This past weekend I bought my first corvette (2006 3lt), and I'm really loving it. However, it's not making the power that the seller and I expected it would. Granted, this was on a Dyno Dynamics which reads pretty low, but I was still expecting a little more. I was hoping I could get some advice on how I can maybe bring the setup to it's full power potential. Here is a list of the power mods:

- 427 forged stroked LS3 shortblock (Eagle rods/crank, Mahle pistons), 11.5:1 cr
- FAST 102 intake
- LS3 heads
- PatrickG Custom grind cam (239/247, .610/.632, 114+2)
- Comp chrome moly 7.425 pushrods
- TEA dual valvesprings w/ ti retainers
- LS7 lifters
- SLP underdrive pulley
- Monster Stage 4 Clutch w/ Lightweight Billet Flywheel
- Z06 engine oil cooler
- Dewitts heavy duty radiator
- OBX 1 3/4" stainless Headers/Midpipes
- Corsa Sport axleback
- Z06 fuel pump assembly
- 57LB FAST injectors


They did a compression check last week while finishing up the tune and I believe it was 185-195 across all cylinders, which seems pretty healthy to me, there are less than 2000 miles on the new motor. Here are my first suspects as to why it might not be making the power it should:

1 3/4" OBX headers - Maybe 1 7/8" or even 2" would make more power?

Stock air intake - I have the K&N intake, but the tuner forgot to put this on before doing the tune, can I just bolt this on without having to retune? Will this make a big difference in power at these levels? I know it might not make as much difference on a stock car, but at this point it could be a restriction.

Misfire issues - the car seems like it will occasionally miss or hesitate, just like my CTS-V did at one point. I installed new TR6 plugs and that gave me a LOT more power on the V (went from not spinning in 1st to spinning at the top of 2nd mid pull). I have new MSD wires and TR6 plugs ready to install later this week. Think this will make a difference?

Four o2 codes because of the headers, I will have to get this fixed, but do you think this will cause a loss of power at WOT on the dyno? Could also be the reason for the hesitation during cruise.

How much power do you think I'd get going to a 102mm TB to match the fast 102 intake? Or porting the 102 intake a bit?


For background, on the same dyno my supercharged 05 CTS-V made 530whp at 9psi (e85) with 1 3/4" kooks headers and corsa exhaust, but it was a stock LS6 internally. I figured the 427ci with a fairly big cam would make around the same power, but it only made 475hp on the dyno. Any help is greatly appreciated!

 

475 is weak sauce.

Hope you get it figured out

 

My advice is, don't get caught up with dyno numbers. I prefer to test a car at the track to determine the power its really making. A dynometer is only a tuning tool, nothing more. Every dyno is different. As for the car there could be so many things going on here but here's a start.

1 I would start by looking at the dyno graph and look at the curve and the A/F ratio.
2 Pull your plugs and check them. Are they burning consistent and are all gapped the same?
3 Get all those 02 codes taken care of. The tuner should've taken care of this.
4 Are you getting any other codes?

The 1 7/8" headers and 102 TB will make more power but I wouldn't be concerned about that right now. I would try and get that combo running right first. Put that K&N on there and get it retuned correctly.

 

significant Misfires and codes indicate things that needed to be sorted out. Rule out problems before swapping things.
I agree about changing the plugs. If your plugs are too hot, it may have caused your tuner to have dialed back the timing.

Do you have the dyno graph? As mentioned look at the A/F. Any unusual dips, jaggedness, or flatspots in the HP curve?

You might also check the car on a second dyno.

 

Thanks for the input guys, the CEL went off today while driving to lunch, so the o2 codes seem to be intermittent. The tuner had apparently fixed the issue, but it came back a couple days later so I need to get it back to him, unfortunately he's four hours away. I'll for sure get the K&N on at that point.

I'm trying to get the dyno graph emailed to me, I forgot to pick it up when I left on Saturday, I'll post up when I get it.

The plugs in it now are TR55 according to the seller, I'm going to pull the plugs this weekend and will check the gap and wear on them.

 

Get a new tuner. You should not be having 02 codes and misfires. Assumming the plugs/wires are okay and no other installation issues. I think it needs a better tune and once dialed it will make better power.

 

FRANK

OMG,, I had the EXACT SAME thoughts! If your tuner is trying to tune the ECU with misfires and O2 sensor codes, he’s wasting your time and money!!


ashanson

Check the wires and plugs. What plugs and wires are you running??

You should be running standard copper core plugs (they won’t last as long but they will perform better) What wires are you running? I run NGK TR6 Spark Plugs in mine and they work very well.

Recommend the GM Performance RED wires if your wires are suspect.

Data log the engine and see if your getting Knock Retard and see what your PE AFR is running at.

I have similar bolt on Mods on my 02 C5 with a LS6 engine making 450 RWHP. Something is NOT working correctly! Those O2 sensor issues need to be resolved although there not in the loop at WOT

BC

 

tune, header size.. were the heads touched up at all?

 

Do you know for a fact the CEL code is O2 sensor related (i.e. you have HPT / EFIlive or a code reader) or are you guessing?

Intermittent O2 codes could be due to a pinched wire or damaged connector.

 

Running stock wires and TR55 plugs now, unknown gap (probably what they come with), will use TR6 in a couple days with new MSD 8.5 wires. What gap would you recommend, I was thinking in the .040 to .045 range, but I'm used to dealing with forced induction.


Yes, I used the obd2 scanner and it brought up four o2 codes at that time. My thoughts exactly on the connection or wire issue.

 

Ive never dealt with FI so I can not comment on that GAP. Need someone who is familiar with FI to chime in on that fact.


BC

 

I run 45 and TR6's, 427 Stroker, 4.125x4.00 stroke 12.1/1 Cr, DCR 8.7
I'm over 600, it took a long time to get it there.
I also had a lot of help from SpinMonster on cam and head selection.

 

Pulled the plugs tonight, still waiting on my MSD wires for almost two weeks, but the car started running really poorly so I decided not to wait any longer. Every single one was black and sooty. My guess is the fuel trims are so rich because of the o2 sensor issue that it fouled the plugs. I'm scheduled next Thursday at DRM so hopefully they can work out the o2 issues.

I got my dyno graph, and it looks like the tune is pretty good as far as A/F ratio is concerned, but I don't know how much timing it's running.

 

Wires were delivered today it shows, sorry for the delay it was un-avoidable

 

I hadn't checked the mail yet, I pulled the spark plugs right after I got home. Found the new MSD wires in the mailbox though, thanks!

 

The likely cause of your plugs being black and sooty is from your AFR which is way too rich. With that engine (and even with the 11.5:1 compression ratio) you should be up into the 12.3-12.5 range.

If that graph is correct the highest I saw was 11.8 and it looks like it even dipped as low as 11.4 at one point.

 

The TR55 spark plugs I pulled were all gapped at .055, which seems pretty large to me. I put in new TR6 plugs gapped at .045 each. It was weird, one box of 4 was pre-gapped at .038 or so, and the other box was all at .060, I hate to see what happens when people just throw spark plugs in their car without checking them first.

Anyway, changing the plugs and wires did nothing, and yes it's running super rich right now, I can smell the fuel just pouring out the exhaust.


Edit: I unplugged the battery for awhile, then started it back up and it runs a lot better, but it still seems like it's running pretty rich, a lot of excess popping on decel and during shifts. After the o2 issue is worked out I'm going to have it retuned.

thesubfloor: I didn't realize you could run in the low to mid 12's range with that high of compression, I'm used to FI cars where 11.5:1 AFR is pretty common. Maybe I'll pay DRM to retune it since it'll be up there next week anyway. Unfortunately I only have 91 octane gas where I live, the 93 is plentiful up there in Minnesota. I'll have to make sure I have some spare gas so they can tune me on the low grade Iowa stuff.

 

You may not have to worry about needing 93 octane as I was pleasantly surprised a few months back at what you can do with 91.

For the last couple of years I've always run a 94-95 octane blend when I race. Back in February I decided to run at the Wednesday night drags in Sacramento and since they don't prep the track there mid-week and I knew it'd be quite cold by the end of the night (meaning I would probably have trouble hooking) I decided to just run 91 octane and detune the car a little.

I richened up the WOT AFR to 12.2 and pulled out 5 degrees of timing across the board and with only 91 octane in my tank I was running 10.2's by the end of the night with several high 1.4 60ft times.

Moral of the story - less can sometimes be more.

Do you have or be able to get a copy of your tune?

 

Could you explain this?

 

Plugs come in different heat ranges. For forced induction/nitrous applications, running a spark plug like the TR6 that is "colder" than stock helps stave off detonation.