911 3.0 SC Dansk Header Size

[racer86]

Hi All,

Apologies if this has been well covered, but after a search I can't find an answer...

I have a '78 3.0sc will a later ROW 204bhp motor. Mods are currently just an Air filter, but may do more later. I am going to delete heat and fit Dansk headers, I'm just mot sure what size to go for, my options are:

38mm OD and 45mm OD.

Could you advise?

Thanks in advance, Rob.

[Dmitry at Pelican Parts]

Hi Rob - if our members aren't able to chime in for this one; please feel free to give us a call at 888-280-7799 and one of our Porsche part specialists will be happy to help you out. Best of luck!

[lvporschepilot]

Because you have early SC heads (35mm ex ports) I would shoot for the larger 45mm OD set as the 38mm OD headers seem like they'll have an ID just a touch too small. I would clarify with Dansk the ID of the headers and if they are indeed 35mm, go with the 38mm OD headers

[racer86]

Thanks guys,

I've gone with the 45mm OD pipes - it will future-proof me for upgrades even if I lose some mid-range in the short-term. Though I thought the later 3.0 204bhp motors had 38mm ports, but I'm probably wrong!

Thanks for the help as always.

Here's a bad-ass RSR to celebrate!

[zedsn]

The 1 3/4" pipes are too large for your motor even with some mods. I would stick with the 1 5/8" OD pipes.

[Bill Verburg]

Originally Posted by racer86

Hi All,

Apologies if this has been well covered, but after a search I can't find an answer...

I have a '78 3.0sc will a later ROW 204bhp motor. Mods are currently just an Air filter, but may do more later. I am going to delete heat and fit Dansk headers, I'm just mot sure what size to go for, my options are:

38mm OD and 45mm OD.

Could you advise?

Thanks in advance, Rob.

the 38mm OD is correct for street 911 up to ~3.0 liter
the 45mm OD is too big even for a 3.8RS type motor these typically want ~42mm OD.

of course there reasons to go bigger, for instance a 3.8 to 4.0 w/ full race cams that is intended for tack use only and revs into the high 7k or 8k range might want 45s

[racer86]

Ah....OK, thanks. I'd assumed these being the only stainless steel option they were pretty suitable for most applications - they are even listed under 2.7! I'd assume ID is more like 42mm when you consider wall thickness....

Realistically, how negatively will it impact performance?

I'm going from SSIs and a 2-in-1-out to these and a GT3 style 2 out....


I just want glorious sound, no heat and a bunch of bananas, I don't want to lose power/ torque!

[Bill Verburg]

Originally Posted by racer86

Ah....OK, thanks. I'd assumed these being the only stainless steel option they were pretty suitable for most applications - they are even listed under 2.7! I'd assume ID is more like 42mm when you consider wall thickness....

Realistically, how negatively will it impact performance?

I'm going from SSIs and a 2-in-1-out to these and a GT3 style 2 out....


I just want glorious sound, no heat and a bunch of bananas, I don't want to lose power/ torque!

Realistically for street use you wouldn't notice a difference.

There are 2 phenomena at play in the exhaust

1) flow

2) acoustic tuning to enhance the '5th stroke'

1) for a muffled system you just want to flow an adequate amount of gas, correctly sized and configured pipes optimize this, too small will choke the motor noticeable as revs rise, too big will have some loss of flow due to overly slowed/turbulent flow but it's no going to be a big deal unless you are counting tenths. Sizing depends on displacement/revs/cams/valve and port size. 1.5"OD works great for 3liter to a little over 215hp, but put that on a stock 3.6 and they will choke the motor noticeably as revs build.

2) w/ smog cams which have little to no overlap acoustic tuning is moot anyway especially so w/ most mufflers. headers work best when a cam w/ lots of overlap is used, 1.5" headers on a 3liter w/ S cams are simply amazing compared to a non tuned exhaust.

The aural quality is going to be more a function of the muffler you use.