does size matter

What size header is used with a mild 521 planning on building new header this winder... Now im using 1 3/4 on my 460 but would like to step up to a stroker ...

I ran 2" / 3 1/2" collector on mine.

I ran 2'' with 3 1/2'' collectors on my 460 and had them on my 552 and ran 6.19 in the 1/8 and 9.79 in the 1/4 at 3165# truck. Just built some 2 1/8'' with 4'' collectors fender exit hadn't ran it with them yet but now with the truck lighter at 2940 with me in it really can't say how the bigger headers would have helped. If you do go 2'' headers go with the 460 kit that Speedway Motors sale if you are building them yourself the kit is $149 comes with flanges, gaskets, pipe kit, and new header bolts. I bought my 2 1/8'' header kit from Jegs but it didn't come with flanges I cut them off the old 2'' headers and opened them up to work with the 2 1/8'' pipe and saved about $100 on the 2 1/8 kits I seen with flanges.

Imo, it would have a lot to do with combination and intended use.With A heads I wouldn't use less than 2 1/4 and oem style heads 2 1/8. 2" will work for street use.

2" with 3.5" collector IMO.
That's what I have on my car that has been 5.87 & 9.25 at 3200# N/A with A429 Aluminum CJ heads.

D. Sea wrote:2" with 3.5" collector IMO.  
That's what I have on my car that has been 5.87 & 9.25 at 3200# N/A with A429 Aluminum CJ heads.

I'm running the A429 heads the engine is a 472 with 10.2-1 solid flat cam victor have been running it sense 97..Motor runs great just would like a little more the best pass ever was 11.33 with Dave D slicks been 10.76 on 125hp hit... Been kicking around a 521 build forever just need to get off the pot and get it done... would like a 600hp build that would push my truck 11.00 to 10.80 ... I need to get this going before I blow up the 472 spraying those cast piston to many bottle have been thru it already

With a well matched package I don't see any reason why you can't go even quicker with just the engine.

521 with more compression and the correct combination from front to back (Entire vehicle). Have the heads been ported? What about the intake? Custom cam? Perhaps you could start a build thread and then get opinions when listing your specific goals and what you have as well as what you may need.

In the past I had a very detailed build thread with my combo and fortunately I received a lot of very good advice from friends which resulted in a very well running combination.

Mine is 534 cubic inches with a little over 13 to 1 compression. Nothing real fancy, just very well matched combination.

Good luck and I'd be glad to answer any questions (As well as many other BBF members).

I had a set of hooker S/C headers that were 2" x 3 1/2" and I switched to 2 1/8" X 4" custom race headers and it made no changes in ET or MPH and mine is 12.5 to 1 and a solid roller and a dominator.

I am running a429 heads I just about bet the 1 3\4 are choking the exhaust my 2" was covering some parts of the exhaust ports but my head has had port work done on them. When I built the 2 1/8 headers they just do clear my ports now.

When I got headers for my 514 project, I was told that my mill fell in between 2-1/8/4" and 2-1/4/4" based on my specs and intended rpm range. Also, I am running A429 heads.