Can someone help me design a set of headers?

There is plenty of info online for calculating sizes and lengths for 4into1 headers but I’ve only found 2 sources for 4-2-1 headers and they provide quite different results.

Does anyone know a good source that covers choosing 4-2-1 primary/secondary diameters and lengths?

Or maybe someone here has pipemax software or similar?

Engine in question is NISSAN KA24DE it’s being fit to a 620 Datsun so off the shelf headers may not fit plus I’d just like to make my own.

Capacity 2389cc / 145.79ci

Bore 89mm / 3.5”

Stroke 96mm / 3.78”

Rod length 165mm / 6.49”

Stroke to rod length 1.71

Compression Ratio 9.2:1 - 9.3:1

Stock Power 110Kw / 147HP @ 5600rpm

Stock Torque 208NM / 153Ftlb@ 3600rpm

Stock Head flow

Intake

.100” / 2.54mm = 99.3 CFM / 78hp

.200" / 5.08mm = 171.1 CFM / 149hp

.300" / 7.62mm = 223.4 CFM / 181hp

.400" / 10.16mm = 241.8 CFM / 188hp

.500" / 12.70mm = 243.6 CFM / 190hp

Exhaust

.100" / 2.54mm = 75.8 CFM 76%

.200" / 5.08mm = 144.5 CFM 84%

.300" / 7.62mm = 173.9 CFM 78%

.400" / 10.16mm = 182.9 CFM 75%

.500" / 12.70mm = 183.6 CFM 75%

Stock Cam

Intake opens 1° BTDC

Intake closes 53° ABDC

Duration 232°

Intake 9mm lift

Exhaust Opens 32° BBDC

Exhaust closes 4° ATDC

Duration 216°

Exhaust 7mm lift

In future I’d like to change to this Kelford Cam (https://www.kelfordcams.com/index.php/au/camshafts/nissan/ka24de-det/213-a-camshaft-set.html)

But if the header required is very different I’ll make a new set to suit that cam later as not sure how long it will or if i even will get that cam.

I want to preserve the down low torque as it’s my workshop parts getter Ute/mini truck no race car.

In the process of rebuilding the engine, I’ll be giving the head ports a basic clean up and gasket match, block bored 020 and the rest stock. Likely a Custom intake, ecu/tune and new cam later on

I was thinking of using a 2.25” exhaust or would a 2.5” be better?

The best spec I’ve come up with so far using the “hootsbuild” calculator and setting the target rpm at peak torque of 3600rpm but not sure if that’s right or if I should be setting the rpm to the peak power rpm?

1.62” / 41.28mm Primary’s OD

15” primary length

2” secondary OD

32” secondary length

2.0” OD collector

5.76” collector length

Exhaust Diameter 2.25”

Tailpipe length 44.6” minimum

Thanks heaps in advance!

I am not a expert, but from a book i have.

Rpm for road engine is set at maxium torque.

i could be wrong in mi calculation (never did dis)

P(total lengt ) 47"

Inside diameter 1.455" Fist section

Inside diameter 1.91" second section

for primary length length dont have formula, only says that for primary minium of 15" (best low end) if use a lot larger primary (best top end)

Tail pipe inside diameter 1.959"

Remenber the primary

I found a web that uses the formulas of the book, you can try, it has more details http://www.mezporting.com/exhaust_length.html

It seem that de diameters are to small but is for a engine that has torque at 3600rpm and street engine. (Probably you can use a bit more diameter, in fact it has tables to use whithout need the use formulas and the diameters are a bit bit (not to much, still being small)

in tables 1.875 primary, 2.0 Secondary, 2.5in tail (for 180/220 hp engine)

I've looked, off and on, for exactly this information but...

It's quite old now, but still one of the best reference works, which may help - https://www.amazon.com/s?k=exhaust+design+Phillip+Smith&i=stripbooks-intl-ship&crid=2GTLKPULI83SB&sprefix=exhaust+design+phillip+smith%2Cstripbooks-intl-ship%2C224&ref=nb_sb_noss

There is a LOT of math'!