Did the typical top end on my 1997 SS M6 w/ 88K and dropped it off for a tune last week. Drove the car for about 150 miles which included the trip to the tuner. Car seemed to drive well and was sporting the default 28lbs injectors and stock throttle body. The tuner ordered a set of 42LB green tops and installed and tuned. They were going to do some baseline pulls and then switch to a 52 or 58 throttle body to see what the difference was and go from there.

Stopped down Friday and numbers were way off.. This is a very reputable experienced shop who has delt w/ the LT1’s/LS’s forever. I have read lots of people say its just a number etc… I see the results they get from similar cars and lots of newer cars w/ different add ons.. The numbers always look as they should relating to the mods on the particular setup.. They use a Dynomite Dynamometer 1300 and I see the numbers for similar cars and newer ones. The numbers Friday were 330hp and I think 347 trq with AFR in mid 12’s.. I think he said when leaning did nothing and adding fuel decreased HP. Peaked power @ 5500..

Below is the setup.
LE2 Heads w/
205 cc intake port
Manley 2.00/1.56 6000 series valves
Patriot Gold Extreme springs (155 lbs seat and 400 lbs open)
victor reinz head gasket
ported intake
Custom Comp Cam 223/231 571/556 LSA 112
Comp Ultra Pro Rockers 3/8 1.6
Comp Push Rods part#7938-16 5/16 7.100
Plugs - NGK TR6 plugs gapped @ .050
Fuel Pump - Racetronix fuel pump
Thermostat - 160 degree
Exhaust - Pacesetter long tubes and high flow cats
Ignition - Stock Optispark and Coil
LE2 Ported Heads & Ported Intake with 58MM Throttle Body Holes
Pacesetter long tubes
2 high flow cats
new NTK O2's
new taylor 8.5's
for now stock TB
stock 3.42
315/35/17 nitto rears
T56 Center
centerforce stage 3
tuned out airpump

Just got an email from the shop tonight:
Swapped plugs to NGk 55 “pretty sure gapped to .035” what they recommended when I dropped it off.
Verified the injector connectors where correct.
Compression check on cylinders all within 2% 175-180
Checked ignition wires, Optispark high and low pulses, fuel pressure and regulator, cleaned MAF..
The said it was still down 50-70hp.. didn’t say what I pulled today but sound like it did on Friday..

What could it be?

 

Seems like it should be peaking at a higher RPM with that head/cam combo. Are they running it to 6500? I'd like to see what it's doing power-wise from 5500 up. Normal culprits for high-RPM power issues are valve float, spark, and fuel. Given that you have a fully upgraded valve train and fuel system and the Opti tests good, I'd be looking very closely at that stock coil.

 

I suggested the coil tonight.. I was also thinking about the 02 sensors.. I forgot to order 02 extensions and we ended up extending the wire on the 02 sensors.. Could they be reporting not accurate info throwing things way off? I asked that the rears be tuned out and the front two are BN.. I read tonight extending the o2 is not recommend and it got me thinking.. just stabbing in the dark

 

they only brought it to 5800 because the power dropped off after 5500..

 

Post the graph, if possible.

 

wish I took a picture of it when I saw it Friday.. as of right now I do not have a graph, car is still in the shop..

 

A picture of the graph will help out tremendously. Otherwise we're just fishing in the dark.

 

Did you post those cam specs correct?

 

Yes that was right off the Cam Card from Comp.. With 1.6 Rockers the end result .610/.594..

The HP/TRQ curves were increasing smoothly didnt look like a EKG or anything.. I will try and get a screenshot or photo of the dyno pull..

 

If your dyno curve looks smooth with NO evidence of either valve float or ignition breakup then your problem lies here:

"Pacesetter long tubes and high flow cats".

Your once "high flowing" cats are not high flowing with your new top end set up. The reason your engine is "nosing over" at 5,500 RPM is most likely now due to backpressure on your exhaust side.

Everyone's exhaust set up is different, but, can you easily drop your y-pipe and cats and do a pull through just your LT Pacesetter headers???

One (1) test is worth one thousand (1,000) opinions.

 

The exhaust is band clamped together so a pull w/ open headers is an option.. I am just waiting on a call or may stop down again today and will throw that out there if they are still coming up way short.. Thanks for your inputs..

 

Hey sean its justin from cdcny-- i had the same issue w mine.. low numbers... my car got tuned speed density and it brought me another 43/39 or something llikethat.. i layed down 310/330 then after speed density tune i ended up w 353/369-- i know those guys over there know what their doing but i know the "other" tuning shop in are area did it that way w me. LOL good luck man!!!

 

Thanks Justin.. I am going to stop down tonight afterwork and bring that up... I just want her back missing to many cruise in's and shows..

 

Who installed the cam, and was it degreed in when installed? I had a Comp custom grind that was off by A LOT.

 

Have you tried switching your rocker arms around to a 1.5 ratios? Then 1.5 on the intake 1.6 on the exhaust and vise versa?