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Author Topic: Exhaust manifolds v. Headers?  (Read 4061 times)
sdkar
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« on: February 15, 2007, 08:51:37 AM »

I am installing a 502 motor in my 69 Camaro.  I am up in the air about installing headers or exhaust manifolds.  I like the clean look of a manifold and the ease of installation as well as not having exhaust leaks, burnt spark plug wires and easy access to my spark plugs.  What would the significant different in installing one over the other?  Have headers come a long way and the problems above not as big anymore.

I am either going to go with one of the following and would like opinions.  Thanks guys.

factory exhaust manifolds

http://cgi.ebay.com/ebaymotors/Exhaust-manifold-big-block-w-o-Smog-new-67-68-1969-70_W0QQcmdZViewItemQQcategoryZ33632QQihZ016QQitemZ260084202526QQrdZ1

or
Hooker ceramic coated headers.

http://store.summitracing.com/partdetail.asp?autofilter=1&part=HOK%2D2457%2D1HKR&N=700+115&autoview=sku

Also, it says I can't use ceramic coated headers to break in a motor.  What the heck is that about?
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JohnZ
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« Reply #1 on: February 15, 2007, 11:34:40 AM »

Also, it says I can't use ceramic coated headers to break in a motor.  What the heck is that about?

Because in most "first-fire" situations, the initial timing isn't set properly, the centrifugal advance curve hasn't been mapped and set up properly, the vacuum advance isn't connected (or isn't present on a "hot-dog" distributor at all), and that retarded timing at cam break-in rpm results in extremely high exhaust gas temperature; combine that with no road-speed airflow over the headers, and the tubes exceed the max temperature the ceramic coating can handle. Lots of ceramic-coated headers get fried at "first-fire" due to anxiety to "get it running" without bothering to set up correct initial timing and the advance map.
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sdkar
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« Reply #2 on: February 15, 2007, 12:13:46 PM »

Also, what effect on the horsepower and torque is there between headers and exhaust manifolds? 
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rich69rs
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« Reply #3 on: February 15, 2007, 02:12:16 PM »

As we all know and have heard many times the engine is fundamentally nothing more than an air pump.  At the exhaust, turbulence and backpressure can adversely affect performance, especially at the high end of the power band.

Most headers are designed to improve performance at the high end of the rpm band.  For an exhaust gas pressure pulse to move, the leading edge must be at a higher pressure than the surrounding pressure.  The main body of the pulse is essentially at the surrounding pressure while the trailing edge of the pulse is at a partial vacuum.  As the exhaust gas flow and associated pressure pulse moves through an individual header tube, the pulse loses energy and gas flow slows down.  Once the pressure pulse reaches the collector it no longer has the energy to cause significat backpressure at the cylinder head.  Thus, the next pulse is allowed to enter the tube with little restriction. 

A properly designed exhaust system will take advantage of the vacuum created by each pulse to help scavenge subsequent exhaust gasses from the cylinders. This is one of the primary basics in exhaust header tuning, i.e.  varying the length of the primary header pipe in order to time the vacuum generated by a previous pulse, in relation to cam overlap, to help to pull in a fresh intake charge while completely removing (at least in theory) the residual exhaust gases. 

One of the misconceptions that many have with regard to exhaust systems is “that a larger diameter is always better”.  Primary tube as well as exhaust pipe diameters are optimized (not necessarily made larger) depending on what part of the power band you are trying to optimize.  Larger diameters allow the gases to expand, resulting in gas cooling and a slower gas flow.  In conjunction with a cam with a lot of overlap, this may be what you want for a racing application where the engine is always operating in the upper rpm band. In general, this would not be the way to optimize low end torque.  If low end torque and “cruising streetability” is what you are after, stock exhaust manifolds are not too bad a choice.
« Last Edit: February 15, 2007, 02:25:45 PM by rich69rs » Logged

Richard Thomas
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sam
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« Reply #4 on: February 16, 2007, 05:37:15 PM »

Beings you are not going with an all original stock set up the ceramic coated headers are real nice. They look good and keep the exhaust temps down. I think the performance factor is much improved too. Leaks, Headers and gaskets have come a long way. I would bet no leaks at all with a good set of gaskets. Maybe every couple years you can replace the gaskets. With a good free flowing exhaust system and the tune up that goes with a good exhaust system you will be in real good shape. 500 cubic inches needs to breath and flow the gases. I also agree on the tube size. Don't need the biggest diameter header you can buy for a street motor. I like Hooker Super Comps. Grin
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Jerry@CHP
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« Reply #5 on: February 16, 2007, 11:49:29 PM »

Bottom line is this: the car will run and breath better with a set of exhaust headers.  Case closed.  And even better than headers are the newer design "step" headers made by Cook, Stahl, Davis, Burns, and others.  They have picked up 10-15 horsepower on the dyno over conventional headers.  AND I picked up over 1 mph in the 1/8" mile with them on a stocker Z28 engine.

Jerry
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sdkar
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« Reply #6 on: February 17, 2007, 08:50:57 PM »

Jerry,

what is a step header?  Also, what do you recommend for this type of header for a 69 Camaro with a 502.  I have rack and pinion so the steering box is no longer an issue.

Finally, I am more interested in low end torque and off the line response...not top end.  So if I go with mainfolds how bad am I really hurting the power?

Thank you,

Steve
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Jerry@CHP
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« Reply #7 on: February 17, 2007, 11:31:19 PM »

A step header is a header that has two, three or four different diameters in the tubes as they meet the header collector.  For example, my Z28 engine in the Old Reliable has three step headers.  Off the flange at the head, the tube dia is 1-5/8", it goes about eight inches and then steps bigger to 1-3/4" and then just before the collector, the tube steps to 1-7/8".   This design was created in the ranks of NHRA's Stock Eliminator class.  Remember in stock eliminator, we have a glass ceiling as to what we can do to an engine or the car and we're limited to 9" tires.  Our cars have to be stock therefore; you look in other areas to pick up horsepower.  You look long enough, and spend enough money, you find it.

The latest trend now are the merge collectors with a tri-Y entry into to collector.  Very $$ but more power has been found there too.

There will be a big differnece in performance with headers.  Exhaust manifolds do not flow, especially the Camaro designed manifolds.  The mid year BB Corvette design (1965-1967) exhaust manifolds are far superior to what Camaro-Chevelle used.  They almost look like an exhaust header.

Jerry
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sdkar
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« Reply #8 on: February 18, 2007, 12:38:59 AM »

Where can I find a step header to fit my 69 Camaro.  Do you know which brand and/or part number I should get for a Big Block?

Steve
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hotrod68
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« Reply #9 on: February 18, 2007, 12:57:25 AM »

I agree with Jerry...on any engine, manifolds are like going to a pie-eating contest constipated--you can't expel more than you can take in. Headers--any type--are always better. Exhaust manifolds are restrictive and ugly and do zero for performance, gas mileage, or anything else. On top of that, headers make the engine sound so much better it's unbelievable. If you want to royally choke a 502, then go with manifolds. It will only cost you horsepower, torque, and mileage, if there is such a thing as mileage with a 502. Its a HOT ROD with a 502...chuckle. Get the snake tubes. My 2 cents.
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Jerry@CHP
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« Reply #10 on: February 18, 2007, 09:04:57 AM »

Stahl Headers in York, PA would probably be the best for your application.  Jere Stahl has been building headers since the early 1960's and they fit like a glove.  No issues at all.  This is what I'm running on the Dave Strickler Old Reliable car that I race. 

Call York, PA information, I know he's listed.  Think he's on Mt. Rose Ave.

Good Luck,

Jerry
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sam
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« Reply #11 on: February 20, 2007, 07:06:52 AM »

Stahl Headers, 1515 Mt. Rose Ave. York, Pa.  (717)846-1632 Grin
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Flowjoe
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« Reply #12 on: February 20, 2007, 09:59:10 AM »

Stahl headers are spending but worth every penny...I love mine
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