Thorleys or Edelbrocks???

[randymbtech]

Hey guys, I am trying to decide what to do to finish off the exhaust in my '98 ECSB 5.7 Vortec. I already did a complete custom 2 1/4" dual cat-back system w/ Trush welded mufflers, an H-pipe, and tailpipes out the back with 3" polished tips. It sounds great, real deep and mellow, but I would like some more sound out of it.

I want to keep the cats because I tow sometimes, and need as much low end grunt as possible. My options are to get the Thorley headers and weld them to my factory cats, or to get the Edelbrock ceramic coated shorty's and the Magnaflow y-pipe with converters. I really like the idea that the Magnflow pipe replaces everything, and all of the pipes and cats are upgraded to 2 1/4". Then again, I like the idea of the midlength headers on the Thorleys, but they still use the factory cats and the really small pipes after the cats.

Any advice would be much apreciated. These parts are expensive, and I want to get it right the first time. Thanks.

[1ugly88]

couldn't offer any help but would really like to hear her with the thrushes on it please??

[Pauly]

Throleys way over the Edelbrocks. I would check out Dougs Headers as that is where the REAL Doug Throley is now making headers. Thorley headers is the wifes comapny now(for years now).

peace
PAuly

[randymbtech]

I know the Thorleys are supposed to perform well, but I don't like how they use the factory cats and tiny pipes. Any thoughts on that?

[randymbtech]

Sorry, don't have ability to load sound clips. I am a mechanic, not a computer guy...lol.

[Pauly]

I know the Thorleys are supposed to perform well, but I don't like how they use the factory cats and tiny pipes. Any thoughts on that?

Factory cats actually flow pretty well. In fact I read an article years ago where these cats were compared to Dodge Viper V-10 (488cid) and the Vortec 350 cats were close to double the flow of the V-10 cats. There are guys that cut away the stock inlet/outlets of the L31 cats weld up larger inlet outlet pipes. If you are still concerned about teh actual cats, you can always step up to a couple different cats if you wish.

So far as the tiny pipes, IIRC the Thorleys use a mandrel bent headpipe, so even if the Thorley's come with the same 1 7/8" pipe size the stock 1/2 tons use, they will flow better. The stock 1 7/8" 1/2 ton Vortec 350 headpipes have crimp bends that kink down much smaller than the 1 7/8" size. I think that the Thorleys use a 2 1/2" headpipe, which is plenty large for any L31 application IMO.

It appears that these are mandrel bent.
http://dougthorleyheaders.com/view.just.image/src=/ecom/images/product/991.451.600x400.THY-301Y-FED.jpg

Another pic and a diagram
http://www.dougthorleyheaders.com/product.downloads/THY-301Y-FED_INST.pdf


Compared to the stock headpipes(page 2)
http://www.pacificp.com/forum/viewtopic.php?t=9793&highlight=exhaust

To finish off the exhaust, you will need a different muffler or two along with some pipe.

peace
PAuly

[canuckz71]

I'd go with the thorley's. You will get more power out of the mid length tri-y's then you will out of a shorty header.

[randymbtech]

Wow, great info, thanks Pauly. The only thing I'm concerned with is the Thorley head pipes don't continue after the cats to the flange where my cat-back begins. I will have killer headers and head pipes, into tiny pipes after the cats to the flange, then it will open back up to my 2 1/4" cat back set-up. I like the fact that the Magnaflow pipe replaces everything to the flange, and it will ALL be 2 1/4" and NEW. Those Thorleys do look sick though, damn.

[randymbtech]

Anyone have a pic of the Thorleys installed from underneath the truck???

[Tigwldr]

Thorleys are your best bet. You can always have the muffler shop replace the smaller diameter pipe with larger like Pauly said.
I dont think you can see what you want, kinda crappy pics.
http://i804.photobucket.com/albums/yy321/992dr/Tahoe%20pics/DSC02326.jpg
http://i804.photobucket.com/albums/yy321/992dr/Tahoe%20pics/DSC02324.jpg
http://i804.photobucket.com/albums/yy321/992dr/Tahoe%20pics/DSC02325.jpg

[Tigwldr]

This is what I did with my mid section. You can see where it bolts up to the mid pipes from the Thorleys.

http://i804.photobucket.com/albums/yy321/992dr/DSC02611.jpg
http://i804.photobucket.com/albums/yy321/992dr/DSC02612.jpg