New (to me) Cats and Mid-pipes for my LQ9

[jough]

When the LQ9 was swapped in, the shop re-used the one piece 5.3 y-pipe assembly.

I have been looking for the 6.0 only two piece cats & mid-pipes and found them today from an '04 Denali with 68K miles.

5.3 y-pipe is 2.5" and merges ahead of the muffler. Between the y and muffler is 2.75" single pipe.
6.0 is 2.75"x2 , then 2.5"x2 into the muffler.
I will keep the 3" factory pipe from the muffler exit to the tail pipe. However, I will delete the post-muffler y.

What performance (hp & torque) might I expect with making the change? Will I lose anything off idle? I realize that the gains may be minor, but I got the parts cheap.

I may just buy the Magnaflow 15734, which comes with 3.5" pipe after the muffler.

I also got the MAF from the 68K mile Denali. I am thinking of using it instead of my 168K MAF.

EDIT: Ordered Magnaflow 15734 cat-back with 3.5" pipe after the muffler. Found a 25% off coupon code (and free shipping) that I could not pass up!

 

[jough]

The Cadillac Escalade/GMC Denali 6.0 Magnaflow 15734 cat-back should be delivered this week.
1. I hope that there is NO drone.
2. I hope that I don't lose low end and that the powerband isn't shifted upward too much.

6.0s with just bolt-ons are right at the dividing line of needing a 3" tailpipe or a 3.5".
An '04 Denali LQ4 has a 3" from the muffler back. I'm not sure about the Escalade with an LQ9.
There are very few reviews or mentions of this specific cat-back on the web.

Of all the major cat-back players, only Magnaflow offers a 3.5". However, on the longer Suburban, XLs and even Silverado SS, Magnaflow uses a 3" pipe. I have asked them why, and still awaiting a response. Magnaflow also offers Silverado SS with two 2.5" exhaust pipes, which is = 3.5". My Z71 cladding dictates a single exhaust.

I did not even consider a Flowmaster. People seem to be Corsa fans, but theirs ys together just before the muffler and the tail section is 3", like stock. I seriously doubt that the Corsa muffler outflows my Jones muffler.

My other option would have been to use the 6.0 cats, reuse my Jones muffler by turning it around and then running the single 3" factory tail pipe. This would likely keep tons of low-end & mid-range while still flowing better than my current 5.3 y-pipe set-up. I would expect exhaust velocity would still be high.

Since there are two 2.5" pipes entering the muffler, the 3.5" gives the same cross-sectional area. A 3" would be a slight restriction, but really only an issue at higher rpms.

In about 2 months, I will know the answer. The computer takes a bit to fully adjust to modifications. I certainly will update this thread, but only after a couple of months of real world conditions...and maybe a few more Dodge Hemi kills.

 

[TheAutumnWind]

I am curious to see how this works out for you.

 

[#1taho]

pictures of the install ?
How do you like the sound?

 

[jough]

I'll have it all installed by this time next week. The used 6.0 cat pipes were CAKED with red clay and road tar. I am still cleaning that stuff off. It is a real pain, but I'm almost done.

Even though the firm I bought the Magnaflow cat-back (15734) is in Canada, it shipped from Lexington, KY and FedEx delivered the box in great shape.

I will ditch the standard muffler clamps for stainless band clamps.

 

[#1taho]

I just read your profil. How do you like the 6.0 and the 4l65?? I am doing the same conversion soon. I almost have everything to do it.

 

[jough]

I love it. Even with larger tires & a small lift, the 6.0 has way more power than my old 5.3 and gets almost the same gas mileage. The only real downside is that I now must burn 91+ octane. You may not have to with an LQ4. It depends on your tune.

 

[#1taho]

I got a LQ9. I hope I dont have to run 91. I am just going for a towing tune. Nothing to high performance. I was a bit more power and try to keep the same miliage or a bit better.

 

[ccapehartusarmyINF.(ret)]

the lq9's compression ratio isnt high enough to need high octane fuel regardless of yer tune
the compression ratio is what determines the need for high octane not a tune a tune adjust your timing becuase high octane fuel has a higher flashpoint then regular
so if you need to tune an engine for highoctane gas then it doesnt need it in the firstplace
the higher the octane doesnt mean better it means it ignites at a higher temp and highperformance engines with high compression ratios like the corvette etc generate more heat
thus the need for slower burning fuel

 

[jough]

My understanding is that the Cadillac 6.0 ** does need 91+ octane, even in bone stock tune. Check the owner's manual or ask the folks at Black Bear. I did. They were adamant about it. The knock sensors can only back out so much timing advance.

The LQ4 has a compression ratio of 9.6 to 1. The LQ9 is 10.0 to 1. I have read that the LQ9 also gets a little more aggressive tune from the factory.

In any event, you are already stuck using premium, so you might as well get a BB tune to maximize performance.

 

[#1taho]

It's on my to do list. But I still hope not to run 91. We will see what happens. I will check the owners manual

 

[jough]

UPDATE #1: Initial problems....1. Must use the 5.3 oxygen sensors with the 6.0 cats. The electrical connectors are different. Donor was a 2004 Yukon Denali.
2. Get a passenger side exhaust manifold from a 6.0. 5.3 PS manifolds have a cone. 6.0s are the same on each side, like 5.3 DS manifold. Also added Magnaflow 15734 cat-back.

Engine immediately began missing and PS cat overheating. CEL came on. Lean Bank 2 and Random Misfire. PS front O2 sensor was covered in black soot after less that 10 miles. Put in new front O2 sensors on each side.

Shop disconnected the MAF and it still ran. They also disconnected the electronic throttle and idle went up. We initially thought there was a vacuum leak. Eventually it began running on all 8 with no CEL. I am so glad I took it to a great muffler shop for the install. The guys are familiar with LS engines.

My guess is that the free flowing cats and cat-back put the engine mapping into an unfamiliar area. My hope is that the ECM will continue to learn and optimize to the new exhaust. I have 2 long highway trips this week. That should help it all settle in. Even now hitting on all 8, power is down at the moment versus previous set-up, but I only have about 35 miles on it.

Exhaust note is now more aggressive, even at part-throttle. Did not notice drone. Did notice louder freeway cruising sound. The 3.5" tailpipe is likely a contributor.

Hope to have power & gas mileage update this weekend.

 

[#1taho]

I am not able to use my passengerside manifold, it has the egr tube into it. good catch on the o2 sensors.
do you think your tune will adjust to your exhaust?

 

[jough]

I think it will. Time will tell.

Exhaust shop switched PS flanges on cats.

 

[#1taho]

I was going over my truck and the 6.0 the other day, I don't know what intake would be better to use. The 6.0intake looks taller than the 5.3 , I have been told they re the same but look different. my thoughts were to use the 6.0 intake and throttle body and change out the fuel system, what did you end up doing?

 

[jough]

5.3 flex fuel intake assembly. Mine has return line.

 

[jough]

After about 1,000 miles, I am loving my new set-up with the 6.0 mid-pipes and Escalade Magnaflow cat-back.
Low end is now stronger. Mid and upper end is significantly stronger. The Magnaflow is a touch louder than I would prefer, but NO drone. I guess that I picked up at least 25hp. Again, it is significantly stronger now. I think that it will pay for itself in about a year, but I'm still collecting mpg data...so far about +1.0-1.5 mpg. I would do this again. Second gear is absolutely awesome.

 

[mattluttrell]

I'll be curious to hear how this goes. I have a tuned 6.2 Escalade and am curious about exhaust.

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