What size headers are best for a 383 where no emissions tests are done? 1 3/4" or larger?

I'm currently running 1 3/4 on mine

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White 92 RS,388 cu.in.N/A
3.73 gears,auburn posi
Best 60 ft : 1.97
Best 1/4 : 12.679
Steve Spohn
Rear Suspension
Autometer guages
Extremely Loud Stereo !
Driven Daily
HOOKER LT's SOON!!! & 4 inch Exh.

1.75" primary pipes are good for N/A 383 or 406.

The issue with the larger engines is the collector and Y-pipe size. 1.75" is enough pipe for one exhaust port, but 2.5" isn't enough for four exhaust ports.
For example the 2.5" collectors on the SLP shorties needs to be increased to 3" and the Y-pipe needs to feed into 3.5" single for the larger N/A engines.
If you add significant RPM or power adder to a 383 then the requirements go up even more. The type of fuel will even make a difference on pipe diameter requirements.
Also the further away from the head the exhaust gets the more the gases cool and reduce in volume which also reduces the pipe diameter requirement. However, if you add obstructions like mufflers or CAT, then the size requirements go back up.
David Vizard uses some good ball-park formulas for predicting exhaust requirements (in CFM) based on CID and RPM. They are just ball-park guesses though because they ignore too many variables like cooling rate and scavenging efficiency. Winston-Cup builders have much more sophisticated methods, but they hardly apply to street cars.

From real-world tests I can tell you that the Hooker 1.75" full lengths with 3" collectors work great on a 383 N/A, and that a single 3" pipe to the back is also a slight restriction.
Hope that helps with your decision.

ODB


[This message has been edited by The ODB (edited February 19, 2001).]

I will add a couple of those hookers to my shopping list. Thanks for the thorough advice.