headers / exhaust manifolds?

-These motors were incredibly choked down at the factory. The logs/2"pipes are a tragedy on a performance motor, the manifolding is fair, the carb is tiny and the cam was mild, particularly the early 70 version. Best rpms are not even 5000 and the engine can spin much higher than that and hold together, even with a 100% stock bottom end. 

-I politely disagree with the statement that the manifolds are not important on a street motor. With stock cam and such as above, MAYBE they are barely adequate. However, a mild cam upgrade and a larger carb alone and you would quickly outstrip the flow of the logs. You don't have to go too much farther to outflow the free flows either. My car sees 5500 to MAYBE 6000 rpms and it definitely needs the headers. As mentioned above, the performance difference is noticeable. 

-The main issue is that there is limited availability of good headers. You don't hear the Chevy guys griping like this because they can get affordable, good quality headers. Now we can get good ones, just not cheaply! 

-Your only choice if you care about stock is the factory logs. The only other choice is (arguably) the Thorley group 19 headers, if you can find a set. 

My personal suggestions is that if your engine is dead factory stock, go with logs. If you care about performance, go with headers but spend the money to get good ones with matching pipes. And BTW, if you have ANY upgrades such as cam, carb, or ANYTHING else performance oriented you will need to have 2-1/4"  or 2-1/2" pipes. Increasing flow at the manifolds is useless with 2" pipes. 

-The free flows (plus larger pipes of course)are adequate for moderate performance work, ie a few bolt on upgrades to an otherwise stock engine. They look good and have good ground clearance. 

Just my opinions from observing various engine combinations with different pipes and mufflers. Other results may vary!

Chris 

 

Massaged Freeflows - 366hp/401tq

Edelbrock shorties - 368hp/411tq

Long tube headers - 382hp/430

Long tube headers seem to be in a bit different category than the ff's or shortys. They have better scavenging and the seat of the pants feel gives a definite advantage in the mid range. If you are willing to spend the money and give up a bit of ground clearance then they are the way to go. However, at below 5000 rpm I doubt there is a huge advantage to them, other than the mid range boost. 

Don't forget the rest of the pipes and mufflers. A friend of mine put a set of headers on his SC/360 back in the day and got no performance increase at all with the stock 2" pipes UNTIL he uncorked them and he got a HUGE difference with open headers! Similarly, I went to straight through type mufflers from stock types and gained .7 seconds in the quarter mile with no other changes. Lesson, the system will only flow as much as the weakest link. 

I would use free flows, 2-1/4"+ pipes and straight through mufflers. It does not sound like your engine is carrying a hairy cam or wild induction system so likely that will be enough. You will have a stock-ish look, good flow and a nice sound, plus no header issues like leaks or high cost.

Chris