I'd also shoot for 12.8 AF for your best tq and 13.2 for best HP.

LS6's have a real effecient chamber design that reacts different to timing. They don't like nearly as much as GM's other heads.

Thanks!

Every vehicle is a little different.

243 heads, unmilled, unported, bone stock.

OK. Remember, every car is a little different so it is best to tune your car individually - on the street and on the dyno (eddy current if you have it) - rather than looking at generic tunes or maps.

Very true. :cheers:

:seeya Arun

After doing further investigation, I wonder if my exhaust is a restriction - it would explain why torque was low even on the stock cam.

I was told it was LG longtubes, and it is indeed longtube headers, and resembles LG's, but the OD on the primaries is only 1.745". I called LG and they said they never made a 1 5/8 ID longtube, but with .047" wall thickness, that would be what these are.

The interesting part is they have merge collectors. I can't find any C5 corvette 1 5/8 longtubes that have merge collectors. The car also had cats- unbeknownst to me. I thought they were resonators (doh!). I'm hoping removal of them helps in the power and torque area, as one may have been clogged.

One of the headers also has a dent/crush in one of the primaries. I thought that would limit peak power, and not reduce power everywhere. I'd replace these with 1 3/4 long tubes before fixing that primary though.

I'll get some pics up to see if anyone may be able to Identify the headers.

Anyone else think 1 5/8 headers would reduce overall power and torque?

Here's some pics of the exhaust - can anyone identify it?

Headers and x-pipe

http://i902.photobucket.com/albums/a...adersxpipe.jpg

Merge collectors:

http://i902.photobucket.com/albums/a...collectors.jpg

Primary size:

http://i902.photobucket.com/albums/a.../PrimaryOD.jpg

Collector choke:

http://i902.photobucket.com/albums/a...mergechoke.jpg

Collector exit:

http://i902.photobucket.com/albums/a.../mergeexit.jpg

Passenger top (not a great pic)

http://i902.photobucket.com/albums/a...sengerside.jpg

Looks like LG headers....looking at merge collectors.

I agree, but only a 1.7455 OD primary? LG said they never made 1 5/8 longtubes.

I'm stumped.

Headers are measured from the OD of the pipe-not the ID.

Those are LG 1 3/4 headers.

:iagree:

I don't see cats in the system either.

My XS power headers measure 1.84" OD, not all the pipes are the same.
So I think this dimension varies between manufacturers, but as Arun said, headers specs for tube diameter are typically OD.

The length of those headers if anything should boost midrange torque.

Ron

Whoa whoa whoa, stop the clock.

For real? I always thought the ID was what was referenced in headers.

The XS Powers are 1.84 OD? That would make sense with a .047" wall thickness - it would put the ID right at 1 3.4.

I'm so confused now.

FWIW, the CATS are further down from the x-pipe, and are slip fit. I don't think my friend got a pic of them, but they look EXACTLY like the ones that LG has on their website.

I just measured them again and right at 1.843". Can't really get the calipers on all the tubes.
So the XS Power are different from the norm. I had asked that question on the tech forum some time back.

Cat's further down the line. Ok, must not be too effective that far away from the engine. At least when idling.

I really don't think your headers are the issue. You have good parts. I would think a plugged cat would kill the hp, I guess you could pull them off and have a look. It would be quite obvious.

I never thought about it that way as far as distance, and now I wonder -

The cats are installed after the x-pipe. Could they have been put on the wrong end, and perhaps the x is too close to the headers causing reversion or something?

If I do dismiss the exhaust as the issue - what else could I be looking at? I know the first thing people yell "cam is too big" but again, I didn't LOSE any HP or torque, I just didn't gain any below 4000 rpms, and it still seems low based on comparable setups. Heck, even before the cam, torque was low relative to other z06s.

I'm halfway tempted to order a smaller cam just to see how low torque would go. I don't believe that I will magically gain 30 ft. lbs of torque. If that were the case, isn't the LS6 cam small enough to be a torque monster, which it clearly isn't in this example.

Out of curiousity, What made u go w/such a big cam in a virtually stock car? Just pulled a Whiplash II out of my buddies car and switched him to EGs Mayhem II cam. And he is more than happy w/the switch, that smaller cam is much more drivable for a street car IMO and still sounds wicked

Did you ever do the borescope thing?
Low compression ratio will affect torque. Also requires more timing.
I suppose the engine could have been built for boost before you owned it......just thinking out loud

I plan on heads and even a 6.0 swap eventually. I have no complaints with this cam - don't get me wrong, it may come across that way since I don't just say, yay 420 rwhp.

Engines are mechanical devices and people seem to think there is a component of magic within, and I disagree. Numerous people have made excellent power with this cam, and more than abundant midrange.

I see too many people say they would be happy with more low and midrange - ok, sure if you're in traffic. I'll downshift.

Perhaps I should change my question - why is torque still low above 4000 rpms? This cam is more than proven to make 380+ TQ with the same combination.

Hell, numerous stock and bolt-on z06s make in the 350- 360 tq range. There's a definitive reason why this motor makes less, and I'll find it.

If I were to switch to a smaller cam, would everyone not agree that I could gain some midrange, with a sacrifice to top end? If that's the case, I'd need to gain an abnormal amount to compensate for the loss at the top end. I don't see gaining that much more average HP and TQ going to a smaller cam, but perhaps. We could always look at the stock LS6 cam as a comparison - low and behold, torque is the SAME below 4000 RPMs.

I'm open to suggestions, but an unequivocal "that cam is too big for 346" reminds me too much of the LT1 crowd that used to say anything bigger than a hotcam was way too big, until I blew their doors off with a GM847.

Not yet - my friend doesn't have one. Totally shocked me -he has everything you can imagine, but not that. I did put silly putty (couldn't get a mirror to see) on the block casting and it is indeed an LS6 block, the heads are indeed 243s.

The only other things I can think of is either replacement pistons (unlikely) or thicker headgaskets (more probable), but would thicker gaskets really lower compression enough to matter?

I did remove the cats - one was pretty messed up - couldn't see hardly any light through it, and was deteriorating pretty bad. Other looked fine. I'm going to try and make it back to the dyno this week, as well as have the tuner take a look at airflow to see if we have a noticeable increase when datalogging.

FWIW, I'm running TR6 plugs gapped at .042 - I don't see 30 ft. lbs hiding there, but you never know. Would a hotter plug with an increased gap help?

Good find on the cat. If bad enough, it forced you into a semi single exhaust! Perhaps you have just found the issue?

Got a photo?

Bad cats will kill power. That could be your smoking gun. Let us know the outcome. :cheers: