How much power gain should be expected from a mild 430 with a cam and the addition of shorty headers? What do you expect, because I have no idea. Expecting a 350hp engine if not a little more, so imagine it flowing that much air.....
I also found this quote from JW in 2003: "Headers will always be 15-30 numbers better on both the torque and HP." Probably still true today? Another JW quote: "Don't get me wrong, I love manifolds for some builds.. I just pulled a 375HP 437 for a 67 Riv off the dyno last week.. all iron, all stock, with a 212 cam. No reason in the world to put headers on that motor. Love the nice quiet manifolds.."
On a healthy engine yes, they will pick up some power , the long tube version. Shorties dont offer the same advantages as long tubes But they certainly won't hurt power, you may would see 5 to 10 at peak
5 hp @ 5200 is what they average out to provide, but this assumes that the motor is not already jetted to the lean side of what things should be.
Depends on the combo, if we look at around 500 HP, long headers are about 25-30 numbers HP/Tq on average. Shorties in the test I did, were 8 HP less. On a stock engine, there is little need for any header, because the engine simply cannot ingest enough air to overcome the capacity of the exhaust manifolds. JW
Thank you for the reply. If the cam has a heavier emphasis on exhaust duration (like the 118) would you expect more scavenging to occur? Currently working with a 275/296 adv. 219/238 @ .050 109 LSA .490/.460 grind.
almost all headers improve exhaust flow, depending on how inefficient cast iron manifolds are , will be the deciding factor, shorty's do not scavenge like a long tube header will . but usually , are more efficient than cast iron, but....... once you connect to an exhaust system, everything changes, its like having a 4-5 ft long collector. and it adds back pressure, most headers are designed to work at mid to upper rpm, and it unlikely you would see improvement at idle to 2500-3000 rpm, unless the tubes were smaller and designed for lo rpm , tri-y are a good example of low end headers, (dougs are the only one I remember building them) when people buy/ install big tube headers, it actually hurts low end and mid range power, as its like turning on your garden hose and running it thru a fire hose, there is just not enough water to use that big of a hose. the other issue...... most people do not drive at 4000 to 6000 rpm, yes race cars do, but 99% of street cars spend most of their time in the 2000-4000 rpm range. I'm no expert, but I did work for Hooker headers for many yrs as a designer, and fabricator, and did quite a few of the well know racers of the day, (pro stock)(1970's-1980's)
Good info here. Although it seems to be asked alot, I can never get enough testimony, especially from a header designer. I am building a 500 hp 455, so it's nice that JW used that hp level as a benchmark. I WANT to use stock manifolds for a sleeper look, no leaking, and easy spark plug changes, but I NEED the 17-22 hp that shorties would provide. Sooo.. IF i use manifolds... I want to get that 17-22 hp back. My question is... Do I go electric fans, and no power steering pump ( 3,000 car w/ skinnies ), and no AC compressor?? Does anybody still port manifolds?? Extrude hone?? Any input is appreciated.
A lot has to do with the motors compression and stroke to pump out the exhaust! Old style 426 hemi's stroked to 472 with stock externals in class racing with tons of limiting rules are making 699 hp thru there iron exhaust Manifolds. A undersquare 8.2 comp motor needs a good flowing Exh side way more then the same motor with even just 10 to 1 comp!
https://www.teambuick.com/reference/library/455_ken_bell_php/ I can't get to link but how did long tube headers add .5 sec and 4 mph on a still relatively stock 70 stage1 at this point?
Cut and Paste from Team Buick, Keep in mind this car weighed 3600 lbs. Not really sure these results are realistic though.
The 4.78 gear may have had something to do with it picking up that much, being that the engine was spending much more time at the top of the rpm range, it would benefit more from the headers,...
