Should have time to install Friday! I'll take videos.

 

Install is finished! Took me right at 8 hours total, following these self-made steps (based upon a lot of research):

1. Disconnect Negative Battery Terminal

2. Remove both 'Corvette' valve covers with Torx T30, disconnect breather tube that might be in way.

3. Remove fuse box (optional) -- Use impact on large nut securing battery cables at top of box. Remove fuse tray.

4. Remove spark plug boots (and spark plugs if desired) -- Use screwdriver to pry out

5. Remove manifold heat shields. Soak header bolts in PB blaster.

6. Lift car. Remove tunnel brace. Spray PB blaster on everything underneath.

7. Drain oil (replace bolt when done, put oil container in front seat so you don't forget to add before start). Don't forget to remove oil fill cap to help drain.

8. Unbolt/remove Xpipe. Install new gaskets on xpipe. Remove/swing diagonal aluminum bars out of way.

9. Remove oil lines (or see if can just remove starter) -- Make sure to tie-off to prevent oil drip.

10.Remove OEM cat pipes - Use two-wrench method if needed (see picture saved in phone) or pass-thru socket set. Use ONLY 6 point sockets, fully seat all sockets before loosening. Can remove studs with socket if bolts are siezed. Considerloosening manifold bolts (to block) to ease access.

11. Disconnect O2 sensors -- Pull the white tab up and flip connector to the back and insert flathead between the connector and twist/pry-apart.

12. Remove starter heatshield

13. Remove manifolds -- Use only 6 point sockets.

14. Soak O2 sensors on manifolds in PB blaster.

15. Remove O2 sensors (using heat) and install in new headers. Take note of which sensor goes to which pipe. Inspect gaskets and decide if using OEM or provided.

16. Cleanup header bolts and coat in blue loctite

17. Install headers from bottom (or passenger from top) along with gasket. Hand-thread bolts, leave loose. Note: Make sure to install gasket correctly based upon its labelling.

18. Attach O2 sensors to car. Zip tie safely from heat/touching pipes.

19. Install cat pipes.

20. Torque header bolts to 18ft/lbs

21. Jig everything up loosely. Check clearance to tunnel brace, starter, and frame. Need 1/2" of clearance to tunnel brace -- Push pipes to adjust.

22. Make sure no wires are touching header (including spark plug wires)

23. Tighten everything down. Torque specs: x-pipe to header 18ft/lbs, small tunnel bolts 20, large tunnel bolts 75, bolts for assembly of cat pipes to header ???

- Push the pipes up into the tunnel when tightening the rear clamps or the may hit the tunnel plate.

24. Reverse order everything above.

25. Install oil filter, add new oil. 9 quarts, then start and check. Don't forget to add oil cap back on.







Oil change procedure here: https://www.corvetteforum.com/forums...ump-specs.html



Overall install wasn't too tough considering I had access to a lift. With that being said, I can't provide impressions yet because upon first drive I noticed a misfire. I don't have a CEL, but can feel it under various conditions. I suspect that a plug wire is damaged/loose, or the plugs were damaged during header install (I didn't actually pull the plugs, like I should have). On tuesday I'm going to have new plugs/wires delivered and I'll install, hopefully fix the issue, and then share my impressions in detail.

 

I found the spark plug wires to be VERY tight. I went around 3 times and on the fourth time round still found one plug wire that had not seated properly. When you get your new wires in check and recheck multiple times... Awaiting some sound video

 

All --

I just changed all 8 spark plugs. Only one looked bad (cracked porcelain). I double/triple checked the seating on all plug wires... they all feel secure. I'm still getting a misfire.

After running the car for 30 seconds with a small rise in RPM, I do not get a CEL, but data logging suggests:

Misfire counts for last/current driving cycle -- Cylinders 1, 5, 6, 8 all show one misfire each, while cylinder 3 shows 6 misfires. Before changing the plugs Cylinder 5 showed 5 misfires, and cylinder 3 showed 0. I'm at a loss as to what it could be now...

 

Could still be a damaged plug wire. Change the plug wires around and see if the misfire follows. If not then you could have messed something up during the install such as damaged an O2, damaged the MAF, forgot to tighten down the intake tract post MAF sensor. I assume you checked the gap on the new plugs before installing.

 

Thanks for the reply. I'll replace all plug wires tomorrow and see if that helps. I didn't disconnect any parts of the intake during install. I also didnt check gap on new plugs since they were pregapped - which in hindsight was an oversight. I started a new thread just a bit ago and did some data logging. Each time I start the car a different cylinder misfires... Which makes me wonder if it's an O2 issue. O2 voltage seems to be moving up and down on all 4 sensors which is good.. But...

I'll try plug wires tomorrow to start.

 

Keep in mind there will always be a couple misfires logged. A very low number isn't anything to really worry about. If you have a single cylinder that has an issue, it's misfire count will be exponentially higher than the rest. If all cylinders truly are misfiring then I would start looking at things that could affect all or most cylinders. Are the coil packs plugged in tightly, are O2's good, no melted wires etc. Also, you should still start by replacing all plug wires first. Even though the OEM plug wires may look fine, they can easily be compromised in places you can't see. It's not uncommon for the OEM wires to be garbage after removing them for such an install.

 

All -- i'm back up and running (fingers crossed). To summarise my issue: After installing headers I took my first drive, and noticed a big misfire under heavy load of the engine. I proceeded to investigate, and ended up changing all 8 spark plugs, as I found one plug (cylinder #5) that I had cracked during the header install. REMOVE YOUR PLUGS BEFORE INSTALL -- I tried to be uber careful and still cracked one.

With that all being said, the misfire (on cylinder 5) made me extra aware/nervous of the sound/feeling of the C7's idle. I convinced myself that I still had a misfire at idle, and thus I spent several days trying to chase down a non-existant issue. The C7's idle just sounds/feels like it is missing normally and I wouldn't have ever noticed if I wasn't already overly cautious.

My car drives great now -- I'll drive it for a few days and then provide some impressions of the sound and experience. I'm currently running ARH Mids w/ cats, Borla XPIPE, stock NPP.

 

Glad you got it figured out. I can’t wait to hear the sound clips. Please don’t do them in a garage or put the recording device too close that it overpowers the mic.

 

Alright -- This will be the first post out of a few to offer my impressions of the midlength headers. I'll work on videos of the sound, both outside and in-cabin for the next post.

I've driven about 300 miles since putting on the headers, and each time I drive it grows on me more. Up front upon cold start you're going to notice the volume increase. The cold start is approximately 20-25% louder, than a 'track mode' cold start (where the NPP Valves are open. I have fuse 42 pulled). After 30 seconds or so (when the car progresses to normal timing as the cats warm up) the volume drops to just a tick louder than the car sounded with stock manifolds.

As far as driving goes, the headers increase volume across the whole RPM range by 25% if I had to guess. With that being said, the 'characteristic' of when/where the engine makes noise stays the same -- At idle things are quiet, under 3000rpm things are still pretty quiet, over 3000rpm things get louder, and then WOT the engine is 2x or 3x louder in general. When cruising at steady RPM the engine is nearly silent, as it was with the stock manifolds.

Now, the 3 big obvious benefits/differences that I notice with the new midlength headers include:
- Volume increase -- The car is noticable louder under load in any gear. It is not painfully loud (interior panels don't resonate or anything). The loudest it gets is around 6000 RPM at WOT -- I would imagine anything could hear you coming within a mile when at WOT. With that being said, as a guy who loves the sound of the engine, but doesn't want to be obnoxious/embarrassing under most driving conditions, these headers are perfect.
- Sound quality change -- The tone of the engine note is much more 'raw' and 'intense' with the headers over the stock manifolds. It's a bit like taking earplugs out of your ears -- There is so much more clarity and definition to the exhaust note. The best comparison I can think of is that of an old vacuum-tube guitar amp, where the vacuum tubes produce a really desirable 'overdriven' sound when the volume is increased and the tubes are driven hard. Adding these headers is like pushing the tubes harder, bringing out a violent, dominant sound. Overall the engine sounds more 'dirty' -- It pops and crackles more, and sounds more rough-around-the-edges. When approaching high-RPM WOT, you'll notice some rasp as the volume reaches its peak. I'm not a huge fan of this raspy part, but I realize that it is how the LT1 engine actually sounds -- so I can appreciate it more. Overall, the new exhaust note gives me a rush of adrenaline, and I find myself seeking out opportunities to accelerate just for enjoyment.
- Increased power -- They say that these midlength headers only provide a gain of 20-25hp without a tune. This may be true (and may seem insignificant) but I can tell a noticable difference in pull across the RPM range, with certainty. Peak horsepower matters very little to me, but I can definitely appreciate the torque gained 'under the curve'.