calculating header design

grumpyvette

Administrator
Staff member
popular hotrodding said:
http://www.popularhotrodding.com/tech/1 ... ength.html

Tube Diameter

To decide on the right primary tube diameter, there are numerous formulas used in the design of race headers, but for a street car, Don Lindfors of PerTronix (makers of Doug’s, Patriot, and JBA headers) says the following is a great rule of thumb: 200-325 hp look for 1.50-inch diameter primaries, 275-425 hp use 1.625 inches, 400-500 hp use 1.75 to 1.875 inches, and 500 hp and up look for 2 inches or bigger. If you’d like to get more specific, keeping in mind that smaller diameters set a lower limit on peak torque, a 300hp motor could use 1.5- or 1.75-inch primary depending on whether you want the torque at a lower rpm, or to allow it to keep moving higher at a higher rpm. Just a .25-inch increase in primary diameter will push the torque peak up by about 700-800 rpm.
Flowmaster Scavenger Series Collectors Flowmaster’s retrofit-style 4-2-1 Scavenger Series “C” Collectors are inspired by the high

We know many hot rodders like hard numbers, so if you’d like to get as specific as possible and try to size your primary tubes to work effectively within a specific rpm range, try these formulas out:

Primary Pipe Area (PPA) = (peak torque RPM ÷ 88,200) × 1 cylinder ci

To find the PPA, we use A=πr²
For a few common header sizes, this is:
1⅝ = 2.07
1¾ = 2.19
1⅞ = 2.53
Exhaust Flow By separating the ports from one another in a true header, exhaust velocity is maintained

For example, for a 350ci engine with a peak torque goal of 5,000 rpm:
PPA = (5,000 ÷ 88,200) × 43.75 ci
PPA = 2.48

To see what the theoretical peak torque rpm of a certain set of headers is for your particular engine, just rearrange the formula:
Peak torque rpm = (PPA × 88,200) ÷ 1 cylinder ci
1⅝ (2.07) = 4,175
1¾ (2.19) = 4,415
1⅞ (2.53) = 5,100

So theoretically, our fairly high-winding 350 with a peak torque of 5,000 rpm should run a set of 1⅞-inch headers. But if your street-oriented 350 makes peak torque at a more typical 4,000 rpm, a set of 1⅝-inch headers would make more sense.

Primary Tube Length
Small Block Chevy Headers Flowmaster These long-tube small-block Chevy headers from Flowmaster are a traditional design, but fe

How long should your primary tubes be? In most cases, this one is going to be mostly dictated by your chassis constraints and emissions considerations on a street car, and what is available in the aftermarket for it. In general, the ideal overall length of the primary header pipe is governed almost exclusively by the target engine’s rpm range. Typically, a lower engine rpm range likes a longer primary pipe, while a high-rpm engine prefers a shorter primary. Also, the longer the primary tube, the greater the emphasis on torque production below the peak-torque rpm of the header. Making the primaries shorter will slide the emphasis above the peak-torque rpm. So, with slightly different length primary tubes you can actually tune the engine’s powerband, and increase torque at a slight cost of peak horsepower.

More esoterically speaking, primary-tube length also works to control the timing of the exhaust pressure wave that is travelling near the speed of sound. Some of that pressure will exit the collector through the exhaust pipes, but the remaining pressure wave will reflect back up the primary tubes with a negative pressure. This effect is called scavenging. Lindfors explains: "The idea is to time this negative pressure wave to coincide with the cam overlap so the low pressure helps draw the incoming intake charge into the cylinder for more complete filling of the cylinder while at the same time pushing out any residual spent exhaust gases. The timing of these events is mostly controlled by the length of the primary pipes in the header design."

Much like length, there are several different formulas to calculate a theoretical ideal length for a header primary tube.

One example is:
Primary Tube Length = [(850 × Exhaust Duration) ÷ RPM] − 3
Hedman Shorty Headers Shorty headers, like this Hedman system for fourth-gen F-bodies, are designed as a well-cr

Exhaust Duration = 180 + the number of degrees before bottom dead center (BDC) that the exhaust valve opens

RPM = the engine speed we are trying to tune the primary length for

For example: the exhaust valve opens at 60 degrees BDC, so the exhaust duration is 60 + 180, or 240

Using the same 350ci engine running in the 5,000-rpm range from before:
Primary Tube Length = 850 × 240 = 204,000, then 204,000 ÷ 5000 = 40.8, then 40.8 − 3 = 37.8 inches
Canister Style Collector The top illustration shows the turbulence inherent in straight-cut primaries dumping into

So a good starting point for the length of the primary tube (as measured from the back of the exhaust valve to the collector (not the exhaust port) should be around 37.8 inche
 

philly

solid fixture here in the forum
that little snippet from PHR explained a whole lot in a very short timeframe. thanks for that, grumpy
 

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
autowiz said:
....................

but hey, while I have you here with all of your awesome graphs n stuff, can answer this question that has been bugging me for a while, now?............. do you think primary sizes on longtube headers less important on engines with cams with 117.5 or other insanely wide lsa?

THATS APPLES VS ORANGES TO SOME EXTENT
the wider LSA (GIVEN EQUAL DURATION OF COURSE ) will reduce the overlap and kill off most of the effective exhaust scavenging, as theres less effective TIME for the lower exhaust pressure wave to pull the intake charge through the cylinder, but keep in mind the exhaust gases are forced out by the piston as it reaches TDC while INTAKE gases are PUSHED in by outside atmospheric pressure, and sucked in by exhaust gas inertia exiting the cylinder. the pipe size is usually calculated by the required exhaust flow rate and cylinder volume.
READ THE LINKS CAREFULLY
http://garage.grumpysperformance.co...-calculators-and-basic-math.10705/#post-50173

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

http://garage.grumpysperformance.co...lsa-effects-your-compression-torque-dcr.1070/

http://garage.grumpysperformance.co...ful-exhaust-valve-size-and-header-info.11265/

http://garage.grumpysperformance.co...ipe-diam-for-your-application.1730/#post-4310

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

http://www.rbracing-rsr.com/lovellgascalc.html

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

http://garage.grumpysperformance.com/index.php?threads/building-custom-headers.961/

cycl51.png

lsadig.jpg

lclcomp.png

pistonposition2.jpg

GLOWING RED HEADERS

think it through ...thats USUALLY the result of a good deal more HEAT exiting the engine in the form of HOT exhaust gasses,exiting the cylinder and entering the headers..
hot exhaust gasses result from either overly lean fuel/air ratios
OR
a retarded ignition timing, that delays the burn of the compressed gases, and allows still burning fuel /air mix to exit the exhaust port.
OR
cam timing that is causing very effective cylinder scavenging that allows some of the fuel/air mix to enter the headers after passing through the cylinder , as inertia drags it out following the previous exhaust gases ,before the exhaust valve closes.
OR
very rarely miss firing injectors throwing excessive fuel
honestly a bit of basic engineering and thinking about a cause and effect relationship and a bit of testing can go a long way toward isolating a logical search for any problem.
 
Last edited by a moderator:
8

87vette81big

Guest
Autowiz is mechanic too Grumpy.
They don't pay us as well as most people think.
 
8

87vette81big

Guest
Shop owners make the big bucks.

At least think Autowiz is reading and researching.
 

NewbVetteGuy

Active Member
I think this video is amazing as it shows the 1st, 2nd, and 3rd "reflected wave", but instead of showing it inside of an exhaust system or an intake runner it shows it inside a sewer tunnel after an explosion is set off. Helps to visualize the intake / exhaust wave tuning concept for me, anyway... :
-It's really easy to see how each progressive wave decreases in intensity, just like in the exhaust and intake, too.

The Fuelling-like "anti-reversion baffle" is shown for a second in this thread way above, but I think it's worth covering "anti-reversion mufflers" a bit more in this thread. So many circle track racers swear by them, and with too many people buying oversized headers, they seem like they could be $200 well spent for many people who just bought headers with too large of a primary inside diameter...

I know David Vizard and "Cyclone" used to sell "anti-reversion cones" that went in the end of the muffler, but they were known to limit peak power and everyone else seems to have gone with a Fueling-like AR chamber. I believe that John Grudynski @ HyTech has the rights on the original Fueling Patent now; last I checked the ones he sells are designed for a custom header builder to install on a set of racing-style stepped header and they have the Fueling chamber at the 2nd step. -I have heard that this type of anti-reversion device is most effective the closer it is to the head, so this DOES seem like the ideal place to put it. -Last I checked they were $25 each, so for a V8, there's +$200 of expense to your custom header, unless of course you make your own.

-I'm guessing the cost and "pain-in-the@#$#-ness" of AR chambers built into the first header step is why most folks just buy an "AR Muffler" type AR device.

Hendren Racing designed these, they were made by DynaTech for a while, I see them sold directly on the www.CrateInsider.com site. It seems like MANY circle track guys run them and many circle track supply sources carry them.

I believe the 3" collector version is typically recommended for a 602 circle track crate motor and the 3.5" collector version is recommended for a 604 crate.

Crate Insider dyno tested them and found on a 604 crate engine they increased the torque between 2,500-4,500 RPM by 15-25 ft lbs. The guideline from Crate Insider was that the longer the primary is the closer you want the AR muffler to the collector; shorter primaries like 12-14" before the AR muffler.

As a reminder a 604 crate is a 383 with a 275/280 adv duration, 208/221 @ .050", .474"/.510" lift CAM on a 112 LSA and with a 1.5:1 rocker ratio. -My understanding is that with larger durations and tighter LSAs reversion gets worse and the potential down-low gains of an anti-reversion muffler get bigger with a simple, older-style 4:1 collector.

The purpose is to "prop up" low to mid range torque as you get a bigger cam or any engine with more reversion.

My understanding is that high-velocity headers / exhaust systems like "appropriately small" TRI-Y's and headers with modern merge-collectors with merge spikes, already have built-in anti-reversion from their high-velocity nature and will leave less to be gained from an AR muffler.

(If you've bought headers a size or two too big for your engine size and RPM goals, the anti-reversion mufflers make particular sense to me.)
-I see tons of C3 Corvette guys just heading straight for Hooker Super Comp 1 7/8" headers for their 300-400 HP small blocks and I just think of the "Reversion Factory" engine they're building. Fitting an AR chamber on the side exit headers seems like a non-starter and even if you could make it happen it would look ridiculous. At least the rear-exist exhaust system header guys who go a size or two too big might be able to spend $200 to bandaid their poor choice in header size with an AR muffler???...

The CrateInsider AR mufflers from Hendren are $99 each https://crateinsider.com/anti-rever...cing-engines-priced-per-each/#product-reviews


1652308665504.jpeg



Adam
 
Last edited:

NewbVetteGuy

Active Member

That's SOOO true! My Profiler SBC heads are definitely a worst-case scenario for header fitment. They're D-port, RAISED (.250"!!), AND for some unfathomable reason, Profiler decided not to center the bolt holes on the now raised port, but keep it in a stock location. -> That means that for any 1 5/8" header you have to not only port it wider if it's not a D-port design, but you have to weld in the bolt holes and drill new ones to scoot the header up so it's not blocking the highest velocity air at the top of the port!

I was happy to find that SPDEXHAUST.COM sells a custom flange for my heads, but very discouraged to find that none of the big header companies that sell headers for my car, will even let me PURCHASE these flanges and send them to them, to have them build a header using the flange that fits... (ARH sells VERY NICE, "top-shelf" $1,100-$1,300 304 stainless headers for my car, but they won't build their typical "shelf-header" using a supplied flange for your heads, so I'm not sure what good these flanges do unless you've got the skills and patience to build your own header.)

I'd LOVE IT, if some of the "shelf header" companies that are still making their headers in the US, would build them with flanges for a specific head, or at least allow the customer to mail them to them at their expense. ;-(

If anyone knows a US header MFGR who makes a header for C3 Corvettes who MIGHT be convinced to build one with a flange for a specific head, PLEASE let me know!




Adam
 

Indycars

Administrator
Staff member
@NewbVetteGuy

If you have a header that you can send as a template and a flange, then why not contact a couple of custom build companies. I've dealt with GP Headers and there is also Stainless Headers, both in Minnesota.

 

NewbVetteGuy

Active Member
@NewbVetteGuy

If you have a header that you can send as a template and a flange, then why not contact a couple of custom build companies. I've dealt with GP Headers and there is also Stainless Headers, both in Minnesota.

Last time I looked at 2 custom header companies they were a MINIMUM of twice as much as a top-shelf stainless shelf header from ARH.

The ARH's are up around $1,000 -$1,300 for C3s which in 2022 and for what they are seems reasonable for the quality and the fact that they're made-in-the-US still. Having someone make essentially the exact same header but with a flange from SPDExhaust instead of their usual standard flange for them and charging 2x - 3x feels exploitative...


If I had a magic time machine, I'd definitely go back and stop myself from buying the raised exhaust port Profiler heads and I would've bought the alternative casting that lost a few flow numbers but was at standard height so a standard header would work. -I'm definitely paying "stupid tax" on this one.

Maybe my best option is just to go up one size in primary diameter so it fits better and just lose some low end torque from one size too large of primaries...



Adam
 

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
we all mostly learn though making mistakes... its referred to as the "LEARNING CURVE" OR "PAYING YOUR DUES"
BUT HONESTLY, HAVING ACCESS TO A DECENT MIG or TIG welder ,
and a die grinder and drill press can allow you to make a good many corrective mods
 

Indycars

Administrator
Staff member
Last time I looked at 2 custom header companies they were a MINIMUM of twice as much as a top-shelf stainless shelf header from ARH.
Seems your pretty right on the mark, I paid $2600 (included 2 v-flanges) for my headers from GP Headers. But that was for SS and POLISHED. They don't give you enough PVC which does not include any straight pieces either. Also all you get for angles is 45° and 90°. So I bought several 22.5° and 60° elbows that cost considerably more that the 45/90's, and I had to do both sides. If you are interested, I could ship them to you for the cost of shipping, that includes all the straights you see in my thread below. Just don't give them away or sell them without asking in case I want them back.

Their mild steel header are $1900. Their kits are $500 and is applied towards the header.

Maybe you have already read this thread, but if not in involves using Pipemax 4.7 mostly, although it mentions Dynomation 6.


I just wondering out loud ..... my Brodix IK200s on your Vette and your Profilers on my TBucket ? That would fix your header problem.
Negotiate some difference, but many details like port size, etc etc.
 

NewbVetteGuy

Active Member
Seems your pretty right on the mark, I paid $2600 (included 2 v-flanges) for my headers from GP Headers. But that was for SS and POLISHED. They don't give you enough PVC which does not include any straight pieces either. Also all you get for angles is 45° and 90°. So I bought several 22.5° and 60° elbows that cost considerably more that the 45/90's, and I had to do both sides. If you are interested, I could ship them to you for the cost of shipping, that includes all the straights you see in my thread below. Just don't give them away or sell them without asking in case I want them back.
Wow. A very interesting and generous offer!

I'm definitely going to try one more option before I give up on the ARH header. I'm going to see if they have a gasket that their head flange matches and I'm going to match it up to my heads to see how far it's off.
(My current FlowTech header that was a TERRIBLE match had 1 5/8" primaries; the ARH I'm looking at have 1 3/4" primaries and I expect to fit much BETTER, but I'm still expecting that they could block right at the top of the port where I least want them to...)


Adam
 
Top