New/Modified Header Design?

Tech tips and how to's

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Daryl Smith
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New/Modified Header Design?

Post by Daryl Smith »

I posted this on the roadster mailing list and got no response, so thought I would try here for those not following the mail list. I think the 35+ year old header could use a redesign for more performance. Your response is appreciated. Also if you may be interested in purchasing such a header, Let Dean at Fairlady Prod. know, as he has let me know with enough response he will see what can be done. THANKYOU!

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"Part of the incentive for vendors in making new parts, that are better than whats been around, or justifying improving a design, is the promise or commitment of customers to acknowledge and actually purchase the items."


After some study, I have concluded that equal length, certain length, 4-2-1, 4-1 etc., while all have their value for the "absolute top HP/Torque", the two most important factors are the "correct" tubing size (overestimating your horsepower/tube size can cost you!) and a good collector. ( My own unexpert opinion ) (We are really limited with available space.)

What are the chances of getting a header built by your regular supplier, on
the same jig, with 1 1/4" or 1 3/8" pipe, adding about 5-6" ( have to check on collector length/frame clearance) either without a collector, or with a "merge" type collector? Eliminating the resonator/muffler under the driver is a forgone conclusion.

1 1/4" should be good for stock 1500's and 1600's (up to about 90 hp) Do they use the same header?
1 3/8" should be good for modifed 1600's (up to about 110 hp)
1 1/2" (up to about 155 hp)

These three sizes should cover about 95% of what is needed. And should give a noticeable performance boost with a "good" collector.

With these minor modifications it shouldn't (?) be much of an increase in
price, especially without the collector.

I have a 1600 engine that I think I would like to try the 1 1/4" on.

If anyone has anything to add to this, good or bad, I would definately like to hear your opinions.

Thanks
Daryl (serious header issues)

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S Allen
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RE:Headers

Post by S Allen »

Daryl,

I think you are right on the money concerning headers and horsepower. This is a well known fact among many gearheads. I thought Dean replied to you on the "List" regarding feeling out interest. I purchased a 2 liter race header that had a longer than usual collector on it. Darn near went back to the cross member on the frame. The key is generating enough interest. I have a vendor supplied stock header on my stroker and would not mind putting something on that might give me a few extra horses. The roadster pool is not that big and many ideas have come and gone due to lack of response. It never hurts to think out of the box. So, count me interested but it will take a lot more than two of us to get anything going.

Steve
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Post by dbrick »

The trick with headers is not how much HP, but where you want it.
On 4 into 1 style, long primary and short secondary (collector) are for top end power band and a longer secondary are for a lower rpm power band.

This is with an open header or very low restriction exhaust. A small diameter and or restrictive exhaust will negate most of the difference between header styles

A tri Y is generally considered to be a very good compromise.

The quality of the welds and tube joints in the collector make a very big difference in how well the header extracts gasses. Some are really horrible, the one I got from an unnamed vendor is very well done.
Collectors purchaced as seperate items and retrofitted.If anyone wants to cover the shipping they can have my old U20 header to experiment with. Collector welds are crap, but that would be cut off anyway

One option would be to use a standard 4 into 1 header cut it and add this collector. A trip to the dyno and the question is answered.

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Post by SLOroadster »

Merge collecters are a wonderfull thing. I'd be all over a high performance header, ceramic coat it and make it look good, but also pick up some HP due to higher exhaust gas temp, and it will keep the underhood temp down. I refuse to have anything to do with Fairlady products. That is my only thing against it. I think there is quite a bit of power that can be found with a little modern technology. I heard that Classic Datsun Motorsports was trying to reproduce the BRE header, but I haven't heard anything more on it. I have heard that someone in Austrailia was building one that was dyno proven to be a 15 hp gain.

Will
Sorry, I find modern engine swaps revolting. Keep your G, R, or U series in your Roadster!
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Headers?

Post by Daryl Smith »

Steve,
Dean and I have been discussing this via email, I just thought to bring it to the lists.

Dave,
The exhaust "system" as a whole is (as far as I am concerned) is quite under-developed. Many people think that bigger has got to be better, for the header as well as the tailpipe. This simply is not true. Free flowing may be good, but the right size tailpipe (after the header) will keep what was started with the header working properly (scavenging the cylinder) and actually create a vaccuum for the next exhaust pulse. This saves the engine from wasting power pushing the exhaust gasses out.

I have been considering modifying a couple of the old headers to check out different configurations/collectors. Did I understand correctly that you bought and fitted a different collector?

Problem is I need to go down to at least 1 3/8" for the 1600, I would prefer 1 1/4". And I don't think there are any old headers in those sizes, so I have to start from scratch. Might be able to use the flange. Try a slip-fit collector.

Using a calculation from "Scientific Design of Intake and Exhaust Systems" by Philip Smith and John Morrison, the stock 1600 should have 45" primaries, and an H20 with a 270 deg cam should have 60" primaries. (advertized duration used - my notes don't tell me if I should use .050" lift). Less duration means a shorter length. We don't have that kind of room.

I would prefer a 4-2-1 (tri-Y), the stock manifolds were sort of tri-Y, but I haven't found the calculations to design one yet & going with trial and error I would prefer to keep the costs down and modify the existing design, although it could be turned into a tri-Y....

I have to figure out the sizing etc. for the rest of the exhaust. Any notes? Calculations? Tables?.....Anybody?
Thanks
TR

Post by TR »

When people start to talk about exhaust systems and "scavenging" and one pulse pulls the next and that bigger is not better...I start to roll my eyes. Lets really think about this:

Scavenging - There is nothing collecting the exhaust gas at the end of the tailpipe!

One pulse pulls the next - Of course there is a low pressure region behind a high pressure wave, that is the definition of a pressure wave! Does it "pull" the next wave? No, high pressure always travels to lower pressure.

Bigger not better - Take it to the extreme, no exhaust. Sounds like a drag car, right? These guys make money by making horsepower, they put as little exhaust as possible to make the dB limit.

The amount of horsepower a motor can create is governed by thermodynamics and mass transfer. You cannot do much about the thermodynamics but you can increase the mass transfer of combustibles in and wastes out. Provide the "easiest" path in and the "easiest" path out of the cylinder and you get more HP.

And don't rush out to get your headers ceramic coated...Yes, you are keeping more energy in the exhaust gas instead of having it disipate through the header wall, but that heat doesn't turn the flywheel! Unless you can convert that heat into downward motion of the piston, it is wasted.

I guess I have just always had problems with the snake oils and such that make high HP, super efficient engines.

Sid, didn't you once post about someone that tried every "enhancement" at one time, figured he had created a SULEV that got 200MPG???

Now the "One pulse pulls the next" is a glorified way of saying, don't build an exhaust system that makes all of the pulses crash together. This is where some benefit is to be had when stuck with having to have an exhaust system of limited size.

Off the soapbox, TR
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Post by spl310 »

Yeah, he had to get rid of it though. It got annoying having to pull over every hundred or so miles to have the tank drained off...
"Wow, a Roadster!" Stuart Little

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Post by spl310 »

Alvin,

Man, you made me work! I did not realize that I had been so verbose - over 400 posts!! Well, I searched and searched for the thread that TR referenced and here it is:

http://www.311s.org/phpBB2/viewtopic.ph ... light=fuel

Enjoy the read!!
"Wow, a Roadster!" Stuart Little

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Post by dbrick »

I won't try the merge collector, not enough horsepower return for the money. I agree that a 4 inch exhaust on a 4 cylinder is a waste, but a crappy muffler or a small diameter pipe will negate any effort on the header.

WWBSD I was thinking, Bob Sharp was getting paid to go fast, and he did not seem to dwell on the header much, just clean up the exhaust, get rid of the resonator and use bigger pipe. He says only 9 hp on a full race engine going to a header over the stock manifold. I don't know how far BRE went, but they show "Custom built 1 1/2" diameter equal length headers, dumping into 3" collector, exiting ahead of the drivers' side rear wheel." in their specs.


I put three inch exhaust and a race flowmaster on my truck to replace
2 1/2" pipe and rusty factory muffler. No dyno, but I'm driving it harder and getting better mileage, from 11 up to 13mpg. No header, just less restriction. loud as hell, but fun.

Dollar per horsepower, anything beyond a quality 4 into 1 header and clean exhaust may not be worth the trouble and expense. Better places to invest. Synthetic oil in engine trans and rear and a K&N filter with cold air tube would probably gain as much or more rear wheel power than a complete header redesign. Header wrap might help, but cuts header life in half.

I had a friend who raced road bicycles, those guys will spend hundreds to reduce the weight of the bike by a pound. His solution, eat smaller breakfast, use rest room before race and don't wear a shirt. Same net weight savings or more. Spent his money on gearing gatorade and tires.
(engine guy vs. chassis guy at the most basic level)

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Post by Chris Coker »

Ceramic coatings can be very useful, especially with the roadster's exhaust, due to it's proximity to the intake manifold. I forget the exact rule of thumb, but you gain something like 1 hp for every 10 degrees you can drop the temperature of the intake air. Keep the heat inside the header, and away from the intake manifold, and you will gain hp.

A good header design will gain you a few hp, and most racers agree that the header has seen the least amount of R&D in our cars. The catch here, is that everyone's engine combination is just a little bit different, and if you want to maximize your hp gains, each header design needs to be tuned (preferably on a dyno) to that particular combination of cam, valve size, carb modifications, etc.

Regards,
Chris
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Daryl Smith
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Headers?

Post by Daryl Smith »

No Snake oil.
No one is talking high hp or extreme milage. Just a better header/exhaust system for moderate gains throughout the powerband.

I simply see a part of the roadster which could use a little improvement and brought it up to the community. If this is the standard response then I understand why it hasn't changed in 35+ years. As Chris Coker stated the header/exhaust is probably the least developed area of the roadster. I would like to change that. I, like most of the people racing roadsters, could go out and get a custom header built for my car and not care what anyone else is doing. However I thought there might be more than a few others in the roadster community that might share my view.

As always it is a game of compromises when building anything related to automotive performance. As stated By Chris "everyones engine is a little bit different" and would require a slightly different header for "maximum" hp gains.

It would be nice to have a listing where you can go and say " I have this engine with these modifications" and choose a header/exhaust size/system which would be the best "compromise" for your vehicle. Or even some educated guesses to point you in the right direction.
And, hey, for some the stock system will be good enough.

Scavenging: I will stand by what I wrote, although "vaccuum" may be a bit of an oversell (sorry no experience here). The exhaust gasses have mass and they have momentum. they do not simply stop in place when the exhaust valve closes.
Example: Road racing they are all using long tube headers to take advantage of this. Many up to 48" or longer.
The "headers" referred to in the drag race example are called "zoomies" (one short tube for each cylinder) and are really only used on extreme horsepower supercharged engines - Almost ALL others will use a collectored header.

Below are a few websites which have articles on headers, some are self promoting, but all have useful information. Read what you like, believe what makes sense to your background.


http://www.headersbyed.com/common.htm
http://www.ssheaders.com/header.htm
http://www.burnsstainless.com/TechArtic ... heory.html
http://www.chevyhiperformance.com/techa ... index.html
http://www.centuryperformance.com/heatwraps.asp
http://performanceweldingheaders.com/headertech.htm

TR,
I would be VERY HAPPY to read any material you can come up with to promote your point of view.
TR

Post by TR »

Hey Daryl,

I don't think this is the standard response from the roadster community, and please don't count my comments as representing the whole community, I am just one bozo typing away at my PC...

Also, I think there is a group who would be interested in an improved header. This same group would be interested in having their stock exhaust not crack and/or the replacement header not crack, but that is a different story.

However, I would say you are crazy to try to make a header for the masses as roadster owners are very finicky (as is any and every car enthusiast) when it comes to parts on their cars!

I do agree with you and Chris about every engine being a bit different and to take full advantage, the header would need to be specific.

As for scavenging, if you feel exhaust flowing passed your hand at your tail pipe, it is flowing from higher pressure to lower. This takes work to do. Unless you pull the exhaust all the way through the system (have a vacuum at the tailpipe), the best that can be done is to keep the pulses from getting to the collector or an exhaust valve at the same time. The momentum the gas has flowing down the exhaust is nothing compared to how hard it is being pushed out. If there was a low pressure, sufficient enough to "scavenge" (pull the exhaust out of the cylinder), it would also pull (with equal force) the exhaust that is causing this scavenging toward the cylinder - then you would have two flows in the same pipe heading toward each other...That can't be good!

On the other hand, if you can phase in the pulses so that they line up and march down the exhaust in an orderly fashion, it creates the least restriction. Think of cars merging onto a highway, if there is a spot for the car to merge, everyone can continue at speed. If there is a car in the lane then a jam results.

You can really help this scenario when tuned without a muffler (a toll booth after the merge in the above example). But in a low dB world, performance gains are limited.

I don't have any websites to reference, but the "equal and opposite reaction" scenario, that is a fundamental law of physics. Also note that most of those sites (who build damn good product) correctly refer to what they describe as "theory", not fact.

So, I hope I haven't made you feel unwanted here, I was just airing dirty laundry accumulated over years of comments about black hole headers that have such great sucking properties, people use them to pump up bike tires when removed from the engine...

Sorry the laundry was thrown your direction, I hope to meet and have a beer with you at Shasta or Solvang some day...TR
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Post by dbrick »

I join the Bozo with a pc faction. I didn't want to step on anyone's opinion, Just had 15 minutes to kill and an interesting subject.

Got another 15 minutes, so here goes

No doubt there is always room for improvement on any component, I just thought there was a low return for the effort and expense compared to other areas. Granted if the other systems are already optimised, this is the next step.

There is definatly a scavenging effect, same way fuel is "pulled" into the venturi of a carburetor or sand is sucked up the tube of a sandblaster by the air pressure drop. Not sucked actually pushed by pressure differential.


If you were to do the development, what about making up a modular header with slip fit joints, so you could change primary and secondary lengths without rewelding every time? I've had headers for American cars where 1 or 2 of the primary tubes had a slip fit so it could be put in after the rest of the header is installed, didn't leak. For you race guys, could tune for different tracks.

I only wondered how, without a dyno you could tell if you were on the right track. So I looked and found this
http://www.racepages.com/softdown.htm

has a header design program, Whoodathunk??

BTW offer still stands if anyone wants a free header to chop up and play with

Dave Brisco

Take my advice, I'm not using it"

66 2000 The Bobster
64 1500 in pieces for sale
1980 Fiat X1/9
2009 Volvo C-70
08 Expedition EL, STUPID huge but comfy
1962 Thompson Sea Lancer, possible money pit