Stupid Header Question Number 84212

[hoffman900]

I think you're off on your measurements.

High end 4-2-1 headers seem to follow this general formula:

Primary id that matches the port area. One step in size (so 1/8") anywhere from 8-12". Primaries seem to end up in the neighborhood of 18-24" (obviously depending). Secondaries are two steps larger than the last primary diameter (so 1/4" step up). Choke merge collector, then they either run back dual, x pipe, or into a single exit. Single exit seems to work very well for Calvin.

I would not be afraid at all of using 1.625 at all off an even larger port area. I do it all the time for Cobra Automotive and their nostalgia mustangs and cobras. 1.63@8-1.75@10, 2" secondary for 12-14", (not a typo) and a 2.25" choke at the final collector. 620hp no problem and all sorts of bottom end. Especially for such a small motor and road racing

It all feeds into a single 3" tailpipe.

Incar here:


I thought the NASCAR stuff is about 1.88-1.91od off the head, 2"od step, 2.25 secondary... X pipes because one pipe would be too big to fit under the car (plus aero, NASCAR mandating how the exit can be, etc.).

However, looking at eBay, there are several set ups with steps in the secondary just before the final Y. I have my guesses on what that is about...

[hoffman900]

I ran some simulation scenarios with a tapered secondary. It provides a slight boost (1.5%) starting at torque peak to peak power, but loses more than that below.

I suspect it may prove to advantageous on certain NASCAR tracks. I have a hard time looking at what they do consider they race on a wide range of tracks. Without knowing the application of a certain part, it's hard to look at what they do and apply it to something else.

[Tom1500]

I think you're off on your measurements.

High end 4-2-1 headers seem to follow this general formula:

Primary id that matches the port area. One step in size (so 1/8") anywhere from 8-12". Primaries seem to end up in the neighborhood of 18-24" (obviously depending). Secondaries are two steps larger than the last primary diameter (so 1/4" step up). Choke merge collector, then they either run back dual, x pipe, or into a single exit. Single exit seems to work very well for Calvin.

I would not be afraid at all of using 1.625 at all off an even larger port area. I do it all the time for Cobra Automotive and their nostalgia mustangs and cobras. 1.63@8-1.75@10, 2" secondary for 12-14", (not a typo) and a 2.25" choke at the final collector. 620hp no problem and all sorts of bottom end. Especially for such a small motor and road racing

It all feeds into a single 3" tailpipe.

Incar here:


I thought the NASCAR stuff is about 1.88-1.91od off the head, 2"od step, 2.25 secondary... X pipes because one pipe would be too big to fit under the car (plus aero, NASCAR mandating how the exit can be, etc.).

However, looking at eBay, there are several set ups with steps in the secondary just before the final Y. I have my guesses on what that is about...

Got any photos of the cobra automotive headers? Must be a tight fit in the 65 chassis.

[hoffman900]

I think you're off on your measurements.

High end 4-2-1 headers seem to follow this general formula:

Primary id that matches the port area. One step in size (so 1/8") anywhere from 8-12". Primaries seem to end up in the neighborhood of 18-24" (obviously depending). Secondaries are two steps larger than the last primary diameter (so 1/4" step up). Choke merge collector, then they either run back dual, x pipe, or into a single exit. Single exit seems to work very well for Calvin.

I would not be afraid at all of using 1.625 at all off an even larger port area. I do it all the time for Cobra Automotive and their nostalgia mustangs and cobras. 1.63@8-1.75@10, 2" secondary for 12-14", (not a typo) and a 2.25" choke at the final collector. 620hp no problem and all sorts of bottom end. Especially for such a small motor and road racing

It all feeds into a single 3" tailpipe.

Incar here:
https://www.youtube.com/watch?v=SAZXMXuBbrM&t=303s

I thought the NASCAR stuff is about 1.88-1.91od off the head, 2"od step, 2.25 secondary... X pipes because one pipe would be too big to fit under the car (plus aero, NASCAR mandating how the exit can be, etc.).

However, looking at eBay, there are several set ups with steps in the secondary just before the final Y. I have my guesses on what that is about...

Got any photos of the cobra automotive headers? Must be a tight fit in the 65 chassis.

You can buy them here: http://store.cobraautomotive.com/compet ... t-headers/


What Bill said who builds those engines:

I have multiple sets of sb ford dyno headers that Calvin made for us. They are configured in a way that allows us to experiment with secondary pipe lengths and swap firing order easily. We have made 650+ hp with the dyno configuration of the headers in the picture posted by hoffman 900. They match or beat the lower end power of any 1.625 dia straight tube header and beat the top end power of any 1.75 header we have ever tested. They are far superior to any "catalog" header .

Does anyone know when 4-2-1 arrived in NASCAR?

Anyone seen Yamaha or Suzuki's Headers used on current MotoGP bikes? I would love to know how they get it all in behind the radiators.

2nd-3rd Harmonic pipes paired up = Power Chord = great sound
3rd-4th Harmonic pipes paired up = Inverse Power Chord = great sound & if you have no overlap @ .050" then there is no power to loose.

1995, at least for Calvin. He goes over it here: http://www.exhausting101.com/?p=233

Look at the Akrapovic stuff for bikes. The Ducati and Honda SBK stuff uses thin casting to control the bend off the port. Take a look at the HRC WSBK system for the Honda CBR1000RR-R.
https://riders.drivemag.com/news/honda- ... c-exhaust/