I looked in the tech wiki, The regular cam for the USA delivered A15's ex B310 is the:

Part Number
13001-H5700

@
?

Ex. Dur
256

In. Dur
248

In. Open
14

In. Close
54

Ex. Close
20

Ex. Open
56

Lift (in)
0.331

going off those numbers the calculated ideal primary length to the collector is estimated at 37.12 inches. [for peak power at 5000 RPM]. The length gets shorter as the RPM /peak power increases

The kicker is though, the reference material doesn't specific if the numbers quoted for the timing event are "advertised" or at "50 Thou"

I'M Using the stock a15 camshsft.but i dont know the the timing events at 50 thou lift.

Here are three points to consider.

-A reduction in primary pipe Diameter of 1/8 of an inch will move the torque peak down by 650-800 RPM. Conversely an increase in diameter of the header will raise the engine speed at which max torque occurs,by approx the same RPM,for each 1/8 of increase.

-Adding length to the primary pipe will increase low speed and mid-range power, with corresponding reduction in power at max RPM.

-Shorter primaries give an increase in high speed power, at the expense of reduction in the midrange. However,there will be little change in peak torque or the engine speed at which it occurs.


source: straight from Graham A Bell - Four Stroke Performance Tuning.

To take the guess work out of this, you really need to know the timing events of the exhaust valve. What camshaft are you running? Do you know the timing events at 50 thou lift?

Hi me again.Looking at getting my headers made up by saturday.I'm now focusing on collector lenght,I dont kno any sizes that there made at.My rpm range would be 2,000 5,000 for street.If that would help for some suggestions.

Oh and im getting them made 4 into 1.

Thanks I haev a barrel at the back of the car




Heres a pic of the exhaust system the car has on presently do you kno what size it is by looking at it ?

4 into 1 or Tri-Y should work just fine for your application. For an essentially tame engine, I would not go any larger than 2" in the main exhaust system. Probably even go 1-3/4" and put a 2" tip for looks.

If i gonna use the car for hillclimbs what sylye should i consider using 4-1 or 4-2-1, 1 3/4 or 2'' pipe?

Calculations for determining the primary and secondary exhaust pipe diameter and lengths, you will need to know the Camshaft specs and desired RPM, In particular the opening and closing events of the exhaust valve. In simple terms the inside diameter of the pipe relates to regulating the exhaust gas flow potential and the length relates to controlling the effect of reversion waves.

If money, time and effort are plentiful, then stepped headers could be something to look into. However saying that, stepped headers have less of an effect on collector lengths under 26 inchs.

From my calculations based on my camshaft timing event in my race engine. @ 50thou Opens Bbdc 58 and closes Atdc 23.5. the apparent ideal collector length for max power at 6000 rpm is 30.8 inches. My race engine is tuned to deliver peak power at 8000 rpm and has a collector length of 22.3 inches.

For your application, its probably easier to buy a set off the shelf as they are made to fit the B110 straight off the bat. Ebay US had a few from memory, if you are unable to find some local to you. My vote goes for set with 38mm primaries for the inside diameter.

here is a link to the headers made in the US on fleabay.

A-series headers



cheers

Yes triY would be the best setup for me.
Thanks for the information I have some pics of how i would like to make them.

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Photos of extractors are a start on collector length. First choose whether you're going Tri-Y or 4 into 1. Tri-y collects 1 and 4 together and 2 and 3 together before merging the two secondary pipes.

My extractors (on a A15) have primary pipes of about 400mm and the secondaries would be around the 1 meter mark. You'd probably be happy with a length around 1.5m for 4 into 1 extractors (based on observation this is about how long they are). YOu'll notice the GX exhaust also has about 1.5m before the 4 cylinder pipes merge.