I spent 2 years working for Hendricks Motorsports modeling engines and designing and fabricating headers. Ideally the cross sectional area of the primary tubes should be the same as the cross sectional area of the exhaust port. Otherwise, the speed of the exhaust bolus must change at the interface and this creates turbulence and unnecessary pumping losses. Would love to compare notes with you.

I love this series...great platform. Please recommend and link additional reading on the subject. You’re making it easier to buy from Summit.

[(Peak Power RPM * 1 Cyl displacement)/ 88,200]=PPA little bit of a mix up on rearranging the formula

I saw the math part of the header build in Hot Rod a whole bunch of years ago. I wish the Hot Rod staff had collected all the tech articles from the magazine and published them as a series of books. They would be most useful.

Excellent information, helps me decide how large to build the headers on my 415CID small block.

At what RPM does your peak torque occur? And will this change in the future? Let me know which one you want us to plan for and we will get you a tube size :)

Hi, this is really one of the best summit quick flix I've seen. Norm is absolutely the right guy. I've seen a couple of other vids from Norm and there just simply awesome. Congrats Norm!!

This man is smart and communicates his theories with pinpoint precision. Thank You, Sir.

Please give us a call on our tech line and we will help figure out what headers are actually available for your application. 1-330-630-0240. Thanks for watching!

got it i missed a lot of steps there but now i got the formula and realize that i need to convert to cubic inch for it to work (duh). thanks for taking time to explain it i think i needed to see it with my application plugged in to understand it. thank summit!!

Thank you! Glad we could help. Let us know if you have any questions.

Absolutely most informative video I've ever seen about tube diameter. How would you figure the math on a stepped header application. I run tri-y stepped headers?

Thank you for getting rid of the sales engineering this was very well done keep up the good work.

Good stuff... Us motor heads love all the info we can get

this was the most usefull video i ever saw on youtube, thanks...

Primary pipe area = (3000 x 22.2) / 88200 Primary pipe area = 0.7555 inches square Doing some more math I used 0.040 for the wall thickness for my mild steel circular tubing. The formula for the area of a circle = pi x radius x radius; and I pulled the wall dimension out.

I plugged the 4900 RPM that you supplied into the formula and come up with a theoretical PPA (primary pipe area) of 2.61 inches square. Doing the math for the surface area of a circle and using 0.040 inch for the wall thickness I have a 1 -7/8 inch primary tube outside diameter coming in at 2.53 inches square and a 2.0 inch version coming in with 2.94 inches square. I would use the 1 -7/8 inch set unless you plan on a dramatic change in displacement and/or peak torque. Hope this helps good luck!

Awesome tech, please more vids like this!!

How do we calculate muffler size. I am making a gokart and so i need the muffler size. Since i am participating in an event i need to show the calculations also. Plz help

I tried 1.25 inch OD and got 1.075 inches square for the pipe area (above), remember we are trying to solve for primary pipe area. Then 1.125 inch OD which yielded 0.86 inches square; followed by 1.0625 inch OD which got me very close with 0.76 inches square. So it looks like a 1 -1/16 inch OD tube with a wall of 0.040 inches is your theoretical primary pipe diameter for your particular single cylinder displacement and peak torque RPM. I hope this helps; let me know what you think.

I ordered the 1 5/8 shortys for a LS swap in a 35 coupe. I did not know this. I am tight on room for my steering shafts. The smaller size will help with that.

anyone how would u work out peak torque rpm for a stepped header? thanks

Thank you sir, I appreciate the feedback.

Dear Roman, Sorry for the delay. Primary tube diameter is used to enhance the amount of torque developed at the peak torque RPM. That’s why knowing the actual or theoretical RPM where the peak in torque occurs is built in to the equation. Do you know the actual RPM or the theoretical RPM where your 350’s peak torque occurs? Let me know.

This formula is set up for cubic inches or better yet inches cubed.

Though we’ve not compared them side by side, they are most probably different considering the chassis’ of the cars have changed completely. The reason you are having trouble finding Shorty’s for your application is because that car has ample room for a long tube and they respond so favorably to long tubes.

Dear Eggiman930. I‘m sorry, I did not understand… Is the mentioned 1.6L displacement the displacement for the entire engine or the displacement of the single cylinder? Or better yet, what is the total engine displacement and the number of cylinders regarding the engine in question? Let me know, I’d like to help.

A good teacher fist teaches the definition of important, pertinent words and acronyms in alphabetical order, then proceeds in an orderly step by step manner including an orderly, step-by-step diagram or formula listings, in chronological order with simple clear explanations of each. This is followed by simple to solve formulas with round number plugged into the formulas so the students can clearly and easily focus on the formula in a meaningful manner. When the student clearly understands all of the aforementioned, then the student can begin solving problems or questions which require mathematical computations . Therefore, I agree with Garth Giggity who posted the Einstein quote; which I will herein expand on as follows: "if a person cannot explain something simply, in an organized and proper chronological order, they don't a.) understand it well enough and b.) they don't know how to teach". Students learn best by progressing from rote to skill then to understanding, and finally to comprehension. Skipping any step can cause confusion in a student's little grey cells which result unsatisfactory results, whether it is getting a good grade in a class or when building a combustion engine or an electric motor. By the way, a vehicle that runs on fuel has an engine - not a motor - motors are powered by electricity.

how did you calculated the length of primary pipe? also please help me with my engine. I have EX500 engine of Kawasaki ninja and I'm using it for my formula racing car . will you please give me the calculations for primary and collector length ?

sir can i get the reference of the formula that you have used for calculating header pipe diameter. if possible please share reference with me

Does this formula work for single and multiple turbo diesel engines also?

What can I do to help my lower end torque ? I have 2in fenderwell headers with 3.5 outlet. Can I build a collector to help keep the speeds up. Also the primary tubes are 42 inch long & I'm running a stroked big block mopar and looking at near 600 hp.

QUESTION PLS HELP. if im doing exhaust piping fully 3" and in the middle reduce to 2.5" and then increased back to 3'" again towards the back end (tips), does this mean the whole flow is changed to 2.5"effect or 3" . or for example i want full 3"piping but im missing a 3" flange so i reduce one small part to 2.5"just for the sake of using 2.5"flange. but the rest is back to 3".. NOTE that one flanged part is reduced to 2.5" . can you please explain the effects. ty

Is this how one can tune for peak performance at desired rpms? Or is this how one would enhance the constant performance curve of an engine? I just got a small block 350 engine, so this really helps since I am new to this and eager to learn. Thanks

I'm having a hard time figuring this equation for my displacement and peak torque rpm. i took my peal torque rpm which 2500 and divided it by 88200 and multiplied it by one cylinder displacement of 364.25cc (its a small engine 1.6liter) and got 10.3245 do i move the decimal over? and get 1.03 i don't understand the 5k thing . my peak torque is 81lb at 2500

So what size primaries do i need on a 393 ci Ford Windsor with a solid roller cam .680 lift 258/268 duration at .050 and a 108 lobe center with a max RPM of 7,000? I am running AFR Renegade 220 heads with a compression ratio of 12.3 to 1 and a Super Victor intake and a 850 Mighty Demon carb. This will be a drag car that i plan on spraying 200 - 250 HP of nitrous.

great job Norm. I'm going to do a feature on Holleys for the Australian market on KZfaq any advice would be appreciated Regards Smithy

this probably the most in depth im gonna get on youtube

OK. So PPA = PTRPM / (88200 x 1 Cyl displacement). Area = (OD (-) total wall thickness) x (3.14 x radius squared)? Am I on the right track? Thanks.

Great video, great information. Raymond Boudreaux, P.E.

What would be the best primary tube OD for a 2012 SS L99 Camaro? Was looking at a 2-1/2 in with a collector of 3 in. With the exhaust of 3 in all the way out. Want the best hp output. Please Help.

I have a 1.4 liter turbo charged 4 cylinder car that has a complete down pipe through exhaust and muffler of 2.5 inches, mandrel bent. I would like to know if 2.5 inches is enough for my 205 WHP and 257 FT/LB of TQ to the wheels. It is a single pipe. My redline is 7k. 83 cubic inches. my guess it that peak torque is around 2k rpm.. This car is modified. It was suposedly at peak torque from the factory at 1850 Rpm's. When it was stock it had 140 bhp and 150 ft/lbs of base torque. That is 120 WHP..

hi there how do you computer for the 1 cylinder displacement? supposed i have a 4 cyl 1600Cc engine? do i divide 1600 with 4 ?

What is the best pipe size for my 3 cylinder car?

Laid down a good foundation. Cheers.

would be nice to be given some idea of where 88,200 came from

For example 1.25 inch OD pipe (a circle) minus the wall thickness twice (2 x 0.040 = 0.080)…so, 1.25 inches minus 0.080 = 1.17 my corrected inside diameter… so, 1.17 inches / 2 = 0.585 inches for my radius. Now 0.585 x 0.585 x 3.14 = 1.07458 inches square.

Now if you had those tuned length headers put on, ie: each size, i bet my life the difference in power would be so little that in the car you really would not notice it,especially after a tune for each one, so the most important fact is this, if you had a 350 chev engine which can rev out to over 8,000 RPM then what you need to go over 1/ 7/8 " DIA headers i dont think so, because its all about when your peak torque comes in and ends nto how far your engine will rev out too ? Also if you have a street driven car like say the new Holden Chev SS which has a 6.2 lt engine and also considering everything under the bonnet which can get very hot and also gets in the way, then you can only do so much as far as the design of those tuned length headers, if you have not restrictions under the bonnet then no worries at all, then you would have the collector of each header pipe start out in the same direction as each exhaust exit angle and then mandrel bend the pipe so to fit and collect at a point to fit under your engine bay and not touch anything and more importantly easy access to spark plugs, other wise like most companies out there they simply copy each others designs and thats what is on the market right now, in australia and overseas as well ?

I agree with Scott. The 1cylDisplacement needs to be on top of the line. Unless the rules of math have changed since I went to school.

So smaller and longer helps low rpm and vice versa. Sweet!

The math is wrong for tube area; 1 5/8" he didn't subtract any wall thickness. 1 3/4" & 1 7/8" he only subtracted the wall thickness once (.080") if that is the thickness of the tubes..he should have subtracted .160". 1 5/8" OD pipe with .080" wall thickness has an area = 1.686" (( 1.625 - (.080*2))= 1.465ID /2 = .7325 for the radius, squared = .53655625 * PI (3.14159) = an area of 1.6856 square inches. 1 3/4" OD tubing (.080 wall) = 1.986 square inches 1 7/8" OD tubing (0.80 wall) = 2.31 square inches

Great video ! To your calculations, are you suggesting a short header will have more torque it it leads to smaller collector per say 1 7/8 to a 2" than a long tube header 1 7/8 to a 3" collector

what would be the best size for honda accord 2.0 lt vtec head and the ruuners how long i want to use it for drag. i would be so glad sir if you will reply to this comment thank you sir

so what would be the pro's and con's of using the stock tubing size on a slightly modified motor?

what do you mean that 88,200 is your constant? pls explain

what about stepped tube headers ?

Why would i want to make more torque at peak tq? Wouldn't it be more beneficial for performance to have the headers tuned above peak torque and use long primary, like 32"? I have very mild 302 combo, peak torque at 3400RPM with stock headers, so i was thinking 1-3/4" long tubes.

The two formulas do not jive. Not sure which one is correct but in the first one the constant (88,200) is on top and the single cylinder displacement is on bottom. In the second one they are both on the bottom. This can not be correct.

What units should be used for cylinder displacement? Cubic Inches? CCs?

2300cc 4 stroke ,Peak TQ wanted @7k so primary diameter from inside would be?

Hi Norm, I was just trying to do the numbers for my 327 cu.in engine. Is it possible that there might by a mistake on your whiteboard? 2,07 in2 for the 1 5/8" tube seems to be considering the OD instead of the ID. Shouldn't the PPA consider ID instead of OD? Please correct me if I'm wrong. Take care, Claudio

I converted the single cylinder displacement of 364.25 cubic centimeters over to the common units of the formula - inches. The formula works with displacement in cubic inches all the way down to square inches for surface area and even inches for primary pipe diameter. Plugging you in, I have single cylinder displacement at 22.2 cubic inches and I used your supplied 3000 RPM to finish the equation and solve for the primary pipe area and then subsequently the primary pipe diameter.

so a 4.6l would require somewhere around 1.99in^2 primary tube headers for 5k torque

i have oversized my piston, done port and polish should i change my headers? a 1.5 liter engine turned out to be 1.6 liter output right now, is there a need to increase the pipe diameter of my headers>?

The math for find Primary tube area PPA is also incorrect: It should say, (TQ peak rpm * 1 cyl. displacement) / 88,200

Hi, why is the constant for the Peak Torque RPM equation a value of 88,200?

HOW U GET 88200???

Its hard to say, tube length is specific to engine size & vehicle application. Give us a call and we’ll help you pick something out. 1-330-630-0240

Hi guys. This link explains in more detail, and these are the formulas. For street motors. Peak rpm (torque)= ppa*88200/individual cylinder displacement Ppa=peak rpm torque*indiv cylinder displacement/88200 books.google.com/books?id=yEe6nll_wdEC&pg=PA149&lpg=PA149&ots=fqPa5LAunF&focus=viewport&dq=peak+torque+rpm+x+1+cylinder+displacement&output=html_text

I've never thought of customizing tube diameter and length to RPM, I always thought "go big, bigger is better!".

First, 1-5/8" is 2.07 but the other two are wrong; 1-3/4" = 2.40 & 1-7/8" = 2.76 Next, the second formula is incorrect; PtRPM x 1 cyl. Displacement / 88,200 = PPA Finally, an alternative formula to pi r squared is Diameter x Diameter x 0.7854 (Example: 4.00 x 4.00 x 0.7854 x 3.480 x 8 = 349.85 (350))

How many times have you said uh?

I thought I knew math. My area calculations came out different from yours then I have no idea how you ended up with the peak torque from the area measurements you displayed. I will look for a better explanation

I don't get why just put the largest pipe you can on if its about moving exhaust out? get some 5" diesel pipes on there.

i dont se where he talks about how to calculate primary header pipe lenght? ore am im missing something?

410 lb ft torque at 4900 rpm for the 2012 SS L99 Camaro.

This is the voice I hear when shopping at Acme.

best size for a 69 corvette 427 big block .. ? Thank you

Why does he say “theory “? Do we not know by now the exactness of the internal combustion design ?

i thought 1 5/8 was to small now i see it is perfect as my peak torque will be at 4400rpm

Are these measurements based on i.d. Or O.D.

I didn't know Bill Clinton worked for summit racing NICE!

So what length ??????????

what the batter for trail blazer. 4.2L

So if I understand this correctly on a 440 1 5/8 = 3319 Rpm, 1 3/4 = 3511 Rpm, 1 7/8 = 4057 Rpm. On a 505 1 5/8 = 2892 Rpm, 1 3/4 = 3059 Rpm, 1 7/8 = 3534 Rpm.

First, I want to start out by saying that I love Summit for my 1977 Corvette! But some constructive criticism is that you keep distracting overly loud intros out of the video. Additionally, distracting words like "uh, and like" reduce the learning when you are teaching Math. Lastly, the only diameter I found on summit for my 77 350sb was 1 5/8". Thanks for the videos though!!!!

305sbc with 1.5" primaries peak at ~3400rpm, works for me

i agree and very detailed on how he explains the facts.. yet he says.." ummm" a lot..

1.6l thats the entire engine the single displacement for one cylinder is 364 cubic centimeters.

So how many iterations does it take to nail it down? You use a peak Tq rpm value for an unknown exhaust to design your new headers. Then you put your new headers on to find you changed peak Tq rpm to recalculate and find you need a different size tube......😂😂😂. I’m thinking the ppa doesn’t dictate the peak Tq rpm!?! Whole lot of other factors like head flow and valve timing events!

Norm, your is jacked. If your PTRPM equation is correct, manipulating for PPA = (PPRPM x displacement)/88,200

Everytime he says "uuuhhhhhm" take a drink

Why does he want 5k for the torque peak?

Not for the lehman but very informative

"...hopefully all the spent combustion gasses to be evacuated from that cylinder.." *EGR valve laughs diabolically*

wrong equation for PPA. displacement goes on on numerator multiply with RPM leaving 88200 only in denominator.

You didn't do the second equation correctly when solving for PPA. If you want to solve for PPA based on the first equation you would multiply PtRPM X 1cl displacement and divide by 88,200.

2 1/8 " on ddc if you smaller you lose power

God, I wish this was in metric!

top drawer.