My thought's are that if the cats are 20% plugged it wouldn't let the overlap of the cam do what it's designed to do & cause reversion in the intake & reduce power by a % what % I have no idea. We don't know what % they are plugged but if it's 20% there will still be 80% going out the tips.in this case I would guess that a 20% restriction could cause a 10% reduction in power. I am by no means a expert though.

 

I'm right there with ya man, totally get what you're saying. Well that wasn't the issue. Got it all done and took it out on an old backroad and got about the same results with my dragy. Had some wheel spin off the launch but not 2 seconds worth. At this point I am taking it back to my builder/tuner and letting him figure it out. Thanks for all the input though.

 

Cats look fine. Looks you you physically stabbed them but they aren't melted at all. I would go over the tune up and the cam timing.

When they are melted they look like a mess and pieces come off in dusty chunks. Those cats look good so I doubt they were holding back more than 10 whp.

 

Have to agree, and yes that was where I stabbed them to see if maybe the center of it was melted. Really starting to think the cam is off a tooth, really cannot think of anything else that could cause me lose what feels like half my power.

 

How many separate times have you run the 1/8th between when it was stock and each mod or in the case of multiple mods, what were they?
Maybe I should ask what the mods were, on every time you've been to the track? Trying to see a pattern here.

 

Never ran it stock. Ran it with headers/xpipe, CAI and tune, and ran it with all the other mods.

 

Before breaking into the engine, I'd make sure both the intake and exhaust have no restrictions. I've cleaned rat nests out of several tractor intakes and pickup intakes. Fairly easy to do on both sides. I believe there's a vacuum port between the throttle body and intake manifold. There should be no vacuum there at WOT. If there is, you have a restriction upstream of the intake manifold.

The exhaust side is a little more involved, but not too bad. You have to drill and tap an exhaust pipe ahead of mufflers/cats to add a hose barb. Connect a pressure gauge via vacuum line. You should have little to no pressure in the exhaust system at WOT. Add a plug when you're done.

 

Since you have no base (stock) numbers for reference, the problem either existed before you owned the car or was created when modded the first time. I say that, because those first mods didn't really make any noticeable improvement in dragstrip times from what an average bone stock car would run and the second set of mods had no real change on your timeslips either. That knowledge alone, pretty much eliminates the cam timing thinking, since the stall converter alone on the second set of mods easily accounts for a .1 second timeslip change.

Let's assume the previous owner never messed with anything beyond normal maintenance and the headers/x pipe and cats have now been eliminated as a restriction. It's time to focus on fuel, air, and the tune that controls them.
1. Check fuel pressure and volume first, since it's the easiest to do.

2. Pull off the CAI to inspect the filter, the MAF sensor, and especially to check the WOT operation of the throttle plate as it is controlled by that skinny foot pedal. Sometimes the simple things, like a block taped to the backside of the pedal to prevent your teenage son from accessing the full power have been utilized.
You might even consider putting the OEM air filter box back on for testing purposes.

3. If those both pass muster, you (actually a qualified tuner) need to dig deeper into what was done on the first tune and wasn't changed on the second one. Preferably do testing on the street vs a static dyno. A 10-70 mph WOT burst is enough to spot tuning issues, because it eliminates the launch, runs through the full rpm range, and includes a good portion of the shift and 2nd gear performance data. Test in both D and S modes without using paddles to control the shift.

Dragstrip info and testing scans are where keeping detailed records will be of most benefit. Your best investment should be HP Tuners to digitally document the performance and tuning, so the tuner knows how your car is working. It's the same reason your doctor keeps records of your weight, blood tests, BP, EKG, etc, to know what changes are needed when your body isn't working right.

 

my stock LS2 mn6 got 347 to the wheels, the cats look good now hw has screwed them up, who ever did the work is taking him to the cleaners

 

The car is back at his shop, he honors his work and will fix it, which is rare these days. He's one of the best tuners in the southeast and sometimes **** just happens I guess. But, at least he is gonna make it right.

 

With those #'s he obviously has not a clue about tuning or building, you should have gone to Vengeance Racing in Cummings Ga

 

Good to hear. It could be as simple as a plug wire that popped off or a marginal coil. If the tune up was really off, losing 100 hp wouldn't be out of the question, but it sounds like he is an experienced tuner and we can assume that the tune is ballpark if not better. However, being a tooth off in cam timing would absolutely show a power drop. I am sure he will check the basics first--spark at each cylinder, compression test, leak down (if compression test was questionable) and fully opening throttle. And of course making sure there are no exhaust blockages.

 

Shoulda, coulda, woulda....I have no issue letting them fix their own work.

 

knock sensors? They can start to go bad, pull timing, and not throw a code. That’s one way to give up a lot of power

 

Have him do a cranking compression test you should be like 190-200 psi. If way down either cam is off a tooth or motor is really worn out or a few cylinders are bad. With these cars and previous owners 90,000 miles could be like 900,000 miles.

 

Started with shorter push rods and adjusted pre-load. It's possible the longer pushrods were leaving the valves hanging open a little. It passed leak down and compression though, which is a relief. Heading to the track tomorrow night so we shall see. If I don't see low 7's I think we may still have an issue.

 

On an LS there is no pre-load to adjust! This isn't a SBC. Preload is adjusted by pushrod length. The rockers are simply bolted down to 22 ft/lbs and the plunger in the lifter will take up the length. There is around .200" of plunger travel in the stock hydraulic valvetrain which come with LS7 lifters.
Longer pushrods simply push the plunger down further. The only way they would hang the valves open is if the plunger bottomed out at which point it would cease being a hydraulic lifter-(the pushrods would have to be WAY longer)

If your mechanic doesn't know this very basic info, I would begin to wonder about what else he doesn't know.

 

Man I really hope this isn't the case. I took the car out on my dragy yesterday (track was closed for weather) and my best was 7.8 @ 94mph eighth mile. There is No way I can make up almost a full second just based on track/street conditions...still really no change. I realize its the street and I'm on drag radials but I still feel like the car should be dipping into the low 7's even with a small amount of tire spin off the launch. Taking the car back in this week. It's really getting depressing. FML.

 

7.8 is about a 12.15 1/4 mile (using the common 1/8 to 1/4 calculators) You should be WAY quicker! Your car should be high 10s on a good tire. I would start to look at something mechanical.
Where do you shift at? You probably have the stock, long runners in the FAST intake which are good for low rpm. You can get the grey medium runners and they will shift the powerband up 300-400 rpm. When I had FAST medium runners in a similar sized cam motion cam, I was shiftimg around 6900/7000 rpm.

I would take the car to a 3rd party dynojet dyno and get a baseline. I would also have a 3rd party tuner to look at the the tune up.

I would also verify that you aren't one tooth off on the cam gear. There IS a way to do it without tearing the engine down and without a cam degree wheel. You basically compare the rising vs dropping valve springs on the #1 cyl as you near TDC (obviously with the VC off and springs exposed) while slowly rotating the engine. It is EXACTLY how I realized that I timed my cam one tooth off--after following this method, I tore the damper and front cover off and SURE ENOUGH, the cam was mounted one tooth retarded! Let me see if I can find and link the article for you.

 

Cam was pulled and it was one of the things we were suspicious of.....incorrect grind. Basically a stock cam not allowing the big TB, intake and heads breathing room....what a relief. Thanks for the inputs.