Hey all,.... I got a few questions here,... I have a '85 z with an auto trans and the LG4 305,..... I measured my y pipe and it is a 2 1/4 diameter pipe. My middle pipe from the cat to the muffler is a 2 1/4" pipe as well. What I was wondering,.. I work at an automotive dealership of poor maker choice ( ahem,.. a Ferrrrd dealership :S ) and I have access to the walker/dynomax exhaust catalog on computer there in the parts department. What I want to know is this.,...... does the L69 ( high output) 305 have the same manifolds as my Lg4 engine does? The Y pipe diameter appears different between the two,.. the Lg4 is the aforementioned 2 1/4 " while on the computer the HO 305 has a 3" y pipe. Obviously if the manifolds are the same,.. the two y pipes will interchange the only differece being pipe diameter. What I am thinking about doing is putting the bigger y pipe on if it will fit (?????) and then put the larger pipe from the cat back as well,.. the 2 1/2" off the ho as well. A third idea is to put a 3" pipe from the pipe back to my muffler and have a 3" exhaust Anyone ever do anything remotely like this? If there are any ideas I'd appreciate them,.. I have fulllength headers, but at the time I am not sure I wanna use them since I am thinking of putting a big block in and this is a better choice of exhaust for the time being to save $$$, you know? THANKS IN ADVANCE GUYS!!! :hail:

 

From my understanding the HO models got slightly better exhaust than the LG4 meaning a little larger I believe. Hopefully someone can say for sure.

 

Yep, they did. The stock L69 setup is a little bigger than the LG4 setup. It's still fairly restrictive though, and would definitely benefit from a new y-pipe and cat back.

 

Definately bigger. I did the complete swap, to include manifolds, from LG4 to L69. Easy to see why the LG4 has a bad reputation for restriction. I went this route because the parts were essentially free. I was surprised, however, to learn that all catback aren't created equally. For example, the catback that I was using before the swap was 2 1/2--shoot the "stock" L69 is 2 3/4.

JamesC

 

One more pic. After-market intermediate pipe on top, the stock L69 below.

JamesC

 

So can anyone tell me for SURE,..... are the manifolds the same? I would like to keep my emissions crap all together since it is still working. If they are different manifolds,... does anyone know where I can get the L69's? If they are different manifolds,.. does the emissions stuff still hookup the same in same locations and all? Does the y-pipe bend in all same locations and mount in same locations at manifolds? Basically if I can get by with replacing the Y pipe and intermediate pipe, and also the two tailpipes,... I'll be happy. Thanks again ya guys in advance.

 

The L69 manifolds are different in size at the outlet, and as a consequence, you can't hook up an L69 y-pipe to an LG4 manifold. Emission stuff hooks up in the same places. Perhaps, the best/easiest way to obtain better flow is to simply buy headers, y-pipe, etc. for an HO car and stick them on to your LG4. Note my sig.

JamesC

 

Well, in that case,.. anyone know where I can get a set of stock L69 manifolds,.. uncracked and all, air tubes still functional etc,... for a decent price? Just to be totally clear on this,.. if I get the L69 manifolds,.. and then the 3" y pipe , and intermediate pipe for a L69 ,.. all would be well in the world,.. birds would sing and women would fall at my feet like raindrops on the ground? Err,.. or something to that effect? I'd just like something somewhat economic( READ: Cheap *** but good value) since I have a budget for two camaros,.. and the other one is my drag car,.. this is my street car. Thanks for your help again...

 

My car had the stock larger y-pipe and piping. I believe it was 2 3/4 but I never had a chance to really measure it. It did look exactly like that bigger one in the photo.

 

I think it's birds suddenly appear and stars fall from the sky, but when I walked by, it was usually the other way around...

FWIW, LB9 manifolds are dimensionally the same as L69. Happen to have a set with A.I.R. tubes but no y-pipe in the garage attic.

 

Another option: TPI manifolds are the same as the L69 manifolds; however, the TPI's don't have the heat stove on the driver's side and the air tubes are facing toward the rear of the car. You might swap the LG4 air tubes and heat stove to the TPI (I believe the stoves are available from GM if that's a problem. I saw the part numbers in Metzler's Parts and Illustration Catalog on disc). I suggest this because finding the TPI manifolds might be easier than locating the L69s--Better talk to Five7kid. Worth the effort to swap on the cheap? You bet.

JamesC