First off let me say... Its MY truck and I can do what I want with it. Dont tell me im being stupid, just need a little advice. Ok, so I bought some headers for the truck (I know I know...the 4.3 doesnt benefit much from headers) But I got a great deal with them online at over half off. Next, my buddy is selling me his two flowmaster 40's for $30 a piece. Also, my dad is a welder and my grandpa has a car hoist in his garage and pipe benders. So my question is this... if the two flowmasters are 3" in/out would it hurt the 4.3" Going straight 3" from the headers all the way back? Im assuming the flowmasters are 3". They are coming off of an 04 gto which has the 5.7 v8. Obviously im not spending much here so im going big or going home. I already have a CAI and am planning on doing a performance tune.

Oh...truck is an 01 ZR2

 

You always want to maintain an equal ratio of in to out. Is your intake stock?

 

Dont know where but I think Read somewhere that you dont want to go over 2.5 because of needed back pressure

 

No I have a cold air intake, otherwise all stock. Ive read on this site both ways about back pressure. Some have said you need a certain amount and others say you dont. Going 3" wont cost much extra for me so ill do it if its safe.

 

Keep researching before you start. Like I said I`m not sure. Wouldn`t want to lose any gains made with headers and duals by going up to 3 inch

 

It could be a good experiment. If you keep all your original stuff you could always mix and match your pipes, or go back to what you had pre 3"

 

OK let me help out here, NO! its not a good idea to go 3'' at all! If your under 250hp than 2-1/2 would be max! At 150hp 2'' is best. Now anything above 250hp-300hp than 3'' is fine and of course the more power the bigger the pipes. Now if your going with a dual set up than 2-1/4'' is best. Remember our trucks have only one cat so unless your going catless a dual muffler set up is a waste of money. You can do a single inlet to a double out let (my set up) Or run pipes all the way back and have the muffler as resonators
I hope this helps and post a pic of the headers I'm looking for some just for sound

Also posted a helpful clip below

 

 

Well I do plan on doing some internal engine mods but that wont be for a while. Ill keep doing some digging and see what I can find about 3" for our motors. Probably be going with 2 1/2" though.

These are the headers I got.. 96-01 Chevy S10 / Blazer GMC Sonoma 4.3L Ohv 4Wd Stainless Manifold Header Exhaust

 

As for cats...for the purposes of this forum and not getting this thread locked ill be running cats