Help me choose headers

[beepbeep]

I hope there are some CI's around that would help me pick optimal design.

Engine is 2.3L fourbanger, 1-3-4-2 firing order from the left. Being somewhat budget-limited I decided to model the headers in CSG first, so I could approximately know how much tubing I should buy and how har it would be to weld it together. I also tried to follow usual design rules and to keep the pipes short and with so few bends as possible. Equal-length pipes are out of question beacuse of spactial constraints, so here are my final two designs:

DESIGN 1

This one pulls 1-4 and 2-3 together into it's own intake ports on turbo, they say it shortens spool-up but pulls down top-power. Disadvantage is that i'm forced to use two merging 90-degree bends on 1-4 collector and i'm afraid pulses might go back to another cylinder instead of down into turbo:



DESIGN 2

This one is easier to weld as there are no sawed-then-welded 90 or 45-degree bends and there is merging collector bade of two straight pipes with 40-degrees inbetween just before turbo-intake, so it will be much harder for pulses to bounce back into it's neighor pipe. Disadvantage is that merge isn't optimal from firing-order point of view, but they say it's not a big deal as i run twin-scroll turbo and that it's better for max power and slighly worse for spool-up:





So what do you think?

[cstreit]

I think -- I like biscuits. -Invader Zim

My only thought would be that if you were running an agressive cam, that scavenging may be important, which might be an issue in design 2?

[jluetjen]

To be honest I don't have a clue because the turbo changes the whole set of design requirements. As to the correct trade-off of cylinder scavenging versus boost affects, I don't have a clue. My understanding is that the pressure on the inlet side tends to push the exhaust out of the cylinder no matter what's going on in the exhaust design. But I could picture the off-boost performance being much worse if your design doesn't maintain the momentum and heat of the exhaust into the turbo.

Two places that you might want to check for information would be...

Forced Induction Performance Tuning by A. Graham Bell. If that book is anywhere near as good as his "4 Stroke Performance Tuning", it will be very helpful.

The other person you might want to check out is Dave Walker of Cars and Cars Conversion fame. He's got a long history of giving advice as part of his C&CC column as well as test and debunking many conventional wisdoms. He also is responsible for a pretty slick little mappable ignition system that I'm seriously considering for my 911 (There, now this column has some 911 content )

[beepbeep]

Originally posted by jluetjen
My understanding is that the pressure on the inlet side tends to push the exhaust out of the cylinder no matter what's going on in the exhaust design.

Hmm..i heard that you should try to minimize this type of draught, that's why turbo cars have so mild cams.

But I could picture the off-boost performance being much worse if your design doesn't maintain the momentum and heat of the exhaust into the turbo.

Well from the heat point of view you want to carry as much heat as possible trough the turbo. If gasses cool down they loose volume (PV=nRT) so there is less to spin the turbo, that's where "free energy"- talk from turbo guys comes from :-)

To places that you might want to check for information would be...

Forced Induction Performance Tuning by A. Graham Bell. If that book is anywhere near as good as his "4 Stroke Performance Tuning", it will be very helpful.

The other person you might want to check out is Dave Walker of Cars and Cars Conversion fame. He's got a long history of giving advice as part of his C&CC column as well as test and debunking many conventional wisdoms. He also is responsible for a pretty slick little mappable ignition system that I'm seriously considering for my 911 (There, now this column has some 911 content )

Thanx for the links! I'll check them out...

P.S. Of course there is a 911 content, engine is going to be installed in -79 SC!

[304065]

You are putting a BMW motor in an SC?

[beepbeep]

Nope, SAAB 2.3L fourbanger... , check my signature