Equal Pulse Headers
 

Has anyone made or seen a set of headers for an early 911, six 24 inch equal length, equal pulse primaries into one 12 inch long collector with a 18 inch long megaphone?

Also what is the best way to combat the 15 pounds of atmospheric pressure that the exhaust gases has to deal with.
Any tricks here?

You might want to check around, because you might have most of what you're looking for right in front of you. Apparently Porsche's early style heat exchangers (Prior to '75) should be pretty close. If you look at them you'll see that Porsche went to some trouble to get them to be equal length. Apparently the inside diameter is 1 5/8 which is large enough for engines through 3.2's. If you have an early engine (lets say a 2.0 like I have) I doubt that you'd want anything bigger since you'd start to lose the tuned affect resulting from the higher gas speeds. I don't know the length of the individual pipes since I've never measured them off of the car.

Aside from the heat exchanger shrouds, the biggest difference that I can see between a set of headers and the factory design heat exchangers is that the headers stop right after the collectors to allow room for the installation of long megaphones. The factory exhaust continues to the back to mate up with the muffler. I've also not seen a whole lot that other people have come up with a better noise/power compromise then the factory muffler. You can get more HP, but only for significanly more noise. Besides, I don't know of many tracks (at least not near where I live here in the Northeast) where open megaphones would even be allowed because of the wonderful noise that the produce. I think that most of the tracks near me have a 103 or 105 db limit. The SCCA's maximum is 103 db, and some tracks or events are often less. A stock 2.4S put out 98 db at full throttle while a 2.8RSR with megaphones was way up at 106 db. You might want to check your local track rules to ensure that you don't go to a lot of cost and trouble designing an exhaust system that is too loud to use. There are a lot of other threads on this BBS that discuss mufflers and exhausts, so you might want to do a search of those topics.

Personally, as my car evolves into a race car, I'm tossing around the idea of just cutting off the heat exchanger baffling and putting the stock headers back on the car. The big question to me is the value of having a working defrost system when racing in the rain. So I'm leaning towards just leaving the whole thing alone and just replacing the muffler for something less restrictive such as a 2 in/2 out or Phase-9 system (105 db). Those are just my $.02.

You're talking about the "bag-o-snakes" racing exhaust.

I've seen 'em, don't know where they come from, do know they are expensive.

If no one chimes in I'll find a vendor for you.

http://www.rennsportsystems.com/~porsche/exhaust1.jpg

Got this image from www.rennsportsytems.com

The system I was referring to is an actual pulse based unit with only one collector. Very convoluted mess of tubes. Probably a bit of a challenge to install. Our regional mechanic did a set of these a few years back. That's where I saw them. Never had the opportunuty to speak to the owner to see how he liked the setup.

Not these?

http://www.scargoracing.com/graphics/911Esm.gif

From the S-Car-Go website. I can only assume the price is a misprint, as one could buy 4 sets of SSIs for the same price....

Perhaps they are hand made by an old guy and each set takes a few months out of his life, I dunno.

The Rennsport headers look to be similar to the factory heat exchangers without the heater boxes installed. The big difference is that the Rennsport headers (as well as the factory models) stop right after the collectors. The key is the length of the primaries and the internal diameter. Since it is from Rennsport I doubt that it is any different then the 1 5/8 that I quoted since I pulled that from Rennsport's site. It's also the same as the BA's recommendation and the factory set-up, so I figure that it is pretty accurate. I don't know anything about the rest of the exhaust behind that point and how it compares to anything else. Aside from a back-to-back dyno run, I'm not sure if anyone could say that it is an improvement. It does LOOK effective though.

The S-Car-Go headers do look to be a different beast. They appear to be shorter and packaged a little tighter which might make them easier to fit in the engine bay. If you look closely at the collectors, they appear to have brackets on the side. I used to have a FF with a header similar to this which allowed the user to increase or decrease the length of the primaries by moving the collector in/out by about 1-1 1/2 inches to adjust the torque peak. It would shift it by about 500 RPM. That could be a useful feature for the tuner. Other then that as long as the length and internal diameter are right, they should work. Are you sure that those are "911" and not "996" headers?

By they way, I guess the biggest mistake that you can make with headers (assuming that it has equal length primaries and a reasonable collector) is to make them too big or too short. If the internal diameter is too large, the gas speed drops and you lose the scavenging affect from the tuned pulses. If the primaries are too short, you might run out of rev's before the headers hit the right "key" and never get the "tuned" affect.

Boomy, Check out all of the above.

I want to see a pic of that "bag o' snakes" ;) Thanks Two Oh!

Hey 930fan,

That Rennsportsystems link wasnt working for me? Anyone else?

Could you please repost it.

Thanks!

Boomy, equal pulse into two.....

Very nice! I have to find that pic of the Ford Indy motor with the headers "bag o' snakes" in the V and the carbs on the outside. Then I need to get my scanner working again so I can post it. I take it the car in that pic is a GT-40? One of these days (after I win the lotto LOL) I'll build a GT-40 kit with a wicked twin-turbo 1200+HP smallblock, the motor's the easy part it's everything else that's way expensive, like a transaxle to handle the power. ;) BTW, I'm not certain about Porsche cars but there's a place up in New Jersey, Cook's custom I believe that will build pretty much any header you'd like but they have to have your car in there shop and it's not cheap, 5-6 years ago they quoted me a starting price of $3000 for equal-length stepped headers for my drag car, I passed and went with custom 2" headers from Pro Mustang Performance.

Rennsport Links is:

Rennsport Exhaust