haljensen

I just bought and received used Z06 manifolds and cats with the intention of installing them on my '08 LS3 A6. Hoping for a HP gain and to still appear stock for Inspection since there will be GM manifolds and GM cats in a stock location (even though it's a Z06 location). Looks like I also have to have a Z06 mid pipe to splice a 3" front mid pipe to a 2.5" rear mid pipe for my existing NPP mufflers.

Seems to be a problem with the manifold/head port shapes. From various pictures in the CF the LS3 heads have a round exhaust outlet while the Z06 manifolds have a "D" shaped port.. How can there be HP gains when the manifold shrouds part of the exhaust port? Are the Z06 exhaust manifolds compatible with the LS3 heads? Which gaskets do I use, LS3 or Z06?

camikeva

I did this, or had it done, on my 2008 A6. Use the gaskets for the Z06.

RichieRichZ06

It bolts right up, but is only worth about 8-10RWHP on the 3 that I have seen done.

haljensen

What about the port shape miss-match?

haljensen

ttt

HOXXOH

A search for exhaust gaskets will turn up several threads. All LS3, LS7, and 6.2 truck numbers will work equally well. All the gaskets have excess clearance in any port configuration.

Transition from the 3" Z06 H-pipe to the 2 1/2" original pipes near the rear of the H-pipe to retain the same spring hanger.

HP gains for Z06 cars going to LT headers range from 5 to 12. C6 owners report an average of 25 HP for LT headers. So it stands to reason that the Z06 system on a C6 will produce 13-20 HP increase.

If you ever intend to purchase a wideband o2 in the future, I'd reccommend welding in the required bung as part of the install.

haljensen

One cat pipe already has a wide band bung.

My question still is about the difference in the shape of the ports, round to "D" shape can't be good. The manifold "D" covers part of the heads round port.

martysauto

I am not familiar with ls3 heads first hand, but I did google images "ls3 exhasut ports" and they looked d shape to me. They appear to be the same style as ls7's. I've read here, alot of people have had good results with the zo6 man/cat swap.

HOXXOH

It's been a while since I did that install, so my memory may be wrong. But something makes me think the round of the LS3 port fits within the shape of the "D".

Simple check is to take the Z06 manifold to a dealer and lay an LS3 gasket on it while matching the bolt holes. Take pics and post here for everyone to see. Worst case is to port match the manifold.

haljensen

I swapped exhausts on a couple of LS2's and they are definitely round exhaust port heads, I've seen LS7 heads and they are D shaped exhaust ports heads. I haven't had the exhaust off the LS3 yet

I've got a couple of hours search time trying to find a clear picture of the LS3 head exhaust ports with no clear results, nothing but small pictures at extreme angles. If the LS3 is a "D" port head then why are all aftermaket headers a round port the same as the LS2? Just money saving by the manufacturers?

Part of my problem is understanding how a round port header (All headers for Corvette) that fits the LS2 can fit an LS3 with a "D" port and/or an LS7 with a "D" port. Shouldn't the header/manifold port shape match the head port shape?

HOXXOH

Ideally a manifold port matches the head port. However, aftermarket headers utilize round tubing, so it's more economical to slightly oversize the tubing in relationship to the head port. The exhaust gases will quickly transition to what ever the shape is at any point. The real concern is reduction of turbulence. Notice the shape change within the Z06 manifold itself ( http://www.vetteweb.com/features/vem.../photo_06.html ) and the transition from the manifold to the cat pipe.

You still have the option to reduce turbulence by port matching.

haljensen

Port matching? I'm doing this on my daily driver, my only vehicle. Any changes have to be completed the same day. I'm an amateur backyard mechanic, I know I can't pull and disassemble the heads, port match the manifolds, clean and reassemble the heads and get it all back together in a day. Has to be quick and cheap, that's why the Z06 manifolds/cats. Almost legal and a performance gain for about $700 by the time I buy used parts, rent a lift, pay for cutting/welding the mid pipe and buy gaskets/bolts, etc.

AirBusPilot

The LS3 exhaust ports are "D" shaped. There is no mismatch.

http://www.highperformancepontiac.co.../photo_11.html

HOXXOH

You don't need to port match. I only mentioned it as an option to reduce turbulence, while answering your question regarding aftermarket header shapes and noting that the Z06 manifolds also have internal transitional shapes.

wooden

You don,t have to port any thing just put them on as every body else including myself and forget it, I used ls7 gaskets, the shape of the ports may be slightly different but they still flow better and give you a hp increase, don,t try to over think it.

Vegas Panton

I put a Z06 exhaust system on a 2006 LS2 and picked up some good HP. It had a D port exhaust port and a round port gasket. I used LS7 exhaust manifold gaskets--Worked great. I just put the same system on my 2009 LS3. It has a D port and once again I used the LS7 manifold gaskets. I did notice that Chevrolet used the same cast exhaust manifolds and round port gaskets on both the LS2 and LS3. Saves money I guess.

SpinMonster

The only round GM exhaust ports were on LS1 heads and none of the proven headers were D shaped. Youre making a big deal of something irrelevant. I'm not a big head porter but John Lingenfelter who designed the D-port for GM's reworking of the the original 241 design went into great detail about how high and low rpm ranges used the top vs bottom of the runners depending on the rpm.

Some tuners who port the 243 heads actually use trapezoidal intake runners to keep overall cc's down on the runners, opening up only the part of the runner used for high rpm power while not widening the low rpm part of the runner. The D-port on the exhaust side was for the same reason; minimal cc's for overall size while having more area at high rpms for the roof. After the runner straightens out (at the header inlet) there is no loss by having round primaries for headers or exhaust manifolds. The flat part of the d-shape runner is actually an extention of the short side radius from the valve to the header. Holding the GM gaskets over any of the heads' exhaust runners shows there is nothing being covered by gasket or manifold. The runner isnt bigger than the gaskets because the flat part of the 'D' isnt bigger, its smaller to make the runner's size not grow where it didnt need it for flow. 'Port matching' here isnt needed because port matching opens the path when a bigger runner meets a restricted opening.....not the case since the ex manifolds are bigger than the exhaust runners on the heads.