what size primaries do i need?1 7/8 or 2 inch?i have dart iron eagle heads with big ports.

depends how crazy the combination is, I like 1 7/8 tubes for anything slower than mid 10's(650hp). bigger tubes for the higher hp stuff.

This may sound overly simplistic, but how big are the exhaust ports on the heads? You want tubes that don't block those carefully designed ports.

All BBC ports are basically the same size. They differ in shape and location (Round, square, W, D, and raised). A smaller tube will fit better and if running mufflers will do just as good a job as the larger tube. If you're building a drag car to run only open exhaust you want the biggest tube size you can find (favors WOT use) and cut off anything that gets in the way of the tube or collector with a torch.

It is because of this restriction on the exhaust side that Chevy runs a split duration cam with the dual pattern favoring the exhaust side. I personally think the W port was the best design then the D port then the round but everyone who casts heads still centers on the square.


Larger Dave

what size primaries do i need?1 7/8 or 2 inch?i have dart iron eagle heads with big ports.

Headers are like any other engine part, you need to select the part that performs best in the range of rpm's that you operate in. You don't want a set of 9-second headers on your 13 second car.

my heads are dart iron eagle.can i use 1 7/8 on the huge ports?will it damage the head?i would not think so but i need to know.

Disagree with Larger Dave above,..exhaust ports ARE NOT basically the same size for all heads.

But again, you need to find some tubes that won't block any of the exhaust port. Some tubes have a more square opening,..some are round. Go to your speed shop and witness all the different port shapes and sizes for different head-to-header gaskets for BB's. You could start by measuring the inside diameter of the widest part of the exh. port opening on your head.

After picking headers that match the exh. ports, find a set of tubes that fit.

On a 496, I'm running 2" Hookers, part # 2205-1 (the -1 is the coated version) and they fit great. These tubes have a square-ish opening which perfectly fit over the exh. ports of my GM Performance O-port heads (these are the same heads as Edelbrock's but branded by GM,..I think Edelbrock calls them "rovals"). The exhaust port is somewhat "D" shaped.

You might call the company who makes your heads,..see if they have a recommendation.

FWIW...

Fwiw, the late John L. used to say that for mild up to 496 BB's, a 1.75" tube would be fine b/c they build torque so weigh all the comments!!

I put them on my 496 for grunt too.

pdq67

will 1 3/4 headers hurt my heads?what about 2 inch tubes into 3 1/2 collectors and 2 1/2 full exhaust?

One of the largest errors street enthusiasts make is in running too large of a primary pipe, and too large of a collector. For example, NHRA and IHRA Stock teams using Burns' headers in H/SA in traditional small-block powered musclecars are running 1.5-inch diameter primary pipes- much smaller than many street machines are trying to use.

You can use the 2" headers with the 3.5" collectors and your motor will run just fine, down on power but it will run. Necking the collector down to 2.5" will reduce the area by 50% and create a large disruption of the wave action. Scavenging will be minimal. Here's a link the the article I quoted:

http://www.popularhotrodding.com/tech/0310phr_jack_burns_exhaust_manifold_header_tech/

I think its easier to find a good quality 2" header than a 1 7/8 for a big block.Either way your OK. Stay small and you'll make more power.Ive recently stepped down on 2 of my cars from 2 1/8" to 2" and picked up ET and MPH on both !! 454 and 496 motors with 12+ compression !!! Hooker competition headers are great quality for the money !!!

I've got el'cheapo FlowTech 1 7/8" headers in my 67 camaro, they fit great and I have no complaints. if your heads have massive exhaust ports then you may need to use bigger tubes so as not to intrude on the port opening, but try to stay as small as possible on primary tube size if its a street car. I know plenty of guys that are using 2" tubes on street cars simply because they couldnt find 1 7/8 to fit their cars. a freind of mine actually ran 10.78 @ 127 in a 56 chevy 468" ported stock heads(by me) using 1 3/4" headers - which cover the corners of the stock square ex ports!!.

i have dart iron eagle heads with big ports.


They are not "BIG" ports.I run merlin Aluminum heads and the ports on a set of 2" hooker competition headers are bigger than my cylinder head ports.
I'm sure any header he chooses will be fine against his heads.

they look big to me.