924Board.org

[924RACR]

Back in the archives, once upon a time, I had notes with dimensions that were supposed to be an optimized stepped header design for the 2.0L NA motor.

I finally have resources and time to try making one of these, but I can't seem to find my notes!!!

Does anyone have this info kicking around??
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Fifty50Plus]

Check with Dan. He might have some info.
_________________
1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car

[Mike9311]

Vaughan, I finally went full circle last night and made the connection. Saw this get vacuumed by one buddy and then another whisked away it into a hot hatchback on its way to you

You have some good friends


_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

[924RACR]

Guilty as charged.

Now if we could just figure out the steps.

Dan said he'd dust off his hard drive, but if I didn't have it on mine...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Fifty50Plus]

If this is better than the MSDS header, I'm in. Three of us in the DC area are going to race our 924s in H-Production and the engine performance is a bit different than the stock blue-printed NA. Cam has less lift but more duration and piston shape is free up to 11:1 compression ratio. Other goodies too
_________________
1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car

[Cedric]

Well depending och ports, cam, intake length/design, RPM range target etc all cars will have different "optimum" exhaust design
_________________
1980 924 Turbo
www.instagram.com/garagecedric/

[Mike9311]

I am a larger and long tube guy

Large to raise torque peak. Long to shift torque from after peak to before peak to fill it in under that lower part of the curve

Of course Cedric's right. Every car is different
_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

[jacobroufa]

I'd be in for one on my soon-to-be-supercharged NA..

Do you plan to build this to mate up with the stock exhaust under the car?
_________________
1980 Porsche 931
1981 Porsche 924 Weissach

[924RACR]

No, this is not expected to mate with any stock exhaust - this is intended for racing. For stock compatibility, you're best off with an MSDS header I believe.

Man, really wish we had an engine dyno setup to properly test this stuff... Chuck, any chance you have plans for such, or will it all be chassis dyno development?
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Mike9311]

[BTRacing]

I am using MSDS header in my Martini. It has Euro pistons ,mild head and intake porting, Audi throttle body and thinnest available Cometic MLS gasket. Motor came out really good, revs freely in comparison to typical US market setup and is very happy. Pulls nice, much better then stock. For me car feels like NA 944. I am loosely estimating power at about 140 on the crank.
_________________
www.btrpalmbeach.com
1979 931 GTR Le Mans replica to be
2008 Audi S4 Avant daily driver
2008 Aston Martin Vantage
1974 Moto Guzzi Cafe Racer
1979 Glastron CVX 20

[Fifty50Plus]

Vaughan,
Interesting question about a dyno.... I used to run a Stuska engine dyno back in the mid '80s when I was doing a lot of development work on my 911 race car. We used the same dyno for BMW 2002 engines with different mounts.

A couple years ago, I bought a complete Stuska engine dyno system like the one I used to use. I had it shipped here from AZ and bought all the connectors and plumbing for a recirculating water torque system.

I bought it since it came with a 356 Porsche engine/tranny mount and my plan was to run in engines under load that I had just built. It sits at the back of my shop not yet hooked up, surrounded by about 10 partially disassembled or assembled Porsche engines (including three 924 long blocks).

I also have a neighbor lady that hates me and calls the police about noise whenever I start an engine. So my options are limited. I already use a truck muffler after the stock Porsche mufflers and that's only for 2000-3000 RPM ring break-in. Until she dies I don't think I'll be able to get away with WOT runs.

The good news is that there is a business with a chassis dyno about 5 miles from my house and I used to use them for my race cars. What I found out though was that with the Inovate CO system and data capture, I get all the data that the dyno provides. I now do all my changes at the track and use the Inovate date to support the goodness/badness of the change. I find that easier than packing everything to take to the chassis dyno. And if it works or doesn't work, I'm already at the track
_________________
1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car

[924RACR]

Damn... good and yet bad news. I don't think we'll really be able to properly iterate on the header design without the engine dyno. It's just too beyond painful to swap a header to be considering that on the dyno, I'd think.

Too bad people suck.

My hope was that you'd be able to verify experimentally a good design. Even to the extent of just comparing MSDS/Bursch vs. the Stahl 4-1.

Second option is using some simulation SW, some is better than others; biggest challenge here will be to get good input data for it. Maybe if you're going through the flow development etc on head and cam, that might get us enough to get a reasonable answer. Even just to do some simulation of stepped vs. non would be helpful. At this end, my car designer is a retired Chrysler Advanced Powertrain Engineer, very much in his wheelhouse (lots of racing experience too), so while he won't necessarily do it all for me, his advice is invaluable. He has experience with the $20k+ simulations too...

It's also becoming extremely clear that the cam design is key into this whole mix too, so back to your experimentation...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Mike9311]

I really think in your (our) case this will have to be done by experimentation. Way too much going on to think about or even possibly know for each engine. Hidden steps creating reflections you aren't thinking about etc. If the port doesn't exactly match the pipe alignment or size you can have a reflection working for you or against. Crank, cam, head flow velocity, etc. Its literally nuts

This is a good read. Not some 'possible' BS from just any source but an educated and reasoned read. If you scroll down there is a Step section but the whole article is great. Other stuff on the site is great too (Rod article F1 vs Stock Car). All related directly or indirectly to Race Engine Tech magazine my fav for all things race engine and inside stories (I also have the Blair book he references). My guess is you'll find it interesting

http://www.epi-eng.com/piston_engine_technology/exhaust_system_technology.htm

I have also thought of coating a Stainless header short of some all out complicated heat shielding, just to keep the velocity high, via the Stainless + Coating
_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

[Cedric]