hardmansonfan

Hi ....
I have a chevy small block i just had it rebuilt & bored out from 0.30 to 0.40
I want to buy new headers being the old ones are rusted & pitted (no holes). I measured the exhaust holes (oval shaped) on the block i belive they are 1 7/16" or 1 3/8". Im havin trouble finding that size. Is it possible to put on a different size ? Or do i have to find that specific size? I have tryed ebay, summit, ect..... I cant find them please help tanxxx guys ✌🏼️

gerry72

The header flange and pipe diameter will almost never be a precise fit to the head's exhaust port dimensions. Unless anyone is referring to a race head, the pipe will be larger and overhang the port. This is just fine. The one thing you don't want to happen is where the header flange/pipe are smaller or out of position and the port overhangs the flange/pipe, meaning the exhaust gasses hit the flange. You are not going to have this problem. The smallest primary tube you will find is 1.5" and those are not all that common. The most common size is 1 5/8 for cheaper headers and these will be a good fit for your port and usually offer fewer fitment problems. More expensive headers, like Hooker Super Competition, will use a 1 3/4" pipe. Some headers use a 1 7/8 pipe. Larger than that and you have to get port plate adapters.

So, in summary, you are just fine with any header you choose.

NewbVetteGuy

What's the top-end of your engine look like and are your goals geared towards low to mid range torque or high RPM and max HP?


The header diameter you should go with is based upon your build and goals; the more HP, the larger diameter; BUT the general rule is that you'll maximize air velocity and therefore mid to low range torque if you go with the minimum required size. Going too big actually HURTS low end torque and therefore acceleration from a stop.

1 5/8" is a good size for what is called a "mild" build; but from what I can tell the definition of "mild" goes far beyond what I'd call mild up to like 400HP gross.

I'm targeting an eventual top-end rebuild with 400-425hp gross and I'm still going with 1 5/8" because my goals are all focused on low end torque and acceleration and if push comes to shove I'll give up max airflow at high RPM and max HP in exchange for tire burning torque.


Fitment should be VERY high on your list of considerations when picking out headers. If you think you might ever do a Borgeson power steering box conversion or a rack and pinion install, if you have angle plug heads, or might switch to angle plug heads you need to make sure that the header that you choose will fit.

Hooker headers (comp and super comp) are the fitment champions and they seem to work with everything thrown at them, but you'll pay a premium for not having to worry about them.


Many generic "SBC" headers have fitment issues with C3 corvettes so be careful there; you'll likely have to pay the "Corvette premium" for a corvette-specific header to ensure no fitment/ install issues.

Quite a few brands have a pretty intense downward angle on the passenger side, which annoys some people, so choose carefully if that's a concern of yours.

Also lookout for raised port heads and header fitment issues. I have no idea if D-port style heads actually require d-port style headers or not, but they do exist.


If you're on a budget definitely scour a country-wide Craigslist search engine because there a lots of take-outs that get resold for a reasonable price. There's also quite a few budget brands available from summit, jegs, etc... that are reasonably priced and fit well because they're clones of the bigger brand name options.



Adam

NewbVetteGuy

In terms of it actually fitting up to the head; SURE. But there are plenty of other fitment issues to think about.

I might be in a minority, but I don't want to have to "dimple" / dent my headers to ensure clearance.


Adam

Derply_78

I found these links helpful.


http://www.sandersonheaders.com/lets-get-technical.html

http://www.wallaceracing.com/header_length.php

gerry72

Then do as I wrote and get the smaller primary tube diameter. To wit: "The most common size is 1 5/8 for cheaper headers and these will be a good fit for your port and usually offer fewer fitment problems."

As far as clearancing your headers -if that should be necessary- then you'd find this link of interest:

hardmansonfan

Hey guys first off thank you very much for all your help you guys really opened my eyes on information that I did not know.
Secondly this is my first built I also do not know much about engines I am a amateur in Mechanic work, my car will be driven almost every day. If i do race it it'll be very rare that i do that (probaly at a red stop light). Now you guys was talking about 1 5/8 or 1 3/4 is that inside diameter or o.d. ??? (i saw a vid on that thanks to you guys) if so how can i tell what im getting ?? Thank you so much

hardmansonfan

Hey guys i have another question. Its about connecting the collector, I want to know how can I measure the pipe that connects to the collector being that I have the old headers with me and I am not sure if the original headers were the right size from the start. I would like to have the right size "header collector" So i do not have to add any adapters or anything like that. I would like to have it bolt on & play

hardmansonfan

This is what is under my car now that connects to the collector end of the headers how can i measure this ??

hardmansonfan

This is Just to have a idea what i have running




Before

hardmansonfan

"After"



But before last weeks engine rebuild. It also has a holly 4 Barrel Aluminum Street avenger carb "650" & msd 6al-2 ignition box

gerry72

Tube is always measured in outside diameter. You'll know what tube diameter you're getting by the specifications for the headers. Go to Summit or Jeg's and prowl around for some headers and you'll see what I mean. As to the fit to the collector, you'll probably have to farm out some exhaust work to a muffler shop. Unless you replace your old headers with new ones of the same manufacturer and model number, the collector reducer is not likely to be a perfect match to the header flange. Most header collectors are 3" diameter. The 1.5" headers tend to use 2.5" collectors. The large tube -1 7/8" and up- use 3.5" or larger collectors.

hardmansonfan

Ok thanks I was just asking because the pipe that connects to the collector has a flair at the end so I wasn't sure exactly how to measure that pipe so I'll guess I'll just connect the header and then just take it to a shop and have them connect the collectors the correct way

hardmansonfan

Again thank you very much. You guys are awesome any more answers are always welcome thanks