DIY porting Throttle Body( 4g15 siemens)

[jswong]

can show us your equations and calculations? Mr. Einstein?

If you had paid attention in college during engineering maths you'll know that it's a simple solution.

The butterfly area remains unchanged at approximately 40mm. The original TB opening size is 45mm, the ported TB is 50mm.

Butterfly area = 12.56cm^2
Original throttle opening area = 15.9cm^2
Ported throttle opening area = 19.6cm^2

(Increase in opening area = 23.27%.. this will affect the CFM value if we want to use if for calculations).

But let's just look at it in terms of percentage, without considering the measurement units. Let the velocity of the air after the TB = v2, and the velocity of incoming air = v1. The increase or decrease in gas velocity when moving from one cross-sectional area can be simplified as

v2=(A1/A2)*v1

if we don't integrate the airflow over the reducing/increasing radius, and if we consider an ideal airflow model without turbulence.

Original differential in airflow before and after the throttle body
= (15.9/12.56)*100% = 126.6%

That's a 26.6% increase in gas velocity entering the throttle body.

Differential in airflow with ported TB
= (19.6/12.56)*100% = 156.05%

That's a 56% increase in gas velocity from the intake pipe into the intake manifold!

Therefore, a ported throttle body opening (with stock-standard butterfly area) will increase the gas velocity entering the intake manifold at any given vacuum level compared to a stock standard TB opening.

Q.E.D.

 

[aquado]

I guess it's about same concept as CAI - colder air: more oxigen
larger intake - in some way allowing more oxigen intake.

I guess fuel consumption should be better. But then not confident to port it without under proper guidance...

 

[xtorm]

If you had paid attention in college during engineering maths you'll know that it's a simple solution.

The butterfly area remains unchanged at approximately 40mm. The original TB opening size is 45mm, the ported TB is 50mm.

Butterfly area = 12.56cm^2
Original throttle opening area = 15.9cm^2
Ported throttle opening area = 19.6cm^2

(Increase in opening area = 23.27%.. this will affect the CFM value if we want to use if for calculations).

But let's just look at it in terms of percentage, without considering the measurement units. Let the velocity of the air after the TB = v2, and the velocity of incoming air = v1. The increase or decrease in gas velocity when moving from one cross-sectional area can be simplified as

v2=(A1/A2)*v1

if we don't integrate the airflow over the reducing/increasing radius, and if we consider an ideal airflow model without turbulence.

Original differential in airflow before and after the throttle body
= (15.9/12.56)*100% = 126.6%

That's a 26.6% increase in gas velocity entering the throttle body.

Differential in airflow with ported TB
= (19.6/12.56)*100% = 156.05%

That's a 56% increase in gas velocity from the intake pipe into the intake manifold!

Therefore, a ported throttle body opening (with stock-standard butterfly area) will increase the gas velocity entering the intake manifold at any given vacuum level compared to a stock standard TB opening.

Q.E.D.

:retarded: :shocked: keng......

if the throttle body didnt change in size, it shouldnt effect it too much, instead the air get in much easier and lesser throttle is needed

 

[jswong]

Well, as we know, the area of a circle is a function of its radius squared. A small increase in radius can result in a sudden jump in area.

I guess that when porting the TB, we can do it either one of two ways:

1) Enlarge only the inlet, to increase of gas velocity going into the intake manifold (hence reduce incidences of sluggish throttle response since the intake manifold fills up faster)

2) Enlarge the TB inlet and outlet, and enlarge the intake manifold's inlet as well. This will result in more air volume at all times. I guess this would be more beneficial if the engine head is also ported and gasket-matched accordingly, hence it's able to breathe better and would require more airflow.

As for whether or not the increase in airflow will cause the engine to run 'too lean' - it won't, for the simple reason that even with a self-learning ECU like the Siemens EMS400 or EMS700, the engine is running an almost-stoichiometric mix only from idling to around 3000 or 3500 rpm. Above that, the AFR drops to 12:1 or lesser.

Running at 15:1 or 16:1 is not 'too lean'. Peak power happens at an AFR of roughly 12.1:1, while peak fuel efficiency (while ensuring complete combustion or air and fuel) occurs at 15.4:1. 14.7:1, the stoichiometric ratio, is just a weight-to-weight ratio for complete burn.

If the engine block can bleed off heat quickly enough, a normal engine can operate up to 22:1 AFR (but not for too long). GDI engines typically run at AFRs far above 20:1.. Mitsubishi's do it at 40:1 or even 45:1. Honda's can run as lean as 65:1.

Maybe in our fathers' time, with primitive technology and outdated 'textbook knowledge', the wisdom of the day is to run at AFRs no higher than stoichiometry, and preferably at a rich setting like 12:1 or less. But with modern engine blocks using fuel injection, with lambda monitoring, and plenty of aluminium parts and better engine cooling methods, the rules of yesterday can be bent a wee bit more.