2" primary headers loss vs. 2 1/8

[Rory428]

If you ever go to a NHRA National event, take a look at the size of the header primary tubes on a 950 HP SS/AH Hemi Mopar, or Competition Eliminator V8, I think many would be suprised at how small the header tubes are. And believe , those guys don`t leave any crumbs on the plate!

[gt350hr]

    Jack Davis (rip) formerly of Hooker headers claimed he was the "inventor" of stepped headers. He built hundreds of sets for NHRA drag racers in all different classes from stock to Pro Stock and went to North Carolina several times to build Nascar headers. Jack tried two step and three step designs that really made a difference on the dragster I was crew chief for. He made me a set for my Shelby that ran the same as the former non stepped set. That was  ahead scratcher.
     Looks like Calvin Ellston makes most of them now.

[Joe-JDC]

Yes, Elston makes the 289 headers for Vintage racing classes with stepped tubes.  They are listed on Cobra web site.  They start at $3500.00 and go up from there.  When I called him to ask about making a set for my Thunderbird, he would not talk to me at first, then quoted me $3500.00 and bring my car to him in NC and leave it.  That trip alone would have cost $3000.00 with hotels and food.  Joe-JDC

[Falcon67]

That sounds excessive - but the stainless 2"~ 2 1/8"you see on most of the BBC dragsters start at $1200~1400 or so.  A good friend did the once on my car, thankfully as best quote I had was $1300.  I have about $650 in them for parts and the coating - some for the custom water jet flanges that mate to the AFD exhaust ports and a dragster header pipe kit for a BBC that we repurposed.  Plus some cool megaphone collectors he engineered from scratch on the bench. 

[C8OZ]

Here's the instruction sheet for anyone as easily entertained as I am.
You just don't see bumper jacks mentioned enough nowadays.

[TomP]

People with only bumper jacks tended not to have welders to put those tabs on.

I think they listed the three step #6374 headers for a couple years, 1 7/8", 2" and 2 1/8" tube steps. But i wonder if they ever made any? I've never seen a set and when i tried to get some they were not available.

[fastf67]

Here is a Formula
 

Area of the Primary Tube (PPA) = (peak torque rpm ÷ 88,200) x (c.i.d. ÷ number of cylinders)

For example, let's look at a 350 c.i.d. small block with a peak torque goal of 5,000 rpm.

PPA = (5,000 rpm ÷ 88,200) x (350 c.i. ÷

PPA = 0.057 x 43.75 c.i.

PPA = 2.49 square in.

PPA   Primary Tube Diameter
1.78 square in.   1 1/2 in.
2.07 square in.   1 5/8 in.
2.41 square in.   1 3/4 in.
2.76 square in.   1 7/8 in.
3.14 square in.   2 in.

There is several links if you search exhaust header size. Mike

[482supersnake]

People with only bumper jacks tended not to have welders to put those tabs on.

I think they listed the three step #6374 headers for a couple years, 1 7/8", 2" and 2 1/8" tube steps. But i wonder if they ever made any? I've never seen a set and when i tried to get some they were not available.

I saw a set on a C/SA car at Seattle several years ago but I don't remember who's.

[WerbyFord]

I checked a few ~600hp engines in the Gonkulator - as a rule, 2-1/8 headers are worth 5-10hp more vs 2" headers (not very much out of 600 total), and about the same on torque - sometimes the bigger 2-1/8 even lose a few ftlb. Not worth going for the extra 1/8 unless of course you have em already.

[frnkeore]

Can you do stepped primary's on your Gonkulator or add a merged collector with different size and length collectors?

[WerbyFord]

Can you do stepped primary's on your Gonkulator or add a merged collector with different size and length collectors?

I haven't put a lot of effort into that because:
a] the Gonkulator routine I normally use here is a fast one so makes more approximations for headers.

b] I'm not sure I understand the gains yet. Seems like a lot of work to do all the steps, and the gains might only show up if you have open headers. And, those gains are going to be convoluted with the fact that the smaller pipe sections can now be less bend-constrained and therefore flow better.
So you'd have to do some pretty deliberate design & testing to separate out the effects of JUST the steps vs less kinks & bends.
Maybe they're worth it, I just don't know. Would be nice to see more data before I put more effort into it.

Great question!

[Stangman]

Werby whats the difference from 1 7/8 to 2 inch, just curious.
HP and torque

[WerbyFord]

Werby whats the difference from 1 7/8 to 2 inch, just curious.
HP and torque

OK here is a bored 428 t-wedge, Gonkulates to 632hp, with just exhaust changes:

2.125   632hp
2.000   621hp   -11
1.875   604hp   -28
1.750   579hp   -53
CJ-iron 534hp   -98hp

All the headers are of course way better than the 428CJ iron manifolds.
Also, the smaller tubes might lose a little less in reality, because you have more room to be more generous with the bends.
I did NOT gonkulate that because it's too subjective - only a dyno would tell that.

[jayb]

Werby, here are a couple of data points for you that may help you make a more accurate simulation.  This is from a 504" dyno mule that I used for testing the 351C intakes.  HP loss with the smaller 1-3/4" tubes is about 35 on this 700 HP engine, vs the 2-1/8" tubes.  Torque GAIN with the smaller tubes in the lower speed ranges was about 35 foot pounds.  If you want details from the engine look at the Dyno Mule to Test 351C Intakes thread on page 2 of the Member Projects forum.

Also I would point out that step headers are far easier to build than headers of a uniform tube size.  This is because at the step, you can slip one tube inside the other to hold it in place.  I'm currently building headers for the dyno mule to run my new cylinder heads and with most of the tubes I can mock them up completely before tacking them, simply by tacking the first tube to the flange, and then slipping the next tube over the first one by 1/2" or so.  That tube can then be rotated to the right position or pulled off and modified or recut if necessary to make the tube as a whole work.  This works all the way into the collector, in my case 3 of the 4 tubes on each side were completely assembled this way before being tacked in place, stepping from 2" to 2-1/8" to 2-1/4". 

Finally, I think it would be a great idea for you to try to figure a way to include tube bend radius into your simulator.  My testing has shown that a larger tube bend radius makes more power; you don't want to bend the exhaust any more than you have to.  This is way more important than equal primary tube length, which seems to be the thing that everyone focuses on.

Hope that helps - Jay

[Joe-JDC]

I have come to believe that cubic inches is a driving factor in tube sizing up to a certain horsepower level.  IE 600 hp with <400 cubic inches works better with the 1 5/8"-1 3/4" steps to a 3" collector with a 2 1/4" merge cone.  Above 400 cubic inches and over 600 hp, the tubing will need to be increased depending on both factors.  Average torque and average horsepower makes dyno testing very interesting if you have the time and parts to verify what works and what is just theory.  Joe-JDC