Intake question

[81pw]

Just wondering does anyone have short intake runners on there engines? I'm looking at moding mine to short and fat intake runners but is it really worth it?

[rob020]

my efi manifold is made from a tr manifold, which has the longest runners.. but theyve been cut down nearly in half.. i also cut the runners at a 45 degree angle so the cross section of the openings to the plenum is larger than the cross section of the runners, only because trumpets are expensive and i wanted to maximise flow

are you thinking carby or efi manifold?

cheers,
rob

[rob020]

also you can only make the runners so much bigger than the valves before it achieves nothing

[81pw]

I was thinking really short runners about 1-2 inch long, like this pic http://www.google.com.au/m/search?site= ... unners#i=3

[Superscan811]

I'm looking at moding mine to short and fat intake runners but is it really worth it?

Long runners will give you more torque down low. Short runners are usually used for forced induction or VERY high revving engines.

The theory is air has mass and if you move enough of it (long runners),
you will create a higher pressure behind the valves, which will increase the amount of air that will enter the cylinder.
This will of course increase power.

"Tuning" the runner length just increases the pressure at a fairly specific rpm. Some modern engines have 2 different runner lengths to improve power in multiple rpm ranges.

It all comes down to what you are trying to achieve and how much money you are wanting to throw at it.

Cheers.

[81pw]

Not to worried about the money cos I'll do the cutting and welding. I'm looking at pushing though about 16pound. I haven't seen it done to a sigma before. Am I just wasting my time trying to get 1-2 kw or will it be a decent gain like 10+ kw. Thanks for your feed back.

[Superscan811]

For a boosted application, you would probably get better gains from cooling the air (possibly water injection) before the turbo and an inter-cooler after the turbo, rather than playing with the runner length.

Again, in theory, a shorter runner in a boosted application means that the turbo doesn't have to fill up as larger volume to achieve the same pressure.
In practice, it wouldn't make all that much difference.

Cheers.

[rob020]

im playing with water injection at the moment.. having water injected before the turbo and running an intercooler would make all the water pool in the intercooler wouldnt it?