Supercharged exhaust recommendations

[JohnJL]

I am finishing up a 3.2 supercharged experiment, shooting for 450-500 hp at the crank. I am using SC heads, mild porting on the intake side, stock on the exhaust side, stock OEM valves, DR20 cams. This is a track-only car with mildly-inforced noise restrictions.

I am keen to hear header/muffler recommendations. I have a set of Bursch headers from our host (http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search.cgi?command=show_part_page&please_wait=N&make=POR&model=911E&section=EXHpip&page=2&bookmark=7&part_number=PEL-BURH-911-02) but I'm not sure of the ID (they are 1.75 OD) and if they will flow efficiently/effectively enough. I've seen those into Phase 9s or MK stingers but there is no cross-over in that setup. I also have a spare Bursch-into-2-2Flowmaster setup.

Would love to hear recommendations, with performance being the key.

thanks

[RarlyL8]

Short, fat, and unrestrictive.
Supercharging exhaust physics is easy - they don't like any!
Get the shortest big tube headers you can find and the largest ID straight through bullet mufflers. Crossover is not necessary for the boxer 6.

[Rodsrsr]

I think Rarly is right, especially if you have a roots type SC. I noticed that with a linear setup like the Paxton, I lost a little low end torque when I jumped to 1 3/4" headers on my 3.2, so I put the 1 5/8 back on and it runs better. I would think that its because my SC builds boost with rpm, it still feels very much like a Porsche, coming on strong as rpm increases. John, how much boost are you running and have you made changes to the comp ratio?

[JohnJL]

Thanks guys.

Yes, the cylinders are 98MM 8:1 coated JE pistons in new perfectbore cylinders. Planning on running 12-14 lbs boost. Supercharger is a twin-screw Autorotor.

Wouldnt the same principles as a N/A engine of 6.4 liter NA engine apply? Wouldnt the same principles of our NA engines apply, just with additional flow requirements? I thought our NA engines liked some crossover or at least meeting at the muffler rather than separate outlets like headers-straight-into-stingers?

Anyone put any weight to these tools...

Header sizer: http://www.autolounge.net/calculators/exhaust/headersizing.html

Using an effective displacement of 6.2L I get 2.25"

Exhaust sizer calculator seems to be missing from the site.

[RarlyL8]

The dynamics change when you force air through the engine instead of pulling it through.

[JohnJL]

Thanks Brian. First thing that came to mind is my engine is now a "farter!"

Any other advice about the header sizings? is 1.75 going to be enough?

[RarlyL8]

Lots to consider. Assuming the engine is not an all-out dragster your primary tube sizing should complement the flow. If the SC is a whipple then short fat tubes, it a centrifugal then longer more narrow primaries. What size will your exhaust ports be?

[JohnJL]

The supercharger is an Autorotor, model 420. Its the same as the Kenny Bell units. Its a twin-screw internal compression-ratio unit. Details herehttp://www.hi-flow.com/HP7Super.htm This is a very similar model to what Corky Bell discusses in depth in his Supercharged! book. Basically an update and up-size of the 3150 model (specs also on that page.)

Exhaust valves are 41.5 and the exhaust ports are 39mm.

the car is track-only. 1050kgs, full weld-in cage, ERP suspension, G50 transmission. Open-class racer up against GT3s, Turbos and GT2s.

thanks

[RarlyL8]

There are a couple of guys here on the board with surpercharged engines, I was hoping they would chime in.

A few years back a fellow PCAer campaigned a whipple supercharged SC. Ran a conservative 260HP to the wheels and used SSI exchangers. You are looking for ~320WHP and may want to use a bigger ID tube. One very simple and fairly inexpensive route would be a set of 993 heat exchangers. They are big enough to support the power and short enough to get it out quick.

Here is a picture with the heat exchangers removed:

[mb911]

I would use georges euro headers (largetube and a nice 2in 1 out or 2 in 2 out of your liking

[Facey]

+ 1 on georges, not any experience with supercharging, but on my engine(s) i've had everything from stock, to SSI's, 2 different B&B's, and for the last 1 1/2 have been running georges and i love them!

edit: i am running a 3.5L so some flow is required... made 278rwhp with the B&B setup and this feels like more.

[JohnJL]

My feeble search skills arent turning up a source for "george's" only lots of discussion. I guess I'd normally feel funny asking but I've already bought 2 sets of Burches here so...how big are the Georges? One of my Burches are 1.75 already...

[RarlyL8]

If you have the Bursch headers then give 'em a go. 1.75 OD should do for your power goals.
You don't want to run much muffler at all. Short straight through with a 3" or better ID per side or 3.5" if both sides combined. Any noise restrictions? If not just use a set of turn downs right off the headers.

[mb911]

Originally Posted by RarlyL8

If you have the Bursch headers then give 'em a go. 1.75 OD should do for your power goals.
You don't want to run much muffler at all. Short straight through with a 3" or better ID per side or 3.5" if both sides combined. Any noise restrictions? If not just use a set of turn downs right off the headers.

All good points but He is going to need something to keep it quiet and most supercharging principles come from long runs on a muscle car

[RarlyL8]

One of the muffler options in the original post was the M&K track stingers. That's pretty loud but would work for the application. The supercharged SC track car that I am familiar with had turn-downs right off the SSIs. No mufflers at all.