Thanks for the reply. I had forgotten how the plug heat range works. I did a little internet hunting after my post and found this PDF that seems to explain it well: http://www.boschautoparts.com/Techni...gHeatRange.pdf

 

1st don't change any parts, you have enough hardware to make more power.

2nd If you are dealing with misfires and code, you are not ready to do WOT dyno pulls yet. Your tuner should have dealt with that 1st.

3rd The tune looks a little off. On a WOT pull, with a setup like yours I would like to see it come in at about 12.3 at peak tq and then come up to about 12.5 to redline. Where is your peak timing coming in at?

4th Too late now but I never buy a car that "should make 550rwhp" or is 95% done. When it come to a project like this the devil is in the details. I hope you got a deal because the seller may have just sold you his problems.

That being said, anything can be worked out. Hopefully it dosen't cost you too much.

 

Well I took the car to DRM this past weekend and they disabled the o2 heater codes that were being set off, probably from the headers putting the sensors so far back from the motor. With the new TR6 plugs it seems to run a bit nicer, and I also installed the K&N air intake, then took it back to the tuner. He did some more work on it and it drives a lot nicer now, with the 427 and big cam sometimes it wanted to buck at cruise but it's a lot better now. (tuner couldn't replicate the o2 heater issues we had on the dyno, which is why they weren't addressed the first time)

I'm not sure what's up with the dyno wideband reading in the 11.5:1 range, it was a tailpipe sniffer and can obviously only read one of the four outlets, they should all be the same, but maybe it's not calibrated that well. It was tuned with a wideband in the rear o2 location which is a lot closer to the motor and it was set to be around 12.5-12.6 peak AFR. I still need to ask him what sort of timing the car is running.

Also I wanted to note that I forgot the dyno numbers were uncorrected, which means they are going to be on the low side. I'm not going to worry about it and just enjoy the car now that its running great. Thanks everyone for the help!

 

Did Pat tell you what the cam has made in other builds? I think a 239 intake duration is huge. Phil (formerly the owner of DTE) made 500/500 with an LS3 stroker, stock LS3 heads, and a 230/242 114 cam.

LS1tech is loaded with strokers making 480rwhp with cams in that 240 intake duration range....ported LS3 heads no less. You would think they would figure that the formula doesnt work. Keep in mind that the LS3 stock-stroke, makes 500rwhp with cams in the 227 to 230 intake duration range.

I think this build will hit 500rw when the tune is corrected but its a 427. LS3 heads just dont make power with overlap that high. A smaller cam for low 500's or Trick Flow 235 heads that match the bigger cam will vault this into the 550range.

Good luck with the project.

 

I made 450 RWHP with the same spec cam in a C5 LS6, heads, cam fast 90 bolt on...

BC

 

FYI: Some wide bands can loose accuracy after a while. When they do, they generally read leaner. So if your tuner's WB is showing 12.5, its possible its actual at 11.5. That happened to me with Bosch WB02 sensor and the PLX controller. Some controller allow you to calibrate them but not the PLX controller.

I've posted this before, but the NGK TR55 plugs are designed to be gapped at .055-.060" and the TR5 at .035-.040". The correct plug per NGK for the Corvette is TR5 gapped at .040". When I contacted NGK regarding the gap, the tech said the website was wrong for my year!!

I had the TR55s in my car for a while but switched back to the OEM spec AC Delco. I did not notice any difference is power or the way they run. I really don't know why so many shops are using the TR55.

I don't think this would explain the OPs low power but wanted people to know about the confusion.

The NGK TR6 plugs are one heat range cooler and I hear guys run them in F.I. cars. My car is N.A., so I can't comment on them.

Another thing to check is exhaust and vacuum leaks. Any leaks either in the exhaust system ahead of the O2 sensors or in the intake track can throw off NBO2 readings and that will affect fueling. While the PCM goes into open loop at WOT, if you have any +- fuel trims immediately before it goes open loop, they stay in place during WOT.

If it were me, and I invested that much money in a 427, I would get a second opinion on a different dyno and tuner. I've seen a number of tunes which...how to say this politely...less than ideal.

 

239 is huge in a 5.7.

 

Also - ask that question over in the tech section, perhaps Spinmonster will chime in.