what are headers going to gain me

grumpyvette

grumpyvette

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Staff member
Junkman2008 said:
Hey Grumpy, you always hear that headers give you more horsepower. How does that work and what formula can you use to determine the horsepower gain that a given set of headers may bring?
Click to expand...

that questions a bit like asking how good a girl might be in bed based on the color of her hair brush, yes theres a mathematical formula , in fact several, but theres a whole bunch of factors that determine the results, like cam timing, compression,cylinder head flow, back pressure,engine displacement , header primary and collector length and diameter,exhaust temps,etc.
the more back pressure the exhaust system beyond the header collectors has the less effective the headers will be, but if you have a low restriction exhaust and a ram tuned intake with a matched cam timing, a tuned header can in some cases produce gains in excess of 60 hp.
as a general rule Id say your safe expecting a 25-40 hp increase in peak hp from good long tube tuned headers over stock cast iron exhaust manifolds that come on most passenger cars, but with properly matched components on a high compression engine more can be gained.

READ THESE

http://victorylibrary.com/mopar/header-tech-c.htm

http://garage.grumpysperformance.com/index.php?threads/calculating-header-design.185/

USE THE CALCULATORS to match port size to intended rpm levels... but keep in mind valve lift and port flow limitations
http://www.wallaceracing.com/runnertorquecalc.php
http://www.wallaceracing.com/ca-calc.php
http://www.wallaceracing.com/area-under-curve.php
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php
http://www.circletrack.com/enginetech/1 ... ch_engine/

http://www.pontiacracing.net/js_header_length1.htm

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

http://www.wallaceracing.com/Calculators.htm

https://robrobinette.com/et.htm

https://www.gregraven.org/hotwater/calculators/qm-from-wt-hp.php

http://www.bgsoflex.com/auto.html

http://www.mk5cortinaestate.co.uk/calculator5.php

http://www.can-of-whoopass.com/index.php?pageID=car_stuff&calculator=primaries


http://forum.grumpysperformance.com/viewtopic.php?f=56&t=495&p=613#p613

http://forum.grumpysperformance.com/viewtopic.php?f=56&t=1303

viewtopic.php?f=56&t=572&p=35352&hilit=rams+horn#p35352

http://forum.grumpysperformance.com/viewtopic.php?f=56&t=185

http://www.chevydiy.com/chevy-small-block-engine-guide-exhaust-systems/

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I find this graph very useful, it shows stock corvette exhaust manifolds vs headers on the same 496 BBC engine dyno test
headersvsman.jpg

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notice coated headers make a huge difference in lower engine compartment temps and the 18" collectors noticeable increase the torque curve

keep in mind headers work by increasing the cylinder scavenging efficiency and noticeably helping the fresh intake charge fill the cylinders, this only works effectively over a fairly narrow power band and both cam timing and header design will effect your results but no header can work effectively if theres any significant back pressure or restriction to exhaust flow

viewtopic.php?f=56&t=495

but what always amazes me is how few people bother to buy and use a simple vacume/pressure gauge to actually test and measure back pressure.
without, testing and having the facts,and knowing what your dealing with it seems foolish to rush out and spend hundreds of dollars on a new exhaust that may or may not solve your problems or to ignore a problem that you can easily test for and verify before spending any money on a problem you can prove is caused by a restrictive exhaust system, basing your parts selection on what your trying to accomplish, and whats required to reach your goal, rather than random guess work seems to be the cheaper route in the long run in my opinion.
drilling a small easily re-welded test hole in the header collector , or an adapter on an oxygen sensor bung gives you access for testing back-pressure
you might be surprised at what a few tests show you and how much time and money you can avoid wasting

you drill a 1/8" hole in the collector to insert a temporary test probe made from 1/8" copper tubing attached to a section of vinyl hose back to the test gauge, angle or point the end of the test probe tube,toward the exhaust exit not the engine, that hole you drill for test access can easily be brazed closed after the test, OR in an ideal world you weld a 1/8" Nation Pipe Thread bung on the collector, so you can test with a removable screw threaded adapter and close the threaded bung with a brass plug when your done, a buddy reads the gauge with the line run into the passenger seat and the gauge or in an ideal world you mount the gauge in the car as a reference for tuning


BTW if youve got one of these nearly worthless (for a true high hp application)fuel filters, that can break and cause a fire hazard,
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if youve ever wondered why Ive suggested no one use the cheap glass fuel filters, its because they are prone to leak, with less than safe results.
engine fire.png

they can be quite useful inserted in the vacume line between the exhaust or intake your testing and the gauge your testing with as they make a rather effective pulse damper or reducer that limits the gauge needle rapidly twitching making it harder in some applications to get a clear reading, anything over 2-3 psi at peak rpm indicates an exhaust flow restriction thats costing you power
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http://www.harborfreight.com/fuel-pump- ... 93547.html

http://garage.grumpysperformance.co...-descriptions-dont-tell-you.12357/#post-61139
 
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nce the engine rpms exceed about 3000 rpm its the inertia or rush of exhaust gas mass exiting through the headers that draws in the majority of the intake charge much more effectively than the outside air pressure forces in the fuel/air charge at idle, Id also point out that even at idle the overlap helps considerably, and remember at only 850 rpm that whole cycle is going on 7 times a second, by 7000 rpm, your filling/emptying the cylinders 58 times a second, you would have greatly reduced power above about 4000 rpm without that exhaust scavenging/overlap

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