no idea why it wasn't already in the car..) and installed it. The tank in a C4 is not in a great spot from an engineering perspective, but it sure is user friendly! WOT pull and it stayed at 60 psi, yay! And by yay I mean..

FUCK ME TO TEARS AGNUS - WHAT HAVE I BEEN MISSING!?! 

Probably 50 HP at WOT from 2500 rpm on up, that's what! It pulls hard all the way now. I'm not sure at this point I gave up anything to the previous 408.

I'm not sure if I got shitty gas after putting in the O2 sensor when I topped off the tank or it just built up water from sitting for a while. All I know, I've been missing out for years and this has been a great discovery!