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Do you have a picture of your header?

Erland

I am doing a group A head for a C20XE and I found this picture.
This is the proper side of the plenum to put the throttle:



Erland

Det ska bli intressant att se vad den ger.

Erland

Then I would guess that the header makes your engine run lean and that is why you loose hp.
Do you have a wideband lambda?

Erland

What is the difference in secondary length, diameter and the final pipes diameter.
Also the difference in length to the rirst muffler.
The runners of the intake manifold need some porting too.

Erland

Yes, With bigger throttle you can either use less cone or use larger end diameter.

Erland

Before the plenum after the throttle so that the size increases from 55mm at the throttle to 85mm at the plenum.
Cone length 110mm:s.




Erland

A diffusor converts the kinetic energy in a duct back to pressure.¨ So if atmospheric pressure is 1 bar getting 1 bar in the plenum is 100% efficiency. A short diffusor is maximum 2 diameters long and can have 8 degrees taper per side, 16 degrees included. So för a 55mm throttle the 16 degree taper ...

Yes I meant E but I thought of K-jet.

Erland

I wrote top and bottom but I meant from the side. Instead from the long side the flow should go in from the short side. Flow should always go into a cavity surrounded by walls and not into a big space without diffusing walls. Welding a bigger inlet hole and using a larger throttle or mowing the thro...

The inlet should be from the bottom of the plenum instead of from the top.
As it is now there is a huge expansion and flow loss whwn entering the plenum.
How big modifcations are you allowed to make?

Erland

The manifold can be cut in half at the plenum and ported.
But the dumping of the flow from the throttlebody into the plenum is the worst offender and saps flow 20CFM.
So first you need to diffuse the flow into the plenum.

Erland

That header is the old type that Volvo sold in the 60:s.
There are better ones now with the middle pipes outboard so that primary length is more near.

Erland

The B230F manifold is really restrictive.
I ported a 405 head for a group A engine with stock valves and got 205 CFM:s at 12mm lift.
With the nmanifold attached flow dropped to 165 CFM.

Erland

The manifold for what engine?
Most of them you have to cut apart and weld together after porting.

Erland