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  #46 (permalink)  
Old 01-15-2009, 11:39 AM
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Like I said, interesting thread. I'm sure the originator has the info he needs r.e. which manifolds to use on his '49 p/u as neither headers or corvette ram's horn manifolds will fit.

So I'm just going to make a couple of final comments about the relative merits of headers vs. manifolds. There have been a few comments about the relative usefulness, or uselessness, that in my view need substantiation or at least elaboration. Otherwise, somebody might be influenced to make the wrong choice.

Irregardless of the finer points of header design, if anyone has evidence they can post showing that stock cast iron manifolds will outflow any reasonalby suitable headers at higher rpms, above the peak after which header performance is supposed to fall off rapidly, I'd like to see it.

Because while I enjoyed the discussion of the effect of tube length and collector design on supersonic shock waves, the exhaust gasses also have mass. This also creates its own type of energy. The mass of exhaust gasses crashing into each other in the common chamber of a stock cast iron manifold on the way to the header pipe is not conducive to high rpm flow. The cast manifolds will perform adequately at low rpms, at part throttle, etc., but will be overwhelmed by the sheer volume and mass of exhaust gasses at mid- to higher rpm levels.

On the other hand, both types of energy can be used by headers that are not poorly designed to create more power. A practical example of this is the observation that following their installation "headers induce a lean mix at part throttle and can cost you TQ...."

Yes, they can. But why? Because you have increased the volumetric efficiency of the engine. Due to the header's ability to better scavenge exhaust gasses from the cylinder, more combustion mixture is now drawn into the cylinder. Your 400cid engine that was operating at 70% volumetric efficiency prior to installing headers is now operating at maybe 75%. So effectively, instead of only utilizing 280 cubic inches of available combustion volume, you are now using 300. However, you now have to increase the amount of fuel to match the increased amount of air; that's why it's lean.

I don't see evidence of a header doing a better job than manifols, the job it was intended to do, as some sort of ding against headers. Headers are part of a system; they effect other parts of the system.

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Old 01-15-2009, 12:36 PM
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Originally Posted by BinderDriver
A practical example of this is the observation that following their installation "headers induce a lean mix at part throttle and can cost you TQ...."

Yes, they can. But why? Because you have increased the volumetric efficiency of the engine. Due to the header's ability to better scavenge exhaust gasses from the cylinder, more combustion mixture is now drawn into the cylinder. Your 400cid engine that was operating at 70% volumetric efficiency prior to installing headers is now operating at maybe 75%. So effectively, instead of only utilizing 280 cubic inches of available combustion volume, you are now using 300. However, you now have to increase the amount of fuel to match the increased amount of air; that's why it's lean.

I don't see evidence of a header doing a better job than manifols, the job it was intended to do, as some sort of ding against headers. Headers are part of a system; they effect other parts of the system.

That was pretty well said. In another similar thread I did a no-no and used the "B" word (backpressure)

I think if we were sitting around a table disgussing exhaust systems I would have been dragged into the courtyard and flogged for that

It made me reflect on what might have been more apropriate terminology and Im sure that increased scavanging is part of the story. But I think the bottom line is that headers increase the volumetric "capacity" of an exhaust system and whenever this happens a system that is based on pressure waves is going to use it. Ive seen people use the "B" word and suggest that an engine "needs" backpressure. With that I disagree. However when it is present, (BP) it will effect flow capabilities and that can be viewed as a plus or a negative depending on what you want to do.

I dont know, but I suspect that if we had a well tuned system and then uncaped the headers and ran around town the result would be a motor with more "POTENTIAL" for horsepower and slightly less bottom end and mpg. Of corse the bottom end effects would be relative to the specific power plant.

As for factory exhausts, the way one well educated fellow put it to me was that we should think of exhaust pulses as little balls of energy. Any time they run into turbulence, like the front edge of a manifold, casting defects, tight turns and such, it will break up the balls and creates a disturbance in the flow, hence the effectivness of headers with their smooth straight flowing tubes.

Extrude honing is probably a good idea, another thing Ive heard of to improve cast manifolds is to have them ceramic coated. It gets up inside the parts of the manifolds where we cant get porting tools and will help to smooth out the rough surfaces.

Last edited by 65smallblock; 01-15-2009 at 12:42 PM.
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Old 01-15-2009, 01:08 PM
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Originally Posted by willys36@aol.com
Nope. The pressure pulse (shock wave) with which the header is tuned moves at the speed of sound and is independent of the speed of the flowing gas. The 'compact' smaller tube definitely maintains the energy of that pulse but does not affect it's velocity. Length of the primary tube is the only consideration in tuning the header for the rpm range. Diameter comes into play in balancing maximum signal strength while minimizing friction flow losses. For 4-tube headers the collector only needs to be large enough to provide a volume for the pulse from the individual tubes to be independently reflected back up the tube without interference from the adjoining tubes. When the exhaust valve opens, a positive pressure pulse travels down the tube at the speed of sound. When it reaches the collector, it catastrophically expands sending a negative pressure pulse at the speed of sound back up the tube. You want that negative pressure pulse to reach the exhaust valve just as it is closing which 'supercharges' the cylinder by scavenging exhaust gas out and sucking more unburned fuel in. All during that time the gas is flowing down the tube at a much, much slower speed than all the shock waves. Since the speed of sound is a constant at a given gas composition and temperature, the tuned speed is solely a function of the length of the pipe to allow two traverses of the tube by a shock wave between the time of valve opening and closing.

Tri-Ys use a little different application of this organ pipe or Hemholtz resonator technology but the principle of shock wave @ the speed of sound determining tube length still holds true.

Fairly available suggested reading on this topic are

Huntington, Roger: "Carb Ram Duction", Car Craft, Vol. 14, Num. 5, August 1966, p. 38-42.

Kopper, John B.: "Intake and Exhaust Tuning", Road and Track, Vol. 17, Num. 9, May, 1966. p. 93-98.

Smith, Phillip H.: The Scientific design of Exhaust and Intake Systems, Cambridge, Mass., Robert Bently Inc., 1970.

All the above should show up on ebaY from time to time. The first two are REAL technical magazine articles by educated men, not the ignorant ramblings of the 'tech' articles in modern car mags. Huntington for sure you can take anything he wrote over the years to the bank.

The book is an an exhaustive coverage of the topic and a necessary primer for anyone truly interested in delving deeper into the topic.

I have several technical papers on the subject from ASME conferences but unfortunately ASME destroys all their technical papers after a time period and they are no longer available.
Unfortunately the plot is even thicker as the speed of sound changes with temperature and pressure and if you can find anything in an exhaust header's tubes, it's going to be changes in temperature and pressure. That makes exact design by computation a lot more difficult. Gets back to Smokey's "cut and try" methods.

Bogie
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Old 01-15-2009, 02:34 PM
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You got it Bogie!! Engineers have a lot of sophisticated equations (Actually engieers don't give a crap where the equations come from as long as they work. Physicists are the ones who do the real brainy stuff). However as you point out, it is virtually impossible to come up with an equation that pefectly models the real world. Thus, the major contirbution of the engineer is to add an "f" factor to every one of those sophistcated equations. That factor is an arbitrary number inserted to make the equation work!!
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Old 01-15-2009, 03:10 PM
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Binder,
LOL,,,
I retract that "lean" partial throttle comment....
(it was a wrong/vague choice of words)

but basically and most common,
unless the primary pipes are equal length,,,just some cylinders will be "too lean" at various rpms part throttle costing you power....
that can be a beeetch to tune out.....

add the fact that the carb dual plane intake runners demensions are all different,,,,, working with all the exact same cam lobes,,,,, and it is almost "black magic" that off the shelf headers do make more power...

can't think of a application where headers would be a major NO NO,,,use them if you want to...

my point is look at the whole story

Last edited by red65mustang; 01-15-2009 at 03:48 PM.
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Old 01-16-2009, 08:40 AM
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Binder; I think we are debating a distinction w/o a difference. You are 1000% correct that headers, combined with a reasonably designed exhaust system, will always reduce back pressure over any stock system and that for sure will result in greater VE and more mid-range and top end power. That alone argues for headers.

The above is totally different from the phenomenon I am talking about. If flow loss reduction were the only consideration, headers could be any length, actually the shorter the better for less friction loss. It is the 'Hemholtz resonator' or 'organ pipe' effects that come into play in doing a technical design on a header. Here is where pipe length, diameter etc. become important parameters. And it is this phenomenon of extreme instantaneous pressure pulses which yields power increases above what one would expect from a steady-state flowing system at certain, designed engine speeds. However, the same phenomenon can cause reduced power at certain rpms. As I said before, I have never seen a header vendor show his power/torque curve below 2000rpm. In the lab tests I did on college, I found that a header designed for peak boost @ 2500-3500rpm suffered a torque and power loss compared to a stock system @ ~1500-1800rpm. If you are running an engine at those low speeds, it will be slightly less efficient w/ headers because friction losses are low due to low gas flow rates and the pressure pulses are arriving at the valves at undesirable levels. Conversely, if you run it in the designed power range, it will be significantly more efficient and powerful.

In virtually any engine parameter, if you get gains in one area, you suffer losses in another (induction systems, ignition, cam shaft design, compression ratios, exhaust systems, you name it). Stock exhaust systems specifically design out this pressure pulse phenomenon and are happy with better low end but worse top end performance since most of their customers spend their lives @ the former condition. Give me a stock car and put me up against a ####hp motor with an cam @ 350deg duration, A couple winds of overlap and an inch or two of lift and let us race to the local 7-11 and back (observing the traffic laws all the way of course) and I will wipe the street with him. If for no other reason, he will need to stop A 7-11 and refill his tank! Put us on the drag strip and I will need an immediate transfusion and any other life support help I can get!!!

For sure anyone wanting a more powerful engine and good top end performance, MUST convert to headers. However they MUST also design those headers for the speed range they want the most improvement. Someone wanting a relatively low speed, tow, cruise, never-raced car might be better served leaving the stock stuff there.
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Old 01-16-2009, 11:12 AM
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Willys,
determing those low rpms numbers is where a DD is soooo helpful...
you can scale it to whatever rpms...
(carefully input the variables and you should get darn close to real world results)

did a "quicky" input example just for illustration:
stock sbf 5.0 "HO" carbed motor with 700cfm (overkill) free flowing muffler exhaust system:

stock sbf cast iron "log" manifolds at 1500=64HP/227TQ
1-1/2" x 38" x 2.5 collectors headers at 1500=66/232TQ

even multiplied by the tranny and rear gears,,,you can't "feel" a 5ft/lbs gain at the flywheel in a 3400lb car...

"if" I went thru and entered every last motor tuning variable combo possible (cam advance/carb spacer/timing/whatever),,,I might-maybe (????) be able to tweek it up to a 5% gain, 238ft'lbs at 1500 with headers...
"but" the stock manifolds would also show improvement!!!

edit:
forgot to post,,,
stock manifolds =220HP/267TQ peaks on that illustration
the full length headers=239HP/286TQ peaks
yup, the do work at the cam rpms peaks....

Last edited by red65mustang; 01-16-2009 at 11:29 AM.
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Old 01-16-2009, 11:44 AM
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From Vizzards book a few pieces of info I found rather interesting. Here he is talking about using Iron manifolds with some porting done to them;

"On engines in the 280-350 hp range, it was common to pick up at least 10 hp, with 15 being the norm, and on one occasion I saw as much as 22. I have to stress @ thins point that the porting done was only basic."

And oppisite of that page there is a graph titled "Headers vs stock manifolds" where he ran the same '81 camaro with both stock iron and headers, quote; "This represents an increase of 16 HP and 22 ft lbs of torque".

Nearly identical results as the above comparison with just porting!

In another place he clearly states that Profesionaly worked cast manifolds produced about 65% of the gains possible by using typical race headers on "the types of motors we're dealing with here".

"The types of motors we're dealing with" ...... I take that to mean the 400-500 hp engines that the book is geard toward. Soooo, If we read between the lines, one might conclude from this that a set of ported iron manifolds on something up to 350 hp would do extremly well, while higher horsepower engines exceeding 400 hp can expect a bit more gain from headers as opposed to ported iron.

Last edited by 65smallblock; 01-16-2009 at 11:56 AM.
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  #54 (permalink)  
Old 01-16-2009, 12:56 PM
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Quote:
Originally Posted by 65smallblock
From Vizzards book a few pieces of info I found rather interesting. Here he is talking about using Iron manifolds with some porting done to them;

"On engines in the 280-350 hp range, it was common to pick up at least 10 hp, with 15 being the norm, and on one occasion I saw as much as 22. I have to stress @ thins point that the porting done was only basic."

And oppisite of that page there is a graph titled "Headers vs stock manifolds" where he ran the same '81 camaro with both stock iron and headers, quote; "This represents an increase of 16 HP and 22 ft lbs of torque".

Nearly identical results as the above comparison with just porting!

In another place he clearly states that Professionally worked cast manifolds produced about 65% of the gains possible by using typical race headers on "the types of motors we're dealing with here".

"The types of motors we're dealing with" ...... I take that to mean the 400-500 hp engines that the book is geard toward. Soooo, If we read between the lines, one might conclude from this that a set of ported iron manifolds on something up to 350 hp would do extremly well, while higher horsepower engines exceeding 400 hp can expect a bit more gain from headers as opposed to ported iron.
Interesting. I am not familiar with his work. He must be getting those gains through the reduced back pressure route, he obviously isn't improving the tuned aspect of the manifold. Also need to know where those power numbers are kicking in. Surely there is a point at the top end where he finds the iron pipes will fall off the table compared to free-flowing pipes. Again this all ignores the resonator tuning gains which is a header's claim to fame. In short, it's a complicated solution but only starts to really matter at the upper end of the rpm band.

Red; You used 'street' length primary tubes in your header example which should perform better than the stockers at low Rs. 38" pipes are correct for the 1800-2400rpm range. Try those dyno runs with too-short, too big headers like 90% of the vendors sell. Plug in 25" long primary pipes @ 1 3/4" and run them at 1500rpm. I have a copy of DD but am too lazy to to the deed myself!! Also, I don't know what calcs DD uses for the resonator affect - my guess is that it is a simple analog equation which works well in the middle of the parametric range (i.e., 2000rpm-6000rpm)but probably struggles at the boundaries.
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Old 01-16-2009, 01:21 PM
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"Interesting. I am not familiar with his work."

Thats too bad, you really should remedy that.


"He must be getting those gains through the reduced back pressure route, he obviously isn't improving the tuned aspect of the manifold. Also need to know where those power numbers are kicking in."


What do you mean "where they are kicking in"? They are peak HP #s from basicaly stock motors. The headers vs stock manifolds graph shows them both peaking @ about 4500 r's. About what you'd expect from a stock 350.. Whats the point?



Surely there is a point at the top end where he finds the iron pipes will fall off the table compared to free-flowing pipes.


I already gave you a good idea of where that will happen. 350 hp will require a certian amount of cfm whereas 400-500 and more hp will require more flow. The rpm level @ which peak HP occurs will be relative in reguards to HP, dispacement, flow capabilities etc. An exhaust system that will support 500 hp is an exhaust system that will support 500 hp reguardless of how you get there..



"Again this all ignores the resonator tuning gains which is a header's claim to fame. In short, it's a complicated solution but only starts to really matter at the upper end of the rpm band."


I thought it sounded pretty simple but your analogy is giving me a headache.. And here I thought that free flowing attributes and bigger pipes were a headers claim to fame. Silly me..

FWIW, youve got my .02c.. Others can draw their own conclusions.

Have a great day..

Last edited by 65smallblock; 01-16-2009 at 01:33 PM.
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Old 01-16-2009, 01:40 PM
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Willys,
I did plug in some wrong headers combos (30"long or 1-3/4 pipes, etc),,,didnt post them because they are all close results at only 1500
(yeah I'm lazy also and only type with two fingers!!!)
I picked that motor package to try help hedge the low rpms calculations errors,,,Ford heads are biased for low end TQ....

I went back and plugged in shorty (unequal length production style) headers on the same model
1500=65HP/229TQ,,,226HP/273TQ

then I plugged in "stream lined-improved" stock manifolds
1500=65HP/229TQ,,,,226HP/273TQ
(double checked, numbers just happen to be the same)

which given the ford versus chevy heads I/E flow ratio differences does basically agree with Vizards very roughly 3-4% improvement,,,
(I maybe-probably could tune the motor variables in the DD to reach 10HP/10TQ gain with the improved stock exhaust manifolds,,,but would lose more than the small gain at 1500)

Last edited by red65mustang; 01-16-2009 at 01:56 PM.
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Old 01-16-2009, 01:52 PM
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David Vizard's personal web site is www.gofastnews.com
There are days of his technical information on that site.

In my own words, not from his site.

DV is a graduate engineer with almost 50 years of performance engine building experience in every venue of racing and street performance.
He has done special cam research for major companies such as Crane, etc. and is a consultant with major racing car teams.
DV teaches engine engineering at UNCC, University of North Carolina Charlotte, and maintains a fully functional and fully staffed dyno facility that works 6 days a week on special projects. Yes he drives a hot rod car. Be careful of smiling old guys in hot rods at stop lights.
He regularly writes for PHR Magazine.

DV holds patents for innovative designs and is one of the most highly respected engine builders and engine engineers in the world, and is well respected in Europe and around the world.
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Old 01-16-2009, 03:36 PM
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Thats too bad, you really should remedy that.

As you can probably guess, the world is jam-packed with stuff don't and never will know!!

What do you mean "where they are kicking in"? They are peak HP #s from basically stock motors. The headers vs stock manifolds graph shows them both peaking @ about 4500 r's. About what you'd expect from a stock 350.. Whats the point?

Oh, I usually have no point. Just rambling I guess . . . . It's that darn Partzheimers!!

I already gave you a good idea of where that will happen. 350 hp will require a certain amount of cfm whereas 400-500 and more hp will require more flow. The rpm level @ which peak HP occurs will be relative in reguards to HP, dispacement, flow capabilities etc. An exhaust system that will support 500 hp is an exhaust system that will support 500 hp reguardless of how you get there..

Please forgive my impertinence. I'll try to do better next time.


I thought it sounded pretty simple but your analogy is giving me a headache..

A lame attempt at humor. Sorry for the slip.

And here I thought that free flowing attributes and bigger pipes were a headers claim to fame. Silly me..

Nope, free flowing is a side benefit but a tuned header's claim to fame is the Helmholtz resonating effect. Otherwise, no need to care if the tubes are equal length or any particular length at all.


FWIW, youve got my .02c.. Others can draw their own conclusions.

That is one thing we agree on - I am the worlds foremost authority on my opinion!!
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Old 01-16-2009, 03:45 PM
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Quote:
Originally Posted by red65mustang
Willys,
I did plug in some wrong headers combos (30"long or 1-3/4 pipes, etc),,,didnt post them because they are all close results at only 1500
(yeah I'm lazy also and only type with two fingers!!!)
I picked that motor package to try help hedge the low rpms calculations errors,,,Ford heads are biased for low end TQ....

I went back and plugged in shorty (unequal length production style) headers on the same model
1500=65HP/229TQ,,,226HP/273TQ

then I plugged in "stream lined-improved" stock manifolds
1500=65HP/229TQ,,,,226HP/273TQ
(double checked, numbers just happen to be the same)

which given the ford versus chevy heads I/E flow ratio differences does basically agree with Vizards very roughly 3-4% improvement,,,
(I maybe-probably could tune the motor variables in the DD to reach 10HP/10TQ gain with the improved stock exhaust manifolds,,,but would lose more than the small gain at 1500)
That's what I thought. DD doesn't have a very rigorous algorithm and it really doesn't matter since it doesn't make much difference what exhaust you use at normal cruising rpms except stock ones will never hurt the small amount of HP there where tuned headers could have a slight boost or degradation depending on the tuned range.
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Old 01-16-2009, 08:03 PM
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Originally Posted by willys36@aol.com
Interesting. I am not familiar with his work. He must be getting those gains through the reduced back pressure route, he obviously isn't improving the tuned aspect of the manifold. Also need to know where those power numbers are kicking in. Surely there is a point at the top end where he finds the iron pipes will fall off the table compared to free-flowing pipes. Again this all ignores the resonator tuning gains which is a header's claim to fame. In short, it's a complicated solution but only starts to really matter at the upper end of the rpm band.

Red; You used 'street' length primary tubes in your header example which should perform better than the stockers at low Rs. 38" pipes are correct for the 1800-2400rpm range. Try those dyno runs with too-short, too big headers like 90% of the vendors sell. Plug in 25" long primary pipes @ 1 3/4" and run them at 1500rpm. I have a copy of DD but am too lazy to to the deed myself!! Also, I don't know what calcs DD uses for the resonator affect - my guess is that it is a simple analog equation which works well in the middle of the parametric range (i.e., 2000rpm-6000rpm)but probably struggles at the boundaries.
If you want to see a dyno chart of the professionally modifed manifolds Vizard mentions in his book vs. stock manifolds, here's a link:

http://www.castheads.com/log_systems.php#dyno_chart

It's at the bottom of the page. When Brzezinski does his modifications he also welds deflectors inside the manifolds.

I think its a sign the thread has gone on too long when sources & data discussed on page 1 are rediscovered on page 4.
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