Twin Turbo exhaust header sizing

[porsche 930twin]

Hi all back on the Dyno and yes still chasing my tail... fabricated new intercoolers thinking this was choking the engine. But with new setup engine still will not make decent power we up up to 358.7HP @ 1.2 bar boost .at the wheels ..now we are thinking maybe the header pipes are to small they are 32mm going to turbos ... i am still waiting on confirmation from engine builder on exhaust port sizes... I am running Dougherty 993SS cams and engine builder assures me there are setup correct....
So any ideas where the ponies are hiding... i assumed i would see around the 600HP at the wheels ...

[dannobee]

32mm primary pipes are really, really small. What other options do you have available?

[lite75]

Those are small primaries for sure. What size are your exhaust ports?

[quattrorunner]

Wow!

[GJF]

What turbos do you have?

[TurboKraft]

On a 98mm 3.4L Twin Turbo? Try 1-5/8" O.D. tubing for the primaries, that's 1-1/2" ID (38mm).

32mm ID = 1.26" ID so ~1.375" (1-3/8") OD, assuming standard 16-gauge SS.
We don't use anything that small even for wastegate dump pipes.

What possessed your fabricator to use something so small? All he'd have to do is hold a tube up to a head's exhaust port and know he's starting out wrong.

[jpnovak]

Don't think its the Zork Tubes.

Agree. Primaries are too small. I bet they are really glowing trying to get that much air through them.

[porsche 930twin]

Hi all ...well spoke with engine builder and as it turns out i have 39mm intake ports and 35mm exhaust ports and the inside diameter of the header tube is 32mm...
there lies my problem..... this is an oversight on my behalf i cant throw anyone else under the bus... so i think i will need to fabricate new headers in 38mm i/d tube ... will be tight around the head studs but will have to work through it...does anyone have pictures of there headers ...
I think now the car is running and driving i will finish painting and assembling it put a few KMS on the car then do the pipes...

[RarlyL8]

1 3/8" primary tubing? Yes that's going to choke things pretty good.
At 35mm your exhaust ports are not very large which also may be a limitation. A 1.5" primary header would work with them nicely if low and mid range torque is the goal. Transitioning from 35mm port to 38mm primary will lose velocity but allow more top end power.
We've done a few rear mount twin turbos using 1 5/8" primary tubing with 38mm exhaust ports. Below is a set we built recently. I'm planning another twin turbo build and just completed a second set. If you would like them give me a call. Should be easy to adapt to your current setup.

[porsche 930twin]

Rarly PM sent...

[dannobee]

He's looking for 100hp/cyl. I'd be more inclined to go 1 3/4" primaries, even if he had to use a 1 5/8" step at the exhaust port.

Which turbos is he using? The steps could even help the power if it has modern turbos.

[RarlyL8]

He's looking for 100hp/cyl. I'd be more inclined to go 1 3/4" primaries, even if he had to use a 1 5/8" step at the exhaust port.

Choke point is the 35mm exhaust ports. Larger primaries would just create a lag monster.

[K24madness]

How about a pic of the dyno sheet? While it sure sounds like you have a header diameter problem I don’t think I would go straight after that without first trying to optimize what you have. That number is low in spite of the header diameter.

AF ratios, boost and timing logs would be great!

[K24madness]

Originally Posted by dannobee

He's looking for 100hp/cyl. I'd be more inclined to go 1 3/4" primaries, even if he had to use a 1 5/8" step at the exhaust port.

1 3/4” not needed at 600hp. Even 700hp seems to be ok with 1 5/8” from what I’ve seen.

Just as another point of reference, with 1 5/8” headers I made 430whp (mustang awd dyno) at 6psi of boost. Granted this was a 993 on 100oct so not apples to apples. I focused on all the same airflow items that make for a good NA build and then put some boost to it.

The OP needs to look at the entire system for choke points. The dyno plot really helps tell that tale.

[Mocker]

Sounds like the OP needs to massage/open up the exhaust ports, too?

[porsche 930twin]

Firstly thanks all for the input ..this is why i love this forum... second to achieve around the 650-700HP what should the cylinder head intake and exhaust port sizes be.. i know there is a combination of factors to achieve this but lets start there..
Also what combinations are people running to achieve BIG HP numbers...

[dannobee]

The later air cooled 935's used 43mm and 41mm ports. With 1.4bar boost made around 750hp, give or take.

[TurboKraft]

Originally Posted by TurboKraft

On a 98mm 3.4L Twin Turbo? Try 1-5/8" O.D. tubing for the primaries, that's 1-1/2" ID (38mm).

Is 800whp enough for you?

[porsche 930twin]

Hi Chris what engine combination could make that sort of power... i always thought getting those real world numbers was a myth ...

[dannobee]

BA_sprint_4